EPA-660/3-75-025
JUNE 1975
                                         Ecological Research  Series
Tidal Flats  in  Estuarine  Water
Quality Analysis
                                         National Environmental Research Center
                                           Office of Research and Development
                                           U.S. Environmental Protection Agency
                                                   Corvallis,  Oregon 97330

-------
                      RESEARCH REPORTING SERIES


Research reports of the Office of Research and Development,
U.S. Environmental Protection Agency, have been grouped into
five series.  These five broad categories were established to
facilitate further development and application of environmental
technology.  Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in
related fields.  The five series are:

          1.   Environmental Health Effects Research
          2.   Environmental Protection Technology
          3.   Ecological Research
          4.   Environmental Monitoring
          5.   Socioeconomic Environmental Studies

This report has been assigned to the ECOLOGICAL RESEARCH STUDIES
series.  This series describes research on the effects of pollution
on humans, plant and animal species, and materials.  Problems
are assessed for their long- and short-term influences.  Investigations
include formation, transport, and pathway studies to determine
the fate of pollutants and their effects.  This work provides
the technical basis for setting standards to minimize undesirable
changes in living organisms in the aquatic, terrestrial and atmospheric
environments.

This report has been reviewed by the Office of Research and
Development, EPA, and approved for publication.   Approval  does
not signify that the contents necessarily reflect the views and
policies of the Environmental  Protection Agency,  nor does  mention
of trade names or commerical products constitute  endorsement or
recommendation for use.

-------
                                           EPA-660/3-75-025
                                           JUNE  1975
    TIDAL FLATS IN ESTUARINE WATER QUALITY ANALYSIS
                            by
                      David A. Bella

             Department of Civil Engineering
                 Oregon State University
                 Corvallis, Oregon  97331
                   Grant No. 16070 DGO
                  Program Element 1BA025
                  ROAP Task No. 21A1T/01
                      Project Officer

                     Richard Callaway
Pacific Northwest Environmental Research Laboratory (PNERL)
       National  Environmental Research Center (NERC)
                 Corvallis, Oregon  97330
         National  Environmental Research Center
           Office  of Research and Development
          U.S.  Environmental Protection Agency
                 Corvallis, Oregon 97330
              For Sale by the National Technical Information Service,
              U.S. Department of Commerce, Springfield, VA 22151

-------
                                  ABSTRACT








     This report summarizes the results of a research project entitled "Tidal




Flats and Estuarine Water Quality Analysis."  The initial phases of the study




involved mixing processes and tidal hydraulics, however, the study emphasis




shifted to estuarine benthic systems as the importance of these systems




became more apparent.  The sulfur cycle was given particular emphasis because:




     (1)  sulfides, resulting from sulfate reduction within the benthic




          systems, can influence the benthic oxygen uptake rate,




     (2)  free sulfides are highly toxic to a variety of organisms, and




     (3)  the release of hydrogen sulfide may contribute to a deterioration




          of air quality.




     The  sulfur cycle is of particular importance in tidal estuaries because




 of the high sulfate  concentrations of saline waters in comparison to fresh




 waters.   A conceptual model of estuarine benthic systems was developed and a




 classification system of estuarine benthic deposits which is based on the




 availability of hydrogen acceptors and reactive iron was developed.




     Field studies demonstrated that estuarine waters overlying organic rich




 tidal flat deposits  could contain significant concentrations of free sulfides




 even when dissolved  oxygen was present.  Field studies of benthic oxygen




 uptake and benthic sulfide release were conducted.  Water quality profiles




 within the deposits  were also determined.  A number of laboratory studies




 were conducted to determine the rate of sulfate reduction.  Results from




 experiments using extracts from benthic deposits and algal mats demonstrated




 a  close relationship between the rate of sulfate reduction and the sulfate
                                     11

-------
and soluble organic carbon concentrations.  A general systems model of




estuarine benthic systems was developed, however, specific definition of




all processes was not possible without further experimental results.   A




variety of activities which could contribute to significant environmental




changes with estuarine benthic systems were identified.




     Methods of determining dispersion coefficients from salinity profiles




were examined and an improved method was developed.  The build-up of a




pollutant in the vicinity of the outfall during the slack water period of




the tide was studied through a field experiment and mathematical model study.




     This report was submitted in fulfillment of Grant 16070 DGO, by Oregon




State University in Corvallis under the sponsorship of the Environmental




Protection Agency.  Work was completed as of November, 1973, with minor




revisions made in August, 1974.
                                    111

-------
                            CONTENTS

Section                                                            Page

  I      CONCLUSIONS                                                  l

  II     RECOMMENDATIONS                                              4

  III    INTRODUCTION                                                 6

             General Background                                       ^
             General Approach                                         °
             Detail and Perspective                                   8
             The Evolution of the Study                              10

  IV     DESCRIPTION OF BENTHIC SYSTEM                               12
             Introduction                                            12
             General Benthic System                                  12
             Larger Plants and Animals                               20

  V      DESCRIPTION OF SITES USED FOR FIELD STUDIES                 26

  VI     STUDIES OF BENTHAL OXYGEN UPTAKE                            32

             Initial Laboratory Studies                              32
             Experimental Design and Procedure for
                 Field Studies                                       32
             Mathematical Model of Benthal Respirometer
                 System                                              34
             Calculation of Leakage                                  37
             DO Uptake Rate Calculations                             37
             DO Uptake Results                                       38
             Sensitivity Study                                       45

  VII    FREE SULFIDE IN OVERLYING WATER                             47
             General                                                 47
             Model of Free Sulfide Transfer Through
                 Aerobic Zone                                        48
             Model of Free Sulfide in Overlying Water                50
             Free Sulfide Measurements at Other Sites                57
  VIII   CONDITIONS WITHIN BENTHIC SYSTEMS                           58

             Field Measurements                                      58
             A Classification of Estuarine Benthic Systems           59

  IX     STUDY OF SULFATE REDUCTION USING EXTRACTS                   66

             General                                                 66
             Media Preparation                                       68
             Methods                                                 71
             Relationship Between Sulfide, Sulfate and
                 Organic Carbon                                      73
             Rates of Sulfate Reduction                              76
                                IV

-------
Section                                                            Page

  X       SULFATE REDUCTION STUDY USING S-35                         95

               General Approach                                      95
               Sample Preparation                                    95
               Initial Conditions                                    97
               Collection of Sulfide                                 97
               Rates of Sulfate Reduction                           101

  XI      OTHER ESTIMATES OF SULFATE REDUCTION                      103

               Diffusion of Sulfate                                 103
               Incubation of Benthic Cores                          105
               Summary of Sulfate Reduction Rates                   107

  XII     BENTHIC SULFIDE RELEASE                                   109
   »
               General                                              109
               Modified Benthic Respirometer                        109
               Results of Sulfide Release Measurements              110
             '  Profiles of Free Sulfide                             114
               Summary of Benthic Sulfide Release Experiments       114

  XIII    MIXING WITHIN DEPSOITS                                    116
  t
               General                                              116
               Tidal Mixing                                         117
               Periodic Scour                                       122

  XIV     GENERAL BENTHIC DEPOSIT MODEL                             125

               General                                              125
               Principal Assumptions                                126
               General Description of Soluble Materials             126
               General Equation for Insoluble Materials             128
               Biochemical Model I                              .    128
               Biochemical Model II                                 135

  XV      ENVIRONMENTAL IMPLICATIONS FOR ESTUARINE BENTHIC SYSTEMS  141

               General Implications                                 141
               Changes in Organic Deposition                        142
               Changes in Inorganic Deposition                      142
               Construction of Dikes,  Jetties, Wharves, etc.        142
               Hydrodynamic Changes                                 143
               Tideland Filling                                     143
               Transient Conditions Due to Dredging                 145
               Long Term Particle Size Change                       146
               Spoil Disposal                                       146

-------
Section

  XVI     LOWER LEVEL RESOLUTION STUDIES                            148

               General                                              148
               Advection Errors                                     148
               Estimating Dispersion Coefficients in Estuaries      149
               Slack Water Build-up in Estuaries                    149
               Tidal Measurements                                   150

  XVII    REFERENCES                                                151

  XVIII   PUBLICATIONS                                              158

  XIX     APPENDIX - FINITE DIFFERENCE MODEL                        160
                                  VI

-------
                                  FIGURES

                                                                     Page

 1   AREAS OF FEEDBACK                                                11

 2   GENERAL BENTHIC SYSTEM                                           13

 3   CONCEPTUAL MODEL OF LARGER ANIMALS WITHIN BENTHIC SYSTEM         21

 4   SITES LOCATED ON YAQUINA ESTUARY                           "      28

 5   TRANSECT A SITE 1 - SUMMER 1970                                  29

 6   SUMMARY OF CORRECTED BENTHAL OXYGEN UPTAKE RATES AT
     SITES 3 AND 4.  (1969)                                           39

 7   VARIATION OF BENTHAL UPTAKE RATES AT SITE 4 (1969)               41

 8   RANGE OF FREE SULFIDES IN OVERLYING WATER                        52

 9   DISSOLVED OXYGEN AND FREE SULFIDE PROFILES AT SITE 5             55

10   DISSOLVED OXYGEN AND FREE SULFIDES AT SITE 5                     56

11   EXAMPLES OF ESTUARINE BENTHIC TYPES                              60

12   QUALITATIVE DESCRIPTION OF ESTUARINE BENTHIC SYSTEM RESPONSE
     TO CONSTANT DEPOSITION CONDITIONS                                62

13   EXPERIMENTAL RESULTS OF CULTURE 1 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        81

14   EXPERIMENTAL RESULTS OF CULTURE 2 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        82

15   EXPERIMENTAL RESULTS OF CULTURE 3 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        83

16   EXPERIMENTAL RESULTS OF CULTURE 4 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        84

17   EXPERIMENTAL RESULTS OF CULTURE 5 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        85

18   EXPERIMENTAL RESULTS OF CULTURE 6 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        86

19   EXPERIMENTAL RESULTS OF CULTURE 7 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        87

20   EXPERIMENTAL RESULTS OF CULTURE 8 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        88


                                     vii

-------
                                  FIGURES (cont)

                                                                     Page
21   EXPERIMENTAL RESULTS OF CULTURE 9 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        89

22   EXPERIMENTAL RESULTS OF CULTURE 10 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        90

23   EXPERIMENTAL RESULTS OF CULTURE 11 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        91

24   EXPERIMENTAL RESULTS OF CULTURE 12 COMPARED WITH EQUATIONS .23,
     24 AND 25                                                        92

25   EXPERIMENTAL RESULTS OF CULTURE 13 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        93

26   EXPERIMENTAL RESULTS OF CULTURE 14 COMPARED WITH EQUATIONS 23,
     24 AND 25                                                        94

27   RELATIONSHIP OF SULFATE REDUCTION RATE TO SULFATE DIFFUSION
     ASSUMING STEADY STATE                                           104

28   BENTHIC SULFIDE RELEASE WITHIN RESPIROMETER - SITE 5 - 8/3/71   111

29   BENTHIC SULFIDE RELEASE WITHIN RESPIROMETER - SITE 5 - 8/9/71   111

30   BENTHIC SULFIDE RELEASE WITHIN RESPIROMETER - SITE 5 - 8/20/71  112

31   HYDRAULIC SURFACE DURING EXPERIMENTS AT SITE 1                  119

32   CONDITIONS AT SITE 1 DURING DRAINAGE EXPERIMENT                 119

33   FREE WATER ELEVATIONS DURING EXPERIMENTS AT SITE 1              120

34   RELATIONSHIP BETWEEN TOTAL SULFIDE (ACID SOLUBLE) AND REDOX
     POTENTIAL WITHIN DEPOSITS AT SITES 1, 2, 4, AND 5               123

35   TEMPORAL CHANGE OF TOTAL SULFIDE (ACID SOLUBLE) PROFILES
     AT SITE 4                                                       123

36   BIOCHEMICAL MODEL I FOR ESTUARINE BENTHIC SYSTEM                129

37   BIOCHEMICAL MODEL II FOR ESTUARINE BENTHIC SYSTEM               136
                                    viii

-------
                              TABLES
 1        PARTICLE SIZE FOR SAMPLING SITES                          30
 2        BACTERIAL COUNTS PER GRAM OF WET SEDIMENT
             (SUMMER)  1970                                         31
 3        DEFINITION OF TERMS FOR RESPIROMETER MODEL                36
 4        SUMMARY OF BENTHAL OXYGEN UPTAKE RATE                     44
 5        ESTIMATED PARAMETERS APPLICABLE TO SITE 5
             DURING LATE SUMMER AND EARLY FALL PERIOD              53
 6        CLASSIFICATION OF ESTUARINE BENTHIC SYSTEMS               61
 7        SUMMARY OF SOLUBLE ORGANIC EXTRACT PROCEDURES             70
 8        EXPERIMENTAL YIELD RATIOS AND MAXIMUM RATES OF
             SULFIDE PRODUCTION FOR EACH CULTURE                   74
 9        SUMMARY OF YIELD RATIOS                                   75
10        SUMMARY OF S-35 RECOVERY                                 102
11        SULFATE REDUCTION IN CORES AT ROOM TEMPERATURE (25°C)     106
12        COMPARISON OF THE RATES OF SULFIDE PRODUCTION
             MEASURED IN THIS STUDY WITH THOSE OF
             PREVIOUS INVESTIGATORS                               108
13        ESTIMATES OF SULFIDE RELEASE RATES AND OXYGEN
             UPTAKE RATES AS MEASURED IN RESPIROMETER
             EXPERIMENTS AT SITE 5                                113
14        POTENTIAL BENTHIC SULFIDE RELEASE RATES                  115
15        PERMEABILITY AND VOID RATIO AT SITE 1                    121
16        DEFINITION OF TERMS FOR BIOCHEMICAL MODEL I
             OF ESTUARINE BENTHIC SYSTEM                          130
17        DEPENDENCE OF REACTIONS OF BIOCHEMICAL MODEL I
             ON INTERNAL BENTHIC CONDITIONS                       133
18        DEFINITION OF TERMS FOR BIOCHEMICAL MODEL II
             OF ESTUARINE BENTHIC SYSTEM                          137
19        DEPENDENCE OF REACTIONS OF LOWER RESOLUTION MODEL
             (MODEL II) ON BENTHIC CONDITIONS                     138

-------
                              ACKNOWLEDGMENTS






     The writer wishes to acknowledge with appreciation the support of this




grant by the Environmental Protection Agency.  The assistance of Mr. Richard




Callaway who served as EPA Program Officer is particularly acknowledged.




     The contributions of research collaborators whose names appear as authors




in the publication list of section XVIII were essential to the success of




this project.  I express my gratitude for their dedication, and enthusiasm




and for the capable work which they performed.   Special appreciation is given




to William J. Grenney, Alan E. Ramm, Paul Peterson,  Peter Wong and Ralph C.




Olsen.

-------
                                 SECTION I
                                CONCLUSIONS


1.   Benthic systems are significant regions  of estuarine  systems  and  should
     not be merely treated as boundary conditions  to the overlying waters.  The
     processes occurring within estuarine benthic  systems  and,  in  particular,
     the sulfur cycle, are of major importance  with  regard to sound  environ-
     mental management of estuaries.  A description  of estuarine benthic
     systems is provided in sections IV and XII.
2.   Free sulfide (produced within deposits)  can be  found  at concentrations
     of approximately 1 mg/L in oxygenated  tidal flat waters overlying high
     organic deposits.  Free sulfide concentrations  of 50-100 mg/L and higher
     can be found within the interstitial waters of  high organic benthic
     deposits within several centimeters of the deposit surface.   Such con-
     centrations can be toxic to a wide variety of organisms.
3.   The presence of high organics within the deposits, available  sulfates,
     low concentrations of available iron,  poor drainage,  low water  velocities
     and the absence of significant scour are  conditions which lead to  the
     build-up of free sulfides within estuarine benthic systems.   A  variety
     of human actions can contribute toward these  conditions.   (See  Section XVI)
4.   In addition to the conditions described  in conclusion 3, low  dissolved
     oxygen concentrations and shallow water  depths  are conditions which
     favor higher free sulfide concentrations with the overlying waters.
5.   Rates of sulfide production ranging from approximately 10  mg(S)/l-day
     to 70 mg(S)/l-day were measured by a variety  of methods.

-------
6.   Rates of sulfate reduction within laboratory  experiments  using  algal



     extracts were found to be primarily dependent on  the  sulfate  and



     organic carbon concentrations.   The rate of sulfide production  in mg(S)/



     1-day (4^-) is given by the following equation

                 .  _  77


               dt  "
     in which L is the sulfate concentration and C is  the  soluble organic



     carbon concentration.  The rate of soluble organic carbon utilization  is



     given by
               f  -  -*•»<&
     The rate of sulfate removal is given by
               dt
7.   In situ benthic oxygen uptake rates within tidal flat areas  without  burrow


                                             2                 2
     holes ranged from approximately 1.4 gm/m -day to 2.1 gms/m -day with the



     higher rates associated with higher water velocities.  Benthic oxygen uptake


                                        2

     rates up to approximately 8-9 gms/m -day were measured in regions  with



     large numbers of burrow holes.  Within such regions,  correction of respiro-



     meter leakage had to be made.



8.   Estimates of benthic sulfide release in tidal flat  regions of high organic



     content were limited and highly variable.  These limited results,  however,

-------
                                                                          2
     suggest that benthic sulfide release rates  of approximately 1  gm(S)/m -day


     and higher are not unreasonable in tidal flat regions  displaying the


     characteristics described in conclusion 3.   It is  not  now  unreasonable  to


     suspect sulfide release from estuarine benthic systems,  particularly  in


     tidal flat regions, as a major contributor  to atmospheric  sulfur.


9.   The errors associated with common, finite difference models  of advection


     can be classified into three general categories:   (1)  oscillation errors;


     (2) skewness errors; and (3) dispersive errors.  The use of the  upstream


     difference method permits correction of these errors.


10.  The use of the steady state assumption for  measuring longitudinal dis-


     persion coefficients from salinity profiles can  lead to  a  false  rela-


     tionship between fresh water flow and the magnitude of the  dispersion


     coefficients.  An improved method of estimating  dispersion  coefficients


     from salinity profiles was developed.

-------
                                 SECTION II




                              RECOMMENDATIONS









1.    The magnitude and extent of benthic sulfur release to the atmosphere




     should be examined on a large scale.   It is possible that increases in




     this release due to a variety of human activities can result in major




     inputs of atmospheric sulfur.




2.    The extent of estuarine benthic deposits containing significant amounts




     of free sulfide and the influence of human activity on this extent should




     be examined.




3.    A more comprehensive (low level resolution) understanding of the system




     properties of estuarine ecosystems must be pursued.   Only with such an




     improved understanding can the significance of the more common environ-




     mental concerns (e.g. low dissolved oxygen, higher free sulfides,  stream




     flow regulation) be appreciated with regard to the functioning of




     estuaries within the biosphere.  Such studies must place a greater




     emphasis on the long term consequences of human activities.




4.    A more qualitative description of the formation of combined sulfides




     within benthic deposits should be developed.  Such a description would




     enable a refinement of the systems model presented in section XV.   Such




     a study should proceed at two levels of resolution.   The finer resolution




     would likely deal with the reactions of iron within benthic systems.  The




     lower resolution model should deal with a measurement of the "chemical




     sulfide demand" (CSD) of a deposit.  The CSD would be a measure of the




     sediment capacity to tie up sulfides in insoluble forms.

-------
5.    Studies are needed to quantitatively define the rate of sulfate reduc-




     tion particularly in the top regions of the anaerobic portions of deposits




     and immediately below algal mats.  Attempts should also be made to




     develop a measure of the "biochemical sulfate demand" (BSD) of deposited




     material.  The BSD might be a useful concept to incorporate into the




     lower resolution model of section XV.  The ratio,  BSD/CSD, would be an




     indicator of potential sulfide release for a given deposit (generally




     within the top several centimeters).




6.   The concentrations of free sulfides within waters  overlying deposits and




     the amount of hydrogen sulfide released to the atmosphere will depend,




     in part, on the rate of oxidation of free sulfide.  Additional study is




     needed to better estimate the rate of sulfide oxidation within estuarine




     waters, particularly at low sulfide concentrations.  The age of the water




     sample should be an important consideration as it  appears that recently




     collected estuarine waters display a more rapid oxidation rate than




     waters stored for a period of time after collection.

-------
                                 SECTION III
                                INTRODUCTION
GENERAL BACKGROUND
     This  is  the  final  report  on a three year study entitled "Tidal Flats in
 Estuarine  Water Quality Analysis."  This study was supported by the Environ-
 mental  Protection Agency through Research Grant No. 16020DGO.
 GENERAL APPROACH
     The  technical material presented within this report is generally arranged
 in logical order  rather than in the chronological order that the work was
 performed in.   The writer feels that it would be of value,  however, to briefly
 discuss the general approach used during the study and briefly discuss how this
 approach  often changed  the direction of the research.
     The  general  objective of this research is to learn more about estuarine
 systems and in particular the tidal flat systems, with particular emphasis
 given  to  how man's activities  can disrupt these systems to the eventual dis-
 advantage of man.  The  numbers of components and relationships occurring
 within these systems are so numerous and complex that a complete understanding
 is essentially impossible.  Research effort must be thus directed to study those
 areas  which appear to be of greatest importance.  The difficulty is that our
 knowledge of what we determine to be most important changes as we learn more
 about  the  systems.  This knowledge (obtained from all sources) hopefully
 indicates  new areas which may be of great importance.   A research project must
 be flexible enough to respond to new information yet stable enough to lead to
 sound results.  Lack of flexibility often results in the pursuit of those items
 which are  already known quite  well, while lack of stability can lead to nothing.

-------
     In the reported research project, an approach was used in which emphasis




was alternately given to mathematical models and experimental results.  That




is, the experimental results improved the mathematical models while the models




in turn suggested where further experimental results might be most profitable.




As an example, the oxygen demands of tidal flat areas, particularly the benthal




deposits, was recognized from the start as an important consideration.  First,




laboratory studies were made to study the benthal uptake.  Next, a simple




mathematical model was developed.  From this model, an in situ benthal respiro-




meter was designed, built and run.  The results from the in situ benthal oxygen




uptake rate studies appeared to be effected by leakage from the respirometer.




A mathematical model of the respirometer system was developed and from that




model, correction for the leakage was made.  The corrected benthal oxygen uptake




rates were then studied.  The mathematical model results indicated that the




experimental results could be best explained if a substantial portion of the




measured oxygen uptake rate was due either to the dissolved oxygen, DO, diffusing




into the deposits or due to the release of a material which was oxidized rather




quickly  (half life of several hours or less).  Both of these processes suggested




that a portion of the benthal uptake (not including benthal plant respiration)




might be due to a quickly oxidizing material; the material being oxidized either




within the aerobic region of the deposit or within the overlying water.  The




literature suggested that free sulfides might be such materials.  Because free




sulfides (particularly hydrogen sulfide) are quite toxic, their presence within




the water might often be of greater significance than the low DO values which




result, in part, from the oxidation of the free sulfides.  It was generally




felt at the time, however, that the rapid rate at which free sulfides are




oxidized would prevent its presence in waters containing measurable DO.  Thus,

-------
it was felt, that the free sulfides which were released from  the  anaerobic




regions of the deposit would normally be completely  (or near  completely)




oxidized within the aerobic zone of the deposits.  The literature also




reflected this notion.  A mathematical model of the  aerobic zone  of the  deposits




was developed.  This model included the downward diffusion of DO,  the  upward




diffusion of free sulfides and the reaction between  the two.   The model  results




indicated that under certain conditions, the free sulfide concentrations within




overlying waters could be significant.  Experimental methods  were then developed




and significant concentrations of free sulfides were measured in  certain areas.




Field studies and an exhaustive literature review then led to a qualitative




description of what appears at this time to be the important  processes leading




to both the oxygen uptake and the release of free sulfides.   The  description of




the benthic system exposed important processes for which very little experimental




data was available and expansion of the mathematical models without  further




experimental results would have been unjustified and misleading.   Thus the most




profitable results during the final phase of the project centered around field




and laboratory studies.  A general benthic system model was developed, however,




it was determined that specific definition of a number of processes  required




further experimental efforts.  The author was reluctant to speculate on  certain




specific descriptions within the model because such speculation might  be too




easily accepted without further experimental results.




DETAIL AND PERSPECTIVE




     The general research approach followed in this study not only involved a




feedback between mathematical model results and experimental  results,  but




also involved a feedback between different views or perspectives  of estuarine




systems  as  described below.

-------
     The real world appears to be organized into an integrated hiarchy of

organizational structures.  On an extremely small scale, atoms are organized

to form molecules.  On a large scale, the planets and sun are organized to form

the solar system.  Large numbers of intermediate structures, some obvious and

some not, are of course present.  The definitions of different structures and

the disagreements of these definitions will not be pursued.  Rather, the point

to be made is that a given structure or entity is both made up of components and

is also a component of a higher structure.

     In order to understand the natural world, man has found it necessary to

group what appear to be natural structures into larger groupings.   As an example

of a functional grouping, individual organisms with similar functions have

been grouped into trophic levels.  This grouping has enabled man to study the

relationships between large groups of organisms.  Such a grouping thus

enables one to gain perspective, yet. because of this larger grouping, one loses

detail.

     The same real world systems may be studied at a fine level of resolution;

(different degrees of grouping).  A fine resolution leads to a gain in detail

with a sacrifice of perspective while a low resolution leads to a gain in

perspective with a sacrifice in detail (precision}.

     Different investigators (and different professions} often look at the

same real world system from different levels of resolution.  Such a varied

resolution approach often leads to information concerning detail and

perspective.*

     This project, from the start, has studied the tidal flat system (a loosely

defined system having, however, some unique characteristics) from two general
* Author's Note:  Some information may require both detail and perspective
simultaneously.  Such information may well be essentially unattainable.  At
this time, however, I will not pursue this rather philosophical question of
"ecological uncertainty."
                                     9

-------
views  (i.e. at two general  levels  of organization.]   Related component parts

which make up the tidal  flat  system  were  studied.   In addition, the larger

estuarine system, of which  the  tidal flats  are  components,  was also studied.

     Feedback occurred between  the results  gained  from the  different views;

that is, results gained  at  one  level of organization influenced the direction

of work done at the other level of organization.   As an example, the disper-

sion of saline water within an  estuary has  been a  common subject of study.

In the early phases of this project,  the  examination of estuarine dispersion

coefficients was pursued.   The  intrusion  of sea water results in conditions  within

estuaries which are uniquely  different from most fresh water streams.   Most
                         f
mathematical models of estuaries,  however,  are  very  similar to those used in

fresh water streams with the  most  common  difference  being a temporarily

varying hydraulic regime.   Saline  water contains sulfate concentrations many

times higher than found  in  fresh waters (sea water contains 2655 mg/L of sulfates]

The significance of these higher sulfate  concentrations is  not apparent until

one increases the level  of  resolution of  his view.   These higher sulfate concen-

trations have significant effects  upon the  benthic systems  which, in turn,

influence the water quality.  One  does not  appreciate these effects until one

views the estuarine bottoms as  systems of interacting components and processes

rather than boundary conditions  to the larger "estuarine systems."  Thus, a

significant result of the salinity dispersion examined at one level of resolu-

tion cannot be appreciated  until a finer  level  of  resolution is examined.

THE EVOLUTION OF THE STUDY

     The general approach followed in this  study can be most simply described

as an "evolutionary" process  involving feedback between the four general

areas  illustrated in Fig. 1.


                                   10

-------
                         Math models
          low level
          resolution

          high level
          resolution
Experiment
                         FIG. 1 - AREAS OF FEEDBACK



     The study, evolved with the direction of this evolution loosely guided,

through the feedbacks, by the three following questions:

     1.   Is it important?

     2.   Has it been done or is it being done?

     3.   Can you do it?

     This evolutionary process serves to explain how a project which initially

emphasized dispersion coefficients and dissolved oxygen (DO) balance (two

popular subjects) shifted to a systems study of the sulfur cycle within estuarine

benthic systems (a neglected subject of potentially significant importance).
                                   11

-------
                                 SECTION IV








                       DESCRIPTION OF BENTHIC SYSTEM




INTRODUCTION



     The following section will provide a general description of estuarine




benthic systems.  This description has been developed during the course of




this research project through extensive literature searches and field and




laboratory investigations (1)(2)(3).








GENERAL BENTHIC SYSTEM




     Any approach to an understanding of estuarine benthic systems must




involve the complex interactions of the biological, chemical, physical and




hydraulic processes.  The basis for understanding such systems involves the




development of conceptual models.  An investigator seeks to develop a




simplified model capable of satisfactorily describing certain important




aspects of an actual system whose complete complexity is beyond the capacity




of the investigator to perceive.  In developing a model of a system, one




must trade between detail and perspective.  Too great a detail makes it




difficult to define the relationships between the many components of the




model.  Sacrifice of detail leads to a better perspective yet eliminates




useful information from the model.  The level of resolution of the conceptual




model presented herein (Fig. 2) was selected to explain certain concepts




which are of importance to environmental quality.  Omission of certain




processes,  reactions or other influences should not imply that these omis-




sions are unimportant.   Periodic reference to Fig. 2 will help to clarify




the following discussion.
                                   12

-------
                                                                           AIR
i

\ EXTERNAL
| SOURCES
\l

INSOLUBLE
INORGANICS

G
\ '
V~^ ^
k i
V"
, t

^-/CHEMOAUTOTROPHICTS
Jv. BACTERIA J
f t t
''/A'-

	 	 	
/ 	 ^ ^ E
^fi PHYTOPLANKTON ) \ Ł
/ ^X \ ^
/ W' HETEROTROPHIC V * no,-...,
-X.--7- "*V BACTERIA J*-* ORGAN
" x ' S' ' 	

XTERNAL
OURCES
/
cs WATER

                                                                       ANAEROBIC
                                                                         DEPOSIT
     LINES f?EPftŁSENT PHYSICAL TRANSFER PROCESS
CHEMICAL REACTION NOTED BY •

* DENOTES AVAILABLE Fa (also Zn, Sn, Cd, Hg mil CuJ
FIG.  2  - GENERAL BENTHIC SYSTEM

-------
     Inorganics and organics are deposited to estuarine benthic  systems.




Inorganics, including sands, silts'and clays, are introduced  into  estuaries




from the ocean, upstream rivers and localized runoff.  Organics  originate




from sources outside the estuary, as well as from primary production within




the estuary.  The system which results from such deposition is illustrated




in Fig. 2.



     Decomposition of deposited organics is most often largely roicrobial




with bacteria predominating.   (The influence of larger detrital  and deposit




feeders is discussed in the following subsection.)  The type  of  bacterial



decomposition occurring at any location is determined principally  by the avail-




ability of hydrogen acceptors.  When available, dissolved oxygen,  DO, is used



as the hydrogen acceptor.  In its absence, oxidized forms of  sulfur, princi-




pally sulfate, become the principal hydrogen acceptors.  Because nitrate



concentrations are nearly always far less than sulfate concentrations within




estuarine systems, nitrate reduction, which will occur before sulfate reduc-




tion, will not be discussed.  The absence of suitable concentrations of both



oxygen and oxidized sulfur necessitates the use of endogenous hydrogen




acceptors.  (For a discussion of endogenous and exogenous hydrogen acceptors



see Schroeder and Busch(4)).




