United Slates
Environmental Protection
Agency
Research aTO Development
invironmental
Laboratory
Gulf Breeze FL 32561
Middle Atlantic Region 3
5th and Walnut Sts.
Philadelphia PA 19106
Chesapeake Bay Program
THE CONSEQUENCES OF NUTRIENT
ENRICHMENT IN ESTUARIES
Bruce Neilson
CBP-TR-003E
-----
[mill
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600R81112
THE CONSEQUENCES OF NUTRIENT
ENRICHMENT IN ESTUARIES
Bruce Neilson
CBP-TR-003E
t-USRAfLV"
CHESAPEAKE BAT PROGRAM
2083 WEST STREET - SUITE SO
ANNAPOLIS, MARYLAND 21401
3
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
THE CONSEQUENCES OF NUTRIENT ENRICHMENT IN ESTUARIES
5. REPORT DATE
January. 1981
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Bruce Neilson
8. PERFORMING ORGANIZATION REPORT NO.
CBP-TR-003E
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Virginia Institute of Marine Science
of the College of William and Mary
Dr. William J. Hargis, Jr., Director
Gloucester Point, Virginia 23062
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
R-806-189-010
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Chesapeake Bay Program
2083 West Street
Annapolis, Maryland 21401
13. TYPE OF REPORT AND PERIOD COVERED
Project Report
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A "paper study" was conducted to determine the consequences of nutrient
enrichment in an estuary. First, a classification scheme was developed to assign
a "Level of Nutrient Enrichment" to a water body based on concentrations of Total
Phosphorus and Total Nitrogen. The impacts of nutrient enrichment on the various
uses of estuaries there were described and assessed. Finally, "safe" nutrient
levels for Chesapeake Bay and its tributaries were recommended.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI I'icld/Croup
Chesapeake Bay
Eutrophication
18. DISTRIBUTION STATEMENT
Unrestricted
EPA rof.-r. 2220-: ;Sev. 4-77)
19. SECURITY CLASS (This Report/
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
PREVIOUS EOI riON 1C OBSOLETE
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THE CONSEQUENCES OF NUTRIENT ENRICHMENT IN ESTUARIES
A Report to the Eutrophication Program,
U. S. Environmental Protection Agency-Chesapeake Bay Program
Grant No. R-806-189-010
Thomas Pheiffer, Project Officer
From
The Chesapeake Research Consortium, Inc.
't)r. L. Eugene Cronin, Director
Annapolis, Maryland
by
Bruce Neilson
Virginia Institute of Marine Science
of the College of William and Mary
Dr. William J. Hargis, Jr., Director
Gloucester Point, Virginia 23062
Chesapeake Research Consortium Publication No. 96
! ;
Virginia Institute of Marine Science Contribution No. 979
January, 1981
__4 nor--
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TABLE OF CONTENTS
Acknowledgements
Abstract
Executive Summary
Introduction
Approach to the Problem. . .
Measuring Nutrient Enrichment. . . . .
Eutrophication in Lakes. ...
':'- -- Nutrient Levels in Estuaries
A Classification System for Nutrient Enrichment in
Estuaries
Impacts on Uses of Estuaries ....
Approach to the Problem. .
Primary Impacts of Nutrient Enrichment
i
Secondary Impacts of Nutrient Enrichment .....
' I '
Tertiary Impacts of Nutrient Enrichment
: . I
Summary :
i
, ' I
{Conclusions and Recommendations. ...f
! References . . 1 !
Page
iii
iv
v
1
1
3
4
.._ 8
8
14
15
15
18
20
23
26
30TTC
ii
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ACKNOWLEDGEMENTS
; The author would like to thank the other scientists with whom he
has worked on the CRC grant, namely, Dr. Donald Heinle and Dr. Christopher
D'Elia of Chesapeake Biological Laboratory; Dr. Andrew McErlean, formerly at
;the Horn Point Environmental Laboratory; and Dr. Kenneth Webb from Virginia
.Institute of Marine Science. Also acknowledged are the members of the VIMS
Department of Estuarine Processes who worked on the project. Special thanks
go to Dr. L. Eugene Cronin, Director of the Chesapeake Research Consortium
;and project coordinator for the grant, who provided assistance at many times
;and in many ways during the study.
iii
f;" A 71 ONi;
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.._. ABSTRACT
A "paper study" was conducted to determine the consequences of
nutrient enrichment in an estuary. First, a classification scheme was , ;
developed to assign a "Level of Nutrient Enrichment" to a water body based on
concentrations of Total Phosphorus and Total Nitrogen. The impacts of .-';,."..
nutrient enrichment on the various uses of estuaries there were described and
assessed. Finally, "safe" nutrient levels for Chesapeake Bay and its tribu-
taries were recommended. j
, l
i I
"JOTTOV" '"!'"
iv
-------
EXECUTIVE SUMMARY
' In response to a Eutrophication Work Plan (EPA, 1977) research was
undertaken to determine the consequence of nutrient enrichment in estuaries.
; i
This research was directed by the Work Plan to proceed with the assumption
that nutrient enrichment in moderation
that at some point, this may decline dramatically. This hypothesis is repre-
_ _ . _ ,!
sented graphically by Figure ES-1. "~ ~ ~ ~ v~
The initial task was to make
more quantitative. Research in lakes has shown that the average level of
biomass (as measured by chlorophyll a concentrations), the clarity of the
I i . '
jwater (as measured by Secchi depth), and the oxygen balance (as measured by
results in increasing productivity but
the assessment of nutrient enrichment
the hypolimnetic oxygen depletion rate) are correlated with total phosphorus i
1 ' ' 'i '
concentrations in the lake (and also total phosphorus loading rates).
Eutrophication (nutrient concentrations?)