     The availability of exogenous hydrogen acceptors (DO and sulfates}




depends upon the mixing and advection within the deposits.  Vertical mixing,




and thus the transport of exogenous hydrogen acceptors, is increased by




greater water velocities, high concentrations of dissolved oxygen  and sulfate




within the overlaying water, high permeability of the deposits,  and a high




rate of turnover by the larger organisms.  This latter factor is,  in part,




dependent on the interstitial water quality.  Advection through  the deposits
                                    14

-------
depends on the permeability of the deposits and the direction and magnitude




of the hydraulic gradient.




     The availability of hydrogen acceptors and organics determines the




nature and extent of bacterial decomposition which, in turn, largely deter-




mines the quality of the interstitial and interfacial waters.  The avail-




ability of oxygen is an important factor affecting estuarine benthic systems.




Oxygen is added to the overlying water by reaeration, photosynthesis and




transport due to water movement.  The interstitial DO concentration of




deposits is determined by a balance between DO transport from above (by




mixing and advection) and DO utilization (both chemical and biological)



within the deposits.




     If the input of organics to deposits exceeds the transfer of DO,




aerobic decomposition will not be sufficient to decompose all of the



organics.  Sulfate reduction will then proceed below the aerobic region.




The reduction of sulfates by heterotrophic sulfate reducing bacteria which




utilize the sulfate ion as a terminal hydrogen acceptor (5) results in the



release of hydrogen sulfide which is found in solution as part of the  pH




dependent system




                          ">S=                                        (1)
In the present discussion, all components of the above relationship will be




defined as "free sulfide."  At a pH of 6.5-7.0, the free sulfide is approxi-




mately evenly divided between H-S and HS  with S~ being negligible (6).  free




sulfides are also produced during anaerobic putrefi cation of sulfur contain-




ing amino acids, but this process is felt to be of lesser importance in the




marine envi ronment (7,8).
                                    15

-------
     Free sulfides form insoluble compounds with heavy metals,  particularly




iron.  Free sulfide quickly reacts with available iron within the  deposits  to




form ferrous sulfide, FeS, which gives benthic deposits  their characteristic




black color (9).  The input of this iron into the deposits  results  primarily




from the deposition of insoluble inorganics, which contain  ferric  oxides  and




other insoluble forms of iron.  Not all of this iron, however,  is  available to




react with the sulfides.  Some additional reactive iron  originates  from the




decomposed organics.  This latter source is usually less and thus  the  supply




of available iron within the deposits is often largely dependent on the nature




and extent of inorganic deposition (.10)-  Other heavy metals such as zinc,  tin,




cadmium, lead, copper and mercury all have solubility products  significantly



below that of ferrous sulfide and thus, the presence of  ferrous sulfide



indicates that ionic solutions of these metals within the interstitial



waters are not likely to be significant.




     Free sulfide concentrations within benthic deposits will remain at low




levels (generally below 1 mg/1) when available iron is present.  If avail-




able iron is sufficiently depleted, free sulfides within the anaerobic




regions of deposits will increase until their production at a given location




is balanced by the advective and diffusive transport, out of that location and




by the loss caused by reaction with any remaining available iron.   Measured




free sulfide concentrations up to approximately 130 Jng/1 were found within




interstitial waters of tidal flat deposits though some loss may have occurred




during the analysis.  Theoretical investigations indicate that Tnaximum concen-




trations  might be several times higher if all available  iron is depleted.
                                   16

-------
     If the aerobic layer of the sediment is thin enough to allow light




to penetrate to the anaerobic zone, populations of photosynthetic purple




and green sulfur bacteria may develop, utilizing the free sulfides as  hydro-




gen donors, and producing free sulfur as a by-product.   This may occur




below an algal mat and is possibly due to the lower compensation point for




bacterial photoreduction, and to the ability of the photosynthetic bacteria




to utilize longer wavelengths of light than can the algae (8,11).




     If the rate of free sulfide production exceeds the rate at  which  it can




be converted to nondiffusible forms, such as ferrous sulfide or  insoluble




free sulfur, the sulfide may diffuse upward into the aerobic regions of the




sediment or into the water column.  Here it will be oxidized to  sulfite,




thiosulfate, sulfate, or free sulfur (7,12,13).




     The chemical reaction of free sulfides in aqueous  solutions has been



studied by many investigators (7,12,13,14,15,16).   Half lives of free  sulfide,




in aqueous solutions, ranging from 15 minutes to 70 hours have been reported.




Several studies have described the oxidation of free sulfides to occur via




second order kinetics (6,7,12);  however, such a description is a simplifi-




cation of an extremely complex chemical temperature, pH, and initial oxygen




and sulfide concentrations are all factors affecting the rate of oxidation




(7,12).  The oxidation of free sulfide is catalyzed by  the presence of




metallic ions, such as of Ni, Mn, Fe, Ca, and Mg,  and is accelerated by some




organic substances such as formaldehyde, phenols,  and urea.   Thus,  the oxida-




tion of free sulfides in estuarine and marine water may be much  more rapid




than in distilled water due to the presence of catalysts.  Within oxygenated




sea water the half life of sulfide has been reported to vary from 10 minutes
                                   17

-------
to several hours (7,13,17).  Studies indicate that estuarine waters stored




for a period of time after collection will display slower oxidation rates




of free sulfides than freshly collected waters (18).  Since HS  predominates




at the pH of sea water, it has been proposed that the oxidation proceeds by




the following reaction (19).




                    2HS" + 202^S2°3 + H2°                              ^2)




Following the above chemical  oxidation, the thiosulfate ion is more slowly




oxidized to sulfate, probably with the intermediate production of other




oxidized forms.  Sulfur oxidizing bacteria of the genus Thiobacillus




appear to be important in this final oxidation step (20,21).




     If the benthic deposits  are overturned or flushed with oxygenated water,




ferrous sulfide will be rapidly oxidized.  Overturned sediments will normally




return to anaerobic conditions.  A portion of the ferrous sulfide iron will




be returned to the sediment as available iron which can further react with




free sulfide to form more ferrous sulfide.  Thus overturning and flushing




of sediment with oxygenated waters results in. a recycling of available iron.




     When oxidation of sulfides occurs, either inorganically or by sulfur oxi-




dizing bacteria, some of the free sulfide and ferrous sulfide is oxidized to




elemental sulfur.  In an anaerobic environment elemental sulfur then slowly




reacts with FeS to form pyrite.  This latter reaction occurs on a time scale




of years and may lead to a more permanent depletion of available iron.




     Free sulfide can be released to the overlying water even if these




waters do contain DO.  Experimental and theoretical results presented  in




a latter section of this report demonstrate that free sulfide concentrations




of approximately 1 mg/1 can persist in shallow tidal flat open waters  as  a




result of benthic sulfide release even when the DO of these waters  is  in






                                  18

-------
the 4-6 mg/1 range.  Hydrogen sulfide may also be released to the atmos-




phere particularly when the water depths are shallow or the benthic systems



are exposed.




     High concentrations of free sulfides within the deposits and the




release of free sulfides to the overlying water and atmosphere can be




environmentally significant for a number of reasons; among these are the



following.




     1.   The release of free sulfides can increase the benthic oxygen




          demand rate and thus lead to a decline in the aerobic zone of the




          deposit and a lowering of the DO concentrations within the over-



          lying waters, particularly with the interfacial regions.  Though




          these interfacial regions constitute a very small fraction of the




          estuarine water mass, they are of high ecological importance.




     2.   Free sulfides, particularly hydrogen sulfide, are toxic at low



          concentrations to fish, crustaceans, polychetes and a variety of




          benthic microinvertebrates (8,16,20,22,23,24).  Actual toxic




          concentrations may be considerably lower than some reported in the



          literature because of initial sulfide concentrations within batch




          tests are often reported.  Average concentrations throughout the test




          period may be considerably lower due to chemical oxidation.   In



          tests which maintained nearly constant conditions, hydrogen sulfide




          concentrations below 0.075 mg/1 (pH 7.6-8.0) were found to be




          significantly harmful to rainbow trout, sucker, and walleye,



          particularly to the eggs and fry of these fish (22).




     3.   The release of hydrogen sulfide to the atmosphere can cause an




          air pollution problem.   Not only does hydrogen sulfide have an
                                  19

-------
          undesirable odor but it is also toxic.  Moreover,  the  release




          of hydrogen sulfide from tidal flat areas may be a significant




          input of atmospheric sulfur  (25)(26)(27).




     If the solubilization of organics at a given depth exceeds  the  downward




transport of DO and sulfates to that depth, decomposition of organics below




this depth must proceed through the use of endogenous hydrogen acceptors  (not




shown in Fig. 2).  Increased accumulation of organics can be expected,  particu-




larly if the absence of available iron results in free sulfide concentrations




sufficiently high to inhibit endogenous decomposition.  Methane  fermentation




will occur below the region of sulfate reduction if conditions are suitable.




Formation of gases (principally methane) within these regions nay lead  to




the disruption of the bottom, and the release of free sulfides to the over-




lying water.




 LARGER PLANTS  AND ANIMALS



     The animal component of estuarine benthic ecosystems can be generally




divided into infauna (animals that live within the sediments) and epifauna




(animals that live on the sediment surface or just above it). Some infauna



make ephemeral pockets in the sediment which are filled as the animal moves




on; others make more permanent burrows and bring overlying water into the




sediment.  Much of the infauna is microscopic, living among  the  sediment



particles.




     Although the separation of benthic animals into infauna and epifauna




can be useful,  the following discussion will rely more on feeding behaviors(2)•




Benthic animals are divided into three feeding types:  selective particle




feeders, deposit feeders and filter feeders,  (see Fig. 3)
                                   20

-------
                                                                             AIR
                       EXTRACELLULAR
                       ENZYMES
                                                                           WATER
                                                                          DEPOSIT
INSOLUBLE ORGANICS WITHIN WATER INCLUDE PHYTOPLANKTON, ZOOPLANKTON, DETRITUS, ETC.
         FIG. 3 - CONCEPTUAL MODEL OF LARGER ANIMALS WITHIN BENTHIC SYSTEM

-------
     Selective particle feeders may be herbivores, predators,  or scavengers.

They may feed on whole organisms which they  actively capture,  or they may

feed on fragments of plants or animals.  Crabs,  some worms,  most fishes,

and other more mobile species fall into  this  category.   The  food contains

little inorganic material and is generally broken  down  by mechanical processes

and then by chemical processes.  The residues,  inorganic materials, undigest-

ible organics, and resistant bacteria, are combined  with mucous and coated

to form distinctive fecal pellets.  Fecal pellets  generally  settle to the

bottom and may make up from 30% to 50% of the sediment,  and  in extreme cases,

where quiet bottom waters occur, they may account  for up to  100% of the

sediment  (28)(29).  The fecal pellets of carnivores  are generally loose pellets,

those of herbivores harder, and those of deposit feeders hardest.  Many of

the pellets have characteristic shapes,  size, and  sculpturing, and are of

taxonomic importance.  Some are quite fragile while  others may persist for

.more than 100 years.

     There are two general types of deposit  feeders.  Some move through the

sediment and  take in the sediment as they go, digesting what they can of the

organic material and discarding as feces the  undigestible organics and the

inorganic residues.  These animals are mostly worms  in  estuaries and are not

generally in  direct contact with the waters which  overly the sediments.  Other

deposit feeders bury themselves in the sediment  but  have siphons or other

extensions through which they "suck up"  detritus that has recently fallen to

the sediment surface.  Certain clams and worms  feed  in  this  way.  Again these

species feed unselectively on the available  food and are usually unable to

sort food very efficiently.  Food of deposit  feeders is broken down chemically,

and in some cases mechanically, and the  residues are formed  into fecal pellets

which contain much greater quantities of inorganic materials than do feces of

other feeding types.
                                   22

-------
     Filter feeders sieve water and remove particulate material.  Mussels,




some clams, and some worms are examples of this category.  Most filter feeders




use cilia to create currents of water over a mucous network which entangles




particles.  These are called ciliary mucous feeders.  Mussels are good




examples.  Other species, particularly tube dwellers, may force water through




the tube with peristaltic body movements.  Urechis caupo, the sausage worm,




is an example.  The particle laden mucous is then taken into the digestive




system.  Some clams "sort" the particles before they are taken into the




digestive system and discard the unusable sizes in mucous masses as pseudofeces,




The food that passes through the digestive tract does not usually require



mechanical maceration and is digested chemically.  The feces of filter feeders




are primarily organic.




     Not all animals fit neatly into these feeding categories.  Some deposit




feeders may be somewhat selective, and some selective feeders may be quite




nonselective if food is scarce.  Some animals like starfish that utilize extra-




corporeal digestion are true predators but do not otherwise fit neatly into




the selective feeding type.



     Animals tend to break down larger particles through maceration and diges-




tion.  The formation of fecal pellets places these particles on the bottom



rather than returning them to the water to increase the turbidity.  The fecal




pellets are finally degraded by bacteria, but may pass through several deposit




feeders before final mineralization.



     Certain animals, particularly ciliary-mucous feeders have a marked effect




on the turbidity of the overlying water (30).  These organisms remove particu-




late matter from the water and compact much of it in the form of pseudofeces




which are larger than the suspended particles and therefore sink more rapidly
                                   23

-------
to the bottom.  This reduction in turbidity permits more  light to reach the




benthic algae, enhancing the photosynthetic process and increasing the daylight




DO.  At the same time, the removal of CO  tends  to raise  the pH during the




daylight hours.  Soluble organic wastes of all feeding  types are discarded




into the water or interstitial water depending on the habitat of the particular




species.



     Some benthic plants also tend to stabilize  the benthic environment.   Algal




mats can serve to reduce erosion of benthic deposits.   When such mats become




extensive, they can significantly contribute to  the formation of free sulfide




in the  deposits below.  Other plants, such as eelgrass, send roots into the




sediment, and many burrowing animals construct tubes that also reduce erosion.




These roots and tubes also provide shelter for infaunal species  and may con-




tribute to their food as well.



     Animals also influence vertical mixing within the  sediment.   There is a




great deal of mechanical mixing as burrowing species construct their tubes




or move through the sediment.  Fecal pellets of  infaunal  species  are frequently




brought to the surface and deposited there.  Burrows may  extend more than  a




meter into the sediment and the constant reworking of sediment insures a




relative homogeneity of the sediment to that depth.  Burrows also provide  a




route for oxygen to reach into the sediment, and although sediments may be




anaerobic a few millimeters beneath the surface, there  will usually be an




aerobic region immediately surrounding each burrow if the overlying water  is




not devoid of oxygen.  Conversely, burrows serve as a route through which




waste materials such as fecal pellets and dissolved organics can move out  of




the sediment.   Burrowing activities also serve to release inorganic nutrients




to the surface water where they may be utilized  by photosynthetic plants.




Wave action over a beach filled with tubes may cause a  pumping action through.




                                   24

-------
the tubes, increasing aeration and, possibly, erosion of the wall of the tubes.




Such mixing can also contribute to the oxidation of combined sulfide (sudi




as FeS) and the "recycling" of iron to combine with produced sulfide and thus




prevent high levels of free sulfide.




     The major role of green plants is to convert solar energy into a form




that can be used by plants and animals.  Through the photosynthetic process




inorganic substances are converted into high-energy organic compounds.   This




primary production is the ultimate source of food for all organisms.  Phyto-




plankton, benthic algae and eelgrass are all important primary producers within




estuarine ecosystems.  Organic materials produced by the plant components are



transferred through herbivores and several levels of carnivores to the sedi-




ments.  Feedback occurs frequently so that the web concept is more descriptive




than the food chain.  In the sediment, these materials are mineralized to




their  inorganic end-products and then may again enter the cycle.



     The role of particles in the marine water often is not appreciated.  Heavy



metals may adsorb to these particles and if the particles remain in suspension




they may be carried far to sea before they settle.  These metal-laden particles




may, however, be pelletized by various animals and deposited.  The role of




animals in removing such particles may be very important.



     Many of the effects that have been discussed deal with the transportation




of materials from the water to the sediment, but there is transport in the




other  direction as well.  Benthic species almost always have pelagic larvae.




Essentially all of these larvae must feed and develop within open water regions,




returning to the sediment for later life stages.  Pelagic stages thus insure




wide dispersal of these species.  Propagation of benthic animals thus depends




on the ability of pelagic life stages to leave the sediment.






                                  25

-------
                              SECTION V




                 DESCRIPTION OF SITES USED FOR FIELD STUDIES








     Five sites were used during various stages of this study for the




field studies.  The four sites located within Taquina Estuary are shown




in Fig. 4.  Site 1 was located on the south side of the estuary immediately




to the east of the Oregon State University Marine Science Center.  This




site lay within approximately one mile of the estuary mouth, and was strongly




influenced by marine water.  High salinities (33-35 parts per thousand), low




temperatures  (45-50°F), and high, tidal current velocities (0.6 - 0.8 feet




per second) were characteristic here.  This area appeared to be fairly




remote from, any major source of industrial pollution, and no excessive




domestic contamination was evident.  The sediments here were heavily




colonized between +4 and +6 feet above mean low low water (MLLW) by large




populations of the mud shrimps Callinassa californiensis and Upogebia




pugettensis.  They were very active in burrowing and mixing of the sedi-




ments at this elevation.  There was a distinct lack of attached vegetation




in this range, but summer growth of the benthic alga Enteromorpha and of




Zostera was extensive below +4 feet MLLW.  At approximately +7 feet MLLW




the sediment was covered by a thin, but very firm mat of unidentified




algae.  A transect of total sulfides, redox potential and volatile solids



at site 1 is shown in Fig. 5.




     Site 2 is located in the eastern portion of the Sally's Bend area of




Yaquina Bay.  Water velocities w.ere high at times though usually slightly




lower than site 1.  Burrowing by frenthic invertebrates was common in this




region.  During summer periods, benthic algal growths: were noticeable.




Only limited studies were conducted at this site.




                                   26

-------
     Site 3 is approximately three miles upstream of site 1 on the east




side of the Yaquina estuary adjacent to Parker Slough.  Waters here are




slightly less saline, have higher temperatures, and slightly lower tidal




velocities compared to site 2.  Burrowing by benthic invertebrates is




extensive, as are mid-summer blooms of the benthic alga, Enteromorpha.




The only studies conducted at this site were measurements of benthic oxygen



uptake rates.




     Site 4 was located about 14 miles upstream and 300 feet east of the




Yaquina River bridge at Toledo.  Unlike site 1, this site lays in an indus-




trialized area characterized by extensive log rafting and wood processing



operations.  The effect of fresh water was reflected in the lower summer




salinities (14-20 parts per thousand).  Water temperature was higher than




at site 1, current velocities still fairly high, and the sediments were often




covered by large quantities of bark chips.  Burrowing organisms and dense



growths of benthic algae were lacking.




     Site 5 was located on the south side of Isthmus Slough in the Coos




Estuary.  This site was located on a mud flat which was relatively



protected from the main channel currents by a dike and log storage area.




Tidal velocities were low, temperatures comparable to those at site 2, and




salinities intermediate between those of sites 1 and 2 (28-30 parts per



thousand during summer months).  A number of sulfite process woodpulping




mills were located nearby.  Extensive algal mats primarily of a salt water




species of Vaucheria were characteristic here, but burrowing organisms




were not evident.  Organic content of the sediments was high.  A general




purplish coloration to the water was very noticeable due to the photo-




synthetic purple sulfur bacteria.






                                   27

-------
     A comparison of particle size for the  three major sites  is  given in



Table 1.  Bacterial  counts for sites 1, 2,  4  and 5 are given  in  Table 2.
              PACIFIC
              OCEAN
                                                      TOLEDO, OREGON
                    Statute miles
                    FIG.  4 - SITES LOCATED ON YAQUINA ESTUARY
                                  28

-------
     60O-
     400-
     200-
is
    -200-1
       o-
    + 200-
                              (A)  TOTAL SULFIDES
               7.2
                                  40     3.1      1.6


                           TIDAL  ELEVATION (feet above MLLW)
                                                       i	r
                                                     -0.8    -2.3
                                                                   -3.6
                              (B)  REDOX POTENTIAL
                                                       i      r
                                                     -0.8    -2.3
                                                                   -3.6
                           TIDAL ELEVATION (feet above MLLW)




                              (C)   VOLATILE SOLIDS
                           TIDAL ELEVATION (feet above MLLW)
               FIG.  5 -  TRANSECT AT SITE 1  -  SUMMER  1970
                                       29

-------
                            TABLE 1.  PARTICLE SIZE FOR SAMPLING SITES
Depth
Site 1
Sand (a) Silt
(cm)
0 -
2 -
4 -
7 -
11 -
1
3
5
8
12
92.2
99.3
87.6
93.1
95.3
and clay (b)
7.8
0.7
12.4
6.9
4.7
Site
Sand

15.8
14.0
8.0
9.7
11.9
2
Silt
and clay
84.2
86.0
92.0
90.3
88.1
Site 3
Sand Silt

2.9
1.3
0.6
2.3
3.9
and clay
97.1
98.7
99.4
97.7
96.1
(a)   Percent of particles larger than 63 microns.
(b)   Percent of particles smaller than 63 microns.

-------
      TABLE 2.   BACTERIAL COUNTS PER GRAM OF WET SEDIMENT  (SUMMER,  1970)
Location Depth
Site 1, 3.1 ft. 0- 1
MLLW
2- 3
4- 5
10-11
Site l,-2.3 ft. 0- 1
MLLW
2- 3
4- 5
Site 2 0-1
10-11
20-21
27-28
30-31
35-36
Site 4 0-1
10-11
20-21
30-31
Site 5 0- 1
2- 3

4- 5
7- 8
11-12
cmCc)
cm •*
«Cc>
cmCc)
cmCc:i
cm^
«)   MPN using modified SIM medium or a modified medium for halophilic sulfate
     reducing  bacteria (30). (numbers per gram of wet sediment)
(c)   Determined on 1 date
(d)   Average on 2  dates
(e)   Average on 3  dates                  31
(f)   Average on 4  dates

-------
                              SECTION VI


                    STUDIES OF BENTHAL OXYGEN  UPTAKE





INITIAL LABORATORY STUDIES


     During the early stages of this project, a series of laboratory tests


were conducted to determine the oxygen uptake rate of deposits removed from


site 4 (32) (33).   Mud cores were obtained by inserting 3-inch plastic tubes


into the deposit.  The tubes, with the deposit, were removed to the labora-


tory where tests were conducted within the same tubes to determine the


benthal oxygen uptake.  Mixing within the overlying water was provided by a


plunger type mixing device.


     These early laboratory results determined a benthic oxygen uptake rate

                         2
of approximately 1.9 gm/m /-day under conditions of low mixing and an uptake

                              2
rate of approximately 3.4 gm/m -day under conditions of higher mixing.  It


was found that the depth of the deposits had no effect on the oxygen uptake


rate between the depths of 5.1 and 30.5 cm.  When HgCl  was added to the water,


the DO uptake rate decreased to one third of its value at both the lower and


higher mixing ranges.  These early laboratory studies provided information for


the design of the field respirometer described below.


EXPERIMENTAL DESIGN AND PROCEDURE FOR FIELD STUDIES


     Light and dark benthal respirometers developed during this research


were constructed from plexiglas half cylinders, 5.64 meters long by 0.152


meters wide (34) (35).  The resulting long and narrow respirometer covered a

                     2
benthal area (0.813 m ) large enough so that small isolated inconsistencies in


bottom muds would not cause great variabilities in uptake rates.  The


long, narrow shape was also required for simulation of actual mixing con-


ditions.  In the respirometer designed during this project, velocities



                                  32

-------
typical of a specific test site were generated over bottom muds by recircu-




lating water in the enclosed long respirometer.  A flow development section




was constructed on the inflow end of the respirometer to distribute the




flow evenly over the respirometer cross section.   With the volume to area




ratio used, reasonable oxygen uptake rates could  be measured in four to




eight hours.  Removable flanges were designed so  that the flange portion of




the respirometer could be inserted into the bottom deposit some time before




the actual respirometer sections were attached.  In this way, the bottom




deposit was allowed to come to equilibrium before attaching the respiro-




meter sections, pump and sampling hoses.  The respirometer sections were




made in about 4-1/2 foot lengths and could be installed on the preset flanges




at low water.  Rubber gasket material sealed all  joints between flanges and




respirometer sections.  Water was recirculated in a 1-1/4 inch PVC pipe




using a 1/4 hp submersible impeller-type pump. A 1-1/4 inch brass gate




valve regulated pump discharge and therefore the  velocity within the




respirometer.



     The respirometer was attached to the preset  sealing flanges at low




tide and a typical sampling run was conducted during the time that the area




was covered with water within a tidal cycle.  Samples, 20 ml in size,  were




brought to the surface and analyzed in the field  for dissolved oxygen using




a "Micro-Winkler" modification of the Standard Winkler-Azide method.   DO,




temperature and salinity were measured both inside and outside of the  respiro-




meter.  The water removed for the samples was replaced with estuary water




through a one-way valve which allowed water to flow only into the respiro-




meter as samples were extracted.  The displaced volume for all samples on the




longest run was less than 4% of the total respirometer volume.  Temperatures







                                  33

-------
were taken in place with thermistors inside and outside the respirometers.




Diagrams of the benthal respirometer have been published (34) (35).




     To measure the amount of oxygen uptake due to free-floating organisms




in the bay-estuary water, planktonic respirometers were developed.  Light




and dark planktonic respirometers were constructed of three inch diameter




plexiglas tubes, six feet in length.  A small submersible impeller pump was




attached to one end and water was recirculated through the tubular respiro-




meter body at approximately 0.2 feet per second.  Exterior hose arrange-




ments used to recirculate the enclosed water were constructed so that the hose




could be brought to the water surface for sampling.  Methods of dissolved




oxygen sampling and analysis were the same as those used for the benthal




respirometers .



     During the second grant year, a simpler benthal respirometer was also




developed and used.  This simplified respirometer had attached flanges, was




4 feet long and had a small recirculation pump not capable of producing the




higher velocities possible with the large respirometer.  Both light and dark




respirometers of this type were developed.




     Tests indicated that only seven to eight percent of the visible light




was obstructed when passing through the 1/8-inch thick plexiglas from which



the respirometers were constructed.




MATHEMATICAL  MODEL OF  BENTHAL  RESPIROMETER SYSTEM



     To more thoroughly explain and analyze the results of the respirometer




study, a mathematical model of the benthal respirometer system was developed.




During the early benthal respirometer runs, excessive leakage was evident at




site 2.  The leakage was found to be principally caused by extensive mud




shrimp burrow activity.  A mathematical simulation and leakage correction






                                  34

-------
model became a necessity for evaluating leakage as well as helping to determine

the importance of different mechanisms or processes of benthal DO uptake.  The

model was applied to all test runs where salinity data were taken, and corrected

DO uptake rates were calculated where leakage existed.  Salinity data were

used to evaluate leakage rates.

     Definition of terms for the following mathematical model are shown in

Table 3.  The mass balance concept is shown by the following expression.

     Rate change of sub-           Rate of substance        Rate of sub-
     stance mass within the   =    input into the       -   stance output
     respirometer volume           volume                   from the volume  (3)

From Table 3 and equation (3), one obtains the following salinity balance:

Salinity Balance:

               d(Sr) = (Q) (Sw)   (QJ (Sr)                              (4)
                dt       Vr        Vr

It was assumed that the only mechanism of salinity change was by direct leak-

age into and out of the system and that the volume of the respirometer was

constant and completely mixed.  0. and Q2 were assumed to be equal to Q.

Some initial changes in salinity might be caused by bottom scour, but such

changes that might arise from diffusion of material into or out of the bottom

deposit were also considered to be small compared to changes due to leakage;

therefore, terms containing Sb do not appear in equation (4).

     A similar approach was used to model the changes in oxygen demand (BOD)

and dissolved oxygen.  The following equations resulted.

Biochemical Oxygen Demand (BOD) Balance:
                               .         _
                                  35

-------
         TABLE 3.  DEFINITION OF TERMS FOR RESPIROMETER MODEL
Term
Sw

DOw


Lw

Sr

DOr


DOri
Ob
               Units

               ml/min

               ml/min

               o/oo

               mg/liter


               mg/liter

               o/oo

               mg/liter


               mg/liter
Lr
Lri
Vr
K
Sb
Lb
Lbr
mg/liter
mg/liter
liter
1/min
o/oo
mg/liter
mg/min
               mg/min
               m
Description

Possible leakage into the system.

Possible leakage out of the system, Qi=Q2-

Salinity in the overlying water.

Dissolved oxygen concentration in the
overlying water.

Oxygen demand of the overlying water  (BOD).

Salinity in the respirometer.

Dissolved oxygen concentration in the
respirometer.

Initial dissolved oxygen concentration
in the respirometer.

Oxygen demand of the respirometer water (BOD).

Initial oxygen demand of the respirometer
water.

Volume of the respirometer.

Decay coefficient of the oxygen demand.

Salinity of the bottom muds and interstitial
water.

Oxygen demand of the interstitial water (BOD),

Rate of input of oxygen demanding material
into the respirometer system from the
covered mud area (A).

Rate of oxygen diffusing into the covered
bottom mud area (A).

Mud surface area covered by the respirometer.
                                      36

-------
Dissolved Oxygen Balance:

               d(DOr) _  (QJ(DOw)   (Q) (DOr)    n f  ,   Ob
               ~dt         VrVr~~ ' CKJ CLrJ " Vr"

     It was assumed that the rate of input of oxygen demanding material into

the respirometer (Lbr) was independent of changes in respirometer BOD (Lr).

No measurements were made to determine the interstitial BOD (Lb). Planktonic

respirometer studies indicated that Lw was negligible.  The diffusion of

oxygen into the bottom deposit (Ob) was assumed to be at a constant rate.

CALCULATION OF LEAKAGE

     The availability of the benthal respirometer model made possible

the calculation of leakage rates for the respirometer system using only

salinity data for water in the respirometer and outside of the respiro-

meter.  By multiple regression analysis, curves could be fitted to

measured salinity data so that the  vj-.- • , Sw, and Sr could be evaluated

at any time.  Respirometer volume was a constant value of 60.4 liters.

Therefore, all necessary values in the salinity mass balance equation

were known, and estimates of leakage rates that occurred could be calcu-

lated using equation  (4).

DO UPTAKE RATE CALCULATIONS

     Equations (4) and (6) were solved using the Runge-Kutta method for

finite difference solutions.  Fourth order solutions were obtained.

Curve fits were used to input required measured quantities such as

(DOr), (DOw), (Sr), and  (Sw).  By solving the salinity equation (4)

and the dissolved oxygen equation (6) simultaneously, total oxygen uptake

could be calculated by assuming (-K(Lr)-Ob/Vr) to be the unknown rate

of benthal oxygen demand exerted within the respirometer.  When the

build up of BOD within the respirometer and the removal of BOD from the


                                   37

-------
respirometer is small, the total benthal uptake exerted within  the




respirometer may be divided by the bottom area of the respirometer  to




obtain the benthal oxygen uptake.  Neglect of BOD build up and  release




will lead to underestimates of the benthal oxygen uptake.  Studies




indicated, however, that this underestimate was quite small and could




be neglected for the reported runs.  Corrections could then be  made for




respirometer leakage.  Therefore, even respirometer runs with high




leakage rates could be corrected to obtain estimates of the oxygen




uptake rates.