Figure ES-1. Hypothetical response of estuarine ecosystem to increasing
I levels of nutrient enrichment (from Eutrophication Work Plan, j
L EPA, 1977). j j 30-
'*- I i '*-'
':!'.'< Or
-------
Therefore, it appeared reasonable to assume that total nutrient concentrations
might play a similar role in estuaries. j
A review of nutrient levels observed in estuaries indicated that i
the variation was great. Nutrient levels in the Chesapeake Bay system varied
over several orders of magnitude, as shown in Figure ES-2. A classification
system was proposed (Table ES-1) which has nutrient concentrations vary
^logarithmically as nutrient enrichment levels vary arithmetically. Although
; i , j
many marine systems are nitrogens-limited, it is not clear that this will be
true for all cases. Therefore, total phosphorus concentrations have been
! : ' i
'calculated for each total nitrogen concentration according to the Redfield
i
ratios. ! j
i : ^ I ;" :..f '
- : i
! The second task was to relate ecosystem consequences to levels of
i .-. -,' :; I
;nutrient enrichment. The terms "ecosystem health" and "ecosystem productiv-
! ' ^
iity" are nebulous and difficult to define in any quantitative fashion.
I ! ! .
'Therefore, efforts were devoted to determining the impacts of nutrient enrich-
i i I !
'merit on water uses. Increased levels of inorganic nutrients (primary impacts)
! ! ! . . I
jprimarily damage only uses of freshwater. Additionally, the levels necessary
to impair uses generally are much higher than levels observed in estuaries.
! . i j
(Increased plant biomass (secondary impacts) reduces water clarity and its
laesthetic value. Additionally, this alters the oxygen balance and the
istructure of the algal community. Increased levels of detritus in the system
I ! I
;(tertiary impacts) alter sediment characteristics (and therefore, also the
! ' ' i
I i i .
jbenthic communities) and generally reduce oxygen levels. The overall impacts
lot nutrient enrichment are shown in Table ES-2.
! It has been recommended that:
! l \
i 1) Analyses of nutrient enrichment should be made more quantita- . so
'~ . tive. . i '_ . j p,1"
"/_' ' . ._ L _'.. ^:;'vi " '.i' .
M OF
,-VnFA:
TV.'. \c
-------
10-
Z
UJ
<
o
O.I-
0.01
11.2
2.13
o
i r
O.I
TOTAL PHOSPHORUS (mg/l)
Figure ES-2.
Total Phosphorus and Total Nitrogen concentrations observed in
the estuaries of the Chesapeake Bay system. i
vii
-------
Key to Figure ES-2.
Algal Bloom
Loftus et al. 1972
2
..3
4
5
; 6
7
8
; 9
10
11
12
13
O /
34
14
15
16
(
Fall Line Patuxent River
Sta. 1 Patuxent River
Sta. 4 Patuxent River
Sta. 6 Patuxent River
Sta. 10 ; Patuxent River
Sta. 14 Patuxent River
Eastern Branch, Elizabeth River
Southern Branch, Elizabeth River
Mouth, Elizabeth River
Potomac River Fall Line
James River Fall Line
Susquehanna River Fall Line
Rappahannock River Fall Line ~~ ~
Mouth, Pagan River
Head, Pagan River
Middle Reaches, Pagan River
Flemer et al, 1970
Neilson & Sturm, 1977
Guide & Villa, 1971
.
Roseribaum & Neilson, 1977
17 York River near West Point
|18 York River near Gloucester Point
19 York River Mouth
i
|20 James River Mouth j
|21 James River in Turbidity Maximum
Sturm & Neilson, 1978
Neilson & Ferry, 1978
'22
!23
;24
25
126
!27
i29
130
131
;32
i33
i
i
!35
i
'36
^37
38
Poquoson River Mouth
Poquoson River
Back River, Virginia
Little Creek Harbor
Lynnhaven Bay
Lynnhaven Bay Mouth
Wicomico River, MD
Wicomic River - Headwaters
Wicomico River Mouth
Neilson, 1976
Hydroscience
Chesapeake Bay near Mouth of Potomac River
Chesapeake Bay near Baltimore Harbor
Chesapeake Bay below Susquehanna River
i
Potomac River Mouth
i
Back River, MD Rocky Point
Back River, MD Stansbury Point
Back River, MD Cox Point
.
Ferguson & Simmons, 1974
viii
-------
TABLE ES-1. Classification Scheme for Nutrient Enrichment in Estuaries.
Level of
Nutrient
Enrichment
- 0 " """ "" """
1
2
; 3'
; 4
j 5
; * -e - "-" -
! :
\ - i ' ** .
i
i s
! 9 "*.- 3"
»'
i ioj
Total
Nitrogen
mg/1
0.003
O.O10
0.032
0.10
0.32
i.'o
3.2 - "-
!
10
>
32
j
100 '
i
1
320 \
Total
Phosphorus
mg/1
0.0004
0.001
0.004
0.014
0.044
0.14
-- ^0.44 "--*
». -. -
0.4 "
4.4
13.8
44
ix
-------
Level of
Nutrient
Enrichment
0
8
10
TABLE ES-2
Public Drinking
Water Supply
Acceptable
Minor
Purification
Required
More
Extensive
Treatment
Needed
Marginally
Acceptable
and
Sometimes
not
Acceptable
Not
Acceptable
Livestock
Drinking
Water
A
C
C
E
P
T
A
B
L
E
Algae
May
Clog
Intake
Pipes
Marginally
Acceptable
Not
Acceptable
Irrigation
Acceptable
Increased
Nutrient
Levels
Could
Enhance
Usefulness
Generally
Acceptable
But
Algae
Could
Clog
Pipes and
Pumps
and
There
Could be
Nitrate
Build-up
in
Ground
Water
Freshwater
Aquatic
Life
Acceptable
(oligotrophic)
(mesotrophic) ;
Problems
Arise
Periodically
> "
(eutrophic)
Marginally
Acceptable
Generally
Not
Acceptable
Impacts of Nutrient Enrichment on Water Uses
a) uses limited to freshwater portions of estuaries.
-------
Level of
Nutrient
Enr ichment
0
8
1C
TABLE ES-2.
Marine
Aquatic
Life
Acceptable
(oligotrophic)
Problems arise
Infrequently
or due to
Local
Conditions
(mesotrophic)
Marginally
Acceptable
(eutrophic)
Marginally
Acceptable
Generally
Acceptable
Recreation
and
Aesthetics
Acceptable
Infrequent
Episodes
when
not
nw IP
Acceptable
Frequent
Episodes
when
not
Acceptable
Not
Acceptable
Industry
A
C
C
E
P
T
A
B
L
E
Algae
May
Clog
Intake
Pipes
Not
Acceptable
for some
Purposes
Commercial
Shipping
A
C
C
E
P
T
A
B
L
E
Problems
May
Arise
with
Hydrogen
Sulfide
. Impact of Nutrient Enrichment on Water Uses
b) uses which apply to brackish portions of estuaries.
xi
-------
2) The estuarine analog to total phosphorus in lake ecosystems '
should be determined. :
3) System responses should be determined Jas a function of the
estuarine analog determined in (2).
4) An overall index of nutrient enrichment should be developed to
facilitate comparisons and allow temporal trends to be charted.
5) More scientific studies are needed to determine the rates and
routes of nutrient transfer. Field studies are especially
important. ;
6) To be safe, nutrient concentrations in the Chesapeake Bay'
system should be kept below Enrichment Level 4, or Total N =
0.32 mg/1 and Total P = 0.044 mg/1.
7) Environmental managers should consider nutrient concentrations
above Level 5 (Total N = 1.0 and Total P = 0.14) to be a
warning or danger signal." ~ - - ~ ~~ ?*
xii
-------
INTRODUCTION
: Eutrophication was identified as one of three high priority problem
areas to be addressed by the U. S. Environmental Protection Agency's j
Chesapeake Bay Program (EPA, 1980a). In response to this ranking, a Eutrophi-
cation Work Group was formed and a Eutrophication Work Program was formulated
(EPA, 1977). This program identified five principal tasks: j
: |
A. Operational Definition of the Study Problem
I
B. Ecosystem Simulation !
.!
C. Data Acquisition and Synthesis
' ! r?.f>-
D. Identification of Control Alternatives
E. Decision Analysis
''"':." '
In October 1978 the Chesapeake Research Consortium, Inc. was awarded a grant
entitled "Definition of Chesapeake Bay Problems of Excessive Enrichment or
Eutrophication" which addresses many of the components of Task A. The work
presented in this report concerns Task A.4 - Relation Between Eutrophication
Level and Ecosystem Consequences. This and the other subprojects of the CRC
grant were "paper studies"; that is, the literature and the available data
sources were utilized. No field or laboratory studies to generate new data
were planned, authorized or undertaken.
j One item not identified in the Work Program which was carried out
was the organization of a symposium, on the effects of nutrient enrichment in
estuaries which was held in Williamsburg, Virginia, in May, 1979. The papers
presented at that symposium especially the invited review papers, have been
used extensively in the preparation of this report; they are identified in
later sections by the author's names arid an asterisk and are listed separately
In the references.
Approach to the Problem I
I I .
\ The Work Program "established a series of tasks and described in
some detail their content and interrelationships" (EPA, 1977) . Since this
document provided the framework for the research conducted, it is appropriate
to review the conceptual model of eutrophication upon which the Work Group
based these tasks. This conceptual model is perhaps best represented by
Figure 1 and the following quote: i !
!_.-. ; | ' j
"In the absence of nutrients, there is no aquatic ecosystem.
-------
As the nutrient concentrations increase, the ecosystem productivity
increases. The hypothesis is that at some point a further increase in
nutrient concentrations will cause the ecosystem health to decline
(perhaps drastically)."
; EPA, 1977
The hypothesis described provides, in general terms, a coherent and
logical, philosophical approach to the problem. However, Figure 1 implies
extensive knowledge of how ecosystems work in a very quantitative and precise
fashion. Difficulties arise when one attempts to construct such a diagram.
For example, the abscissa in Figure 1 is labelled "Eutrophication", yet this
term is poorly defined, at least in any quantitative sense, and is believed
to be totally inappropriate for estuaries by the author and others (Cronin,
1980). Similarly, ecosystem health and productivity (the ordinate values)
are general, non-quantifiable terms and they refer to quite dissimilar attri-
butes of systems. ;
The approach taken by the author has been to opt for the second
label on the X-axis in Figure 1, namely, nutrient concentrations. In the
next chapter, a classification scheme to define levels of nutrient enrichment
is proposed. The task of defining ecosystem health and productivity was " '
judged to be futile and, hopelessly difficult. Instead, the impacts of
nutrient enrichment on beneficial uses of estuaries have been assessed, and
these are pr-esented in the following chapter. The final chapter of the
report includes some conclusions and recommendations.
4J
CO TJ
>s O
CO U
O Pk
O
W
Figure 1.
Eutrophication (Nutrient Concentrations ?)
Hypothetical estuarine ecosystem response to increasing levels
of nutrient enrichment. (From EPA, 1977)
-------
MEASURING NUTRIENT ENRICHMENT
Implicit in the approach outlined in the Work Plan (EPA, 1977), is
the existence of a measure or index of nutrient enrichment. The value of ;
indexes is clear (Train, 1972). For this case, an index would define the
status of an estuary with respect to nutrient enrichment and thereby allow
temporal trends to be charted and different geographical areas to be compared
(See Task A.2 and Figure A of the Work Program for specific intended uses of
the index.). Use of the term index, rather than variable, implies that the
Work Group believed that a combination of environmental factors was important
and that some formulation incorporating all of these factors would provide a
better measure of the level of enrichment than any single factor.
Water quality indices have been used in the United States (Ott, ' "*""
1978), but not to the same extent as air quality and: economic index*^ \
McErlean and Reed (1979) reviewed and evaluated many water quality indexes ;
with respect to their applicability to nutrient enrichment in estuaries. They
also utilized a DELPHI approach to formulate an estuarine index of enrichment.
However, they were not able to test this proposed index. Additionally, \
neither it nor any other water quality index has been used widely in assessing
nutrient enrichment or other water quality problems in estuaries (Ott, 1978).