     During most benthal respirometer runs, slightly more rapid rates




of oxygen demand were measured in the first hour of the run than for



any succeeding time period.  Furthermore, small increases in salinity




usually occurred inside the benthal respirometers at start-up.   Therefore,



during benthal respirometer start-up, water in the respirometer was




replaced by disconnecting the return flow pipe at the PVC union and




allowing the pump to introduce water into the respirometer.  Even then,



rapid initial oxygen uptake often occurred.  Only DO measurements taken




after the initial rapid uptake were utilized in calculating DO uptake



rates.




DO UPTAKE RESULTS



     Light and dark planktonic respirometers failed to show any measureable




oxygen demand or production at either of sites 1,3 and 4.  Large mats of




phytoplankton often found at site 3 were not included within these runs.




Large DO variations, often found in the areas in which these dense growths




appeared, indicated that production of dissolved oxygen and respiration by



these growths is significant.
                                   38

-------
                         Parker Sloueh tests
                                                   Large  amounts of leakage
                                               O = Normal operation, little leakage



                                                  = Severe initial bottom scour
          Q
FIG.  6 - SUMMARY OF CORRECTED  BENTHAL OXYGEN UPTAKE RATES AT  SITES 3  AND 4.  (1969)
                                           39

-------
     Using the large dark respirometer, sufficient field data  to  calculate



leakage and uptake rates were collected during four runs at the Parker  Slough



site and during seven runs at the Toledo test site during the  first  grant



year.  The DO changes within the respirometer runs were corrected for leakage



as described above (34)(35).



     At site 4, benthal uptake rates averaged over each run ranged from 1.4 gm


    2                  2
0 /m -day to 2.1 gm 0»m -day based on projected surface area.  In all runs, the



DO uptake rate decreased with time as shown by the decreasing  slope  of  the curves



shown in figure 6.  Leakage rates and actual DO concentrations within the



respirometer also decreased with time.  This resulted in apparent relationships



between the uptake rate and the DO concentration and water velocity  as  shown



in Fig. 7.  Whether these relationships are true or whether they  merely



reflect the simultaneous occurence of unrelated variations is  not apparent at



this time.



     Table 4 summarizes the average uptake values measured at  site 4 for the



various mixing velocities used.  Table 4 also shows the benthal uptake  rates



for the same muds measured in the laboratory studies.  As can  be  seen,  the



in-lab mixed value is slightly higher than the values for benthal oxygen uptake



measured during this research.  Uncontrolled mixing, sample disturbance,



differences in benthal plant respiration or a benthal deposit  composition change



might all account for these differences in uptake rates.



     Excessive benthal respirometer leakage occurred at the site  3 test site



as was seen by monitoring the salinity changes in the respirometer water.



Leakage rates, calculated by use of the mathematical model, as high  as  60



liters per hour were not uncommon.  Extreme care during benthal respirometer
                                      40

-------
3-
T3
bo





I
I

c
    2i40
    1.92
    1.44
    0.96
    0.48
              i      r
                                            I
                                                            J_
         012           345




                             Dissolved oxygen concentration, mg/1




                 •  = 9-3-69, Velocity of 0. 4 fps



                 V  = 9-5-69, Velocity of 0. 4 fps



                 O  = 9-8-69, Velocity of 0.55 fps



                 A  = 9-9-69, Velocity of 0.8 fps








  FIG.  7  - VARIATION  OF BENTHAL UPTAKE RATES  AT SITE 4.  (1969)
                                   41

-------
placement did not result in a significant reduction of the leakage.  Dye


injections into an operating benthal respirometer at site 3 showed that the


respirometer leaks were caused by the numerous mud shrimp burrows that


penetrated the area.  The mud shrimp burrows apparently formed an interconnect-


ing maze of channels in the tidal flat deposit.  On several occasions at low


tide, surges of water were observed coming from shrimp holes located upshore


from the low tidal water.  The observed surges had the same period as small


waves breaking against the exposed tidal flat.  This further substantiated the


inference that the shrimp burrows formed interconnecting networks and could form


passages for water circulation.

                                                                       2
     Computer corrected benthal uptake rates of from 4.8 to 8.5 gm 0 /m -day


were calculated for site 2.  Before correction for leakage rates, comparison


of DO changes within the respirometers for the four runs at the Parker Slough


site showed little similarity.  The rates of DO change were significantly


different and increases in the respirometer DO were occasionally measured.


After correcting for leakage, the corrected DO changes showed a definite pattern.


Three of the runs displayed quite similar uptake rates (see Fig. 6) while


the fourth run displayed a lower uptake rate.  The leakage rates for this


fourth run were quite high and not reliable due to the small measured salinity


difference inside and outside of the respirometer.  The most reliable results,


therefore,  indicate that the Parker Slough area displayed an oxygen uptake rate


approximately 4 to 6 times greater than that of the Toledo area, or about

      2
8 gm/m -day.


     Simultaneous measurements using both the dark and light smaller respiro-


meters  indicated that the total benthal oxygen uptake depends to a large


extent on the respiration of benthal plants.  In regions of relatively high
                                      42

-------
benthal photosynthetic oxygenation, as determined by a transparent benthal

                                          2
respirometer, uptake rates of 3 to 6 gms/m -day were measured at site 1.  At

                                         2
this same site, a lower rate of 1.4 gms/m -day was measured in a region of low


benthal photosynthesis.  These results, in which the smaller respirometers


were used are probably not as reliable as results obtained through the use of


the larger respirometer.


     The larger uptake rates measured at site 3 compared to site 3 (both


measured by the large respirometer as previously discussed) appear to be due


to the large number of shrimp burrows at site 3 and the larger amount of benthal


plant respiration.  Though no light respirometer runs were conducted at site


3, the extent of benthal photosynthesis was evident by measured DO concentrations


as high as 25mg/l.  Also, the bottom at site 3 was observed to be covered with


fine bubbles (presumably oxygen) on several occasions.  Several respirometer


runs had to be rejected because of the release of DO in the form of bubbles


within the respirometer.  Collection of the gas was attempted with limited


success.  Therefore, only those respirometer runs in which the DO was sufficiently


below saturation to prevent bubble formation were utilized.


     A single small dark respirometer run at site 4 measured an uptake rate

                        2
of approximately 4 gms/m -day.  A study of DO variation within the overlying


water indicated, however, that rates as high as 12 gms/m -day might be expected.


     Both laboratory and field studies indicated that the DO uptake rate was


reduced by 30 to 40 percent when the system was poisoned with mercuric chloride.


These experiments, however, were quite limited.


     A summary of the principal benthic oxygen uptake rates measured in this


study along with examples of rates provided from the literature are snmmarized


in Table 4.
                                     43

-------
               TABLE  4.   SUMMARY OF BENTHIC OXYGEN UPTAKE RATE
Reference
This study (32) (33)
This study (32) (33)
This study (34) (35)
This study (34) (35)
This study (34) (35)
This study (34) (35)
Mekeown et al (36)

Mekeown et al (36)

Rolley and Owens (37)
Edwards and Rolley (38)
Edwards and Rolley C38)
DO Uptake Rates
gms/m^ - day
1.9
3.4
1.4
1.7
2.1
4.7-8.5
0.8

2.7

1.2
2.8-4.8
29
^ 	 __
Comments
Laboratory estuarine sediments,
(site 4) , low mixing
Laboratory, estuarine sediments,
(site 4), high mixing
In situ (site 4), estuary,
velocity = 0.4 fps
In situ (site 4) , estuary,
velocity =0.55 fps
In situ (site 4) , estuary,
velocity = 0.8 fps
In situ (site 3) estuary burrow
holes present
Laboratory, artificial deposit,
no mixing
Laboratory, artificial deposit,
mixing
Laboratory, river muds, frequency
distributions provided
Laboratory, river muds, several
temperatures, magnetic stirring
Laboratory, river muds, magnetic
 Hanes  and  Irving  (39)

Stein and Denison (40)


Pamatmat and Banse (41)
   3.2

  5-6


0.6-1.2
 stirring,  bottom scour

 Laboratory,  magnetic stirring

Laboratory, Magnetic stirring,
some scour

In situ, Puget Sound, belljar,
stirring prop., deep water
                                      44

-------
TABLE 4.  SUMMARY OF BENTHIC OXYGEN UPTAKE RATE (cont.)
  Reference
 DO Uptake  Rates      Comments
,  gms/m2  -  day
  Fair  et al  (42)                 1.2-4.6
  Baity (43)                      1.8-5.4
  Ogurrombi  and Dobbins  (44)
  O'Connel  and Weeks  (45)          4.4
  O'Connel  and Weeks  (45)         0.15-8.5
                      Laboratory, continuous water flow,
                      artificial deposit,  long term

                      Laboratory, continuous water flow,
                      artificial deposits

                      Laboratory, artificial deposits,
                      magnetic  stirring

                      Laboratory, artificial deposit,
                      partial scour

                      In  situ,  water current mixed
  SENSITIVITY STUDY

        To further understand the mechanisms that control benthal oxygen uptake,

   sensitivity studies were made using the mathematical model previously

   described.  Numerical approximations to the solutions of these equations  were

   obtained by fourth order Runge-Kutta methods.   By varying parameters  in the

   dissolved oxygen equation and the BOD equation,  curves of oxygen uptake similar

   to those measured were developed.  It was found  that, with the equations  pre-

   viously proposed, simulated DO variations corresponded to actual measured DO

   variations only if a major portion of the oxygen demand was  due to  one of the

   following:

             A.   the transport of oxygen from the water into the  deposits,

             B.   demanding material  released from the deposit into the water or

             C.   combination of A and B from above.
                                        45

-------
     First order decay coefficients,. K, needed  in  assumption B were 10 to 100




times greater than those normally encountered for  BOD tests  of polluted




waters.  These results suggest that, under normal  water flow conditions,  the




principal oxygen uptake due to tidal flat deposits occurs  in the immediate




vicinity of the deposits.  Sulfides released from  the anaerobic regions could




contribute toward such an uptake, though later  research indicates that this




was doubtful at this location.




     It should be recognized, however, that respirometer studies  of approxi-




mately six hours may be too short to accurately measure the  long term  release




of BOD.  High BOD values in tidal flat waters were not  found,  indicating that




such a mechanism was probably not substantial.  Accurate measurements  of BOD



(possibly COD) throughout a respirometer run might lead to better estimates




of such release.  In general, it was found, however,  that the  BOD values were



too low for sufficient accuracy.
                                  46

-------
                              SECTION VII




                   FREE SULFIDE IN OVERLYING WATER








GENERAL




     During the second year of the project, it became apparent that the




sulfur cycle was of major importance.  From an environmental quality




viewpoint, the benthic release of free sulfide was considered to be of




major interest for three reasons:  (1) Free sulfides exert an oxygen




demand,  (2) free sulfides are highly toxic to a wide variety of organisms




and  (3)  the release of hydrogen sulfide to the atmosphere could be a



major source of atmospheric sulfur.




     In  order to obtain free sulfides within estuarine benthic deposits




it is necessary to have a sufficient production of sulfides, primarily




through  sulfate reduction, for a long enough duration of time to suf-




ficiently reduce the available iron.  Conditions favorable for the presence




of benthic free sulfide include high salinity (and thus high SO.), slight




wave and current scour of bottom (to prevent oxidation of ferrous sulfide




and "recycling" of iron) and a high organic content within the deposits.




Site 5 appeared to best provide all of these conditions; moreover, the




bright purple color at portions of the mud surface and under algal mats




indicated the presence of photosynthetic purple sulfur bacteria and thus




the presence of free sulfides.



     Even if free sulfides were present within the deposits, it was




questionable at that time if they would be found at levels sufficient for




measurement within the overlying water if the dissolved oxygen in this
                                   47

-------
 water were not  depleted.  This  question was  examined by a number of mathe-

 matical  models  at  the  same  time that analytical methods for measurement of

 sulfides were examined.   The  assumptions  made to develop these models

 generally contribute to  conservative (low ) estimates of free sulfide con-

 centrations  in  oxygenated waters.   The following two sections describe two

 models  used  in  this  portion of the  study.

MODEL OF FREE SULFIDE TRANSFER  THROUGH AEROBIC ZONE

      Consider a vertical column of  deposit  of cross-sectional area,  A.   While

 oxygen  demanded substances  (free sulfides)  diffuse upward,  DO diffuses  downward

 from the surface.  A second-order reaction  between the DO and these  substances

 is assumed.  The depth of the  deposit,  z, is  taken as zero  at the surface with

 positive values increasing  with depth.  The chemical loss rate of DO per unit

 volume  of deposit, G,  was taken as

                G = yOCAndz                                        (7)

 in which

                n =  the  volume of interstitial water within the slice

                     divided by the  total  volume of the slice,

                0 =  the  DO  concentration,

                V =  the  second order reaction coefficient and

                C =  the  concentration of  oxygen-demanding material



      The diffusive and advective flux,  F, of oxygen within  the deposit  was

 taken as
                          30
                F =" D0Am IF + Aq°                                     (8)
 in which

                m = the fraction of  the  surface area open to diffusion,
                                   48

-------
               q = the water transport rate per unit area, and



              D  = the effective diffusion coefficient for DO.
               o


     Performing a mass balance on a segment slice of depth dz and taking A,



n, D  m, and q constant with distance, and A and n constant with time leads  to
               80    o  80   q 90

               W=—~2nW-
                        oZ
As an approximation, both m and n may be taken as equal to the porosity.



In the following, advection will be taken as zero.  Thus equation (9)  reduces



to




                           - yOC                                      (10)

Similarly, for the oxygen -demanding substances,
               W ' Dc
is obtained in which D  is the effective diffusion coefficient for C.
                      c


     The benthal oxygen uptake, OD', caused by materials included in C,



is equal to the sum of the DO flux into the deposit and the flux of C out



of the deposit.  Thus





                          an            3P
               OD' = (Dm|Ł)    - (D m^O                           (12)
                       o  8z Z=Q     c  3z z=Q





Respiration of benthal algae and oxygen demand of materials not included



within C will contribute to the benthal oxygen uptake rate but are not included



within OD'.


                                  49

-------
     Approximations to the solutions of Equations  10 to  12 were  obtained

by explicit finite difference methods. (46)  Several runs were also

satisfactorily compared with an implicit finite difference scheme.

     The relationship between the free sulfide concentration, S,  and  C will

depend on (a) the mass of free sulfides oxidized per mass of DO  utilized

and (b) the fraction of C caused by free sulfides.  As an approximation, S

may be taken as 50 to 100 percent of C.  Let


               P  .^H-°                                        C13)
                W     OD!

The model results indicated that P ranged from 0.4 to 0.8 with highest

values associated with low diffusion coefficients, low oxidation  rates (low y)

low dissolved oxygen concentrations in the overlying waters  and high  benthic

oxygen uptake rates .  Additional benthic oxygen demand not included in the

model would result in a further reduction of DO penetration  into  the  deposit

and thus higher values of P .  Thus, the computed values of  P  may well be

underestimates.  The results indicate, therefore,  that substantially  more

than half of the upward diffusing free sulfide would be  released  to the

overlying water rather than being oxidized within  the deposit.

MODEL OF FREE SULFIDE IN OVERLYING WATER

     Consider a vertically mixed column of water of depth H  and  horizontal

area A.  A deposit at the bottom of the column has a total oxygen uptake rate

given by OD.  The upper surface of the water column is exposed to the air,

performing a mass balance of sulfides within the column  and  assuming  a

steady state leads to

                   YP P OD
               s =
                                   50

-------
in which




               S  = the sulfide concentration,




               Y  = the mass of S oxidized per mass of DO utilized,




               P  = the fraction of OD resulting from free sulfides formed



                    within the deposit,




               K  = the first order decay coefficient for free sulfides



                    (equal to yO),




               K.  = the transfer coefficient of H?S across the air-water interface




                    and




               f  = the fraction of the free sulfides present as H?S.








     Because of the simplifying assumptions of equation 14, large differences




between computed and observed value, should be expected.   Estimates of



parameters  for equation (14) which might apply to late summer conditions at site 5




are given in Table 5.   It is emphasized that these parameters were rough




estimates based on a varied and limited amount of information.



     The range of free sulfide concentration, S, in the overlying water




computed by equation (14)  using the parameters shown in Table 5 is enclosed by




the solid lines of Figure 8.  These results illustrate that significant




sulfide concentrations in the overlying water may occur under conditions




similar to those found at Site 5.




     During the late summer and early fall of 1970, water directly above the




sediment of the four sites was monitored during a tidal cycle for dissolved




free sulfides and  DO.   Profiles of DO and free sulfides above the bottom were




determined by simultaneously drawing water into six 50-cc plastic syringes




attached by small-bore tygon tubing to six l.S-rnm inside diameter stainless
                                       51

-------
Cn
ro
            100
             10
            1.0
            O.I
Approx. DO
  (mg/L)
                   o
   4.0
   8.0
              0.01
          O.I            1.0             10

            FREE SULFIDES  (mg/L)
100
                         FIG. 8 - RANGE OF FREE SULFIDES IN OVERLYING WATER.

-------
             TABLE 5.  ESTIMATED PARAMETERS  APPLICABLE TO SITE 5
                              DURING  THE  LATE SUMMER
                              AND EARLY FALL PERIOD
Parameter Range
Y 1.0
Pw 0.8
Ps 0.3-0.4
OD 4.0-12.0 ( gins /m2 -day)
K 8.0-70.0 (per day)
KA 0.5 (meters/day)
Ł 0.4-0.5
Reference
(12)
This work
(32) (33)
This work a
(7) (13) (16) b
(58) (59) (46) c
d
a - estimated  from  field  studies.

b - obtained in  sea and brackish water.

c - reference  (59)  shows  similarity between DO and ^S transfer;  reference
    (58)  gives DO transfers  for low wind  velocities.

d - based on pH  of  approximately 7  at site  5.
                                       53

-------
steel tubes set horizontally at varying heights above the deposit.   Determina-




tion of DO was made on 20-ml water samples collected in 30-cc plastic syringes




by a micro-Winkler method (32).  Free sulfides were determined by immediately




fixing 20 ml of water sample inside the syringe with an equal volume of 50




percent antioxidant buffer solution.  The standard solution, which contained




320 g, sodium salicylate, 72 g ascorbic acid, and 80 g sodium hydroxide and




made up to 11 in distilled water, prevented further oxidation of sulfide and




fixed the free sulfides as essentially all free sulfide ions (6).  Sulfide




content was then determined by measuring potential on a pH meter equipped




with a sulfide membrane electrode and reading the sulfide concentrations from




a standard curve developed prior to each run (47) .  This method was compared




with results obtained titrimetrically with iodine (48) and titrimetrically with



lead perchlorate using the probe as an end-point indicator (47).  Results




showed close agreement among all three methods.



     The variable ionic strength of estuarine waters was a source of error




in the sulfide measurements.  Calibration of the probe was done with distilled




water with the antioxidant buffer solution and thus reported free sulfide



concentrations can be expected to be as much as 20% low.  The method of free




sulfide determination was later changed to the subtraction method (47) to




avoid this problem.  Free sulfide and some oxidation products of sulfide can



be expected to result in lower measurements of DO. Thus reported DO values



may also be underestimated particularly at low DO and high free sulfide values.




     Free sulfide and DO profiles measured during daylight conditions at




Site 5 are shown in Fig. 9.  Because of the benthal photosynthetic oxygenation,




DO values were highest near the mud-water interface.  Significant free sulfide




concentrations were measured despite the relatively high DO values.  Higher free
                                     54

-------
                               DO (mg/liter)
                              5.0         10.0
                                                    15.0
                              0.5         1.0
                           FREE SULFIDE (mg/liter)
                                                    1.5
FIG.  9 - DISSOLVED OXYGEN AND  FREE SULFIDE  PROFILES AT  SITE 5
                            55

-------
                                                                2400
                                        I      I     I     I    I
                                        I	1	1	1
      2000
FIG. 10 - DISSOLVED OXYGEN AND FREE SULFIDES AT  SITE 5
                         56

-------
sulfide concentrations were measured in the low mixed water region  immediately




adj acent to the mud-water interface.




     Results from four sampling periods at site 5 are shown in Fig. 10.



Samples for the runs shown in Fig.  10 were collected above the one  centimeter




distance from the bottom.  These results demonstrate the significant free




sulfide concentrations can occur in waters at site 5 even in the presence




of dissolved oxygen.  The relatively stable free sulfide concentrations



shown in Fig. 10 are plotted with approximate water depth on Fig. 8.




These free sulfide concentrations were within the range roughly estimated by



equation 14 and the parameters of Table 5.




Free Sulfide Measurements at Other  Sites:  Attempts were made to measure



free sulfides in the overlying waters of sites 1 and 4.  Free sulfides were




not detected at site 1.  At site 4, free sulfides were detected at  low levels




(1 mg/1 or less) only for a few samples collected when wave action  appeared




to disturb the bottoms in the immediate vicinity of the sampling.   These




occasional measurable levels may have been false readings due to the inter-



ference of iron on the sulfide probe.  Such measurements at both sites,




however, were quite limited and were not sufficient to determine possible




seasonal releases of free sulfides.




     During the late summer and fall, the Enteromorpha and Zostera




present at site 1 begin to decompose (49).  During this same period, redox




potentials dropped dramatically in  the upper few centimeters of the sediment,




microinvertebrates were observed to migrate from the sediments into the



overlying algal material, and the smell of hydrogen sulfide was noticeable (49)




It is likely that sulfide release may occur at site 1 during this period




where benthic algal growth is substantial, however, sampling was not




conducted during this period.





                                  57

-------
                             SECTION VIII
                  CONDITIONS WITHIN BENTHIC SYSTEMS
FIELD MEASUREMENTS
     While it is true that estuarine benthic systems can strongly influence
the overlying air and water quality, they must not be viewed only as a
boundary condition of the overlying regions.  Benthic systems are of major
importance to the total estuarine systems .  If they are to be understood, a
variety of sediment and water quality measurements must be taken within the
benthic systems.
     During the final grant year of this project a field investigation of
benthic deposits within tidal flat regions was conducted.  Sediment cores
were collected at sites (usually during low tide) using plexiglas coring
tubes.  Cores from which interstitial water was obtained were extruded into
a plexiglas slicing trough and sliced into desired sections.  Sections
were immediately placed into field presses so as to prevent chemical oxidation.
Interstitial water was extracted in the field within thirty minutes after
collection of deposit cores.  Four field nylon presses (50) were constructed
for this purpose.  Pressure not exceeding 150 psi was applied through the use
of nitrogen gas.  Chemical determinations were either conducted immediately in
the field as done with free sulfides or were suitably fixed and determined
within several days.  Soluble organic carbon (500) was measured on a Lira
Model 3000 total carbon analyzer.  Sulfate was determined by the method of
Bertolacini and Barney (51).  Free sulfides were determined with a sulfide
probe using the subtraction method  (47).  Chlorides were titrametrieally
determined (48).
                                   58

-------
     Redox potentials  were determined in the field by fixing the cores in a




vertical  position,  placing a reference electrode on the sediment surface




and inserting a 1mm platinum wire into the core through small holes drilled




at appropriate intervals in the plexiglas core tubes.  The reference electrode




used was  a standard fiber junction reference electrode used in pH, measurements,




modified by fastening a fine-frit Gooch crucible about its tip, and filled




with saturated potassium chloride solution.  Measurements were made following




standardization in  a solution of known redox potential.




     Total sulfides were determined by a modification of the standard titri-




metric method (48].  Volatile solids were determined by drying and combustion (48)




Samples used for total sulfides and volatile solids were kept in the plexiglas




cores and cooled or frozen until analysis.




     Examples of sediment profiles are shown in Fig. 11.  As expected, free




sulfides within the interstitial waters were highest at site 5.




A CLASSIFICATION OF ESTUARINE BENTHIC SYSTEMS



     Under conditions of relatively constant inorganic and organic inputs,



five types of estuarine benthic systems described in Table 6 can develop.




These five types are determined by the exogenous hydrogen acceptors avail-




able to decompose the deposited organics and the amount of iron (and other




metals which form insoluble sulfides) largely from deposited inorganics,




available to react  with free sulfides.  Further subdivision of these five




types based, as an  example, on the extent of methane fermentation or pyrite




formation are possible, but will not be discussed herein.




     Fig. 12 qualitatively illustrates the general response of the estuarine




benthic systems described above to different continuous inorganic and organic




loading rates.  The five regions in Fig. 12 correspond to the five types
                                      59

-------
  S04- MG/L
1000   2000
FREE SULFIDE-MG/L
       30        60
                                        REDOX POTENTIAL-MV
                                          -200   -100   0  +100
IOO    2OO    3OO
  SOC-MG/L
                        1000     2000
                  TOTAL SULFIDE-MG/KG
                         10     20     30
                     VOLITILE  SOLIDS-%
      FIG. 11 - EXAMPLES OF ESTUARINE  BENTHIC TYPES
                        60

-------
                        TABLE 6.  CLASSIFICATION OF ESTUARINE BENTHIC SYSTEMS
Deposit Aerobic
Type Decomposition
1 Dominant
2 SigniŁicanta
3 Significanta
4 Limited to a>b
Significant
5 Limited a'b
Sulfate
Reduction
Limited
(Organic limiting)
Significant
(Organic limiting)
Significant
(Organic limiting)
Significant
(Organic limiting)
Significant
(Sulfate limiting)
a - Dependent on DO in overlying water.
b - Aerobic zone in deposit limited by free sulfides.
c - Also increased accumulation of organics particularly
Intersitial
Free Sulfide
Low
Low
Low
High
High
if conditions are not
Methane
Fermentation0
Small
Small
Significant
Small
Significant"
favorable in
    Methane Fermentation.
d - Possible inhibition by free sulfides.

-------
                       ORGANIC  DEPOSITION RATE
                              (Expanded Scale)
FIG. 12 - QUALITATIVE DESCRIPTION OF ESTUARINE BENTHIC SYSTEM  RESPONSE TO CONSTANT
          DEPOSITION CONDITIONS.
                                       62

-------
described in Table 6. The solid lines of Fig.  12 are positioned by the




availability of hydrogen acceptors while the dashed line is positioned by




the availability of iron.  The precise quantitative definition of each of




these five regions depends upon a wide range of conditions  including,  but




not limited to, the amount of available iron in the inorganics,  nature of




organics, hydraulic conditions, extent of biological turnover, and con-




centrations of DO and sulfate within the overlying waters.   A quantitative




description of each of the regions in Figure 12 is not now  possible.   Fig. 12,




however, does illustrate the general response of the system shown in Fig. 2




to different constant deposition conditions.  Qualitative changes in Fig. 12




due to different conditions can be pictured.  Larger amounts of available




iron within the inorganics, as an example, would lead to clockwise rotation




of the dashed line defining regions 4 and 5.  Smaller amounts of iron  within




the inorganics would result in a counter-clockwise rotation of this dashed



line.  Fig. 11 may not be applicable for very large deposition rates and  does




not apply well when periodic scour occurs.




     Past investigations of marine benthic deposits give some quantitative




descriptions of the different regions shown in Fig. 12 .   Results  of the




Puget Sound study (52) demonstrated a large decrease of benthic fauna  (both




in numbers and types) and a strong hydrogen sulfide odor when volatile solids




became greater than ten percent of the total solids.  This  percentage  might




roughly define, for these locations, the upper bound of region 5  in Fig. 12  .




     Different benthic estuarine systems will support different sets of




plants and animals.  The amount of DO available for respiration,  the toxic




effect of free sulfides, and the amount and suitability of organics for




food supply will all serve to determine the nature of resident populations.





                                  63

-------
Other factors, such as particle size distribution, salinity,  and  temperature,




will also determine the composition of benthic communities.




     The regions described in Fig. 12 define the steady state benthic  types




(shown in Table I) that would be approached if a given set of deposition




conditions persisted.  The actual types present at a given time are  a  result




of past depositions.  Current loading conditions define types which  the




systems are then approaching.  When loading conditions change, systems of one




type may shift toward a different type.  Seasonal changes of  benthic loadings




within Oregon estuaries appear to produce seasonal changes of types.   Sufficient




data, however, are not now available to describe such changes adequately.  The




data to the date of this report indicate that seasonal scour  is an important




factor in estuarine benthic systems.  The above classification system  has the




shortcoming that a relatively constant deposition rate is assumed.   Where




periodic scour occurs, some confusion can result from the use of  this  classification




method.  A new classification method which accounts for scour is  now being




developed.




     The results presented in Fig. 11 can be used to illustrate three  of the




five classification systems.  Fig. HA demonstrates an example of a  type 2




benthal system (though this system may be approaching type 4}.  Below  the 5 cm




depth, organics likely become limited.  Free sulfides were detected  at low levels




(less than 1 mg 1  ) only within the top 2 cm of the deposit.  Burrows in this




region likely contribute toward the transport of oxygenated waters to  deeper




portions of the deposit.  Moreover, water flow through the deposit during low




tide likely laterally transported oxygenated water to the deposit.   Such




transport leads to the oxidation of H2S and FeS (note positive redox potential




of the greater depths).  This oxidation can result in the formation  of elemental
                                       64

-------
sulfur which may serve as an oxidizing agent leading to the formation of




pyrite (53) (note the decrease of total sulfides with depth).   The formation




of pyrite has not been illustrated in Fig. 1, and the decrease of FeS may




have been due to a more complete oxidation.




     Fig. 11B presents a type 3 benthal system in which sulfate becomes




limiting with depth.  The positive redox potential within the  first centi-




meter indicates that aerobic decomposition was likely significant.  No




detectable free sulfides were measured.




     Fig. 11C shows an example of a type 5 benthal system.  Sulfate becomes




limiting and soluble organic carbon increases at greater depths.   Free sulfides




within the interstitial waters were measured at levels above 60 mgl  .  The




concentration gradient of free sulfides indicates that free sulfides were




diffusing upward where oxidation occurred and downward to likely combine with




available iron.  A negative redox potential was measured throughout the  depth.




Aerobic decomposition was likely reduced by the upward diffusion of free




sulfides .




     The highest percent of volatile solids was measured in the type 5 deposit




(Fig. 11C) indicating a high organic to inorganic deposition ration.  The




lowest such ratio is suggested for the type 2 deposit (Fig. 11A)  which had




the lowest percentage of volatile solids.
                                  65

-------
                             SECTION IX




              STUDY OF SULFATE REDUCTION USING EXTRACTS
GENERAL



     At approximately the mid-point of this study, it became apparent that




the sulfate reduction within estuarine benthic systems was of major interest.




Sulfate reduction was examined by three different approaches:   (A) Sulfate




reduction  in organic extracts, (B) Sulfate reduction in mud slurries




employing  S-35 tracer and (C) incubation and measurement of entire benthic



cores.  Due to time constraints, the major investigative effort was given




to method  A.



     As previously discussed, the major producers of free sulfides in




marine  and brackish water appear to be sulfate reducing bacteria.  Those




organisms, belonging chiefly to the genus Desulfovibrio, are ecologically




quite versatile, and are ubiquitously distributed in nature  (54).  They




occupy  habitats embracing a wide range of pH, salinity, Eh, temperature, and




osmotic and hydrostatic pressure.