Thus, although the concept of an index of nutrient enrichment for estuaries is
an appealing one, no true index exists at present. Therefore, an alternate
method to quantify nutrient enrichment was needed. !
j Intuitively, one would expect nutrient concentrations in an estuary
to increase with increasing nutrient enrichment. This might not occur in all
instances, nor is there likely to be an exact formula relating nutrient con- \
centrations to nutrient enrichment levels. Nevertheless, for the moment |
jiutrient concentrations appear to be the best available measure of nutrient ;
enrichment. Since phosphorus concentrations have been used in the assessment
of eutrophication problems in lakes, some of the findings of lake researchers
will be reviewed in the next section. In the following section, nutrient
levels observed in estuaries will be presented and in the final section of
this chapter, a classification system based on nutrient concentrations will be
proposed. j
Eutrophication in Lakes I
! -i ' I . ' ' ' ' !
{ In a recent article, Harris (1980) addressed the response of phyto- ;
plankton to variability in the environment. While much of the discussion j
concerns phytoplankton ecology, the paper also covered models and water j
quality management. Harris divided the models currently being used into two ;
general types: empirically based models and kinetic, mass-balance models. It
is his opinion that the mass-balance models do not adequately represent the -?
temporal and spatial scales of variability in the environment. Therefore he
-------
concludes that:
"Clearly the complex mass-balance models lack biological
realism at a number of scales and ... they may achieve
generality, but they lack both realism and precision. The
predictions are therefore not to be trusted."
(Harris, 1980)
The empirical models of the Vollenweider-type relate average chlorophyll
levels to the amount of total phosphorus in the system. This approach "has
generality and realism; the precision may be low but the model is valid and
the predictions do work" (Harris, 1980). Although Vollenweider's work has
been seminal, most of his publications are not readily available to -American
readers. Fortunately his work, and that of many other lake researchers, has
been, summarized in a report on the North American portion of the OECD Eutro-
phication Project (Rast and Lee, 1978). Very briefly, phosphorus levels
appear to control phytoplankton levels in most lakes. Average chlorophyll
concentrations, Secchi depth readings and hypolimnetic oxygen depletion rates
have been shown to be correlated with.a phosphorus loading function, as
indicated in the following three figures from Rast and Lee (1978). Note that
L(P) = the areal total phosphorus loading_rate (in.mg P/square metre^year);
q = hydraulic loading (in metres/year); z ^ the mean depth (in metres); and
t = hydraulic residence time (in years) = z/q . P^, the steady state total
phosphorus concentration in the lake, has been shown to be equal to the total
phosphorus loading function, (L(P)/q ) / (1 + /z/q) (Rast and Lee, 1978).
Thus, either the external loading or the total phosphorus concentration in
;the water column can be utilized in assessing conditions in a lake.
; Although these empirical relationships are general and imprecise,
they provide guidance to engineers arid managers who seek to reverse the
'eutrophication process and ameliorate its negative effects. They have been
used to design remedial measures in a number of lakes, for example Medical
'Lake (EPA, 1980b), Lake Temescal (EPA, 1980c), and Lake Cobbossee (EPA,
I980d). ; i
I To summarize, researchers have found that the overall biomass in a
lake is related to the amount of total phosphorus available. This empirical
relationship does not tell when peak chlorophyll levels will occur or give
Information on productivity, growth rates or small scale variations. However,
water quality management involves long-term considerations, so that the
'average conditions predicted by the empirical model usually are suitable for
management purposes. j <.
| One might expect that similar empirical relationships can be eluci-
dated for estuaries. Since estuarine and marine systems often are nitrogen-
limited, nitrogen might control, but it is more likely that both nitrogen
and phosphorus need to be considered, at least during initial efforts to i
determine the nutrient-biomass relationships. The experience in lakes further
^suggests that concentrations of Total Nitrogen and Total Phosphorus are more ;
likely to be correlated with system responses than concentrations of the j
Inorganic forms of nitrogen and phosphorus. j
-------
100
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X - ANNUAL MEAN CHLOROPHYLL &
A GROWING SEASON CHLOROPHYLL & -
^X CHLOROPHYLL a. IN FIRST TWO METER
\ S Or WATER COLUM.M
>X '" V SUMMER MEAN CHLOROPHYLL A
+ SUMMER SURFACE MEAN CHLOROPHYLL JL
»
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.too [CHLOROPHYLL Q] »o.7« LOG
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i * iiiiiii i t iiiiii!
(HPJ/^/tuyi^j -0.239
«
i t i i t S t i
..:»""
10
100
1000
Figure 22.
US OECD Data Applied to Vollenwelder
Phosphorus Loading Characteristics and
Mean Chlorophyll a_ Relationship
Figure 2. Lake data showing the relationship between the
phosphorus load (abscissa) and the average level
of plant biomass (ordinate). (Figure 22 from
Rast & Lee, 1978).
-------
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Figure 23. US OECD Data Applied to Phosphorus Loading and Secchl Depth
Relationship (Log-Log Scale).
-------
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0 CL
z I0
o
h-
UJ
Q.
- LJ
O
LJ ^_^
>~ O
O >»
o E 1
^^ ^^
LJ r~T*
"Z.
^s ^*
~ *"^
O
Q_
>-
I
_J
LJ
% 01
-
log oreol hypolimnetic oxygen depletion (g02/m /doy)
I ='OA67 loq[(L(P)/q$)/(l*yTj7")]--|.07
BCf.NTRAL BASIN OF LAKE ERIE
(Ye of ol Dolo Record)
US OECO WATER BODIES
(See Table 14 For Identificotion Key)
A WASHINGTON.USA, AND ONTARIO. ^5 .^
CANADA.WATER BODIES ^^
(Dola Token From, And Wol*;r Bodies ' . 34' ^^^
Identified In.Welch And Perkin$,l977) 5 ^^^
I" A *41 13 ^^^
9 9 'i ^^^
50 *^*^^
45 44_Ai9^^
~ % ^ O ^^^^V43
"* 33 ^^^'~' '
& ^o^ HO -. . . '
A ^^*(I96I) _
A A ^^>^i^ " (19661
1 ^^^^^jfifc ^ »wVf
- A l^f^^ * m (1956) ;
A ^^^ A. A ''" A
^X^ (1931) 0 »
***^ \ | I i it i lit II liiiiil i i iliiti
!> ' 1 10 100 1000
/ 1 / Ol / \ / 1 \ / \
i I 1 1 1 i/ Q f / \ 1 w */ T/ i i
1 (mg/43)
Figure 80. Phosphorus Loading Characteristics and Hypol Imnetlc
Oxygen Depletion Relationship In Natural Waters
-------
Nutrient Levels in Estuaries
Nutrient levels in estuaries vary considerably, as a result of
drainage basin characteristics, discharges from municipal and industrial
wastewater treatment facilities, and other factors. In order to demonstrate
this variability graphically, nitrogen and phosphorus concentrations for
estuaries in general and for the estuaries of the Chesapeake Bay system have
been plotted in Figures 5 and 6 respectively. Since total nutrient values are
not available for many systems, values for total nutrients and for inorganic
nutrients have been plotted in Figure 5, part a and part b respectively. ;
These figures show that there is considerable variation in nutrient
concentrations. Although both nutrients vary over several orders of magni-
tude, the variability in nitrogen levels is somewhat less than that for
phosphorus. Clearly, any rating or ranking scheme for nutrient enrichment
must account for the very large range in nutrient concentrations.
A Classification System for Nutrient Enrichment in Estuaries
Research on eutrophication in lakes has shown that average algal >
biomass-and other factors vary with the nutrient supply. It is possible that
similar correlations exist for estuaries, but first" there must be a teethed to
determine the level of nutrient enrichment. The. ranking system in Table 1
assigns nutrient enrichment level according to the Total Nitrogen concentra-
tion. Nitrogen values vary logarithmically as enrichment values change
arithmetically in order to encompass the broad range of values observed in
nature. As proposed, the enrichment level increases as nitrogen concentra-
tions increase. However, this could be inverted if one desired to have the
high rankings go with "clean", high quality waters and the low rankings be
assigned to low quality, highly enriched waters.
j Even though many estuarine systems will be nitrogen limited, this
;is unlikely to be the case for all estuaries. Therefore, the enrichment
levels have been related to equivalent values for total phosphorus and for
chlorophyll a and dissolved oxygen in Table 2. The phosphorus and oxygen
Values have been scaled according to the Redfield ratios; the negative oxygen
Values indicate that oxygen is released as nutrients are incorporated into
plant cells during photosynthesis, and consumed when detritus is decomposed.
Chlorophyll values have been related to nutrient levels by a ratio in the
range of reported nutrient to chlorophyll ratios (e.g. Clark et al., 1980).
The chlorophyll values give an indication of the biomass that would result
jif all nutrients were taken up and growth were not limited by other factors.
Similarly the oxygen values give an indication of the amount of oxygen that
would be consumed during the oxidation of the biomass. At high enrichment
ilevels these values are not meaningful, but for moderate and low levels of
;enrichment they provide some insights into the magnitude of the problems
which could occur if nutrients were taken up by phytoplankton and if the
algae were to die suddenly. j
-------
4 5 6 7 891
0.1
.0.01
0.1
Total Phosphorus (mg/1)
Figure 5-a. Total Phosphorus and Total Nitrogen concentrations observed
in estuaries.
:Key to
i 1
2
3
A
5
7
Q
8
Figure 5a.
San Antonio Bay Copeland & Wohlschlag,
Galveston Bay Copeland & Frah, 1969
Station 36
Station 3
Station 4
Station 5
Sacramento-San Joaquin Delta; Grizzly Bay
Peel-Harvey Estuary McComb et al *
Western Australia
Harvey
i 10
i 11
L 12
- 13
O'Connor *
Peel
Chowan River, NC
Danish Straits
Station D 31
Station D 3
Escambia Bay
Pensacola Bay
Witherspoon et al,
Gargas, Nielsen and Mortenseu
Olinger et al
Olinger et al
-------
I-
o>
E
z
UJ
o
o
cr
H
z
o
z
<
o
o
z
O.I-
o.oi-
Figure 5-b. Inorganic Phosphorus and Inorganic Nitrogen concentrations
observed in estuaries.
0.001
0.001
1 I
0.01
1 I 1
O.I
- I
INORGANIC PHOSPHORUS (nig /I)
to Figure 5-b.
1
2
3
5
6
7
8
9
10
11
12
13
Peace River at Arcadia
Harbor Station 2
Harbor Station 9
Calico Creek, NC
Werribee Station Max levels
Werribee Station Min levels
St. Leonards Sta. Max levels
St. Leonards Sta. Min levels
Charlotte Harbor, Florida
Fraser & Wilcox*
Sanders & Kuenzer
Port Phillip Bay, Australia
Axelrad, et al*
Apalachicola and Ocklockonee
Estuaries, Florida
Apalachicola Sta. 1A
Apalachicola Sta. 7
Ocklockonee Sta. 2 j s & Iverson*
Ocklockonee Sta. 1 j
Station ML between Apalachicola & Ocklockonee Estuaries
Econfina Estuary Station 12
10
-------
10-
- E
UJ
o
o
H
O.I
0.01
O
I I I I
11.2
2.13
I T I I
I | I I I I
O.I
TOTAL PHOSPHORUS (mg/l)
|Figure 6. Total Phosphorus and Total Nitrogen concentrations observed in the
estuaries of the Chesapeake Bay system. j
11
-------
Key to Figure 6.
1 Algal Bloom
2
3
4
5
6
7
8
9
10
11
12
13
34
14
15
16
17
,1S
19
I
20
21
i
22
23
23
25
26
27
i
28
29
30
31
;32
33
36
37
38
Fall Line
Sta. 1
4
6
10
14
Sta.
Sta.
Sta.
Sta.