     Most  cultures, however, appear to grow best between a pH of  6.2 and 7.9




and  an  Eh  of -50 to -150 mv  (54).  Sulfate reduction itself tends to lower




Eh and  raise pH of environments in which it occurs, the magnitude of such




effects depending upon the buffering capacity of the medium, and  the end-products




of the  oxidation-reduction process  (54).




     Based upon salinity tolerance, there appear to be two general, although




somewhat indistinct, physiological types.  Those found within soil, sewage,




and fresh  water are most active in solutions of less than one percent sodium






                                  66

-------
chloride, and become inhibited at 1.5 - 3.0 percent concentrations.  The




other group, occurring in marine and brackish waters, appears to require




sodium chloride solutions isotonic to sea water or sea water itself (54).




     The trace mineral requirements of these organisms are but imperfectly




known and probably quite variable.  Ferrous iron is essential, due to the




presence of a cytochrome  system in species of Desulfovibrio (55).




     Growth of sulfate reducers has been observed at temperatures ranging




from -11° to 104°C, but the majority occur in the ocean floor sediments  at




temperatures below 5°C.  They appear to grow best at 15 - 40°C(81).




     The organic acids as a group (lactate, pyruvate, maleate, citrate,




propionate)  appear to be the most readily available and preferred energy




source for sulfate reducers (54).  In addition, fatty acids, simple alcohols,




and some mono and disaccahrides are suspect.  Complex carbohydrates do not




appear to be directly utilizable, but the importance of other microorganisms




in the breakdown of these to utilizable forms has been noted (56).




     Sulfate ions appear to be by far the most common hydrogen acceptor  (55).




They are usually in abundant supply in sea water, and there is good evidence




that the process of sulfate reduction may have been dominant and had global




implications during past eras (57).  There is some evidence suggesting that




sulfate reduction is not limited until the sulfate concentration drops below




10 mg/1, but it is probable that halophilic strains become limited at higher




concentrations.  In estuaries, sulfate reduction in bottom deposits is




dependent on both a supply of sulfate and organic material within the inter-




stitial and overlying waters,  and sulfate may become limiting at the head, and




organic material limiting at the mouth of estuaries (31).
                                  67

-------
     In addition to sulfates, the use of sulfite, thiosulfate, hydrosulfide




and several other sulfur oxides, as hydrogen acceptors, has been demonstrated




(54).   These compounds, however, are not generally widely available in nature,




and are considered to be of considerably less significance.  Since more




energy is derived from the more oxidized form, it is probable that it would




be preferentially utilized when available.  The ability of sulfate reducers




to utilize elemental sulfur is questionable (55,54).  Some autotrophic strains




are apparently able to utilize carbon dioxide and the bicarbonate ion as a




hydrogen acceptor (54).




     The question of whether the activity of sulfate reducing bacteria in nature




and in synthetic media is affected by the hydrogen sulfide (or other free




sulfide) produced has been examined by several investigators (54,55,60).




It appears that the levels of free sulfide which may be tolerated are criti-




cally dependent upon pH, available sulfate, the nature of the energy source,




and the presence of cations which may form insoluble sulfides (54).




MEDIA PREPARATION




     Sediment extract media were prepared as follows from sediment collected




from the upper five centimeters of deposits.




     A.   One liter of distilled water was added to one liter of sediment in




          a large erlenmeyer flask, thoroughly mixed, and the resulting




          slurry autoclaved for 45 minutes at 121°C.  After removal from the




          autoclave, the slurry was allowed to cool and the sediment removed




          by centrifugation.  The resulting clear extract was either utilized




          directly as growth media, or lyophilized to produce a powder.  In




          some cases this powder was added to liquid medium to yield one of




          higher organic concentration.  Sulfate concentration were increased




          by addition of sodium sulfate, or decreased by adding barium






                                     68

-------
          chloride.   The pH was  adjusted to near neutral  by  addition  of sodium




          hydroxide.




     B.    One liter  of sea water was  added to one liter of sediment and




          treated as  with the addition of distilled  water as  described  in




          method A.




     C.    One liter  of either three or ten percent hydrochloric acid was




          added to one liter of sediment and treated as with  the  addition




          of distilled water as  described in method  A.




     Algal Extract Media were prepared from the  algal mat  collected at  site 5



by the following methods:




     D.    Two liters  of algae and its associated water were placed into a




          three liter erlenmeyer flask and autoclaved as with sediment



          media.  Following cooling,  the algal material was squeezed using




          a wooden fruit press,  and the liquid collected  and  centrifuged.



          Sulfate concentrations and  pH of the media were  adjusted as




          previously described.




     E.    Approximately 250 ml of 10  percent hydrochloric  acid was added to




          500 ml of algae and treated similar to that in method D.




     F.    Small amounts of liquid were extracted from both sediment (collected




          from the upper five centimeters at the sites') and algae  (site 5)




          by using a hydraulic press  and specially designed squeezing




          cylinder.   In addition, approximately  one  liter  of  extract




          was prepared by squeezing by hand algae which had been  freshly




          collected  from site 5.



     The results of  preparing media by the various methods of organic




extraction are summarized in Table 7.  Early attempts at preparing media
                                  69

-------
       TABLE 7.   SUMMARY OF SOLUBLE ORGANIC EXTRACT PROCEDURES
Sample
Material
Site 1 -
sediment


Site 2 -
sediment



Site 3 -
sediment


Site 3
algal mat


Extraction Soluble organic(a) Sulfate(a)
procedure carbon (mg/1) (mg/1)
A(b) 150 - 250 nm. '
fbl
C 150 - 300 nm.
F (b) 50 3200
B 100 - 150 nm.

A 100 - 800 10 -
c(b) 3200 nm.
Ftb) 60 - 110 100
A^ 200 - 300 200

C^ -* 1600 - 3400 1400
F^ 140 - 310 1000 -
D 1500 - 3000 3400 -
ECb) 5400 nm.
p(b) 2010 4800
F(hand squeezed) 1125 2150
C<0





300





1500
4000



(a)



(b)



(c)
Approximate.




These extracts not used for media.




Not measured.
                                 70

-------
from sediment (methods A and B) inevitably resulted in media having fairly

low organic carbon concentrations (100-800 mg/1).  Extraction methods with

acid resulted in higher concentrations of organic carbon, but a large

percentage of this organic carbon precipitated out upon adjustment of the

pH with sodium hydroxide to neutral.  Hence little was gained in the final

media by using acid extraction.

     An analysis of sugars and organic acids was performed on a number of

extracts.  The general results indicated that the pentoses present at site 4

likely reflected the input of wood products to this area.  Sediment extracts

from site 1 showed small amounts of both pentoses and hexoses suggesting that

the organic material there may come from more diverse sources.  The relatively

lower levels at site 1 reflect the lower organic concentrations measured

here.  At site 5 high concentrations of mannose and glucose, both hexoses, as

well as high levels of propionate, butyrate, and acetate were present.

METHODS

     A number of experimental approaches were attempted in this study.   Only

the last approach, which took advantage of previous experience, is reported.

     Approximately 600 ml of algal extract medium (prepared according to method

D) were placed into each of twelve 500 ml erlenmeyer flasks, organic concentra-

tions adjusted by dilution, and desired sulfate levels achieved as previously

described.  Sodium chloride was added where necessary to adjust the chlorinity

of each culture to approximately 20 ppt.   Two additional cultures were simi-

larly prepared using media prepared by hand squeezing algae from site three.

Oxygen was initially removed by sparging for 15 minutes with carbon dioxide-free
f
nitrogen.  The pH was then adjusted to 7.5 - 8.0 by addition of 3.0  N sodium
                                     71

-------
hydroxide, and Eh lowered to approximately -100 mv by addition of a small




quantity of sodium sulfide.  Each flask was inoculated with two ml of mixed




culture and immediately capped by a rubber stopper fitted with a glass tube




and serum cap.  To prevent leakage, modeling clay was liberally applied




around the edges, and the stopper further fastened down by masking tape.




Each flask was shaken to disperse the inoculum, and initial samples were




taken for analysis.  The flasks were then incubated in the dark at 20°C.  A




control was set up by filling several tubes with sterile extract, and capping




tightly.  No significant changes were measured in the control series.




     Samples were withdrawn from the flasks at appropriate intervals with a




syringe which had been flushed and prefilled with nitrogen.  By exchanging




the gas for the sample, the flask was maintained anaerobic and development




of a negative pressure due to extraction of the samples was avoided.  Flasks




were shaken thoroughly prior to sampling in order to produce a fairly homo-




geneous medium, giving a more representative  sample.  Total sulfide was



measured by adding 10 ml of sample to a known volume of acidified 0.025 N




iodine solution and back-titrating with 0.025 sodium thiosulfate.




     Sulfate was determined by a colorimetric procedure using barium chloranilate




 (51).  Samples were passed through a Dowex 50w-x8 20-50 mesh H  cation exchange




column to remove interferring ions, diluted to 40 ml if necessary, and added




to 50 ml of 95 percent ethanol and 10 ml potassium phthalate buffer. Approxi-




mately three grams of barium chloranilate were added to precipitate the sulfate.




After shaking for ten minutes, the solution was filtered, and the optical dens-




ity determined on the filtrate with a spectrophotometer.  Sulfate concentrations



were read from a standard curve.




     Soluble organic carbon was used as a measure of the soluble organic




material present.  Five ml of centrifuged sample were placed into 20 ml




                                       72

-------
screw cap test tubes in an ice bath, and carbonate carbon removed by acidifying



to pH 2.0 - 3.0 with three percent phosphoric acid and sparging with carbon



dioxide-free nitrogen for 10 minutes.  Determination of the remaining soluble



organic material was made using a Lira Infrared Analyzer Model 3000.  Eh was



measured with a platinum wire electrode, and pH with indicator paper.



Fourteen cultures were run.



     Cultures 1 through 12 contained media prepared from autoclaved algae



(method E), whereas cultures 13 and 14 contained media prepared from squeezed



unautoclaved algae  (method F).  During the initial portions of each run,



sodium hydroxide was added to maintain a satisfactory pH.  After several



days, stable conditions of pH and Eh were achieved, further addition of base



became unnecessary, and active sulfate reduction began to occur.  Day 0 (zero)



of the experiment was set when the pH and Eh became stabilized.  This occurred



three to five days following inoculation.



RELATIONSHIP BETWEEN SULFIDE, SULFATE, AND ORGANIC CARBON



     Dissimilatory sulfate reduction requires an organic source for energy, and



sulfate as a hydrogen acceptor (20,55).  The stoichiometric relationship for sul-



fate reduction is given as (20)





                   SO^ + 2C      .  -*• S= + 2C00
                     4      organic           2




                 -(12)  -(3)         +(4)                               (15)





where the numbers below the chemical formulas indicate the reaction on a



weight basis.  Thus during sulfate reduction, a production of 1.0 mg of



sulfide will theoretically require 3.0 mg of sulfate and 0.75 mg of organic



carbon.  These 'yield ratios' have been calculated for the mixed cultures





                                     73

-------
     TABLE 8.   EXPERIMENTAL YIELD RATIOS AND MAXIMUM RATES
                 OF SULFIDE PRODUCTION FOR EACH CULTURED)
Culture No. Y (b)
1 3.2
2 3.0
3 3.0
4 3.2
5 3.0
6 3.4
7 3.1
8 3.2
9 3.0
10 3.2
11 3.0
12 3.1
13 3.1
14 2.9
Theoretical 3.0
Y (c)
0.82
0.89
1.60
2.00
2.30
6.05
0.86
0.86
0.91
0.80
0.88
1.10
0.94
0.84
0.75
V (d)
max
54
60
54
48
35
10
70
62
51
30
20
10
54
34
—
Sulfate
Limitation
No
Slight
Slight
Large
Large
Large
No
No
No
No
No
No
No
No

(a)   Yield ratios (Y    and Y   )  calculated over the 14 days of
     the experiment.          soc
O)   (mg/1 of sulfate utilized)  /  (mg/1 of sulfide produced).
(c)   (mg/1 of soluble organic carbon utilized)  /(mg/1 of sulfide produced)
(d)   The maximum rate of sulfide production (mg/1-day) as measured
     over three day intervals,  during the 14 days of the experiment.
                               74

-------
over the 14 days of experiments, and are presented in Tables 8 and 9 where
                  _ mg/1 of sulfate consumed
                L ~ mg/1 of sulfide produced                           (16)
and
                  _ mg/1 of soluble organic carbon consumed
                C   mg/1 of sulfide produced                           (17)
It is important to recognize that these yield ratios reflect the activity of

all the bacteria within the mixed cultures of the experiment and not just the

sulfate reducers.



                     TABLE 9.  SUMMARY OF YIELD RATIOS


                                   SulfateV sulfide     Carbon/sulfide
                                         Y                  Y
                                         TL                 *C


Theoretical                            3.0                 0.75

Average overall runs                   3.1                 1.49

Average overall runs
with no sulfate limitation             3.09                0.89



     Agreement between the theoretical value of Y  for sulfate reduction

and the values of Y  determined from the experiment was good.  The slightly
                   L
higher experimental values may be due in part to assimilatory reduction of

sulfate during initial growth of all of the bacteria present in the cultures.

     Y_ was more variable than Y  and exceeded the theoretical value of
      C                         ij
0.75 in every culture.  Since these mixed cultures contain bacteria other

than sulfate reducers, which are capable of ^.utilizing the organic carbon,

this result is not surprising.  That these other bacteria are capable of
                                   75

-------
such utilization was apparent from the drop in soluble organic carbon  in



the absence of measurable sulfate reduction prior to day 0.  In general,



where sulfide production became curtailed by deficiency of sulfate, the value



of Y  increased well above the theoretical, as would be expected.
    LJ


RATES OF SULFATE REDUCTION



     The agreement between the theoretical and experimental yield ratios shown



in Tables 8 and 9 indicate that sulfate reduction was responsible for  the sulfide



production measured.  The maximum rate at which this sulfate reduction occurred



(expressed as mg. of sulfide/1-day) in the extract experiments is shown (V   )
                                                                          nicix


in Table 8.  Rates have been estimated over a three day interval in each culture



in which the maximum rate appeared to be occurring.



     Results obtained in cultures 9 and 10 correspond closely to those of



culture 13 and 14 respectively.  (see Figs. 21, 22, 25, 26, and Table  8).



This close agreement indicates that the effect upon sulfide production of



autoclaving the algae used in the preparation of cultures 1 through 12 was



not significant.  The media for cultures 13 and 14 were obtained by hand



squeezing the algal mat found at site 5.



     To further explain the results of the extract experiments a mathematical



model was used which relates the production of sulfide to the utilization of



sulfate and soluble organic carbon.  Results indicated that the sulfide



production rate increased as the concentration of sulfate and/or organic



carbon increased.  This effect, however, was most pronounced at lower  levels



of sulfate and carbon,  and became relatively small at higher concentrations.



An equation which has been used to describe such a saturation effect at high



substrate concentrations is the common Michaelis-Menton equation shown below:
                                     76

-------
                  = Rmax                                              CIS)
in which P is the concentration of the product. R    the maximum rate of
                                                 max


product formation, N the substrate concentration, and K  the substrate



concentration at which dP/dT = 1/2 R
                                    max


     With sulfate and soluble organic carbon serving as substrates, the



rate of sulfide production may be expressed as
               f = Rmax tK~rT>  %TTl:>                            C19D
where  L  is the sulfate concentration,  C  the soluble organic carbon



concentration, and K  and K  the Michaelis coefficients for L and
                    J_i      C


C respectively.  Bacterial populations are assumed to be relatively high



and stable.



     Since sulfate and soluble organic carbon are being consumed in the



production of sulfide, their rate of utilization may be expressed as
               5F

and
               dt - ~'c W





     The value for Y  for use in the model was obtained by averaging the
                    L


measurements of this yield coefficient for cultures 1 through 12 (Table 8)



Y  was similarly obtained, but by weighting most heavily those values



of Y  from cultures which were not markedly sulfate limited during the
    Li
                                  77

-------
experiment.  Measurements from cultures 13 and 14 were not included in the
average since these cultures were prepared with unautoclaved media.
     Initial comparison of experimental results with calculated results of
equations 19, 20 and 21 demonstrated that production of sulfides responded
more sharply to changes in sulfate concentrations at low sulfate concentra-
tions than is described by the traditional Michaelis-Menton equation.  This
sharper response could be expressed within the model by raising the sulfate
concentration in equation 8 to higher powers.  Based on simulation of cultures
3 through 6, it was decided to raise the sulfate concentration to the 1.3
power, thus replacing equation 19 by
                  = Rmax
                     max
                           L
     Estimates of R   , K! and Kr were obtained using multiple nonlinear
                   max   L      L
regression analysis to fit the combined data of cultures 1 through 12 to
equation 22.  Since the model assumed no lag in sulfide production, data
for the first one to two days of those cultures in which an obvious lag
occurred was not included in the analysis .
     The result of the regression indicated a maximum rate of sulfide
production (R   ) of 77 mg/1 day.  The values of K'  and K., were 320 mg/1 and
650 mg/1 respectively.  A value of 3.1 was used for Y  and 1.0 for Y .   The
                                                     L              0
resulting equations with the fitted parameter estimates are shown below:
                            1. 3        _
                                           >                          C23)
                                  78

-------
                  - -1'0 <>                                         C25)
     Approximations to the simultaneous solutions of equation 23,  24 and




25 were obtained by digital computer using a fourth order Runge-Kutte finite




difference method.  The simulations of cultures 1 through 12 are shown in




Figs. 13 through 24.  Solid lines represent the values of sulfide,  sulfate,




and soluble organic carbon calculated by the mathematical model.  Circles  are




the data taken from the respective cultures of the experiment.   The values




of pH and Eh indicated are from the experiment.




     Agreement between simulated and measured results are especially good  for




those cultures in which the rates of sulfide production were highest.  Agree-




ment was in general best for sulfide and sulfate, while the calculated con-




centrations of soluble organic carbon deviated more from the experimental




measurements.  The selection of a Yr of 1.0 for the simulation  model is




reflected in these results.  The average value obtained for those  experiments




in which sulfate was not limiting, 0.89, would have resulted in closer agree-




ment except where sulfate became limiting.  Part of the difference between




the simulation and experimental results can be attributed to the lag period




which occurred in many of the cultures from day zero to one.  It will be re-




called that the model assumes no such lag, and that data for this  lag was not




included in the regression analysis.  Excluding the lag period  from Figs.  13




through 26 by considering day one the beginning of the experiment,  would result




in a much closer agreement of simulated with measured results in most cultures.
                                  79

-------
     Equations  23, 24,  and 25 were used to simulate production of sulfide




and consumption of sulfate and soluble organic carbon in cultures 13 and 14




(see Figs. 25 and 26.   Simulated sulfide production was within 10 percent of




the actual production.   Soluble organic carbon consumption was under-estimated



as with simulations of all cultures having a Y~ less than 1.0.  A value of
                                              \j


0.89 would have provided closer agreement.
                                 80

-------
         o>
         E
             1600
O       i

K   1200
         (9
         (T
         O

         LU
         -I
         
                                                                                   E

                                                                                  ui
                                                                                  t-
                                                                         to
                                                                                  >
                                                                                  E
                                         2   4   6   8   10  12
                                         TIME(doys)
FIG. 13 - EXPERIMENTAL RESULTS OF CULTURE 1 COMPARED WITH EQUATIONS 23,  24,  and 25.
                                         81

-------
         N

         0>

         E
             1600-
         S   1200
         (E
         O
         LJ
         _l
         CO
              800-
              400 -
         0>

         Ł


         LJ
         O
              800-
              600-
              400 -
              200 -
                0   2   4    6    8   10  12       2   4   6   8   10  12
                                         TIME (days)
FIG. 14  -  EXPERIMENTAL RESULTS OF CULTURE 2 COMPARED  WITH EQUATIONS 23, 24, and 25.
                                          82

-------
                                                                     -1600
                                                                     - 1200  ~
                                                                             •s.
                                                                             O>
                                                                             E
                                                                     - 800    <
                                                                             v>
                                                                             >
                                                                             E
                                                                     - 7
            0    2   4   6    8   10  12
                                              2    4    6    8   10   12
                                     TIME(doys)
FIG.  15 - EXPERIMENTAL  RESULTS OF CULTURE  3  COMPARED WITH EQUATIONS  23,  24, and 25.
                                        83

-------
                                                            10   12
                                     TIME(days)
FIG. 16 - EXPERIMENTAL RESULTS OF CULTURE  4  COMPARED WITH EQUATIONS 23, 24, and 25,
                                      84

-------
          1600
     o
     9    1200
     o
     o
     z
     Ill
     m
      o
      w
          800
          400
      E

     LJ
           150-
           100
           50-
                      1	1	1	1	T
                      1	1	1	1	h
                        o o
                 J	L
                              I     I	L
             024    6   8   10  12
     1	1	1	1	T
                                                       -0     -O-
    H—I—I—I—h
                                               i    i     '    '    '	L
2   4   6    8   10  12
                          400
                          300   -
                                o>
                                E

                                LJ

                          200   
                                                                               E
                                      TIME( days)
FIG. 17 - EXPERIMENTAL  RESULTS OF CULTURE  5  COMPARED  WITH EQUATIONS 23, 24,  and 25.
                                          85

-------
        E   1500
        o
        m
o

z
o
o
        m
        o
        w
            1000 -
             500-
         E
         111
         o
         ii_

         en
                0    2   4    6    8  10   12
                                                    8   10   12
                                        TIME(days)
FIG. 18 - EXPERIMENTAL RESULTS  OF CULTURE 6  COMPARED WITH  EQUATIONS 23, 24, and 25.
                                         86

-------
      §
      0:
      <
      O

      O
      (E
      O
      UJ
      _l
      CD
           1600-
1200-
            800-
            400-
       01
       E

       UJ
       o
       CO
            800-
            600-
            400 -
            200-
              024
                                                           8   10  10
                                       TIME (days)
FIG.  19 - EXPERIMENTAL RESULTS OF CULTURE 7 COMPARED  WITH EQUATIONS 23, 24, and  25.
                                          87

-------
O
ffl
CC
O
O
z
O
CC
O
UJ
CD
       O
       CO
           1600
           1200
            800
            400
       N.
       0>
       8

       UJ
       O
       en
            800
            600
            400
            200
                  -i	1	1	1	r
                   I    i	I
              0    24   6   8   10  12
                                                            H	1	h
H	1	1	1	1	h
                                                i	i	i
                                                                           4000
                           3000  -
                                 v
                                 en
                                 Ł
                                 ui
                           2000  <
                                                                           1000
                           100

                            0

                           -100

                           -200
                                                                                 >
                                                                                 E
                                                                                 UJ
 2    4   6   8   10  12
                                        TIME(mg/l )
FIG. 20  -  EXPERIMENTAL RESULTS OF CULTURE 8 COMPARED WITH EQUATIONS 23, 24,  and 25.
                                            88

-------
        o>
        e

        z
        o
        m
        cc
        o
        cc
        o

        UJ
        _J
        m
        o
        V)
             800-
             600-
             400-
             200-
        01

        E



        LJ
            800-
            600-
             400-
             200-
                                                            8   10   12
                                        TIME(days)
FIG.  21  -  EXPERIMENTAL RESULTS OF  CULTURE 9 COMPARED WITH EQUATIONS 23, 24, and  25.
                                         89

-------
           400
        1     '
        CD
        (E
        <  300
        o

        o

        z
        <
        O  200
        cc.
        o
        00
        o
        en
           100
        o>
        E

        UJ
        Q
        (O
           400
           300
           200
           100
                               ~i	r
O
                                        o
                  H	1	1	h
                                8    10   12
                                                                             4000
                                           3000 ~
                                                ill

                                           2000 <
                                                u.
                                                                                 V)
                                                                            1000
                                                                                 >
                                                                                 E
                                                                                 UJ
                                                                                 i
                                                                                 Q.
                             8   10   12
                                       TIME(days)
FIG. 22  -  EXPERIMENTAL  RESULTS OF  CULTURE 10 COMPARED WITH EQUATIONS  23,  24, and 25.
                                          90

-------
         -    200
         O>
         O
         CD
         L>

         u
         cc
         O

         UJ
         _l
         CD
         O
         CO
         0>
         E

         ui
         Q
         CO
              150
              100
               50
              200
              150
              100
                    -\—I—I—I—I—h
                                  I	I	I
                 0    2   4    6    8   10   12
H	\	1	\
                                                                              2000
                                                                             1500
                           1000
                                                                             500
                                  0>



                                  UJ
                                  CO
                                                                                    >
                                                                                    E
                                                                                    LJ
24    6   8   10   12
                                          TIME(days)
FIG.  23 - EXPERIMENTAL  RESULTS OF CULTURE  11 COMPARED WITH EQUATIONS  23,  24, and  25.
                                             91

-------
     0>
     E
     O
     CD
     K.
     <
     O

     O
     tr
     o
     bJ
     _l
     DQ
     LU
     Q
          100 -
             02    4   6   8   10   12
6   8   10   12
                                     TIME(days)
FIG. 24 - EXPERIMENTAL RESULTS  OF CULTURE  12  COMPARED WITH EQUATIONS 23,  24, and 25,
                                          92

-------
        o
        m
        a:
        <
        o

        o
         o
         cc
         o
         CD
         o
         en
             800
600
             400
              200
             800
             600
         UJ
         Q
         ;r   400
         V)
              200
                                      1	T
                    H	1	h
                                                      1	1	1	1	T
                                                                           -200
                                                                            4000
                                                              3000   N

                                                                     01
                                                                            2000
                                                                           1000
                                                                                  >
                                                                                  E
                                                                                 LJ
                                                                                 I

                                                                                  CL
                                                  2   4   6   8   10  12
                                         TIME (days)
FIG.  25 - EXPERIMENTAL RESULTS OF CULTURE 13 COMPARED WITH EQUATIONS 23,  24,  and 25.
                                           93

-------
         X
         o>

         E
         8
         o

         o
         a:
         o
         m
400
              300
              200
              100
             400
             300
         -   200
         0)
              100
                         1	1	r
                            -1	1	1	L
                024    6   8   10   12
                                                          o
                                                  -i	'    '
                                                                   J	L
                                                                             2000
1500   -

      o<

      E


      LJ


1000   <
                                                                             500
                                                               100



                                                                0



                                                               -100



                                                               -200
                                                                                   UJ
                                                                                   X
                                                                                   a.
                                                  2   4    6   8   10  12
                                       TIME( days)
FIG. 26  -  EXPERIMENTAL  RESULTS OF  CULTURE  14  COMPARED  WITH EQUATIONS 23, 24,  and 25.
                                            94

-------
                              SECTION X




                    SULFATE REDUCTION STUDY USING S-35
GENERAL APPROACH




     In order- to better quantify the extent of sulfate reduction that




occurs within estuarine sediments a laboratory study employing S-35 was




conducted (61).  The study involved the placement of a known quantity of




Na S  0  into homogenized mud samples.  Samples were then incubated.  At




selected time intervals, hydrogen sulfide was driven off as a gas and col-




lected.  The amount of S-35 within the collected sulfide was then determined.




Thus, the percent of S-35 added as sulfate which was converted to sulfide




over a given time interval could be calculated .  With the known initial sulfate




concentration of the sample, the rate of sulfate reduction could then be




computed.  Benthic samples were collected at site 5 with 2-inch I.D. plexiglas




cylinders.  Samples were transferred to the radiation laboratory at Corvallis,




Oregon in a styrofoam cooler.



 SAMPLE  PREPARATION




     Immediately after the samples had been taken to the laboratory, they




were transferred to a portable plastic glove box containing a top loading




single pan balance; a large glass trough; conical glass incubators, each of




which has a side branch sealed with a tight-fitting rubber serum cap; and




other necessary apparatus for sample transference.  The glove box was then




sealed and filled with pre-purified nitrogen which was being used to minimize




excessive air entrainment into the soil samples during the transferring  processes,




The top 10 cm of the cores were  extruded  and homogenized in  the  glass trough.





                                      95

-------
Five (5) gm of the homogeneous soil sample and two  (2) ml  of glass-distilled



water were carefully transferred into each tared incubator which  was  then



stoppered and removed from the glove box.



     Since biological sulfate  reduction requires strict anaerobiosis,  care



was taken to remove all oxygen from the sample and  the incubators used  in



the study.  The gas in each stoppered incubator was replaced with pre-purified



nitrogen by puncturing the rubber serum cap with a  hypodermic needle  connected



to a glass manifold.  This manifold consisted of 6  hypodermic needles,  a three-way



valve, and a U-tube mercury manometer, and was connected through  the  3-way valve



to a vacuum line and to a supply of pre-purified nitrogen.   The incubators



were alternately evacuated and filled with purified nitrogen.  During this



process, a slightly reduced pressure was maintained in the incubators and the



glass manifold, as was indicated by the mercury manometer.   Using this procedure,



intense reducing conditions were achieved in a relatively  short period of



time (15).



     A known amount of radioactivity, approximately 1 microcurie, in  the


                                            35
form of S-35 labeled sulfate  solution (Na S  0.),  was injected through the



serum cap into the sample.  The contents of each incubator were mixed by



shaking vigorously for half an hour.  The incubators were  covered with



aluminum foil to reduce excess growth of photosynthetic bacteria  and  algae,



and were incubated at 18°C in a constant temperature room  or water bath.



     Cylindrical plexiglas vials of six inch long and four inch diameter were



initially used for incubation.  Because these vials leaked and many other



difficulties were encountered during the addition of the radioactive sulfate



solution, modified wide-mouth erlenmeyer flasks fitted with  ground glass



stoppers were used as incubators.





                                      96

-------
INITIAL CONDITIONS



     The initial sellable Sulfate  concentration of the homogenized soil (prior




to the addition of 2 mis distilled water to 5 gms of sediment) was determined




by a  colorimetric procedure using barium chloranilate (51).  Approximately




30 gm of the soil sample were placed in an improved interstitial water sampler




 (50).  Interstitial water was squeezed out when compressed at 80-100 psi and




 collected in a plastic hypodermic syringe.  Then the water sample was filtered




 to remove most of the suspended matter.  After filtration, the sample was  passed




 through a Dowex 50 Wx-8 20-50 mesh H  cation exchange column to remove inter-




 ferring ions.  Ten ml of this extract was mixed with 2.4 ml of barium chlorani-




 late solution and 1.6 ml of acetate buffer solution.  The unused barium




 chloranilate and precipitated barium sulfate  were filtered and 6.8 ml of the




 pink filtrate were mixed with 0.46 ml of EDTA - NaOH solution.  The transmittance




 of the filtrate was determined at 520 my with a Beckman DB spectrophotometer.




 Sulfate  concentration was read from a standard calibration curve.




     The soluble organic carbon concentration in the interstitial water of




 the homogenized soil sample was determined.  Five ml of the squeezed water




 were placed into a 20 ml screw cap test tube in an ice bath.  Samples were




 tested in the Oregon State University Microbiology Department by using a




 Lira Infrared Analyzer Model 3000.



     Water content of the homogenized soil sample was determined by drying




 the sample at 105°C.