Patuxent River
Patuxent River
Patuxent River
Patuxent River
Patuxent River
Patuxent River
Loftus et al, 1972
Flemer et al, 1970
Eastern Branch, Elizabeth River
Southern Branch, Elizabeth River
Mouth, Elizabeth River
Potomac River Fall Line
James River Fall Line
Susquehanna River Fall Line
Rappahannock River Fall Line
Mouth, Pagan River
Head, Pagan River
Middle Reaches, Pagan River
York River near West Point
York River near Gloucester Point
York River Mouth
James River Mouth
James River in Turbidity Maximum
Poquoson River Mouth
Poquoson River
Back River, Virginia
Little Creek Harbor
Lynnhaven Bay
Lynnhaven Bay Mouth
Neilson & Sturm, 1977
Guide & Villa, 1971
Rosenbaum
& Neilson,^.97 7
Sturm & Neilson, 1978
Neilson & Ferry, 1978
Neilson, 1976 .
Wicomico River, MD j
Wicomico River - headwaters !
Wicomico River Mouth j
Chesapeake Bay near Mouth of Potomac River
Chesapeake Bay near Baltimore Harbor
Chesapeake Bay below Susquehanna River
Hydroscience
Potomac River Mouth
Back River,
Back River,
Back River,
MD Rocky Point
MD Stansbury Point-
MD Cox Point
Ferguson & Simmons, 1974
12
-------
TABLE 1. Classification System for Nutrient Enrichment in Estuaries.
Total Nitrogen
(mg/1) (yg-atoms/1)
TABLE 2.
Level of
Nutrient Enrichment
0
1
2
3
4
; 5
; 6
; 7
: 8
" 9
! ;%:;
: 10
Nutrient Enrichment Classification Scheme for Estuaries, including
Equivalent Values for Other Environmental Variables.
0.003
0.01
;0.032
jo.i
;o.32
1
ii.o
b.2
10
32
100
j
320
i
0.2
0.7
2
7
23
71
226
710
2,260
7,140
.;-. f
22,600
Level of
Nutrient
Enrichment
'
o
1
2
3
4
5
6
7
8
9
10
! Phosphorus', Oxygen & Chlorophyll Equivalents
i Total Total Dissolved
' Nitrogen Phosphorus Oxygen
! (mg/1) (mg/1) (mg/1)
1
! 0.003 0.0004 -0.06
'
| 0.010 0.001 -0.2
| 0.032 . 0.004 -0.6
j 0.10 0.014 -1.9
| 0.32 0.044 -6.0
i
i 1.0 0.14
! 3.2 0.44
i
' 10 1.4
! .32 4.4
! 100 13.8
i
! 320 44
:
1
"
-19
-60
-190
-600
-1,900
-6,000
Chlorophyll a
(yg/i
0.6
2
6
20
60
200
600
2,000
6,000
20,000
60,000
13
-------
IMPACTS ON USES OF ESTUARIES
According to the Work Plan, the research program was designed to j
"assure that eutrophication does not interfere with a maximization of bene- ;
ficial uses of the Chesapeake Bay system" (EPA, 1977). Before beneficial ;
uses can be maximized (assuming that this can be done), one must first deter-
mine how nutrient enrichment affects the various uses of estuaries. The !
approach taken in this study has been to formulate a conceptual model which ;
differentiates between classes of effects, to assess the impacts on uses for }
each class, and finally to summarize the overall impacts of nutrient enrich- j
ment on estuaries. I j
Approach to the Problem j .rj.?>- .v%:a.. \
~2~
1
i
Eutrophication in lakes is characterized by a variety of system
changes; these have been summarized in the 1968 Water Quality Criteria:
I
!
"Conditions indicative of organic enrichment are: (1) .A slow
overall decrease year after year in the dissolved oxygen in the
hypolimnion as indicated by determinations made a short time
before fall overturn and an increase in anaerobic areas in the
lower portion of the hypolimnion. (2) An increase in dissolved
solids - especially nutrient material such as nitrogen, phos-
phorus, and simple carbohydrates. (3) An increase in suspended
solids - especially organic materials. (4) A shift from a diatom-
dominated plankton population to one dominated by blue-green and/
or green algae, associated with increases in amounts and changes
i in relative abundance of nutrients. (5) A steady though slow
decrease in light penetration. (6) An increase in organic
materials and nutrients, especially phosphorus, in bottom deposits!'
j (FWPCA, 1968)
' ! ' .
I One would expect similar conditions to develop in over-enriched
jestuaries. However, it is difficult to discuss impacts in terms of degree
of enrichment when the full suite of conditions is considered. In order to
simplify and clarify the discussion which follows, the impacts of nutrient
'enrichment have been classified as follows: Primary impacts are those due to
jelevated nutrient concentrations; Secondary impacts are those due to high
levels of plant biomass; and Tertiary impacts are those resulting from the
accumulation of detritus. The conceptual model for this system is shown in '
'Figure 7.and is perhaps best illustrated in nature by the sequence of events
surrounding an algal bloom. Prior to an algal bloom, inorganic nutrient con- :
centrations will be high. As the bloom develops, the supply of inorganic i
nutrients will be depleted and most of the nutrients will be incorporated into
: 14 "' ' ;
-------
TOTAL NUTRIENT CONCENTRATIONS
External
sources
outflow
T
V
.grazing
excretion
release from
sediments
deposition
Figure 7. Conceptual model showing the three compartments of the total
nutrient concentrations in the water column and some of the
factors which control these nutrient levels.
living plants. Depending on physical conditions,algal species, etc., it is
not unusual for a rapid die-off to follow peak algal levels; this transfers
much of the nutrient supply to the detritus compartment. At least the first
two stages of this sequence were observed by Loftus et al. (1972) following a
heavy rainfall which introduced a pulse of nutrient-rich water into Chesapeake
Bay near Annapolis. As stated earlier, the primary reason for classifying
Impacts is to facilitate the discussion which follows.
Primary Impacts of Nutrient Enrichment
I , j .
| The primary impacts are those which result from elevated levels of
linorganic nutrients without biological uptake. This may appear to be an
academic exercise, but it is not necessarily so. In turbid estuaries, photo-
isynthesis is likely to be limited by light. Acidity, strong mixing and other
'factors also could inhibit biological uptake. !