 COLLECTION OF  SULFIDE



     After incubation at 18°C for desired time periods, an incubator was




 removed from the constant temperature room, and carefully connected to the




 gas collection apparatus.  The incubator was then lowered into a heated water
                                       97

-------
bath.  A small amount, several mg, of elemental mercury was added as a




catalyst (62) into the sample before acid digestion.




     The digesting agent, initially concentrated hydrochloric acid, was added




into the incubator through a 250 ml pressurized separatory funnel connecting




to a supply of pre-purified nitrogen used as a carrier gas for evolved




hydrogen sulfide.    Concentrated hydrochloric acid was later substituted by




hydriodic acid because concentrated hydrochloric acid was found to react




very slowly with several mineral sulfides,   such as pyrite and chalcopyrite




(63).



     The released hydrogen sulfide was carried by a stream of pre-purified




nitrogen through a train of gas wash bottles, each of which contained 100 ml




of 5N sodium hydroxide solution.  The gases being emitted from the sampling



train were tested for any trace of hydrogen sulfide  by using lead acetate




solution or a Kitagawa low concentration hydrogen sulfide  detection tube.




After the complete decomposition of the soil sample, the apparatus was



continuously purged with pre-purified nitrogen for about an hour.




     After acid digestion and the purging of the soil sample with nitrogen, the




pressure within each gas wash gottle was released by venting to the atmosphere



through the 3-way valves connected between the three gas wash bottles.  The




valves were turned off in a reverse sequence; that is, the pressure in gas




bottle 2 was released before that of the first.  Then the nitrogen supply



was turned off.




     One ml of the sodium hydroxide-sodium  sulfide mixture in each wash




bottle was injected into a liquid scintillation counter vial containing 18 ml




of "Aquasol" and 2 ml of distilled water.  The activity of the sodium hydroxide-




sodium sulfide  mixture was measured by a Tri-Carb Scintillation Counter with
                                     98

-------
a photomultiplier voltage gain of 12.2% and window settings of 40 and  1000


respectively.


     During the acid digestion process, condensate was formed and accumulated


in the connection between the incubator and the first gas wash bottle.  A large


Y-connector had been used to join the incubator and the gas wash bottle.  The


sample of the condensate was injected into a  liquid scintillation counting


vial containing 20 ml of Aquasol.  The condensate was found to contain some


radioactivity.    Thus, not all of the S-35 released as hydrogen sulfide was


collected in the gas collection bottles.  It  was felt that this amount was


quite small, however, future studies should account for the amount.


     It was observed that there was a possibility of contamination of the


sodium hydroxide solution in the first gas bottle.  Therefore, it was


decided that any succeeding studies would employ a condenser connected at


the top of the incubator so that only relatively dried and cooled gases could


pass into the gas wash bottles.


     Radioactive tracer assays, based on the  liquid scintillation counting


method, depend on the optimization of the counting efficiency, which is


mainly influenced by two main factors:


     (1)  The figure of merit (64).


     (2)  The counting efficiency of the counter for S-35 isotope.

                            2
     The figure of merit, (S /B) is the highest possible counting rate of


the specific isotope and the lowest possible  counting rate of the background.


It was determined by continuous measurement of the net count rate of the


activity of a known standard S-35 solution(S) and of the background  (B) while


periodically altering voltage gain of the photomultiplier.  The optimum


condition was achieved when the voltage gain  setting established a maximum

                          2
value for the expression S /B.


                                   99

-------
     In order to determine the efficiency of the counter for the activity




of S-35 isotope, the quenching effect had to be considered.  The quenching




effect is any reduction of efficiency in the energy transfer process in a




given liquid scintillation counting sample, said reduction being caused by




color quenchers, chemical quenchers, and diluters.  For the Tri-Carb




Scintillation counter, the quenching effect for each sample is determined




by an external standard, and the result is expressed.as Automatic External




Standard (AES) Ratio (64).



     The counting efficiency, the ratio of the net photon count rate in




cpm to the disintegration rate (decay rate) in dpm, associated with each




quenching condition was determined by adding variable amounts of chloroforni,




a chemical quencher, to a series of samples containing 20 ml of Aquasol and



a known amount of radioactivity  of S-35 (65).  A quenching calibration




curve of the AES ratio versus the percentage counting efficiency was



plotted.




     For each sample that was used in the study of microbial sulfate




reduction, the disintegration rate was determined with the quenching




calibration curve and an average value of the net count rate.  The




disintegration rate was then converted to radioactivity   in micro-curies




by dividing the dpm value with 2.22 X 10 .  Since S-35 isotope has a half




life of 87 days, the experimentally determined radioactivity had to be




corrected using the equation for self disintegration:




                    N  =  N eyT                                       (26)




where               N  =  the measured activity in yc



                    N  =  the actual activity in yc if no




                          self disintegration exists
                                 100

-------
                    X  =   decay  constant = 0.00794/day




                    T  =   time in  days  since the addition




                          of S-35  activity to the soil sample.




     The  total  amount  of  labeled sulfide  generated microbially was  determined




by multiplying  the  summation of  the total actual activity by the total  volume




of sodium hydroxide solution used  to capture the hydrogen sulfide gas.



RATES OF SULFATE REDUCTION




     The  results  of two concurrent experiments are summarized in Table  10.




The results  show  that  sulfate reduction proceeded without a significant lag




time.  The maximum  rate of sulfate reduction was approximately  71 mg of




sulfide (S~) produced  per day per  liter of interstitial water of the original




sample.  Recall,  however, that 2 mis of distilled water were added to 5 gms




of wet sediment.  Within  this mixed slurry, the maximum rate would be approximately




46 mg/L-day. These results are  remarkably close to the results obtained from




the extract  experiments previously described.  If a lag time did occur  within




the first three day period, however, the maximum rate would have been higher.



     The  results  indicate that the experiments were approaching ninety  percent




recovery  of  the original  S-35.   The apparent lack of total recovery  with



time may  have been  due to the experimental proceedure.  As explained, S-35




did collect  in  the  lines  to the  gas collection flasks.  Physical adsorption




and biological  incorporation may also have resulted in a delay  in the



release of the  remaining  ten percent as hydrogen sulfide.




     In addition to maximum rates  of sulfate reduction comparable to the




extract experiments, the  S-35 experiments also suggest that the rate of




sulfate reduction does not become  sharply limited by the sulfate concentration




until sulfate concentrations fall  below 200-300 mg/L.  This observation is in




agreement with  the  results of the  extract experiments previously described.





                                      101

-------
         TABLE 10.  SUMMARY OF S-35 RECOVERY
Incubation
Time
(days]
3
6
9
14
21
28
Recovered
Run 1
37.86
70.02
77.8
79.36
85.06
85.29
S-35 (percent)
Run 2
40.98
68.46
76.24
80.39
83.5
83.71
Study conducted during summer 1971.
                      102

-------
                                 SECTION XI






                    OTHER ESTIMATES OF SULFATE REDUCTION




DIFFUSION OF SULFATE


     It is possible to obtain  an estimate of the rate of sulfate reduction


within a deposit by considering the downward flux of SO .  If the deposit


has remained undisturbed for a sufficient time, a steady state will be


approached which may be approximated by the equation


                   2


               DL~Hr = A                                            (2y)



in which D  is the diffusion coefficient for sulfate (assumed to be constant


with depth), L is  the  sulfate  concentration, z is the depth from the sedi-


ment surface and A is the mass of  sulfate removed per unit time per unit


volume of interstitial water.  Assume that  A is constant with depth until L


becomes limiting at concentration  L1.  Below the limiting depth (the depth


at which L=L'), A will be equal to zero.  The following equation is then


obtained from equation  (27)


                   2DT(L -L1)
               A =   L  °                                             (28)
 in which L  is the  concentration  of  sulfate of the sediment surface and z'
          o

 is the limiting depth  at which  L=L'.  The maximum value of LQ will be


 2655 mg/L (the sulfate  concentration in sea water).  The solution of equation


 (28) for values which  might be  common with estuarine sediments is graphically

                                                        -5   2
 shown in Fig. 27.   A reasonable (9)  value for DL(.5 x 10   cm /sec) is shown


 within a range (10"6cm2/sec to  10"5  cm /sec) that might be expected.
                                  103

-------
                       >.
                       -8
                       3
                         300
                       — 200
                       LJ
                       o:
                       o
                       Q
                       LJ
                       o:
                       UJ
                       C/)
                          100
                                                 D-IO'5cmz/sec
                                                 D=0.5 xlO'5cm2/sec
                                                 D=/0-6cm2/sec
0     12345678
DEPTH TO SULFATE LIMITATION (z')-cm
FIG. 27 - RELATIONSHIP OF SULFATE REDUCTION  RATE TO SULFATE DIFFUSION ASSUMING STEADY STATi
                                              104

-------
     A number of sulfate profiles within the  sediments  of  tidal  flat  areas




were measured and more than twenty such profiles were obtained.   Most did




not appear to be approaching the steady state described above.   That  is, the




variation of L with depth similar to  the solution  of equation  (27) was not




clearly defined.  For most profiles,  scour and partial  turnover  appeared to



have influenced sulfate profiles.  The profile shown in Fig. 10  does  indicate



an z1 value of approximately 3 cm.  It is difficult  to  define  the sulfate




profile within a depth of 3 cm.  Moreover, the uneveness of the  mud surface,



the looseness of the deposit surface  and the  influence  of  partial scour should



be recognized.  Thus the use of equation (28)  can  only  be  expected to provide




an order of magnitude estimate of A.  Using the values,  z'=3 cm,  L -L' =


                         -5   2
1500 mg/L and DT = 0.5x10   cm /sec,  one obtains an  approximate  value of A
               Li


equal to 150 mg/L-day.  This corresponds to a rate of sulfide  production



of 50 mg/L-day  (as S) which falls within the  range of the  experimental results




previously discussed.




INCUBATION OF BENTHIC CORES



     Estimates of the rate of sulfate reduction were obtained  by collecting a



number of sediment cores at a given site in 2 inch I.D. plexiglass tubing.



Cores were incubated at room temperature (approximately 25°C)  and profiles of



sulfate concentrations within the interstitial water of cores  were determined



at time intervals of 1 to 6 days.  Rates of sulfate  reduction  were calculated



by determining the differences of sulfate concentrations between cores



incubated for different time periods. No corrections for  the  diffusion of



sulfate were made.  Effort was made to collect cores from  areas  where the



deposits appeared to be horizontally  uniform.  Variations  between cores from



which the rates were determined, however, did result in considerable  scatter




of results.  A summary of the rates so determined  are given in Table  11.






                                 105

-------
                 TABLE 11.  SULFATE REDUCTION IN CORES AT ROOM TEMPERATURE C25°C)
Starting
Date
10/ 1/71
10/18/71
10/18/71
10/ 2/71
10/ 7/71

(a) (b)
(a)
Ca)
(c)
(c) Cd)
Site
4
4
4
5
5
Sediment
Temp.
(•c)
--
13
13
18
15
Volatile Solid
(%-dry weight)
13-16
	
	
13-20
15
Initial SO.
(rog/D
1000
1100
700
1000
800
SO. Reduction
A
(rag/ 1 -day)
50
40
30
100
70
S Production
(mg/l-day)
17
13
10
33
23
(a)   Values averaged over top 4 cm of core
(b)   Soluble organic carbon =  15-130 mg/1
(c)   Values averaged over top  3 cm of core
Cd)   Soluble organic carbon =  33-215 mg/1

-------
SUMMARY OF  SULFATE REDUCTION RATES



     The rates of sulfate reduction measured during this study are compared



to those reported by other investigators (Table 12).  Maximum rates in the



study by Edwards (60) were higher than those measured in this study.  The



higher incubation temperature (30°C) , and use of sufficient lactate (a



completely utilizable carbon source) to produce soluble organic concentrations



above those in the extract's media  (Section IX) would likely account for these



higher rates.  The maximum rates measured by Nakai and Jensen (66) were within the



range of those reported measured in this study.  Measurements by Ivanov (20)



and Sorokin (21) of sulfate reduction in lake muds were determined through the


                                    35
use of labeled sodium sulfate (NA S  0.).  The difference in units used to



report their rates makes comparison difficult.  If it is assumed that their



mud samples were roughly 50 to 75 percent water, then the reported rates



would range up to approximately 40 mg sulfide per liter per day.  In their



study, 10 cm mud samples were utilized and the rates reported based on pro-



duction of sulfide over this depth.  If the production were occurring within



only the top few cm, however, then the rates reported might underestimate the



actual production occurring within this active upper region.  Accounting for



these factors would produce approximate agreement with the range of those



measured in this study.  None of the studies shown in Table 12 provide



estimates of the rate of sulfate reduction that might occur immediately below



the mud surface.  Within the upper  anaerobic regions of high organic deposits,



rates higher than those shown in Table 12 might be possible particularly



within the regions immediately under dense algal mats.
                                      107

-------
        TABLE 12.  COMPARISON OF THE RATES OF SULFIDE PRODUCTION MEASURED
                    IN THIS STUDY WITH THOSE OF PREVIOUS INVESTIGATORS
   Investigator
Sulfide Production
    rates (a)
              Comments
This study
This study
This study

This study
10-701
   46
   50(

10-23(
          00 C<0
Sediment Extracts, See Section IX
Mud Slurry, See Section X
In situ sulfate profiles, order of
magnitude only, see Section XI
Incubation of cores, limited study,
see Section XI
Edwards (65)


Edwards (65)


Ivanov (20)


Ivanov (20)


Nakai and Jensen (66)



Sorokin (21)

Sorokin (21)


200-250 ^ J


100-150^


0.5-1.5^


12-19^


10-45^



0.1-0.2Cb)

10-15^


In lab, pure batch cultures of D.
desulfuricans on Macpherson's
medium, stable populations
In lab, pure batch cultures of D.
desulfuricans on Macpherson's
medium, stable populations
Field measurements in 10 cm mud
cores from deepest part of lake,
determined with 3^5
Field measurements in 10 cm mud
cores from slope of lake,
determined with S-^
In lab, mixed cultures containing
sulfate reducing bacteria, cultures
consisted of 30 ml sea water and
65 ml wet sediment
Field measurements in lake water
using S-55
Field measurements in muds collected
from slope of lake near river mouth,
S35 used
(a)  Approximate range
Cb)  mg(S)/l- day
(c)  Maximum rate
(d)  mg(S)/ Kg wet sediment-day
                                       108

-------
                                SECTION XII
                          BENTHIC SULFIDE RELEASE
GENERAL

     Attempts were made to measure the benthic sulfide release at site 5

through the use of a benthic respirometer.  A single successful respirometer

run was completed during the summer of 1970.  A sulfide release rate of 1.6 gm
    2
gm/m -day was measured in a 2-1/2 hour run without correction for oxidation
                                                      2
of free sulfide.  An oxygen depletion rate of 3.2 gm/m -day was also measured.

If approximately half of this oxygen uptake rate was due to the oxidation

of free sulfides, then the total sulfide release rate may have approached
        2
3.2 gm/m -day.  The respirometer was later modified to permit nitrogen gas

sparging of DO from the installed respirometer.  Three additional respirometer

runs were repeated at site 5 during the summer of 1971. (67)

MODIFIED BENTHIC RESPIROMETER

     The modified benthal respirometer (similar to that described in Section VI)

consisted of a black plexiglas tunnel, a small submersible pump, an expansion

chamber, a system of hoses, a flow indicator, a sampling port, and a sparging

unit.  The tunnel was 2-7/8 inches in diameter, 49 inches long, with 2-inch

flanges attached to the base, and covered an area of 282 square inches (0.182

square meters).  It was painted black to prevent photosynthetic oxygen genera-

tion by algae covering the benthal deposit.  The tunnel was placed on the mud

at low tide and filled by the rising tide through holes in the top which are

then sealed by rubber stoppers.  Water was circulated at a rate of about 4 gallons

per minute through the device in order to thoroughly mix the contents and
                                      109

-------
facilitate sampling at the estuary's water surface.  Water was circulated




through a 5/8-inch diameter garden hose.  A strip of plastic cloth was




installed to flutter inside a three-inch length of clear plastic tubing to




indicate that flow was being maintained.  Sampling was done with a 30 ml syringe




through a septum installed in a plastic "tee" located on the circulation hose.




Duplicate samples were taken every twenty minutes for DO and free sulfide




measurement by methods described in the previous section.




     At the onset of the 1971 runs, nitrogen gas was sparged into the pressure




line of the pump, collected in the expansion chamber, and relieved through a




valve in that chamber.  This chamber, made from a 27-liter plastic carboy, had



inlet and outlet fittings and an adjustable relief valve.  Nitrogen sparging




was intended to strip the DO from the water, and thus permit the buildup of




free sulfides without oxidation.



     Care had to be used during sparging to maintain the same volume of water




within the device by adjusting the release rate to equal the sparging rate.



Constant volume was necessary to facilitate computation of the mass of sulfide




released from the observed rise of sulfide concentration.  This was done with




the aid of a line on the expansion chamber to indicate a constant gas volume.




The total volume of water within the device, with one liter of gas in the




expansion chamber, was 38 liters.  Excess pressure had to be avoided to pre-




vent pushing the tunnel off the mud, as happened in the earlier runs.



RESULTS OF SULFIDE RELEASE MEASUREMENTS




     The results of the 1971 runs are presented in Figs. 28, 29 and 30.  The




release rate of sulfide in each experiment was expressed by a high and low




rate shown by the lines in these figures and in Table 13.  When DO was present,




the sulfide release rate increased with time.  When nitrogen sparging removed




the DO, the sulfide release rate decreased with time.  A number of explanations






                                     110

-------
                          1200       1300      1400

                                   TIME-hrs


                             • = free sulfide
                             o = dissolved oxygen



      FIG. 28  - BENTHIC  SULFIDE  RELEASE WITHIN RESPIROMETER -  SITE  5  -  8/3/71.
1500      1600      1700

           TIME-hrs
                                                  1800
                                                               E
                                                               I
                                                               •z.
                                                               LJ
                                                               CD


                                                               O

                                                               O
                                                               UJ
                                                               CO
                                                               CO

                                                               0
                             •  =  free  sulfide
                             o  =  dissolved oxygen
FIG.  29  -  BENTHIC  SULFIDE  RELEASE WITHIN RESPIROMETER

          Nitrogen sparging  shown by arrow).
                              - SITE 5 - 8/9/71.  (Period of
                                       111

-------
                     4.0
                   E 3.0
                   i
                  in
                  LJ
                  Q

                  ^j 2.0

                  r)
                  1/5
                      1.0
                       0
                         1300      1400      1500      1600

                                       TIME-hrs
                                • =  free  sulfide
                                o =  dissolved oxygen
FIG. 30 - BENTHIC  SULFIDE RELEASE WITHIN RESPIROMETER -  SITE 5 - 8/20/71.   (Period of

          Nitrogen sparging shown by arrow.
                                           112

-------
   TABLE  13.   ESTIMATES OF SULFIDE RELEASE RATES AND OXYGEN UPTAKE
             RATES AS MEASURED IN RESPIROMETER EXPERIMENTS AT SITE 5
Date
9/ 3/70
9/ 3/71
9/19/71
9/20/71
2
S Release Rate (gm/m -day)
1.6- 3.2Ca>
1.0- 9.2
0.8- 7.2
1.0-15.0
2
DO Uptake Rate (gm/m -day)
3.2
-
15-39^
-
(a)  Upper estimate based on assumption one half DO uptake due to
     sulfide oxidation with one to one sulfide oxygen mass ratio.

(b)  High rates may be due to interference of DO measurements.
are possible and the data are not adequate to select from such explanations.

The initially high rate during the 8/9/71 and 8/20/71 runs may have resulted

from the disturbance of the bottom by the respirometer.  In these same runs,

the decline in the sulfide release rate may have resulted from the input  of

Fe   and the formation of FeS.  The termination of nitrogen sparging may  also

have contributed to the decline in sulfide release.  The high DO decrease in

the 8/3/71 run may be due to sulfide interference of the micro-winkler test.

     The difficulties in performing these respirometer runs should not be

underestimated and the results must be interpreted with these difficulties in

mind.   The results including the 1970 run do indicate that the sulfide release

rate in this region during late summer likely falls in the approximate range

of 1.0 to 10.0 mg S~/m -day.  Any finer evaluation of the results is likely

unwarranted.  More reliable sulfide release rates would likely be obtained

through the use of laboratory flow-through systems.  The benthic sulfide


                                 113

-------
release rates which are possible within a range  of measured sulfate reduc-


tion rates are shown in Table 14.  These rates are maximum values as it is


assumed that all sulfide produced is released.


PROFILES OF FREE SULFIDE


     Free sulfide concentrations were measured within  the  interstitial  waters


of sediment cores.  In general, gradients of free  sulfides  seldom exceeded


40-50 mg/l-cm (see Fig. 11) and this value was approached  only at site  5.


If the release of free sulfides depended on molecular  diffusion only, such

                                                                          2
gradients would result in a sulfide release rate of approximately 0.2 gm/m -day.


Maximum free sulfide gradients within the immediate surface regions  of  the


deposits, however, were likely higher than those measured  due  to the difficulty


of sampling interstitial waters within small distances.  Moreover, partial


turnover of the immediate surface regions can be expected  and  thus the  upward

                                                                     2
flux of free sulfide would be increased.  Thus the value of 0.2 gm/m -day is


likely a low estimate of the higher benthic sulfide release rates attained


at site 5.


SUMMARY OF BENTHIC SULFIDE RELEASE EXPERIMENTS


     Measurement of benthic sulfide release likely occurred for any  prolonged


period only at site 5.  This site had all of the conditions which would contribute


to maximum sulfide releases.  Experimental results were extremely variable and

                                                                        2
one can only conclude that sulfide release rates approximating 1.0  gm/m -day


should not be considered unreasonable for conditions similar to those of site 5.


This estimate is extremely crude, however, given the very  limited and variable


experimental results.  Moreover, site 5 is not typical of  estuarine  tidal flats


and the average sulfide release rates for typical  tidal flats  can be expected to


be considerably lower than those experienced at  site 5.
                                     114

-------
          TABLE 14.  POTENTIAL  BENTHIC  SULFIDE RELEASE  RATES
                           (GMS/M2-DAY)  (a)(b)



W a?
4H 13
O 1
rH
•P M
5 e
B
O O
M-rt
Oi +J
fH O
(D 3
> TJ
< o
(X


20


40

60


80


100


2
0.2


0.4

0.6


0.8


1.0

Depth of
3
0.3


0.6

0.9


1.2


1.5

Sulfate Reduction-cm
4
0.4


0.8

1.2


1.6


2.0

5 6
0.5 0.6


1.0 1.2

1.5 1.8


2.0 2.4


2.5 3.0

(a)  Assume  50% water content by volume
(b)  Assume  all sulfide  produced is released
                                 115

-------
                                SECTION XIII




                          MIXING WITHIN DEPOSITS
 GENERAL




     The vertical mixing that occurs within estuarine benthic systems is an




important factor in determining the conditions within the benthic system and




the influences of the benthic systems upon the overlying water and air.




Vertical mixing within deposits depends on a variety of factors.  Hydraulic




factors, such as tidal changes in water depth, water velocities, wave action




and low tide drainage patterns all contribute toward vertical mixing (68)(69).




The burrowing and movement of organisms within deposits leads to greater vertical




mixing  (38)(70)(71).  Dye tests at site 2 indicated a large exchange of water




through mud-shrimp burrows (34).   The presence of fine particles within the




deposits tends to reduce vertical mixing (68)(69).  Ebbing waters were found




to drain freely through the deposits at site 1 while a lack of such drainage




was noted at station 5.  Water velocities measured at sites 3 and 4 with a price




current meter were generally below 0.6 fps.




     The presence of biological growth may retard the passage of water through




the deposits and thus reduce the hydraulic tidal mixing.  At site 1, permeabili-




ties of 0.04-0.03 cm/min were measured at locations where biological growths




were not noted while, in this same general region, the permeability in the




top twelve centimeters was reduced to 0.0008 cm/min in areas of noticeable




biological growth on the deposit surface.




     In regions where vertical mixing is reduced to that of molecular diffusion,




the departure from straight-line diffusion, due to the deposit particles,




reduces molecular diffusion coefficients by approximately 30 percent from that






                                     116

-------
of pure water  (72)(73).   Electric interaction between particles and inter-
stitial water  can  also  lead to a reduction of molecular diffusion (74).
Diffusion within biological slimes can also be significantly less than diffusion
through pure water (75) .   Vertical mixing can thus be expected to vary from
relatively  large hydraulic exchanges,  often facilitated by burrowing organisms
and large particle sizes  (site 1), to  values less than that of molecular
diffusion in pure  water.   Vertical mixing can thus be expected to vary from
relatively  large hydraulic exchanges,  often facilitated by burrowing organisms
and large particle sizes  (site 1), to  values less than that of molecular
diffusion in pure  water (possibly the  case at sites 4 and 5).
     Care must be  exercised in the use of reported molecular diffusion
coefficients of substances within interstitial water, as the concentration
of sorbed material which  does not diffuse is often included with the material
in solution (74).   Concentration gradients based on the sum of sorbed and
nonsorbed materials will  lead to lower calculated diffusion coefficients than
if only the material in solution were  used to determine the gradients.
TIDAL MIXTURE
     During August and September of 1970, a series of experiments were con-
ducted at sites 1  and 4 in order to study the discharge and recharge process
of tidal flat  pore water  during a tidal cycle (76).
     During the first series of experiments at site 1, measurements  of the
hydraulic surface  within  the flats were obtained by means of pipes driven
into the deposits.  It  was found, however, that the hydraulic response of the
system was  too slow.   During later investigations, the hydraulic surface was
measured through dug holes with the surface referenced to stakes of known elevation.
                                      117

-------
Changes of the hydraulic surface for three stations located  at site  1  are




shown in Fig. 31.  The station elevations are shown on Fig.  32 and the  free




water surface elevations, which were measured during the sampling period




shown on Fig. 33.



     These results suggest that during the ebbing of the tide, pore  water




drains from those areas exposed by the tide.  Drainage is along the  beach,




passing through the surface at the region above the free water surface.  The




slope of the hydraulic surface at approximately 2 hours after low tide  is shown




on Fig. 31.  As seen in this diagram, the hydraulic surface  meets the ground




surface between stations C and D.  Similar hydraulic surface profiles can be




drawn for different times within the tidal cycle from the data given in Fig. 30.




Thus, the data show  that the flow of pore water during the  ebbing tide and during



the low tide period results in a surface flow component at different elevations



at different periods of the tidal cycle.  The magnitude of this surface flow




component depends on the permeabilities found at each location (see  Table 15).




During the tidal cycle, the hydraulic surface within the flats dropped by




approximately 1.5 to 0.5 feet, the larger drops being measured at the higher



elevations.  Above the hydraulic surface, the water content was reduced to




approximately 90 percent saturation.  These percents, shown  in Fig.  31, should




only be considered as rough approximations due to the difficulty of  obtaining



undisturbed one-inch thick samples.




     Using the mixing length description of the diffusion coefficient,  the




data presented above can be utilized to compute rough estimates of effective




diffusion coefficients due to the tidal pore drainage described above.  These




effective diffusion coefficients are approximately 10 to 50  times greater than




molecular diffusion coefficients (for oxygen) in water.  In  addition, oxygen may




be introduced in large amounts to the unsaturated region.




                                     118

-------
     I2
     5
      o
                           \b Sept  (970
                        Time. - Clock Hours
17 Sept
FIG.  31  -  HYDRAULIC SURFACE DURING EXPERIMENTS AT SITE 1,
     -2
           d: cfeptt ofsffaf/e- cm. i -> --><"
       _  n: Wuaie. i/o/as / /o/a/ volume.
                                 ZOO
                          Distance. • feet
                                             30O
                                                        40O
 FIG. 32 - CONDITIONS AT  SITE  1 DURING DRAINAGE EXPERIMENT.
                            119

-------
                                  Ground Surface. - S fat/Off A"
                                  Ground Surface. -Station &
                           Hydraulic Surface.
                                 Station
                                  Ground Surface • station 'C'
                                16 Sept 1970
                             Time. • Clock Hoars
                                                   17 Sept
FIG.  33  - FREE WATER ELEVATIONS DURING  EXPERIMENTS AT SITE 1.
                                   120

-------
            TABLE  15.   PERMEABILITY AND VOID RATIO AT SITE 1
Elevation
[ft above MLLW)
8.3
6.8
6.0
6.0
3.8
1.7
-1.0
Permeability
Ccm/min)
0.04
0.0008^
—
—
—
—
0.03
Vol. Voids/Total Vol.
0.38
—
0.36
0.38
0.44
0.44
0.42
           (a)  Plant growth on surface








     At site  4, no  similar tidal  drainage could be  measured.   Water would



remain within pools  (with  some  evaporation)  until the  flood tide  covered




flats.  Vertical mixing was thus  reduced to  molecular  diffusion  and the turnover




by organisms  within the deposit.   This  later method did not appear to  be sub-




stantial at site 4.   Partial scour of the region was also noted,  due to wave




action as the tide  rose and fell.




     The characteristics of the deposits at  sites 1 and 4 were quite different.




The deposits  at site  1 contained  a reasonably uniform  sand while  large amounts




of silts and  clays were present at site 4.   It appears  that the  difference  in




particle size was chiefly  responsible for the differences in  drainage  character-




istics and thus the differences in vertical  mixing.
                                    121

-------
     During the flood tide at site 1, the hydraulic surface began to  rise




slowly as the free surface approached a given elevation  (see  Fig. 31).  This




rise became abrupt at each location as the flooding waters covered that




location.  A more detailed description of this study has been presented (76).




PERIODIC SCOUR



     Though time was not available to maintain a sufficient sampling  program




to define seasonal changes of conditions with the benthic systems of  tidal flats




the data available do suggest that periodic scour of the deposits, generally to




a depth of 5-10 cm, is an important factor in determining these conditions.




The scour due to wave action, high water velocities and extreme tides can




result in a periodic oxidation of ferrous sulfide and a "recycling" of the




iron.  Such physical disruptions tend to prevent the depletion of available



iron and the subsequent buildup and release of free sulfide.  The influence




of oxidizing conditions upon the concentrations of free sulfides is illustrated




in Fig. 34 which is a composite of results from sites 1,2,4 and 5.  The



sulfates brought into the deposit as a result of a physical turnover  may not




provide for sufficient sulfate reduction to deplete the available iron.




Depletion of available iron may thus require the additional diffusive transport




of sulfate from the surface either through molecular diffusion or through partial




(or limited) scour.  Thus, the buildup of free sulfide is most likely within the




top 5-10 cm.  Periodic turnover of this region sufficiently to oxidize the




ferrous sulfide, however, would prevent this buildup.  The influence  of such




physical turnover is indicated by the progressive change in the total (acid soluble]




sulfides at site 4 as shown in Fig. 35 (free sulfide concentrations were below




detectable levels).  The change appears to be most significant above  10 cm.




The decline of total sulfides as winter is approached reflects the declining







                                      122

-------
                      3000-
                    I
                    Ld
                    Q
                    CO
                       2000
                       1000
                             • • /
                                       *.rv  .''.^i
                             -200  -100   0   +100  +200  +300

                                REDOX  POTENTIAL - mV
FIG. 34 - RELATIONSHIP BETWEEN TOTAL SULFIDES (ACID  SOLUBLE) AND REDOX POTENTIAL WITHIN
         DEPOSITS AT SITES  1, 2,  4,  and  5.
                                500         1000         1500

                               TOTAL SULFIDE-mg/kg
    FIG. 35 - TEMPORAL CHANGE OF TOTAL SULFIDE (ACID  SOLUBLE)  PROFILES AT SITE 4.
                                      123

-------
salinity (and thus sulfates) during this period at this site.  The trend may




also reflect and increase wave action due to storms during this period.




     A limited or partial scour or turnover of the upper layers of deposits




may not be sufficient to result in any substantial oxidation of the ferrous




sulfide.  However, such limited scour can serve to transport sulfate into the




deposit.  A partial turnover which entrained overlying water into the sediments




would normally contain 4-10 mg/1 of dissolved oxygen yet the sulfate concen-




tration could be 2000 mg/1 or greater.  Thus limited turnover could contribute




to a depletion of available iron and a buildup of free sulfide (generally withir




the top 10 cm) if sufficient organics were available.  Such limited scour in




the absence of a more complete scour would be most likely to occur within




protected areas (sloughs, diked areas, etc.) with relatively unconsolidated




sediments of high organic content.
                                 124

-------
                                SECTION XIV




                        GENERAL BENTHIC DEPOSIT MODEL
GENERAL




     As discussed in the introduction of this report, the basic approach




employed in this study involved two distinctive features.  These features




were:




     1.   A complementary feedback occurred between the mathematical model




          studies and the experimental portions of the project.




     2.   The study was approached at several levels of resolution which




          complimented each other.  That is sub-systems were viewed as




          integrated systems with component parts and these same sub-systems




          were also viewed as component parts of a higher level system.




     The objective of this section of the report is to provide a benthic system




model in the language of mathematics.  The model will serve to integrate the




principal processes shown in Fig.  2 and provide a framework for integrating the




results previously discussed into the general benthic system.  The specific




mathematical description of each of these component processes will not,  however,




be given.  Though the previous sections of this report do give insight into




some of these component processes, particularly sulfate reduction, further




definition must be based on continued feedback with experimental results.




     The model will be developed by first stating the principal ass-umptions.




Then, a description of the general distribution in space and time of soluble




and insoluble  materials within benthic systems will be provided.  The major




biochemical reactions which occur within benthic systems will then be presented




in two slightly different models.   The intent of presenting the second model,





                                    125

-------
which is a simplified version of the first biochemical model, is to show how




some simplifications can be made without necessarily sacrificing too much from




the capabilities of the model.  Finally, the distribution equations will be




combined with the biochemical models to obtain two slightly different models




which are relevant to environmental studies of benthic systems.  The models




are developed only for the benthic systems and do not here include the over-




lying air and water.  The system described, however, is nearly applicable to




the overlying water.




PRINCIPAL ASSUMPTIONS




     Several principal assumptions and limitations of the model are listed




below:




     1.  The model will be one-dimensional; considering only variations in




         the vertical direction.




     2.  The model will assume an equilibrium between sorbed and nonsorbed




         materials.




     3.  Compaction of deposits will not be included in the model.




     4.  It will be assumed that the biological reactions are not limited by




         the concentrations of the microorganisms.




     5.  Deposition and scour will not be explicitly described in the model.




         However, the model description is such that numerical simulations




         based on the model will be able to accommodate a wide variety of




         deposition and scour patterns.




     6.  As in all models, many different substances will be grouped into




         large categories.  As an example, degradable organics will be




         grouped into two categories (insoluble  and soluble).  If necessary,




         these groupings may be broken down further.




GENERAL DESCRIPTION OF SOLUBLE MATERIALS




     Consider a vertical section of deposit of cross-sectional area A with a




fixed reference (z=0) at some depth below the surface of the deposit.  Positive





                                 126

-------
depth,  z,  is measured from this reference toward  the  surface.   A positive



interstitial water velocity is in the upward direction and  a  positive con-



centration gradient indicates an increasing concentration from the reference



to the surface.  Taking a mass balance on a slice of  depth  dz  within the deposit



leads to
                                             AdzZH                   (29)
                                                                      ^
                 3t
in which n is the fraction of the deposit  filled  with  water,  S'  is  the



concentration of a soluble material, within  the interstitial  water, F.  is



the  total flux of this substance into  the  slice,  F   is the  flux  of  the



substance out of the slice, ZG is the  sum  of the  sources  and  sinks  of the



soluble material from within the interstitial water and EH  is the sum of the sources



and  sinks of the soluble substance  from  insoluble states.   Hereafter the



prefix, G, for biochemical reactions will  denote  a  rate of  mass  change or  trans-



fer  per unit volume of interstitial water.   The prefix, H,  will  denote a



rate of mass change or transfer per unit volume of  wet sediment.



     The flux of S' due to advection and diffusion  is  taken as
                        P\C T

              F = -D  ,Ant2_ + UAmS'                                   (30)

                    S   o Z
in which D  , is the vertical diffusion  coefficient  for S',  U is  the



vertical velocity  (positive upward)  and m is  the  fraction of A open to dif-



fusion and advection.  Let
              F  = F. +   dz                                          (31)
               o    i   9z
                                       127

-------
Substituting equations  (30) and  (31) into equation  (29)  leads  to







                      ,   ^c^
                 3t            3z            3Z





Assuming A to be constant with distance and time and n to be constant with



time reduces equation  (32) to
                       3(D  ,m(3S'/3z)   ,

                     I - s'  -- 1         + ZG +  i            (33)
                     n       3z         n    8z           n
     If D  , , U, n, and m are further considered as constant with depth and



if n is set equal to m, equation  (33) reduces to
For simplicity, equation (34) will be expanded to include the biochemical



reactions rather than the more general equation (33).   The biochemical reactions



presented herein can be easily be accommodated into equation (33) if desired.






GENERAL EQUATION OF INSOLUBLE MATERIALS



     Following a similar mass balance as above, one obtains the general



equation for insoluble materials shown below







               |^- = EH H- nEG                                          C35)
in which I' is the concentration (mass per unit volume of wet sediment) of



the insoluble materials.



 BIOCHEMICAL MODEL I


     The primary biochemical reactions occurring within the estuarine benthic



systems (see Fig. 2 and Section IV) are shown in the simplified mass transfer



diagram of Fig. 36.  Definition of terras is given in Table 16.



                                 128

-------
6F
                            YFBHFS.
INSOLUBLE
AVAILABLE
IRON
(IF)
i
HIF
r
1
-E
_E


6S^

INSOLUBLE
SULFIDE
(FS)
Nt«,
      /SOLUBLE
      AVAILABLE]
         IRON
                                                               HO
                            ELEMENTAL
                             SULFUR
                              (SU)
   FIG. 36 - BIOCHEMICAL MODEL I FOR ESTUARINE BENTHIC SYSTEM.
             (Available Iron also includes other metals which
             form insoluble sulfides; Zn, Sn, Cd, Hg and Cu.)
                               129

-------
                        TABLE 16.   DEFINITION OF TERMS FOR
                 BIOCHEMICAL MODEL I OF ESTUARINE BENTHIC SYSTEM

GC,   = the aerobic biochemical degradation of soluble organics,

GC    = the degradation of soluble organics by sulfate reduction,

GC    = the non sulfate reduction anaerobic biochemical degradation of soluble organics,
  O
GF    = the oxidation of soluble available iron to insoluble available iron,

GS    = the oxidation of free sulfides (primarily, chemical reaction with dissolved
  1        oxygen but also due to aerobic autotrophic bacteria),

GS    = the reaction of free sulfides with soluble available iron (and other materials
           which form insoluble sulfides),

GS    = the loss of free sulfide through photosynthetic anaerobic sulfur bacteria,

HFS   = the oxidation of insoluble sulfides (primarily ferrous sulfide) with dissolved
           oxygen,

HFS   = the oxidation of insoluble ferrous sulfides with elemental sulfur,

HIC,  = the solubilization of organics under anaerobic conditions,

HIC   = the solubilization of organics under aerobic conditions,

HIF   = the solubilization of available iron,

HO    = the dissolved oxygen demand due to other causes  (e.g., oxidation of ammonia,
           benthic plant respiration),

HP    = the oxidation of pyrite under aerobic conditions,


YCI   = mass of soluble organic carbon per mass of insoluble organic carbon solubilized
           under aerobic conditions,

        mass of sulfide produced per mass of organic carbon utilized in non-sulfate
           reduction anaerobic decomposition,

Ypg   = mass of insoluble available iron per mass of insoluble sulfide oxidized,

YFS   = mass °f available iron Per mass of free sulfide reacted to form insoluble sulfides,

YFSU  = mass of elemental sulfur used per mass of insoluble sulfide transformed to pyrite,

YIC   = mass oŁ soluble organic carbon per mass of insoluble organic carbon solubilized
           under anaerobic conditions,
\C   = maSS °f sulfate Per mass of soluble organic carbon utilized in sulfate reduction,

YOC   = mass of oxygen Per mass of soluble organic carbon oxidized,
                                           130

-------
                                 TABLE 16.  Cont.



Y    = mass of oxygen per mass of soluble iron oxidized,
 OF

Y    = mass of oxygen per mass of insoluble sulfide oxidized,
 OFS

Y    = mass of oxygen utilized per mass of insoluble organic carbon solubilized,
 01

Y    = mass of oxygen per mass of free sulfide oxidized,


Y    = mass of pyrite formed per mass of insoluble sulfide reacted with elemental sulfur,
 P

Y    = mass of sulfate produced per mass of soluble organic carbon utilized in sulfate
 SC        reduction,


Y    = mass of elemental sulfur per mass of insoluble sulfided aerobically oxidized,
 O\J


Y    = mass of elemental sulfur per mass of free sulfide oxidized.
                                          131

-------
     Insoluble materials are shown in the rectangles while soluble materials




are shown in the circles of Fig. 36.  Symbols used to designate concentrations




of materials are given in Fig. 36.  Concentrations of soluble materials are




given in mass per unit volume of interstitial water while concentrations of




insoluble materials are given in mass per unit volume of wet sediment.  A




principal assumption which led from Fig. 2 to Fig. 36 is that the biochemical




reactions are not limited by the concentrations of micro-organisms.




     The relative significance of the different reactions shown in Fig. 36 and




Table 16 will depend on the conditions within the benthic system (See Chapter IV).




Three benthic conditions and the relative importance of the reactions within




these conditions are given in Table 17.  The aerobic regions, (portions of




the benthic system containing dissolved oxygen) are generally located within



the top few millimeters of the deposit.  Such regions also frequently line




burrows within deposits.  Aerobic conditions are also found for short periods




of time after the deposit has been physically overturned.  If organic material




is sufficient, an anaerobic region within which sulfate reduction takes place




is normally located below the aerobic region.  If organics are high, sulfate




may become limiting within several centimeters of the surface.




     Microbial decomposition may occur below the depth of the sulfate limitation.




Free sulfides may diffuse from above and react with available iron in this




region.  In addition, organics and iron may be solubilized in this region




and diffuse upward into the region of sulfate reduction.  Methane fermentation




within this deep region may result in a physical disruption of the deposit



above.




     The biochemical reactions shown in Fig. 36  and Table 16 may be combined




with equations (34) and (35") to provide the following mathematical description




of the benthic system.




                                      132

-------
                     TABLE 17.  DEPENDENCE OF REACTIONS OF BIOCHEMICAL MODEL  I
                             ON INTERNAL BENTHIC CONDITIONS
Reaction
                 Aerobic  Region
Anaerobic-Sulfate
Reduction Region
Anaerobic, No Sulfate
Reduction Region
HICj
HIC2
GCj
GC
GCs
HO
GS1
GS2
GS3
GF
HIF
HFS,
HFS2
HP
none
significant
significant
none
none
significant
significant (g)
very slight
none
significant
slight
significant (g) (k)
none
slight (j) (1)
significant
none
none
significant
slight (e)
none
none
significant
slight Ci)
none
significant
none
significant (d) (j)
none
significant (d)
none
none
none
significant (d) (f)
none
none
conditional (h)
unlikely (i)
none
significant
none
normally slight (d) (j)
none
(a)  DO^-0.1  mg/1;  upper region of  sediment
(b)  DO <0.1  mg/1;  S04> 10-50 mg/1;  below  aerobic region
(c)  D0<0.1  mg/1;  SO, < 10-50 mg/1;  below  sulfate reduction
     region
(d)  likely decreasing  with depth
(e)  normally YgCGC2> YCgGC3
(f)  if conditions  favorable (e.g.,  available degradable
     organics,  no  loxic levels of  free  sulfides)
(g)  normally small suflate source  in  comparison to
     diffusive  transport and exhange  due  to disturbance
     of bottom
                                                              (h) largely dependent upon diffusion of
                                                                   free sulfides from sulfate reduction
                                                                   region
                                                              J^i) light needed
                                                              (j) long term significance; time scale of
                                                                   weeks to years
                                                              (k) likely to occur after sediment over-
                                                                   turned or flushed with oxygenated
                                                                   water
                                                              (1) not included as oxygen loss due to
                                                                   relative slowness or reaction

-------
Insoluble carbon:
             - HIC
                                                                       (36)
Soluble carbon:
                      .
                      dZ
                                             + Y  HIC
                                           1    Li
Dissolved oxygen:
                                                                       (37)
   = °
      0
                       d Z
                                   YOCGC! - YOSGS1 - YOFGF
                                                                       (38)
Free sulfide:
Pjc


If = °S
                       3z
YSCGC2
                              YCSGC3 -
                                                          GS2  -  GS3
Sulfate:
f
                                                                       (40)
                                  134

-------
Insoluble iron (and other material which  form  insoluble  sulfides):



               HE = YFSHFSl - HIF + nYIFGF                              (41)



Insoluble sulfides:
                                 - HFS2
Soluble iron (and other material which forms insoluble sulfides)
                  - D      _ D   +       Y  „_    ™
               9t ~ °F   2   Udz +  n  ~ YFSGS2 ~ GF                     (43)
 Elemental sulfur:
                   = YHFS  ~ YHFS  + nYGS
                 t    SU1 ~  FSU2     SSUl                       (44)



Pyrite:


               j\p
               f = YpHFS2 - HP                                          (45)



     For simplicity, a number of the normally less significant material

transfers have been omitted from the model.  As an example, the additions of

sulfate from reactions GS? and HFS  have been omitted because these addi-

tions will normally be significantly smaller than the diffusive transport

and the exchange due to the disruption of the sediment.

BIOCHEMICAL MODEL II

     The biochemical model shown in Fig, 37 and Table 18 is similar to that

shown above.  Organics and available iron, however, are included in a single

component which is considered insoluble and pyrite is not included (pyrite
                                 135

-------
                  YFOHFSI
                          INSOLUBLE
                          SULFIDES
                            (FS)
                                    VHFS.
AVAILABLE
  IRON
  (AF)
                                    YsuHSF.
                                                 DISSOLVED
                                                  OXYGEN
                                                    (0)
          YFSUHFS2
                     ELEMENTAL
                       SULFUR
                         (SU)
                                       YOCHCI
      FREE
     SULF1DE
       (S)
   YCSHC3
                                                  ORGANICS
                                                   (0
YSCHC2
                                YLCHC2
                            SULFATE
                              (L)
GS
 FIG.  37  -  BIOCHEMICAL MODEL II  FOR ESTUARINE BENTHIC SYSTEM.
           (Available Iron also  includes other metals which
           form insoluble sulfides; Zn, Sn, Cd, Hg and Cu.)
                            136

-------
                 TABLE 18.   DEFINITION OF TERMS FOR BIOCHEMICAL MODEL II
                             OF ESTUARINE BENTHIC SYSTEM


GS   = the oxidation of free sulfides
  1
GS-   = the loss of free sulfides through photosynthetic anaerobic sulfur bacteria,

HAF   = the reaction of available iron with free sulfides,

HC   = the aerobic biochemical degradation of organics,

HC   = the degradation of organics by sulfate reduction,

HC-   = the non sulfate reduction anaerobic biochemical degradation of organics,

HO   = the dissolved oxygen demand due to other causes  (e.g., oxidation of ammonia,
          benthic plant respiration),

HFSi  = the oxidation of insoluble sulfides with dissolved oxygen,

HFS2  = the reaction of insoluble sulfides with elemental sulfur to form pyrite,


Y    = mass of sulfide produced per mass of organic carbon utilized in non-sulfate
          reduction anaerobic decomposition,

Y_R   = mass of available iron per mass of insoluble sulfide (primarily ferrous sulfide)
          oxidized,

Y    = mass of sulfide per mass of available iron reacted to form insoluble sulfides,
 ro

Y _..  = mass of elemental sulfur used per mass of insoluble sulfide transformed to
          pyrite,

YLC   = mass of sulfate per mass of organic carbon utilized in sulfate reduction,

Y    = mass of oxygen used per mass of organic carbon oxidized,
 UL
YQP   = mass of oxygen used per mass of insoluble sulfide oxidized,

Y    = mass of oxygen used per mass of free sulfide oxidized,
 Uo
Y    = mass of sulfide produced per mass of organic carbon utilized in sulfate reduction,

Ygy   = mass of elemental sulfur per mass of insoluble sulfides aerobically oxidized,

^SSU  = mass °f elemental sulfur per mass of free sulfide oxidized, and
                                         137

-------
                             TABLE  19.  DEPENDENCE OF REACTIONS OF LOWER RESOLUTION MODEL
                                        (MODEL II) ON BENTHIC CONDITIONS
           Reaction
oo
             GS1

             GS3

             HAF

             HFS]

             HFS-
Aerobic Region
  significant (g)
     none
  very slight

  significant (g) (k)
     none
Anaerobic-Sulfate
Reduction Region DO
      none
     slight (10
   significant

      none
   significant (e) (j)
Anaerobic, No Sulfate
Reduction Region
HCj
HC2
HC3
HO
significant
none
none
significant
none
significant
slight (d)
none
none
none
significant (e)
none


(f)

       none

      unlikely  00
    conditional  (i)

       none

   normally slight  (e)  (j)
           (a) D0> 0.1 mg/1; upper region of sediment                     (h)
           (b) D0<0.1 mg/1; S04> 10-50 mg/1; below aerobic region        (i)
           (c) D0<0.1 mg/1; S04<10-50 mg/1; below sulfate reduction
                region
           (d) usually YSOHC2> YCSHC3                                     (j)
           (e) likely decreasing with depth
           (f) if conditions favorable (e.g., available degradable        (k)
                organics, no toxic levels fo free sulfides)
           (g) normally small sulfate source in comparison to
                diffusive transport and exchange due to distrubance       (1)
                of bottom
                                                 light needed
                                                 largely dependent upon diffusion
                                                  of free sulfides from sulfate re-
                                                  duction region
                                                 long term significance; time scale
                                                  of weeks to years
                                                 likely to occur after sediment over-
                                                  turned or flushed with oxydenated
                                                  water
                                                 small fraction of oxygen demand,
                                                  primarily biological

-------
can be  simply added).   The increased simplicity of model 2, however, is


purchased by  a loss of "reality" in the model.  Nevertheless, model 2 may be


sufficient  for most investigations and the greater simplicity may be advantageous,


The relative  significance of the reactions of model 2 to benthic conditions


is given in Table 19.   The biochemical reactions shown in Fig. 37 and Table 18


are combined  with equations (34) and (35) to provide the following mathe-


matical description of the benthic system.


Organic carbon:
Dissolved oxygen:
                        2


               f a °0 7T - UH - YOSGS1 - n-
                       d Z
                                                                      (47)
 Free sulfide:
               f - °S 4 - "II * ^CSHC3 * YSCHC2 - Y!
                       oZ




                                                     - GS, - GS,       (48)
 Sulfate:
                           --
                       d Z
                                      139

-------
Available Iron  (and other materials which form  insoluble  sulfides):
                             - HAF                                     (50)
 Insoluble  sulfides:
Elemental sulfur:
                              HFS1 - HFS2                              (51)
                             - YFSUHFS2 + n YOSU
                                  140

-------
                                 SECTION XV


          ENVIRONMENTAL IMPLICATIONS FOR ESTUARINE BENTHIC SYSTEMS
GENERAL IMPLICATIONS


     The  conditions within estaurine benthic systems have important influences


on the functioning of estaurine systems.  The interfacial and benthic regions


are themselves  significant regions of estuarine systems.  Moreover, the


overlying water quality can be strongly influenced by the conditions within


the benthic system.   Depletion of dissolved oxygen and toxic concentrations


of free sulfide may result.                                  ,


     Benthic conditions, particularly within tidal flat areas, may have


significant influences on air quality.  The release of sulfur to the


atmosphere as a result of sulfate reduction within coastal regions may be


of the same order of  magnitude as the buring of fossil fuels (25)(26)(27).

                                                                2
If one assumes  that the total area of estuaries is 1,222,000, km   (77)

                                                                       2
then an average estuarine benthic atmosphere sulfur release of 0.1 gm/m -day


would be  sufficient to be approximately equal to the annual world sulfur release


from the  burning of fossil fuels, 50 X 10  tons/yr.  This figure does not include


the influence of bays, seas, deltas,shoreline areas, saline lakes, etc.


     The  total  magnitude of benthic sulfide release to the atmosphere and the


nature and extent of  man's activities which would contribute toward an


increased sulfur release are subjects of major concern.  The quantitative


evaluation of these subjects is beyond the scope of this report.  It is


possible  however to describe a variety of activities which can result in


a variety of changes  within the benthic systems of environmental concern.


To facilitate the following discussion, reference will be made to the



                                       141

-------
classification system described in Chapter VI and specifically to  Table  6




and Fig. 12.  The possible influences of man's activities  on  estuarine




benthic systems are briefly discussed.  Reference to Fig.  2 will help to




clarify these discussions.




CHANGES IN ORGANIC DEPOSITION



     A general increase of organic deposition to benthic systems can result




from the input to the estuary of additional organics (such as  from waste




outfalls), from the input of inorganic nutrients which  lead to an  increase




of primary production within the estuary, or to the deposition of  organics




re-suspended at some other location.  Such increases result in a shift of




benthic states toward region 5 (see Fig. 12)-  Dredging operations can,




however, remove organics from previously degraded systems  and  thus assist in




their recovery.




CHANGES IN INORGANIC DEPOSITION




     Increased deposition of inorganic material can result in  suffocating




benthic plants and animals.  Toxic materials in these deposits can also




harm these communities.  Again, controlled removal of toxic materials by




dredging may assist degraded systems to recover.




     Potential problems can also occur from reduced sediment transport to




estuaries due to. upstream dams, jetties, channelization, and reduction of




seasonal sediment scouring.  Such reduction may lead to a  lowered  input of




available iron to the systems and thus result in a shift toward regions 4




and 5 of Fig. 12.  This shift would be most pronounced  if  a general increase




in organic deposition also occurred.




CONSTRUCTION OF DIKES,  JETTIES, WHARVES, ETC.



     Dikes, jetties, wharves, etc. can alter estuarine  ecosystems  in several




ways.  These structures may provide a solid substream on which a highly





                                 142

-------
diverse population  of attached plants and animals may develop.  However,




they can isolate  regions  from the estuarine system, thus drastically altering




their nature  and  function.   Partial diking of a tidal flat region can lead




to an increased trapping  of organics and fine particles.  In addition, such




dikes can  reduce  the  more significant periodic scour and thus reduce the




"recycling" of iron.   Benthic systems within such regions may shift to a




type 5  system, as appears to be the case at site 5 investigated in this report.




HYDRODYNAMIC  CHANGES



Deepening  of  channels, filling of tidelands, construction of dikes and




jetties, stabilization of banks and other such activities all serve to change




the hydrodynamic  regime of estuaries.  Changes in advective and diffusive




transport  and scour can result in significant changes in organic deposition,




inorganic  deposition, salinity distributions, temperature distribution,




distribution  of pelagic life stages, inorganic nutrient distribution, dissolved




oxygen  distribution and other environmental factors which influence the




estuarine  ecosystem in complex (and often unknown) ways; often these changes




show themselves most  graphically in altered plant and animal distributions.




Changes which tend to reduce scour may lead to a shift to type 5 systems.




Extremely  unstable bottoms may prevent the establishment of stable benthic




communities.   Reduction of seasonal salinity variations can disrupt biological




cycles, lead  to an increased development of resident populations at the




expense of migrating populations and can contribute to a benthic system shift




toward  type 5 by  reducing the seasonaly variation in sulfate supply to




benthic systems.




TIDELAND FILLING



     Filling  tideland with dredging spoils or other materials can have wide-




spread  adverse effects in an estuary.  In general, tidal flats are highly





                                     143

-------
productive areas contributing a major portion of the food  to  an  estuary.




Covering of this valuable tideland can be critical, not only  because food




sources are removed but because the total high tide volume  of the  estuary




is reduced.  Many estuarine fishes live in the channels at  low tide  and




move over the tidal flats as the tide rises to feed  (a habit  of  fishes




which may account for better fishing on an incoming tide).  Likewise, shore




birds and a few mammals move into the exposed areas at low  tide  to feed.




The variety of species .which function at some stage of their  life cycle in the




tidelands is great.  When tidelands become.covered, diversity is thus likely




reduced.




     Within a given estuary a wide range of localized inorganic  and  organic




benthic depostion rates, DO concentrations, sulfate concentrations,  scour




velocities, and other factors determine estuarine benthic types  that can be




expected.  These conditions, moveover, will change with time.  Thus, dif-




ferences can be expected over temporal and spacial dimensions  of any estuary.




Within unpolluted regions of estuaries, benthic types 1, 2  and 3 will likely




predominate.  The wide variety of benthic systems normally  found in  tidal




estuaries makes possible a larger biological diversity which,  in turn,




likely contributes to the functioning of the entire estuarine system.




     A wide range of man's activities can produce significant changes in




temporal and spacial distribution of benthic types.  Such changes can result




in a decrease in the variety of benthic systems within space  and time.  Such




a reduction of system diversity, if extensive, would likely reduce biological




diversity.  Man's activities might also result in a general shift, likely




toward benthic type 5 (region 5 of Fig.12) which would be considered -undesirable




because of lower DO concentrations and higher free sulfide  concentrations.
                                    144

-------
Environmental  changes  often cannot be explained by a simple casual relationship




to a single  activity.   Thus, the environmental impact of any particular activity,




must be considered along with a host of other activities (both man-made and



natural).




TRANSIENT CONDITIONS DUE TO DREDGING




     Dredging of type  4 and 5 benthic systems would likely have a greater




immediate impact on water quality than would the dredging of types 1, 2 and




3.  The release of free sulfide would be most objectionable because of its




oxygen demand and its  toxicity.  However, because of the rapid reaction




rate of free sulfides  and oxygen in estuarine waters, the,short term




release of free sulfide during dredging of sludge deposits might be preferable




to the long term release by undisturbed deposits.  Thus, in some cases,




dredging operations could be used to assist the recovery of a system which




had been degraded to a type 5 system.  Such dredging, however, could release




heavy metals which had been held in the deposits as insoluble sulfides.




Heavy metals such as mercury and cadmium could have both short term and long




term toxic effects.



     Increased turbidity due to dredging operations can decrease light




penetrations, and thereby reduce photosynthesis.  It can cause mechanical




blockage of gills and ultimate suffocation of many species, simply because




the gills cannot absorb enough oxygen from the water.  Likewise, food




filtering mechanisms,  which are often associated with respiratory organs,




may also become blocked by too many particles in the water.



     The settling of fine sediment from turbid waters over benthic species




may have catastrophic effects on life cycles if pelagic larva or eggs cannot




leave the sediments or if pelagic larvae are prevented from settling in a






                                    145

-------
satisfactory environment.  For example, oyster spat cannot  attach to the




necessary shell substratum if this shell is covered with a  layer of fine




sediment.




     The type of benthic system that develops at a given location can be




dependent on the biological turnover previously discussed.  A transient




environmental condition, such as a temporary depletion of dissolved oxygen,




could eliminate a community which is contributing to this turnover.  A new




benthic type might then develop.  The re-establishment of the previous com-




munity might not be immediately possible due to this change in type even




though the unfavorable environmental condition which caused this change had




passed.  Thus, periodic unfavorable conditions could have a continuous




influence on benthic systems.




LONG TERM PARTICLE SIZE CHANGE




     Significant long-term decreases in sediment particle sizes within




developed estuaries can occur (78) .  Adequate data to demonstrate such




long-term decreases, however, are not available for most tidal estuaries.




Decreases in particle size may occur as a result of upstream dams, continued




dredging, construction of jetties, and other similar activities.  Particle




size reduction could significantly decrease the permeability of deposits




and thus contribute toward reduced transport of exogenous hydrogen acceptors.




This would in turn lead to a reduction, to the left, of regions 1 and 2




of Fig. 12.  A reduction of particle size may also impair the movement of




certain benthic animals within deposits.




SPOIL DISPOSAL




     Sediment removal and spoil disposal can result in a shift in benthic




types at both the sites of sediment removal and disposal.  As an example,






                                146

-------
the oxidation of sulfides and organics during the removal and disposal




operations might result in a shift from an original type 5 system at the




removal site to a type 2 or 3 system at both sites.  The reverse may occur,




however, if during disposal, differential settlings of organics and in-




organics occurred.  After settling, the spoil deposits may shift toward




type 5 due to the higher organics within the upper regions of the deposits.
                                  147

-------
                                SECTION XVI

                       LOWER LEVEL RESOLUTION STUDIES
GENERAL
     In the earlier phases of this study, a conventional viewpoint of
estuarine systems was employed which dealt with the estuary  as  an elongated
water body subject to tidal influences.  A mathematical model  was developed
which, though having a number of unique features, reflected the same
estuarine systems view as the common one and two dimensional estuarine models
Field studies of tidal hydrodynamics and mixing processes were conducted
to  compliment the mathematical model studies.  As previously discussed, the
study shifted emphasis to a finer level of resolution in which estuarine
benthic systems were examined.
     The latter stages of the study were dominated by this  finer level of
resolution view which has been described in the previous chapters.  During
the course of this study, a number of subjects principally  related to the
lower level resolution view were examined.  The principal results of these
examinations are briefly discussed in the following subsections.  Reference
is  made to the publications which provide specific details  and a description
of  the general estuarine model employed is given in the appendix.
ADVECTION ERRORS
     A basic component of most water quality models involves the advection or
movement of materials by flowing waters.  The errors associated with several
finite difference models of advection were examined.  These errors were
found to distort model results and these errors were most apparent when the
                                 148

-------
advection  of  slug loads was simulated.  The tendency to numerically  spread
materials  was found to be a common error, along with the production  of
oscillations  and a tendency to skew distributions.  A method of estimating
and controlling these errors was developed and examined.  Details of this
phase of the  study are found in the following reference.
     REFERENCE:  Bella, David A., and Grenney, William J., "Finite-Difference
     Convection Errors," Journal of the Sanitary Engineering Division, ASCE,
     Vol.  96, No. SA6, Proc. Paper 7744, December, 1970, pp. 1361-1375.
ESTIMATING DISPERSION COEFFICIENTS; IN  ESTUARIES
     Two general methods of determining longitudinal dispersion coefficients
from estuarine salinity profiles (79)  (80") (81) were examined.  In addition
a third method was developed.  The adequacy  of these three methods was
examined through the use of the finite difference estuarine model.  Methods
which employed the assumption of a steady state were found to be seriously
deficient  when river flows varied.  This general conclusion was in agreement
with the work of Ward and Fisher (82).  The method developed in this study
was found  to  be the most accurate of  the three tested.  Details are provided
in the following reference.
     REFERENCE:  Bella, D.A., and Grenney, W.J., "Estimating Dispersion Coefficients
     in Estuaries,"  (technical note),  Journal of the Hydraulics Division, ASCE,
     Vol.  98, No. HY3, March 1972.
SLACK WATER BUILD-UP IN ESTUARIES
     A series of model runs were conducted in which tidal variations were
included.  The Yaquina estuary served as the prototype, although a great
deal of the effort was not spent to model the Yaquina in detail.  The
results indicated that pollutant profiles within estuaries were generally

                                      149

-------
far more sensitive to variations in  the  biochemical  reactions than to




the dispersion coefficients or tidal variations.   This  result had a major




influence in directing the study toward  the  biochemical reactions.