! Nutrient concentrations must reach very high levels to impact water
uses, as shown in Table 3. It is noteworthy that many of the criteria relate
'to freshwater only, for example the criteria for public and livestock drinking
water supplies. The concentrations listed are an order of magnitude higher j
than those found in most estuaries and tidal rivers. Even at such high . - >
.levels, there would be virtually no impact on shipping, aesthetics and recrea-
tion. The presence of nutrients might even enhance the utility of freshwater
for irrigation. In short, the inorganic nutrient levels observed in most
estuaries will have little, if any, impact of water uses.
Secondary Impacts of Nutrient Enrichment
Secondary impacts are those related to increased algal levels.
15
-------
TABLE 3. Water Quality Criteria Pertaining to Primary Impacts.
Maximum
Permissable
Use Level
Nitrite + Nitrate Public Drinking Water Supply
10 mg-N/1
Livestock Water Supply 100 mg-N/1
Nitrite Public Drinking Water
Livestock
Nitrate Industry - cooling water (fresh)
r
Petroleum industry
!. Phosphate Industry - boiler makeup water
Industry - cooling water (fresh)
Industry - cooling water (brackish)
i \
1 Federal Water Pollution Control Administration, 1968. "Water Quality
2 National Academy of Sciences - National Academy of Engineering, 1972.
Criteria 1972".
i
i
1 mg-N/1
10 mg-N/1
30 mg/1
8 mg/1
50 mg/1
4 mg/1
5 mg/1
Criteria".
"Water Quality
' '.
Reference
1, 2
2
2
2
1, 2
1, 2
1, 2
1, 2
1, 2
-------
Changes in the biomass of rooted aquatic vegetation also are important, but
these plants can obtain nutrients from sediments as well as the water column,
so there is no easy way to relate changes in abundance to nutrient concentra-
tions in the water. Therefore, the discussion will be limited to changes in
the phytoplankton community only. =
In general, if more nutrients are available, the size of each of the
compartments should increase. When the standing crop.of phytoplankton
increases, this will affect water clarity, aesthetic values, the dissolved .
oxygen regime, and the algal community structure. . '
Clarity; Clear waters are perceived by most people to be of higher
quality than turbid waters (Bishop and Aukermann, 1970). Clear waters are j
safer for bathers and swimmers, and .the ability of some fish to locate and \
catch their prey will be adversely affected by decreased water clarity (FWPCA,
1968). The increased phytoplankton standing crop sometimes comes at the j
expense of the submerged aquatic vegetation, since the phytoplankton shade the
rooted plants and deprive them of the sunlight needed for growth. |
: The maximum recommended levels of turbidity for warm-water lakes and
streams are 25 and 50 Jackson turbidity units respectively, and for cold-water
lakes and streams the limit is 10 JTU (FWPCA, 1968). Any turbidity in |
drinking water supplies should be readily removed by traditional water treat-
ment methods (FWPCA, 1968). ; ,,. ,. j
; Aesthetics; An increase in the standing crop of algae generally
decreases the aesthetic appeal of waters by changing color and reducing )
clarity. If the algae are of the types which form mats, filamentous colonies ',
;or float on the surface, such "pea soup" conditions are considered objection-
^able by many. In eutrophic lakes and reservoirs, some of these less desirable
algal species give the water a taste and an odor thay may not be harmful, but
certainly makes the water less appetizing to those who drink it. . i
j In an EPA study of the Potomac River, four water quality criteria i
were evaluated. The criterion which proved to be most restrictive was a i
chlorophyll a limit of 25 yg/1 "to enhance the aesthetic conditions in the i
upper estuary" and eliminate the "large green mats (which) develop during the
months of June through October and create objectionable odors, clog marinas, '
cover beaches and shorelines, and in general reduce the potential of the {
jestuary for recreational purposes such as fishing, boating, and'water skiing"
{Jaworski, et al., 1971). In light of .the large sums of money needed to
reduce nutrient levels sufficiently that this criterion is met, it is
unfortunate that there was no documentation of the method by which this
criterion was established. j
i Dissolved Oxygen; The dissolved oxygen regime is affected by the
phytoplankton, since oxygen is a by-product of photosynthesis and also because
the plants consume oxygen. During the summer when the waters are warm and {
!the days long, daily average dissolved oxygen concentrations are likely to be
high and variations about the daily mean large. For example, in June 1976 the
dissolved oxygen concentrations at a station in the upper reaches of the Pagan
'River, a tributary of the James River, ranged from more than 11 mg/1 in late !
afternoon to about 3 mg/1 in the early morning (Rosenbaum and Neilson, 1977).
'Chlorophyll levels for that period were about 100 Ug/1 but varied with tidal ,
stage. The saturation concentration of oxygen in water with the observed j
temperature (29°C) and salinity (about 5 ppt) is around 7.5 mg/1, which is j
also about the midpoint of the diurnal range. Clearly surface waters were j
supersaturated during part of the day, while the early morning values did not
'f '':-- -17 . ;
-------
meet the state's water quality standard of a minimum of at least 4 mg/1. The
daily average, however, did meet the state standard of a mean above 5 mg/1.
Neither the depressed nor the elevated oxygen levels is desirable.
Reduced oxygen concentrations makes respiration more difficult for aquatic
organisms, especially when the water temperatures also are high (Reid and
Wood, 1976). It has been recommended that concentrations of dissolved gases
never exceed 110% of the saturation values (NAS-NAE, 1972).
Changes in Community Structure; Changes in the nutrient supplies
can produce a variety of responses from the algal community. In general, the
larger organisms are believed to be given greater advantage as nutrient levels
rise (Webb*). Even if there are not species shifts, the chemical makeup of ;
the algae can change in response to the availability or non-availability of ;
each nutrient, thereby altering its value as food for other aquatic organisms
(Webb*). Ryther and Officer* have suggested a classification scheme which ;
would allow different algal communities to be compared and rated with respect
to their usefulness for man's purposes. This approach would make analysis of
species shifts much more quantitative than is the case at present. j
j Schindler* indicates that the relative abundance of nitrogen and !
phosphorus is a key factor in species shifts in lakes. Briefly stated, when '.
nutrient additions are nitrogen rich (N to P ratio greater than 16) the -- ^
biomass will increase but there may not be a speciejs; shift. When ^.e. nutrient
addition is nitrogen poor, this favors the blue-gre'en algae which are capable
of fixing nitrogen from the atmosphere. Perhaps similar mechanisms are at
work in estuaries. At any rate, it is recommended that the natural relative
abundances of the nutrients remain constant and not vary as new discharges are
added to the estuary (FWP.CA, 1968; NAS-NAE, 1972).