     These studies did demonstrate, however,  the  high pollutant concentrations




could develop in the vicinity of an  outfall  during the  slack water period.




This pollutant accumulation was studied  through the  mathematical  model  and a




field study.




     A diffuser was installed across the main  channel of the Yaquina River




about 35 Km from the mouth, at Newport,  Oregon.   Rhodamine-B was  injected




at a constant rate for a ten hour period and more than  400  samples were




collected.  The data indicate a significant build-up during periods of




slack water.  The model results simulated average observed  trends reasonably




well, however, calculated peaks were lower than the  field observations.




Details are provided in the following reference.




     REFERENCE:  Grenney, W. J. and  Bella, D.  A.,  "Field Study and Mathematica




     Model of the Slack Water Build-up of a Pollutant in a  Tidal  River,"




     Limnology and Oceanography, Vol. 17, No,  2,  March  1972.




TIDAL MEASUREMENTS




     During the initial phases of this study,  partial support was given to




field studies of tidal elevations and tidal currents in the Yaquina,  Alsea,




and Siletz estuaries.  Because of the changing emphasis of  the study reported




herein, continued support for tidal measurement was  later provided through




the Sea Grant Program (NSF), Ocean Engineering, Oregon  State University.




Results of the supported studies are provided  in  the following reference.




     REFERENCE:  Goodwin, C.R., Emmet, E. W.,  and Glenne, B., "Tidal Study of




     Three Oregon Estuaries," Bulletin No. 45, Engineering  Experiment Station,




     Oregon State University, Corvallis, Oregon,  May 1970.






                                 150

-------
                               SECTION  XVII

                                REFERENCES
 1.  Bella, D.A., A.E. Ranun, andP.E.  Peterson,  "Effects  of Tidal  Flats
         on Estuarine Water Quality," Journal Water  Pollution  Control
         Federation, Vol. 44, No. 4,  541-556, April  1972.

 2.  Bella, D.A.  and J.E. McCauley,  "Environmental Considerations  for
         Estuarine Dredging Operations,"  Proceedings  of  the World
         Dredging Conference  IV, New Orleans, Louisiana.   December 1-3,
         1971.

 3.  Bella, D.A., "Environmental  Considerations  for Estuarine Benthal
         Systems," Water Research, Vol. 6,  1409-1418,  1972.

 4.  Schroeder, E.D. and A.W.  Busch,  "Mass and Energy  Relationships  in
         Anaerobic Digestion," Journal of the Sanitary Engineering
         Division, Vol. 92, No.  SA1,  85-98,  1966.

 5.  Baas Bscking, L.G.M. and  E.J.F.  Wood, "Biological  Processes in  the
         Estuarine Environment.  I.   Ecology of the Sulfur Cycle."
         Proceedings,  Koninklijke Nederlanse Akademie van Wetenschappen
         Amsterdam, Vol. 58,  160-181, 1955.

 6.  Orion Research, Inc., "Sulfide Ion Electrode, Model  94-16," Cambridge,
         Massachusetts, 1968.  19 p.

 7.  Cline, J.D. and A. Richards, "Oxygenation of Hydrogen  Sulfide  in Sea
         Water at Constant Salinity,  Temperature and pH."  Environmental
         Science and Technology, Vol. 3,  No. 9,  838-843, 1969.

 8.  Fenchel, T., "The Ecology of Marine Microbenthos.  IV.  Structure and
         Function of the Benthic Ecosystem,  Its  Chemical and Physical
         Factors and the Microfauna  Communities  with  Special Reference to
         the Ciliated Protozoa," Ophelia, Vol.  6, 1-182, 1969.

 9.  Berner, R.A., "Migration  of  Iron and  Sulfur  Within Anaerobic Sediments
         During Early Diagenesis," American  Journal of Science, Vol. 267,
         19-42, 1969.

10.  Berner, R.A., "Diagenesis of Iron Sulfide in Recent  Marine Sediments,"
         In:  Estuaries (G. Inlauff,  editor), American Association  for the
         Advancement of Science, Pub. 83, 268-272, 1967.

11.  Taylor, W.R., "Light and  Photosynthesis  in  Intertidal  Benthic  Diatoms,"
         Helgolander Wissenshaftliche Meeresuntersungen, Vol.  10,  29-37,
         1964.
                                      151

-------
j.2.  Chen, K.Y. and J.C. Morris, "Oxidation of Aqueous Sulfide  by 02-
          General Characteristics and Catalytic Influence,"  In:   Proceedings
          of the 5th International Water Pollution Research  Conference,
          Pergamon Press, Oxford, England, In press.

13.  Ostlund, H.G. and J. Alexander, "Oxidation Rate of Sulfide  in Sea
          Water; a Preliminary Study," Journal of Geophysical Research,
          Vol. 68, 3995-3997, 1963.

14.  Avrahami, M. and R.J. Golding, "The Oxidation  of the Sulfide Ion at
          Very Low Concentrations in Aqueous Solutions," Journal  of the
          Chemical Society, Vol. A, 647-651, 1968.

15.  Connell, W.E. and W.H. Patrick, Jr., "Reduction of Sulfate  to Sulfide
          in Waterlogged Soil," Soil Science Society of America  Proceedings,
          Vol. 33, 711-715, 1969.

16.  Servizi, J.A., R.W. Gordon and D.W. Martens, "Marine Disposal of Sedi-
          ments from Bellingham Harbor as Related to Sockeye and  Pink
          Salmon Fisheries," International Pacific Salmon Fisheries Commis-
          sion Progress Report, No. 23, 1969.  23 p.

17.  Bella, D.A., "Tidal Flats in Estuarine Water Quality Analysis," Oregon
          State University, Department of Civil Engineering, Engineering
          Experiment Station.  Research Grant No. 16070-DGO of the  Federal
          Water Quality Administration, 1970.  102 numb, leaves.

18.  Ramm, A.E., "Some Aspects of the Sulfur Cycle in Tidal Flat  Areas and
          Their Impact on Estuarine Water Quality," Doctoral Thesis, Oregon
          State University, Corvallis,  1971.

19.  Richards, R.A.,  "Chemical Observations in Some Anoxic, Sulfide-Bearing
          Basins and Fjords," In:  Advances in Water Pollution Research,
          E. A. Pearson, editor, Pergamon Press, London, Vol. 3,  p. 215-243.
          1965.

20.  Ivanov, M.V., "Microbiological Processes in the Formation of Sulfur
          Deposits," tr. by S. Nemchonok.  (Dr. E. Rabinovitz, editor), Israel
          Program for Scientific Translations,  Jerusalem, Israel,  1968,
          297 p.

21.  Sorokin,  Yu.K.,  "Interrelations Between Sulphur and Carbon Turnover in
          Leromictic Lakes," Archives of Hydrobiology, Vol.66, No.  4, 391-446,
          1970.

22.  Colby,  P.I.  and L.  L.  Smith, Jr.,  "Survival of Walleye Eggs  and Fry on
          Paper Fiber Sludge Deposits in Rainy River, Minnesota,"  Transaction^
          of the American Fisheries Society, Vol. 96, 278-296, 1967.
                                    152

-------
23.   Dimick,  R.E.,  "The Effects of Kraft Mill Waste Effluents and Some of
          Their  Components on Certain Salmonoid Fishes of the  Pacific
          Northwest," National Council for Stream Improvement Technical
          Bulletin  51, 1-23,  1952.

24.   Haydu,  E.P., H.R. Amberg and R.E. Dimick, "The Effect of Kraft Mill
          Waste  Components on Certain Salmonoid Fishes of the Pacific
          Northwest," Tappi,  Vol. 35, 545-549, 1952.

25.   Kellogg,  W.W.,  R.D.  Cadle, E.R.  Allen, A.L.  Larus and E.A.  Martell,
          "The Sulfur Cycle," Science, Vol. 175,  No. 4022, 587-596,
          February  11, 1973.

26.   Hitchcock,  D.R.  and A.E. Wechsler, "Water Pollution and the Atmospheric
          Sulfur Cycle," publication pending.

27.   Hitchcock,  D.R., "The Production of Atmospheric Sulfur from Polluted
          Water," publication pending.

28.   Moore,  H.B., "The Muds of the  Clyde Sea Area.   III.   Chemical  and
          Physical  Conditions; Rates and Nature of Sedimentation; and
          Fauna," Journal of the Marine Biological Assoc.  (U.K.), Vol.  17,
          325-358,  1931.

29.   Moore,  H.B., "The Specific Identification of Faecal  Pellets,"  Journal
          of the Marine Biological  Assoc.  (U.K.),  Vol.  17,  359-365,  1931.

30.   Carriker, M.R.,  "Ecology of Estuarine Benthic Invertebrates, a Per-
          spective,"  In:   Estuaries (G.H.  Lauff,  editor),  American  Assoc.
          for  the Advancement of Science,  Pub.  83,  442-487,  1967.

31.   Hata, Y., H. Kadota, H.  Miyoshi, and M.  Kimata, "Microbial  Production  of
          Sulfides  in Polluted Coastal and Estuarine Regions,"   In:   Advances
          in Water  Pollution Research, Second International Conference,  Vol.  3
          (E.A.  Pearson,  editor), Pergamon Press,  1964.   p.  287-302.

32.   Martin,  B.C.,  "The Effect of Mixing on the Oxygen Uptake Rate  of Estuarine
          Bottom Deposits," Masters Thesis, Oregon State  University,  Corvallis,
          1969.

33.   Martin,  D.C. and D.A.  Bella, "Effect of Mixing on Oxygen Uptake Rate of
          Estuarine  Bottom Deposits," Journal  Water Pollution Control Federation,
          Vol. 43,  1865-1876, 1971.

34.   Crook,  G.R., "In Situ Measurement of the  Benthal Oxygen Requirements of
          Tidal  FlatTDeposits," Masters Thesis,  Department of Civil  Engineering,
          Oregon State University,  Corvallis,  1970.
                                    153

-------
35.  Crook, G.R. and D.A. Bella, "In Situ Measurements of the Benthal Oxygen
          Requirements of Tidal Flat Areas," Proc. 25rd Industrial Waste
          Conference, Purdue University, 1970.

36.  McKeown, J.J., A.H. Benedict and G.M. Locke, "Studies on the Behavior
          of Benthal Deposits of Paper-Mill Origin," Technical Bull. No. 219,
          National Council of the Paper Industry for Air and Stream Improve-
          ment, New York, September 1968.  28 p.

37.  Rolley, H.L.J. and M. Owens, "Oxygen Consumption Rate and Some Chemical
          Properties of River Muds," Water Research, Vol. 1, 759-766, 1967.

38.  Edwards, R.W. and H.L.J. Rolley, "Oxygen Consumption of River Muds,"
          Journal of Ecology, Vol. 53, 1-27, 1965.

39.  Hanes, B.N. and T.M. White, "Effects of Sea Water Concentration on
          Oxygen Uptake of a Benthal System," Proceedings of the 22nd
          Industrial Waste Conference, Purdue University, Engineering Exten-
          sion Series No. 129, 1967.

40.  Stein, J.E. and J.G. Denison, "In Situ Benthal Oxygen Demand of Cellulosic
          Fibers,"  In:  Advances in Water Pollution Research, Proceedings
          of the 3rd International Conference on Water Pollution Research,
          Munich, Germany, Vol. 3, 1967.  p. 181-197.

41.  Pamatmat, Mario M. and K. Banse, "Oxygen Consumption by the Seabed.
          ^-  In situ Measurements to a Depth of 180 m," Limnology and
          Oceanography, Vol. 13, No. 3, 537-540, July 1968.

42.  Fair, G.M., E.W. Moore and H.A. Thomas, "The Natural Purification of
          River Muds and Pollutional Sediments," Sewage Works Journal, Vol. 13,
          270-307, 756-779, 1941.

43.  Baity, H.G., "Studies of Sewage Sludge," Sewage Works Journal, Vol. 10,
          539, 1938.

44.  Ogunrombi, J.A. and W.E. Dobbins, "The Effects of Benthal Deposits on
          the Oxygen Resources of Natural Streams," Journal of the Water Pol-
          lution Control Federation, Vol. 42, No. 4, 538-551, 1970.

45.  U.S. Federal Water Pollution Control Administration, Middle Atlantic
          Region, "An In Situ Benthic Respirometer," CB-SREP Technical Paper
          No. 6, 1968, mimeographed.

46.  Bella, D.A. and W.F. Dobbins, "Difference Modeling of Stream Pollution,"
          Journal San.  Engr. Div., Proc. Amer. Soc.  Civil Engr., Vol. 94,
          No. SA5,  995, 1968.~~

47.  Orion Research, Inc., "Determination of Total Sulfide Content in Water,"
          Applications Bulletin No. 12, Cambridge, Massachusetts, 1969.  2 p.


                                    154

-------
48.   American Public Health Association.  Standard Methods for the Exam-
          ination of Water and Waste Water, 12th ed, New York, New York,
          1965.   769 p.

49.   Thum,  A.B.,  "An Ecological Study of Diatomovora amoena, an Interstitial
          Acoel  Flatworm, in an Estuarine Mudflat on the Central Coast of
          Oregon," Doctoral thesis, Oregon State University, Corvallis,
          1971.

50.   Reeburg, W.S.,  "An Improved Interstitial Water Sampler," Limnology and
          Oceanography,  Vol. 12, 163-165, 1967.

51.   Bertolacini, R.J. and J.E. Barney, II, "Colorimetric Determination of
          Sulfate with Barium Choranilate,"  Analytical Chem., Vol. 29,
          281-283, 1957.

52.   Washington State Pollution Control Commission, "Pollutional Effects of
          Pulp and Paper Mill Wastes in Puget Sound," Federal Water Pollu-
          tion Control Administration, Washington, D.C., 1967.  473 p.

53.   Berner, R.A., "Sedimentary Pyrite Formation," American Journal of
          Science, Vol.  268, 1-23, 1970.

54.   Zobell, C.E., "Ecology of Sulfate Reducing Bacteria," Producers Monthly,
          Vol. 22, No. 7, 12-29, 1958.

55.   Postgate, John, "The Chemical Physiology of the Sulfate-Reducing
          Bacteria," Producers Monthly, Vol. 22, No. 19, 12-16, 1958.

56.   Rubentschich, L.I., "Sulfate Reducing Bacteria," Microbiology, Vol. 15,
          443-456, 1946.

57.   Redfield, Alfred C., "The Biological Control of Chemical Factors in
          the Environment," American Scientist, Vol. 46, 204-221,  1958.

58.   Downing, A.L. and G.A. Truesdale, "Some Factors Affecting the Rate of
          Solution of Oxygen in Water," Journal of Applied Chemistry,
          Vol. 5, 570-574, 1955.

59.   Gloyna, E.F. and E. Ernesto, "Sulfide Production in Waste Stabilization
          Ponds," Journal of the Sanitary Engineering Division, ASCE, Vol. 95,
          607, 1969.

60.   Edwards, V., "Analytical Methods in Bacterial Kinetics," Doctoral Thesis,
          University of California, Berkeley, 1967.

61.   Wong,  P.S.,  "Determination of Sulfate Reduction by Using Radio-Tracer
          Methodology," unpublished graduate report, Oregon State University,
          Corvallis, 1972.

62.   Murthy, A.R.V.  and K. Sharada, "Determination of Sulfide Sulfur in
          Minerals," Analyst, Vol. 85, 299, 1960.

                                    155

-------
63.  Jeffery, P.G.,  Chemical Methods for Rock Analysis, Pergamon Press,
          New York,  1970.  507 p.

64.  Wang, C.H. and D.L. Willis, Radiotracer Methodology in Biological
          Science, Prentice-Hall, Inc., New Jersey, 1965.  383 p.

65.  Cooper, T., Research Associate, Personal Communication, Oregon State
          University, Corvallis, 1971.

66.  Nakai, N. and M.L. Jensen, "The Kinetic Isotope Effect of the Bacterial
          Reduction and Oxidation of Sulfur,"  Geochimica et Cosmochimica
          Acta, Vol. 28, 1893-1912, 1964.

67.  Olsen, R.C., "Measuring Estuarine Benthal Sulfide Release Rate,"
          Graduate Project Report (unpublished), Oregon State University,
          Corvallis, 1971.

68.  Branfield, A.E., "The Oxygen Content  of Interstitial Water in Sandy
          Shores,"  Journal of Animal Ecology, Vol. 33, p.  97-116,  1964.

69.  Jansson, B.O.,  "The Availability of Oxygen for the Interstitial Fauna
          of Sandy Beaches,"  Journal of Experimental Marine Biology and
          Ecology, Vol. 1, 123-143, 1967.

70.  Edwards, R.W.,  "The Effect of Larvae of Chironomus riparius meigen on
          the Redox Potentials of Settled Activated Sludge," Annals of
          Applied Biology, Vol. 46, No. 3, 457-463, 1958.

71.  Rhodes, D.C., "Rates of Sediment Reworking of Intertidal and Subtidal
          Sediments in Barnstable Harbor and Buzzard Bay, Massachusetts,"
          Journal of Geology,  Vol.  75, 461-476, 1963.

72.  Perkins, R.K. and O.C. Johnston, "A Review of Diffusion and Dispersion
          in Porous Media,"  Jour.  Soc. Petrol. Engr., Vol. 2, 70,  1963.

73.  Saffman, P.G.,  "Dispersion Due to Molecular Diffusion and Macroscopic
          Mixing in Flow Through a Network of Capillaries," Jour. Fluid
          Mech., Vol. 7, 194,  1960.

74.  Duursma, E.K.,  "Molecular Diffusion of Radioisotopes in Interstitial
          Water of Sediments,"  In:  Proceedings of the Symposium on the
          Disposal of Radioactive Wastes into Seas, Oceans, and Surface
          Waters, International Atomic Energy Agency, Vienna, Austria,
          1966.  p.  355-371.

75.  Bungay, H.R., J.W. Whalen and W.M. Sanders, "Microprobe Techniques for
          Determining Diffusivities and Respiration Rates in Microbial Slime
          Systems,"   Federal Water Quality Administration Water Laboratory,
          Athens, Georgia, 1969.
                                    156

-------
76.   Milhous,  N.T.,  "Water Interchange in an Estuarine Tidal Flat," North-
         west  Regional  American Geophysical Union Meeting, Oregon State
          University,  Corvallis,  October 1971.

77.   "National Estuarine Pollution Study,"  Report of the Secretary of the
          Interior to  the United States Congress, U.S. Government Printing
          Office,  Washington,  D.C., 1970.

78.   Fleming,  G.,  "Sediment Balance of Clyde Estuary,"  Journal of the
          Hydraulics Division, ASCE, Vol. 96, No. HY ll,~pp. 2219-2230, 1970.

79.   Burt,  W.V. and L.D. Marriage, "Computation of Pollution in the Yaquina
          River Estuary,"  Sewage and Industrial Waste, Vol. 29, 12, 1957.

80.   Paulson,  R.W.,  "The Longitudinal Diffusion Coefficient in the Delaware
          River Estuary as Determined from a Steady State Model," Water
          Resour.  Res., Vol. 5, No. 1, 59-67, 1969.

81.   Paulson,  R.W.,  "Variation of the Longitudinal Dispersion Coefficient in
          the  Delaware River Estuary as a Function of Inflow,"  Water Resour.
          Res., Vol. 6, No. 2, 516-526, 1970

82.   Ward,  P.R.B.  and H.B. Fisher, "Some Limitations on Use of the One-
          Dimensional  Dispersion Equation, with Comments on Two Papers by
          R.W. Paulson,"  Water Resources Research, Vol. 7, No. 1,
          pp.  215-220,  February 1971.

                             ADDITIONAL REFERENCES

Bella, D.A.,  "Modeling and Simulation of Stream and Estuarine Systems," Eighth
Annual Workshop, Association of Environmental Engineering Professors, Nassau,
Bahamas, 1972.

Dornhelm, R.B. and Woolhiser,  D.A., "Digital Simulation of Estuarine Water Quality,"
Water Resources Research. Vol. 4., 1317-1328, 1968.

Fisher, H.B.,  "A Lagrangian Method for Predicting Dispersion in Bolina's Lagoon,
California," Open  File  Report, Geological Survey, Menlo Park, California, 1969.

Glenne, G., Personal Communication, Oregon State University, Corvallis, 1969.

Grenney, W. J. and Bella, D.A., "Field Study and Mathematical Model of the Slack-
Water Buildup  of a Pollutant in a Tidal River," Limnology and Oceanography, Vol.
17,  No. 2,  229-236,  March, 1972.

Grenney, W. J., "Modeling Estuary Pollution by Computer Simulation," M.S. Thesis,
Civil Engineering, Oregon State University, Corvallis, 1970.

Ippen,  A.T., "Estuary  and Coastline Hydrodynamics," McGraw-Hill Publishing Co.,
New  York, N.Y., 1966.   744 p.
                                       157

-------
                               SECTION XVIII

                                PUBLICATIONS
1970      1.    Bella,  D.A.,  "Role of Tidelands and Marshlands in Estuarine
                    Water Quality,"  Proc. Northwest Estuarine and Coastal
                    Zone Symposium, 1970.

          2.    Bella,  D.A. and W.J. Grenney, "Finite Difference Convection
                    Errors,"  Journal of the Sanitary Engineering Division,
                    ASCE, Vol. 96, 1352-1361, 1970.

          3.    Crook,  G.R. and D.A. Bella, "In^ Situ Measurements of the
                    Benthal  Oxygen Requirements of Tidal Flats,"  In:  Proc.
                    23rd Industrial Waste Conference, Purdue University, 1970.

          4.    Goodwin,  C.R.,  E.W. Emmett and B.  Glenne, "Tidal Study of
                    Three Oregon Estuaries," Oregon State University Engineer-
                    ing Experiment Station Bulletin No. 45, Corvallis, 1970.

          5.    Crook,  G.R.,  "In Situ Measurement of the Benthal Oxygen Require-
                    ments of Tidal Flat Deposits,"  M.S. Thesis, Civil
                    Engineering, Oregon State University, Corvallis, 1970.

          6.    Grenney,  W.J.,  "Modeling Estuary Pollution by Computer Simu-
                    lation,"  M.S. Thesis, Civil Engineering, Oregon State
                    University, Corvallis, 1970.

1971      7.    Bella,  D.A. and J.E. McCauley, "Environmental Considerations
                    for Estuarine Dredging Operations,"  In:  IV Proceedings
                    of the World Dredging Conference, New Orleans,  Louisiana,
                    1971.

          8.    Ramm, A.E., "Some Aspects of the Sulfur Cycle in Tidal Flat
                    Areas and Their Impact on Estuarine Water Quality,"
                    Ph.D. Thesis, Oregon State University, Corvallis, 1971.

          9.    Martin,  D.C.  and D.A.  Bella,  "Effects of Mixing on Oxygen
                    Uptake Rate of Estuarine Bottom Deposits,"  Journal Water
                    Pollution Control Federation,  Vol.  43, No. 9, pp. 1865-1876,
                    September 1971.
                                    158

-------
1972      10.    Bella,  D.A.,  A.E. Ramm and P.E. Peterson, "Effects of Tidal
                    Flats on Estuarine Water Quality," Journal Water Pollu-
                    tion Control Federation, Vol. 44, No. 4, 541-556,
                    April 1972.

         11.    Bella,  D.A. and W.J. Grenney, "Estimating Dispersion Coef-
                    ficients in Estuaries,"  Journal of the Hydraulics
                    Division, ASCE, Vol. 98, No. HY 3, 583-589, March 1972.

         12.    Bella,  D.A.,  "Environmental Considerations for Estuarine
                    Benthal  Systems,"  Water Research, Vol. 6, 1409-1418,
                    1972.

1973     13.    Peterson, P.E., "Factors That Influence Sulfide Production in
                    an Estuarine Environment,"  M.S. Thesis, Oregon State
                    University, Corvallis, 1973.

         14.    Ramm, A..E. and D.A. Bella, "Aspects of the Sulfur Cycle in
                    Tidal Flat Areas" (title subject to revision), Limnology
                    and Oceanography (in press].
                                    159

-------
                               SECTION XIX




                         FINITE DIFFERENCE MODEL





INTRODUCTION




     The purpose of this appendix is to provide a description of the finite




difference estuarine model which was used in the early phases of this research




project.  The model was developed for the research project and the following




three basic criteria were used in its selection:




     (1)  The model should be accurate.




     (2)  The model should be simple and flexible so that many revisions




          could be made.




     (3)  The model should be reasonably efficient with respect to




          computer time.




     It was not the intent of the investigators to develop a standard computer




program for general use.  We have found, however, that the finite difference




methods selected and described herein are relatively simple (particularly the




water quality model) and thus they should be of general use.  Only a first




order biochemical reaction will be presented below, however, the methods pre-




sented can be simply adapted to a wide variety of biochemical reactions and




processes.




     This appendix is based principally upon two references (Grenney, 1970




and Bella, 1972) and referral to them should be made for additional information.






GENERAL STRUCTURE




     The main computer program is based on the finite-difference method de-




veloped by Bella and Dobbins (46).  The stream channel is divided into equal




length segments (AX) and the mass within each segment is computed for finite




time increments (AT).   In this model, AT is less than a tidal cycle.  Segments
                                   160

-------
are labeled beginning with segment one at the fresh water end of the channel




as shown in Figure Al, where N = segment number on the main channel and n =




interface number.   The program is versatile in that irregular estuary configura-




tions can be simulated by appropriate arrangement of the segments.   Tributaries




can be attached to the main channel as shown in Figure Al where K  are seg-




ment numbers of the tributary intersecting the main channel at segment N.   Mud




flats can be simulated by a series of adjacent short tributaries where material




is transferred across all four interfaces of each interior segment.   A two-




dimensional effect can be achieved by superimposing two or more channels.




     The program was written in Fortran IV for use on the CDC 3300  computer




at Oregon State University.  Figure A2 is a flow diagram of the main program.




Four types of input data are required:




     1.    Finite-difference grid parameters AX and AT.   The amount  of numerical




          error introduced by the finite-difference scheme was  found to  be




          very sensitive to these parameters (See Bella and Grenney, 1970).




     2.    Estuary configuration consisting of the cross section  area,




          channel  side slopes, and mean water depth at  each segment  and  the




          location and configuration of each tributary.




     3.    Hydraulic characteristics of the main channel and each tributary.




          These data include magnitude of tidal wave at the mouth,  speed of tidal




          wave propagation, channel friction,  and fresh water inflow rates.




     4.    Mass transfer parameters and initial conditions.   Those data




          include  the dispersion and decay coefficients and the  initial




          pollution concentration in each segment.   Also included is the




          location of pollution sources and the rate of pollution injection




          at each  source.
                                  161

-------
                       (tributary fresh


                         water flow)
 C VH





 ? OJ
 ri ,d

 C M
 C 4)
               n-1
                        (K-2)
                             N

r-i
                              N
N+l    1
                         n
                                  n+l
                i   ~ ?
                1      o
                                                          0)

                                                          'C "M
FIG.  Al - REPRESENTATION OF  ESTUARY CHANNEL AND TRIBUTARY.
                         162

-------
                      Input data)
               Write  initial conditions
          Increment time by an amount  At
                I Water quantity model
                 Water quality model j
no
          Add pollutant to specific segments
                by subroutine  SOS INK
            Is output desired at this time?
                                               yes
                           no
                                           Write output
      Has time exceeded maximum time for run?
                           yes
FIG. A2 - FLOW CHART FOR THE MAIN COMPUTER PROGRAM.
                        163

-------
     For each time increment, the program begins  at  the  fresh water




end of the main channel  (segment number one) and  calculates  flows in each




successive segment by means of the water quality  model.   As  the calcula-




tions proceed down the estuary, each segment is checked  for  an intersecting




tributary.  When tributaries are encountered, control  is  shifted to a sub-




routine which calculates tributary inflow.  The main channel flow is adjusted




by the amount of the tributary flow and the program proceeds to the next  segment




     After flows have been calculated in all segments, the program returns to




segment one and again proceeds down the main channel calculating pollutant




concentrations by means  of the water quality model.  When tributaries  are




encountered, control is  shifted to a sub program  which distributes  the pollutant




in the tributary.




     When the pollution  distribution has been calculated  for all segments in




the estuary, the program returns to segment number one and proceeds  back  down




the main channel checking for pollution sources.  When outfall  locations  are




encountered pollution is injected by subroutine SOSINK.




     Results are printed in predesignated times.  Output  includes  the  velocity,




area, dispersion coefficient and concentration in each segment.








WATER QUALITY MODEL








General




     Conceptualize a stream as a series of mixed  cells of length AX as shown




in Figure A3.  A number of memory locations are established  in the computer




to record the water quality and quantity conditions within each cell.  The




longitudinal mixing, as an example, that occurs over a small time interval
                                   164

-------
of length AT is simulated by numerically exchanging a given amount of water

and thus pollutant in each segment with the two adjacent segments.  The amount

of such water exchanged between  segments is dependent on the  length of the

time interval, AT, the segment size, and the hydraulic conditions being

simulated in the stream.  The pollutant mass at the end of the time interval is

given by the simple mass balance equation

         / Pollutant Mass\         / Pollutant Mass\       I  Net Mass  \
          in segment at  j    =     in segment at   1   +   I  exchanged  I
         \   time T+AT   /         \   time T       /       \ during AT  I

This "pollutant exchange", of course, involves the addition and subtraction

of the pollutant masses recorded at the appropriate memory locations in the

computer.  These computations are performed for each segment  along the length

of the stream and are repeated for successive time intervals  in order to

describe the change in pollutant mass in each segment (from which the con-

centration can be calculated) over time due to mixing.

     The simultaneous advection and biochemical reactions of  a pollutant can

also be simulated.  Advection is simulated by transferring during each time

interval a portion of the pollutant in each segment to the segment immediately

downstream.  Biochemical reactions are simulated by adding or subtracting

appropriate amounts for each segment over each time interval.  A pollutant
        FIG. A3 - STREAM CONCEPTUALIZED AS A  SERIES OF MIXED CELLS


                                   165

-------
outfall can be simulated by adding pollutant mass to the particular  segment



at the outfall location for each time interval.  The simultaneous  action



of all of these processes is simulated by performing all such  exchanges and



removals for all segments during each time interval.  The process  is repeated



over a sufficient number of time intervals (of length AT) so as to span the



time period of interest.  If AX and AT are sufficiently small, the finite-



difference results will approximate the continuous processes being simulated.



     Each stream segment (Figure A3) will be considered as completely mixed.



The concentration within any segment N at time T will be designated by C(N,T).



That is C(N,T) is averaged over the space interval, AX, but is not averaged



over the time interval, AT.  Concentrations are recorded at the beginning and



end of time intervals.



     The cross sectional areas are similarly defined.  That is, A(N,T) designates



the average cross sectional area of segment N at time T.



     For the present discussion, only first order biochemical reactions will be



considered.  The first order reaction coefficient, K.., may vary with distance



and time.  The value of K- for the entire segment N during the entire time



interval beginning at time T will be designated as K1(N,T).



     The mean water velocity, U and the dispersion coefficients, DT, always
                                                                   lj


appear as products with A, the cross sectional area.  For simplicity these



products will be designated as UA, the total flow rate, and DA, the total



dispersion coefficient.  In order to keep the number of subscripted variables



to two, the following notation is used.  UA(N+1,T) and DA(N+1,T) equal the



average values of UA and DA at the interface of segments N and N+l over a



time interval which begins at time T.  UA(N,T) and DA(N,T) equal the average



values of UA and DA at the interface of segment N and N-l over a time interval



which begins at time, T.




                                       166

-------
     The above finite-difference definitions are not standard definitions.




One must closely examine the definitions used in each modeling approach.  In




the following sections, advection, dispersion, decay and pollutant addition




will be individually modeled in finite-difference form.  A method of combining




these individual processes will then be presented.



Advection




     The advection can be conceptualized in finite-difference terms as a water




transfer from upstream segments repeated for each time interval, AT  (see




Figure A4).  The volume of water transferred in each step is equal to the



flow rate between segments times the length of the time interval as shown




in Figure A4.
               U
                                UA(N,T)   UA(N+1,T)
                            N-l
N
                                                 N+l
                    FIG. A4 - FINITE-DIFFERENCE ADVECTION
 The mass  transferred  into  segment  N will  be  equal  to  the  volume  of water




 transferred  from  segment N-l  to  segment N (assuming direction  of flow  from




 left  to right)  times  the pollutant concentration in segment  N-l.   That is,




 the pollutant mass  transferred into segment  N equals






                UA(N,T)ATC(N-1,T)
                                   167

-------
Similarly the pollutant mass transferred out of segment  N  equals

               UA(n+l,T)ATC(N,T)                                       (2)

The pollutant mass at the start of AT will be equal to

               C(N,T)A(N,T)                                            (3)

while the pollutant mass at the end of the time interval will be  equal  to

               C(N,T+AT)A(N,T+ AT)                                     (4)

     Consider a mass balance of pollutant within segment N.  One  obtains:

(mass at end of AT) = (mass at start of AT) + (mass advected in during  AT) -

(mass advected out during AT).  Substituting equations (1), (2),  (3) and (4)

into this mass balance leads to

                C(N T+AT) = CCN,T)A(N,T)
                HN,I+AJJ    A (N,T+AT)

                            UA(N,T)C(N-1,T)AT
                          +  A(N,T+AT)AX

                            UA(N+1,T)C(N,T)AT                           ,,.,
                             A(N,T+AT)AX                                L J

 Equation  (5) is  the finite-difference model of advection  with variable

 parameters when  the velocity flows from segment N-l  to  segment N.

      Should the  velocity reverse direction, equation (5)  must be replaced by

 equation  (6)

                CfN T+AT) - C(N,T)A(N,T)
                HN,l+AlJ    A(N,T+AT)

                            UA(N+1,T)C(N+1,T)AT
                             A(n,T+AT)AX

                            UA(N,T)C(N,T)AT
                             A(N,T+AT)AX                                l  }


 Equation  (5) and (6) are subject to the restriction

                UAT < AX                                                (7)
                                   168

-------
Explicit Finite-Difference Model of Dispersion



     Consider any stream segment N as illustrated in Figure A5.  At time T,



the beginning of the time interval, equal elements of water, of volume w(N,T),



are exchanged between segments N and N-l.  Similarly, equal elements of water,



of volume w(N-i-l,T), are exchanged between segments N and N+l.  The elements



of water are exchanged and all cells are completely mixed over the time



interval AT.



     The mass of pollutant leaving segment N during this exchange is:



               w(N,T)C(N,T)+w(N + l,T)C(N,T)                             (8)



while the mass of pollutant entering segment N from segment N.-1 and N+l during



AT is :



               w(N,T)C(N-l,T)+w(N+l,T)C(N+l,T)                         (9)



The change in mass in segment n during AT equals



                [C(N,T+AT) - C(N,T)]A(N,T)AX                            (10)



setting the change in mass within segment N equation  (10), equal to the mass



input to segment n minus the mass output from segment N leads to



               C(N,T+AT) = C(N,T)



                                      [C(N-1,T)-C(N,T)]
                         + A MAX   [C(N+1,T)-C(N,T)]                 (11)





     From a mixing length description  the dispersion coefficient may be



considered as



               DT = qh1                                                (12)
                L




in which q is the volume rate of water exchanged per unit  cross sectional



area and h1 is the effective length  of the  exchange.  From the difference



model described above and equation  (12), one  obtains:
                                 169

-------
and
               Dr =
                    WAX
                L   AAT
               w =
    D AAT
     LJ
    If
                                                        (13)
                                                                       (14)
                              W(H,T)    W(N+1,T)



^

                          N-l
                      N
N+l
                  FIG. AS - FINITE-DIFFERENCE DISPERSION
     Using the notation previously given, one obtains
w(N,T) =
                          AX
                                    [c(N_ljT)_c(NjT)]
and
               w(N+l,T) =
                          DA(N+1,T)AT
                             AX
                       [C(N+1,T)-C(N,T)]
                        (15)
                        (16)
Substitution equations  (15) and 16) into equation  (11)  leads  to
               C(N,T+AT) = C(N,T)
                           DA(N,T)AT
                           A(N,T)AX2
                         + DA(N+1,T)AT
                           A(N,T)AX2
                                                        (17)
Equation  (17) enables one to explicitly obtain  the  concentration in segment N
at the end of the time interval.  Repeated use  of equation (17)  will closely
simulate the dispersion  (and diffusion) process if  AX and AT are sufficiently
small.
                                 170

-------
     It is reasonable from the above approach that the  total  volume  of water

exchanged during the time interval should not exceed the volume  of the segment.

That is:

               w(N,T) + w(N+l,T) < A(N,T)AX                            (18)

Substituting (15) and (16) into (18) leads to

               DA(N,T)   DA(N*1,T)  AX2
                A(N,T)    A(N,T)  * AT

     If DL and A do not vary with length, X, one obtains from equation  (19)

the stability requirement for the standard explicit scheme for the approximation

of the diffusion equation:

               D AT
               AX
                                                                       (20)
     To prevent an oscillation error, one should accept the following requirement.

               D AT
               -— - < 1/2                                             (21)
               AX

First Order Biochemical Reactions

     If one assumes that the change of pollutant mass within any segment N that

occurs over a time interval of length, AT, is proportional to the pollutant mass

within the cell during the time interval and proportional to the length of the

time interval, one obtains

               C(N,T+AT) = C(N,T)-K1(N,T)AT(1-6)C(N,T)+6C(N,T+AT)]    (22)

in which e is a weighing function (0 <6< 1).

The Addition of Pollutants

     Pollutants may be added to any stream segment.  By equating the pollutant

mass in any segment N at the end of the time interval (T+AT) , to the pollutant

mass in the segment at the beginning of the time interval (T) plus the pollutant

mass added over the time interval, AT, one obtains:
                                       171

-------
               C(N,T+AT) = C(N,T) H-                                    C23)

in which m(N,T) equals the average pollutant mass input rate  into segment N

over the time interval beginning at time T.

Combining Dispersion, Advection, Decay and Additions

     Equations (5),  (17),  (22) and  (23) can be simply  combined in order to

simulate the simultaneous occurrence of advection,  dispersion,  decay and addi-

tions.  One merely utilizes each of these four equations  sequentially.   The

final concentration results of a given step serve as the  initial  concentrations

for the following step.  As an example, equation  (5) would be used to describe

the concentration changes due to advection alone.   The results  of equation  (5)

would then be used for the initial conditions for the  dispersion  equation (17).

That is C(N,T+AT) from equation (5) would serve as  C(N,T) in  equation (17).

The results  (T+AT) of equation (17) would then serve as initial  (T)  concentra-

tions for equation (22).  The C(N,T+AT) values obtained from  equation (22)

would serve as the C(N,T) values of equation  (23).  Change in the cross  sectional

area, A(N,T), should be included during the advection  step.   The  use of all

four equations would describe the pollutant concentration changes over the  time

interval due to advection, dispersion, decay and additions.   These steps would

then be repeated for successive time intervals (of  length, AT)  until the computa-

tions covered the desired time span being simulated.   The computational  sequence

of equations (5), (17), (22) and (23) can be changed in any order with no

significant change in the results.

     Equations (5) and (6) produce a numerical mixing  error.   This error can

be described by an effective or pseudo dispersion coefficient given by

               D  = | [AX - UAT]                                       (24)

     In order to compensate for this error, D  from equation  (24) must be sub-

tracted from the actual dispersion coefficient used in equation (17) for each

time and length interval.
                                    172

-------
WATER QUANTITY MODEL




     The most simple method  for  estimating stream velocities is to assume




uniform flow throughout the  estuary  and  apply a sinusoidal velocity at the mouth.




A more realistic method is to  determine  water surface elevations as a function




of distance and time and calculate flows from-known  characteristics of the




channel.  This can be accomplished by  solving the continuity and momentum equa-




tion for unsteady flow.  Although this method is  accurate,  a great amount of




computer time is required.   A  more efficient  method  has  been to use changes in




water surface elevations to  calculate  average flows  over small  time intervals,




i.e., (average flow out of segment)  =  (average  flow  in)  -  (change in volume)




(Fisher, 1969).  This method has been  adopted for the present study and  can be




represented in finite-difference terms as  follows for flow  in the direction



shown in Figure Al.




               UA(N,T) = UA(N-1,T) + [A(N,T-1)  -  A(N,T)] |jr           (25)





By using this approach, the  problem  is reduced  to one of finding an efficient




means for predicting water surface elevations  (H).




     Fisher (1969), in studies of Bolinas  Lagoon,  California, used observed




values of H over a few tidal cycles.   The  use of  tabulated  values  becomes




awkward for long period of analysis.   Dorlhelm  and Wollhiser (1968)  predict




H by propagating a sine shaped tidal wave  up  the  estuary.   Tidal actions  in




most real estuaries do not conform to  this  simple representation however.




     Frequently a reflected  sine wave  can  be  used to predict tidal heights along




an estuary (Ippen, 1966).  Consider  the  channel profile  of  length L shown in




Figure A6.   An imposed wave  is assumed to  travel  up  the  estuary from the mouth.




A hypothetical boundary exists at the  end  of  the  estuary which  reflects  a




portion of the incident wave.  The water surface  at  a point x feet from  the





                                     173

-------
         C"
fi
0
• r-i
-t-J

rd



-------
boundary can be predicted by superimposing  the  height of the reflected wave onto




the incident wave.  The effects of  friction can be approximated by assuming an




exponential reduction in wave height with distance.   Mathematically,  the  tidal



height can be represented as (Glenne,  1969):




               H = HQ + a[eyXcos(6T +  kx) + 3e"yxcos (
-------
             (Subroutine AREA]
No
Has program reached the end of
     the current tidal cycle	
                        Yes
     Calculate ordinates of the imposed
        tidal wave at the mouth of the
            estuary for the  next
      	tidal cycle	
 Based on the speed of wave  propagation,  and
      friction of the channel,  calculate or-
        dinates of the incident wave at the
           center of each channel seg-
                   ment
       Calculate ordinate of  reflected
           wave and superimpose
              on incident wave
      Calculate average cross section
      	areas  for each segment
                  Return
  FIG. A7 - FLOW CHART FOR SUBROUTINE "AREA".
                   176

-------
     For any particular time at the mouth of the estuary, T, the ordinate




of the imposed wave at any point, x, in the estuary can be calculated by




determinining the time required for the wave to move up the channel to that




point.  This is the lag time and is represented by TRAV on Figure A8.  For



this study, the time lag was expressed as:




               TRAV = c(l-x)




where c is wave celerity, x is the distance from the fresh water end, and L




is the length of the estuary.  More accuracy could possibly be achieved by



allowing c to vary as a function of depth; however, at the sacrifice of com-



puter time-  Once T  is located (Figure AS), the elevation is obtained by
                   J\


interpolating between points M and M + 1.




     The ordinate of the reflected wave is obtained in a similar manner.   A




portion of the incident wave is assumed to bounce off the boundary at the end



of the estuary and travel back towards the mouth at the same celerity.  The




total lag time for the wave to travel from the mouth back to point x can be




calculated by:



               TRAV = c(L+x)



     Friction is incorporated in the model by reducing the ordinates by an



exponential function of the distance traveled by the wave, i.e., e p^




for the incident wave and e~V^ +X^  for the reflected wave.   The water surface



elevation is then obtained by superimposing the ordinates of the incident and



reflected waves.  Friction need not be represented by an exponential function;



however, it was selected so that existing methods (Ippen, 1966) could be used




to estimate the parameters u and k.  It may not be the most realistic repre-



sentation, however, because the major frictional influence is exerted near the




mouth of the estuary and the frictional effect decreases with distance up






                                 177

-------
                           Time
FIG.  AS -  TIDAL WAVE REPRESENTATION AT THE  MOUTH OF AN ESTUARY
    .2
  s
    . 1
  x
  rt
                     10
15
20
25
30
            Number of increments in tidal  cycle
           FIG.  A9  -  ERROR  INTRODUCED BY LINEAR INTERPOLATION
                          178

-------
the estuary.  Conversely,  in  some  real  estuaries  the effect of friction would




probably be  least near  the mouth and increase with distance up the  estuary.




     Cross section areas are  calculated as  a function of the water  surface




elevation and side slopes  of  the channel at each  segment.




     In order to calculate flows by  means of equation (25)  it is necessary to




know the flow across  the interface of segment one at the upper end  of the




estuary and  in every  tributary.  For a  completely reflected wave all of the




tidal induced flow is reflected and,  therefore, the  flow across the first




interface is equal to the  fresh water inflow.  Physically this  can  be visualized




as a waterfall forming  a complete  barrier at  the  end of  the estuary.  However,




when the upstream boundary reflects  only a  fraction,  3,  of  the  incident wave




amplitude, a certain  amount of flow  will be induced  at segment  one  due  to tidal




action beyond the boundary.   When  this  flow is neglected, significant errors




may be introduced for values  of g  less  than one.




     The tidal induced  flows  at the  boundary  can  be  calculated by extending



the hydraulic model beyond the boundary a distance necessary  for the -unreflected




portion of the wave to  become significantly attenuated by friction.  For




progressive waves with  low friction  this method may  require  excessive computer




time.  One approach to  reduce computer  time and still approximate flows across




the first interface would  be  to increase the  friction coefficient beyond the




boundary.  Errors introduced  by this  approximation would have to be investigated




for each individual case.



     If the reflected wave is not  completely  attenuated  when  it reaches the




mouth of the estuary, the  calculated water  surface elevation will not coincide




with the incident wave  and a  discontinuity  will occur at the  ocean  boundary.




Ippen (1966) avoids the problem by applying the incident wave at the end of the






                                 179

-------
estuary instead of the mouth.  However, tidal fluctuations are generally




not recorded at the upper end of an estuary, and this approach is not  always



practical.




     If there is sufficient friction in the channel, or if g is low, the




discontinuity will be negligible.  When a substantial discontinuity does exist




at the ocean boundary, a driving wave must be found such that superposition of




the reflected wave will result in water surface elevations which agree with




observed data.  Finding a driving wave is difficult, but it can be done by




trial and error for short runs.




     The water quantity model was computed for one tidal cycle by adjusting




the model to fit measured results (Grenney and Bella, 1972).  The single tidal



cycle was repeated to simulate longer runs with a minimum computer time.



     A description of program subroutines is given in Table Al and a listing



of the programs is provided in Table A2.
                                  180

-------
         TABLE Al - DESCRIPTIONS OF COMPUTER PROGRAMS
PROGRAM ESTREF:  main program
    a)  Controls input/output and subroutines
    b)  Calculates initial conditions
    c)  For each AX and AT calculates: average flows, convection, dis-
        persion, and decay

SUBROUTINE INPUT:  reads input coefficients and identification number
    scheme for finite-difference representation of estuary.

SUBROUTINE INCON:  reads initial conditions values for variables;
    calculates cross-sectional areas and stream surface widths for
    mean water depth; and sets up initial concentrations in each
    segment.

SUBROUTINE INAREA:  calculates initial cross-sectional areas at each
    segment given  an initial tidal height at the mouth.

SUBROUTINE TIDE:   calculates tidal height at the mouth as a function of
    time.

SUBROUTINE AREA:   propagates tidal wave inland and calculates cross-sectional
    areas at  each  segment for  each AT.

SUBROUTINE SOSI:   provides  input or  removal of material at specified
    segments  and times  to represent  exogenous sources and sinks.

FUNCTION FLWU:  fresh water flow entering the system at the inland
    boundary.
                                181

-------
TABLE A2---LISTING  OF COMPUTER  PROGRAMS FOR ESTUARY MODEL
               . FSTKEf
        COMMON  AOOuO)  »TI'AV( Jo»' > ,01 -*00>» ID( 300) >EXP(300)»
       lEXPK<300)»<1HK(!50li).UH( JoO), A( 300 • 2 ) . 1 1 ( 300 > » AA2C 300) > NroT»€LM»
       2U.TH».OTM»T»TMAXiCKl»QU(JlO).U.»CI 1 • C ll»» RFPT »[>! H» MTUT.MQ. TCU TE»
       3AnTH»ALFA»LASI .L)X»EL» '-'A?. J JJ. 1 RAVK< 300) , rtKC
     10  CALL  INplll
        THAl»t.O-THA
        OTH«nTM/60.0
        1>T"UTM*60.0
        CK1»CK1/86«00
        RNTuT-NTOT
        OTX»OT/DX
        KIP-0
        K»2
        Jl 1«1
        LASTP]«LAST+1
               INITIAL
        CALL 1NCON
        CALL INARLA
        UA{2)«FL«U(T)
        C1(1)«C11
        ClCLAST+U-ClN
        W»ITF(?.«)0) NTUT»tL.1»OX,OT".ll. ThA,l M.LL
     50  FPHdATflH  .//•// 1H »3V,Ia. '1F12.3 //1H  • 3X. 3K 1 ?. 3. I
        HRITE(2«54) T
     51  FnRMAKlH  ./ Iri ,3X, Kl*. 2)
        ICONl«l
        ICON2»LAST+1
     55
     35 T«TtOTH
        CALL A»tA(K)
                   AVt FLO^b AT ALL SfCTIl)l"!>
        DH d N-2.LAST
        NP«N+1
        UA(2)"FLWU(T)
      8 CONTINUE
        L»l
        on 72 N«?.LASI
     T\  CALL SOSIIT.RATE)
        C1CN)«C1(N)+RATE*I)TH/(A(M,J)+A(N.KJ)/2.0
        L«L*1
     72  CONTINUE
                     CDNVLCTIDN AT ALL SECTIONS
        IF(UA(2» M>oO,60
     61  F1"OA(2)*CH2)
        OPA(2)«-UA(2)*(UX+UMCz)*nT/A(2»K))/2.0
        GP TO 62
     60  F1*UA(2)*CU U
        OPA(?)« IIA(2)*(I)X-UAC2)*I1T/A{^.K. ) 1/2.0
                                   182

-------
TABLE A2 (continued)	LISTING  OF COMPUTER PROGRAMS  FOR  ESTUARY MODEL
               62 l!A»(?)«L'(i')
                  (in 63 N*?.LASl
                  MPsN+1
               6*

                  fin in
               6S F?»lJA(
                  OP AC UP )m UA{»ih>)»<0<-UA(NP)*i>T/A(IMW»K))/2.0
               66
               63 CONFTNUfc
            C           I'lSPFKSiUN  «T  ALL 	...,„
                  F««t(C2ll)-C2C2))*')«A(/))*(i.o-ALf»)
                  DO 9 N«2»L»ST
                              -C21 N) )*uAA( "i+1 )
                9 CDNFlNUt
                          UECAr  Af ALL
                  00  11  N*?.LASl
                  Cl (N)«C?(lx)*Fj
               it cnwriNiiE;
                                o a I p u I
                  IF(uUCKull)-| )  25> -»b»2't
               25 KntJ*KOU+l
                  WRTTE(2.S2)  T
               52 FnHHATtlH  »/  1H »3X. F I S . "5 )
                  WPI rF(?,"i6)  iLOul •Ottl 1 J.C1 I 1 )
               56 FHRMAKlM  . I 5. F 1 2. 4, 26<. F 15. i| )
                  00  21  I»?.LASIPl
                  WRITE<2.">3>  I.Ont I )»VELnr,4( I.KJ.CU I)
               53 FOflMATUH  . ^.F^.l.M'l.a.Fl?. t ,F1S.4)
               21 rnMTlNlIt
               24 inUM*.J
                  J»K
                  K-IOUM
                  IFCT-T^AX)  35>J2>32
               32 IFtl-lKEPT)  «1»«U.«1
               41 CALL  F*1T
                  SIIHKOUTINL  INPUT
                  COMMON  A01300J»HO( 100}»SO{ 3DO)»TRAVC 30(J),D( JOO).Il)(300)»ŁXP(300)»
                 lEXP«(300)»''»riKC50UJ' Jri( JOO) • A( 300.2 J .Cl ( 100J.AA?(300)>NTUT,ELM.
                 2l).THA,nTM»T,TMAx»CKl.()uiSO).LI »Cl l.tlN.ftEPI .OTH. MTOT »MO» fO. TE.
                 3AOTH.ALFA.LASI i.ljX.tL* UA». JJJ. TRAVKl 3UO) . rtKC
                  NTOT'FFIMC 1 )
                  ELM»FFIM( i>
                  THA«FFIN( 1 )
                  TMAX«FF1MC 1 )
                  CK1»FFIN( 1 )
                  NTlME-FFlNf 1)
                  00  
-------
TABLE A2  (continued)---LISTING OF COMPUTER  PROGRAMS FOR ESTUARY MODEL
                 on  3  I-I.LL
                 IDCI)«FFIN(l)
                 CONTINUE
                 10( I+l )«0
                 REPT-FFINU)
                 LAST«NTUT+1
                 RFTURN
                 EN!)
                 SUBKOUTlNfc  INCON
                 COMMON  A.tXP<300)»
                1EXPR< 300) »OHKC500)»UH( 300) . AC 300.2) .Cl( 300) »AA2( 300) .NTiJT.ELMii
                2UiTHA,l)TMpT,TMAXpCKl»nil(SO)»LL»Cll«ClN»KEPIi'DTH»MTOT»MO»TO»Tt»
                3AnTri.ALF»»LASr.OX»tl..  UA».  JJJ. f«AVKC3l>0».it.D)  12*12,13
              12  R0( 1*1 )=1 35.0
              li  CONflNUe
                 SO(I)»SSS
                 TRAV(I)«TTT
                 D( I) "ODD
                 CKD-CCC
                 Y«Y+OX/5?80.0
               1  CONTINUE
                 RETURN
                 ENO
                 SUBHOUTINt IMArtEA
                 COMMON  AOMOO>»BO(300)>SO(30(»>TRAV(300).D(300>>IIH300>»EXP(300>*
                1FXPH(300)>I1HKC>00}.IJH( JO 0).«( 300,2) »C1( 300), AA2t 300). N TUT. ELM.
                2U,TriA,DTM.T.TMAX.CM.OUCiO).LL.C1 1 . C1N .REPT. 0 TH, MTUT . MO. TO, TE.
                3AOTH.ALFA.LAST.OX.EL.  OA?. JJJ. TRAVKC 300) .KKC
                 CALL TIDE
                 J»l
                 LASTP1«LAST»1
                 U«U/?280.
                 TRA(/(l)»RKC*EL/(AOTH*3<>00.)
                 EXP(l)«2.na28**(
                 TRAVRU)«T«AV(1)
                 EXP(LASTP1)»1.0
                 TRAV(LASTPl)«IKAVRtLASIPl ) •KXfPC I. AS IP 1 )»0.0
                 Y«DX/2.0
                                        184

-------
TABLE A2  (continued)—-LISTING OF  COMPUTER PROGRAMS FOR ESTUARY MODEI
                 TRAVX»(T-I>»/A!>TH»'1U
                 1N»LAST
                 DO 4 N*2.LAST
                 Z«EL+EL-Y
                 T»AV(lN)«rtKC*T/(AOTri*3oOO.)

                 Y.Y+OX

               <» CONTINUE
                 DO S IN*1.LASlPl
                 TINC»TRAVXTRAV( IN)
                 M»T1NC
                 HTMC-M
                 OH(IN)»ŁXH(INJ*(UHK{rt}+(OHK(M+1)-U^K(M))*(TINt-HINC))
                 M»T1NC
                 OHR«EXPR(lN)*CUHKC'>l) + (UHKC'1*lJ-LiHKt-1))*(TIi
                 DH( IN)«i^

               5 CONTINUE
                 RFTURN
                 COMMON Ani')00)»dU(3UU)>SO(3QO)*TftAV(30U)>0('iOO)>IU(JOO)»EXP(300J>
                lEXPK(300)»l>MKCiOO)»LlH( JOO) , »{ 3uO. i>) .C 1 1 300 J . AA21 300) . NTUT . ELM.
                2U.THA,OTM»T,TnAX.CKl»|)J(SO).LL»Cll.ClN.«FPr.I)TH.HTUT.m).TO>lE.
                3AOTM.ALKA.LAS1 .OX»EL«  UA?.  JjJ.TRAVtU 30ID.KKC
                 IF(T-TE)  l.^.i?
               ? TO»TE
                 TP«TO*(MTUT-MO)*AOTH
               t TRAVX»( r-TOj/AUTH+MO
                 LASTP1*LAST+1
                 M«TINC
                 RINC«M
                 MaTINC
                 RINC«M
                 nHK*EXPR(l    )*(DHK*{ f I NC-rtlNC ) )
                 DH( D»nH( i )+DH«
                 AC l.K)«AO( 1 )*UH( l
                 00 6  IN-?.LASTPl
                 TINC-TRAVXTRA^f IN)
                 M-TINC
                 RINC«M
                 TINC«TRAVX-TRAVH11M>
                 M.TINC
                 BTNC«H
                                                      ) ) * ( T I^C-
                 A( IN.K)«AO(
                 AA21IN   )»(A(
                 CONTINUE
                 AA?(?)«A( l.K)
                 RFTUBN
                 ENO
                                          185

-------
TABLE A2  (continued)—-LISTING OF  COMPUTER PROGRAMS FOR ESTUARY MODEL
               SUrtHluTIML  HUE
               CfHMON  A(K 3oO)»flOC3UO)»S(H3uO>»TKAVl30d),Ol J00)» IUC 300) • tXP< 300)
              lEXP«(100)»i)HK(50U).Urt( JOO).AC300.i?>»Cl( 300) » AA2( 300 ) » NTU f >ELH.
              2U.THA,OTMf T,Trt*X»CKl»OJ(SO).LL»Cll.ClN.REPT.bTH»HTOT»MO»TO»TE.
              SAnTH.ALf A.LAST.DX.EL'  UA?. JJ J. TKA VK ( U»n ) . HKC
               Tn«r
               MTOI«50
               M0«18
               TX»TO-1
               DO  1  I^
               DHK( I
               Tx»TX+AOTH
             1  CnNTI.MUE
               RETURN
               END
               FUNCTION KLXIJI r j
               Fl WUS950.0
               RETURN
               FNO
               siiRKOuTiNt snsTt T.HA 1 1
               IF(4.9-T) 1.2. Z
             1  RATt-a.bFS
               6H  TO 3
             ?  RAT٫0.0
             1  HFTURN
               END
          CARU  CnilniT      2TH
                                        186

-------
                                  TECHNICAL REPORT DATA
                           (Please read Iwiifuctions on the reverse before completing)
 FRPORT NO.
                             27
 TITLE AND SUBTITLE
 Tidal  Flats in Estuarine  Water Quality Analysis
                                                          3. RECIPIENT'S ACCESSIOf»NO.
                                                          5. REPORT DATE
                                                            June 1975
                                                          6. PERFORMING ORGANIZATION CODE
 AUTHOR(S)

  David A. Bella
                                                          8. PERFORMING ORGANIZATION REPORT NO.

                                                           EPA-660/3-75-025
 PERFORMING ORG \NIZATION NAME AND ADDRESS
  Department of  Civil Engineering
  Oregon State University
  Corvallis, Oregon 97331
                                                          10. PROGRAM ELEMENT NO.

                                                              1BA025
                                                          11. CONTRACT/GRANT NO.

                                                            Grant  16070 DGO
12. SPONSORING AGENCY NAME AND ADDRESS
  U. S. Environmental Protection Agency
  National Environmental Research Center
  200 S_W. 35th St.
  Corvallis.  Oregon 9733Q	
                                                          13. TYPE OF REPORT AND PERIOD COVERED
                                                            Final
                                                          14. SPONSORING AGENCY CODE
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT
 The initial  phases of the study involved  mixing processes and tidal hydraulics;  how-
 ever, the  study emphasis shifted  to  estuarine benthic systems as the importance  of
 these systems  became more apparent.  A  conceptual model of estuarine benthic  systems
 was developed  and a classification system of  estuarine benthic deposits which is based
 on the availability of hydrogen acceptors and reactive iron was developed.

 Field studies  demonstrated that estuarine sediments and overlying wastes could contain
 significant  concentrations of free sulfides which are toxic to a variety of organisms.
 Field studies  of benthic oxygen uptake  and benthic sulfide release were conducted.
 Water quality  profiles within the deposits also were determined.  A number of labora-
 tory studies were  conducted to determine the rate of sulfate reduction.  Results from
 experiments  using extracts from benthic deposits and algal mats demonstrated  a close
 relationship between the rate of  sulfate  reduction and the sulfate and soluble organic
 carbon concentrations.  A general systems model of estuarine benthic systems  was devel
 oped.  A variety of activities which could contribute to significant environmental
 changes with estuarine benthic systems  were  identified.
 Methods of determining dispersion coefficients from salinity profiles were examined
 and an improved method was developed.   The build-up of a pollutant in the vicinity of
 the outfall  during the slack water period of  tide was studied through a field experi-
,ment and mathematical  model
                                      DS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
     estuaries
     estuarine ecosystems
     tidal hydraulics
     mixing processes
     benthic ecology
     bottom deposits     simulation
     sulfides      sulfide  toxicity
                                              b.lDENTIFIERS/OPEN ENDED TERMS  C. COSATI Field/Group
                                               Yaquina Estuary, Oregon
                                                                           05C
18. DISTRIBUTION STATEMEN1

     unlimited
                                              19. SECURITY CLASS (ThisReport)
                                                                             OF PAGES
                                              20. SECURITY CLASS (Thispage)
                                                                        22. PRICE
EPA Form 2220-1 (9-73)
                           A U. S. GOVERNMENT PRINTING OFFICE: 1975-699-188 133 REGION 10

-------