I i
! '
I i . i. '
jTertiary Impacts of Nutrient Enrichment
I . j i -
i Tertiary impacts result from the accumulation of detritus in the
system. This often alters the bottom sediment characteristics and produces
^localized conditions of depressed oxygen tension or even anoxia. Detritus
jis defined as "all types of biogenic material in various stages of microbial
^decomposition ... which includes all dead organisms as well as the secretions,
regurgitation, excretions and egestions of living organisms, together with
jail subsequent products of decomposition which still represent potential
'sources of energy" (Darnell,. 1967). j
| Sediment Characteristics; Increased nutrient loads can result,
either temporarily or for the long term, in increased amounts of organic
[detritus in the system. Slack tides provide the opportunity for this material
ito settle out and accumulate on the estuary bottom. Changes in the organic
Icontent of the sediments obviously will impact the benthic organisms. Since
jsome organisms, such as oysters, require a firm substrate, they will be at
[increasing disadvantage as the organic content of the bottom sediments
'increases. Pearson and Rosenberg (1978) state that the data indicate a
'consistent pattern of faunal changes along a "gradient of increasing organic
jinput to marine sediments". i
j Dissolved Oxygen Levels; Alterations in the benthos are affected by
,the physical environment as well. When the physical conditions provide an
ample supply of oxygen along with the organic load, the resulting benthic
community will be different from that in a substrate with low organic content,
; ' . .''-:. is '" ' :
-------
but nonetheless it will be an active, viable assemblage. If water renewal is
decreased, then the amount of oxygen provided will decrease as well and
eventually oxygen consumption will be greater than the supply. If both the
sediments and the overlying water are anaerobic, few organisms will survive.
These effects are represented graphically in Figure 8, from Pearson and
Rosenberg (1978).
Problems of water renewal and depressed oxygen levels often occur in
vertically stratified systems. Oxygen from both natural reaeration and photo-
synthesis is added to the surface waters; stratification inhibits mixing and
therefore also the transfer of soluble water constituents throughout the :
water column. As dead cells settle they pass through the pycnocline and into
the bottom waters. There decomposition consumes oxygen and releases
nutrients. For this reason bottom waters frequently are rich in nutrients ;
and oxygen poor. Periods of anoxic bottom waters, whether of short duration
or over long periods, will result in the decimation of most of the organisms
residing in those bottom waters and in the bottom sediments. Also, when i
anoxia exists, the biochemical processes of decomposition are different from
those in aerated waters. The production and release of hydrogen sulfide, for
example, often occurs when the water is anaerobic. ' i
5 - -When nutrient enrichment results in sediments having a high organic
content, the aquatic life will be modified; some shellfish species will not
thrive under these conditions. Additionally, the soft, mucky bottom resulting
will make these areas less desirable for swimming. But if the dissolved
oxygen levels are not depressed, the impacts will be relatively minor.
Nutrient enrichment which results in botfThighly organic bottom
sediments and depressed DO levels will produce major impacts. Most forms of
aquatic life will be severely stressed or die as a result of these conditions.
Finfish may be able to avoid impacted areas, but shellfish, being sessile, <
probably will die. Anaerobic water containing hydrogen sulfide is toxic,'
Incut
.1
Well
fluitx
OXIDIZED SEDIMENT
WITH PLENTIFUL
FOOD SUPPLY
HigK Bioturbalic
HIGH BIOMASS
ORGANIC MATTER
\
Sedimentation
HIGH ORGANIC
CONTENT IN SEDIMENT
BACTERIAL
DECOMPOSITION
fO ^^^^^^^^WOOP^CtC
«*o»e7 *-*.
REDUCED O,
IN WATER
>i» Few
AKJOX"" cicrstMF^*
EMERGING Eh AND OVEP.lAYiNG
IN SEDIMENT WATER
niches
POOR 'MACROFAUNA
1
NO MACEOFAUNA |
Figure 8.
Diagram showing changes in benthic macrofauna as a result of
varying physical conditions and oxygen supply (From Pearson and
Rosenberg, 1978). j
19
-------
unsuitable for drinking and aesthetically displeasing. Use for cooling and
other industrial purposes, as well as shipping, could be affected since such
water is corrosive.
Summary
The responses to nutrient enrichment are many, varied and difficult
to characterize. Consequently there is no simple picture.of the effects of
nutrient enrichment. Table 4 provides an overview of the effects by specific
use and incorporates the primary, secondary and tertiary effects discussed
previously. The levels of nutrient enrichment are those presented in the '
previous chapter. The ratings and assignment of impacts on uses is subjec-
tive, based on professional experience with estuarine systems. The .table can
and should be revised as more and better information becomes available.
In general, when the level of enrichment is low (say through level
2), the quality of the water is good and suitable for most or all purposes. I
In the range between level 2 and level 5, there may be periodic episodes when
the quality is poor and uses are damaged, or there could be moderate impacts
almost continuously. Between levels 5 and 8, the episodes of undesirable '
conditions will be frequent and localized conditions may render t;he water j
unfit for some uses. For higher levels of enrichment, the water is suffici-
ently poor in quality to preclude or limit its usefulness for virtually all !
purposes. j
I This table can be used to compare sets of environmental conditions.
'First, ambient water characteristics, in particular nutrient concentrations, !
must be used to determine the level of nutrient enrichment. Then, for that
;level, the suitability of the water for the various uses can be ascertained in
a general sense. At present, only major modifications in water uses are j
indicated. If the table included greater detail, it might be possible to show
how limited changes in nutrient enrichment alter the use of estuaries. j
However, that remains for future studies. j
20
-------
TABLE 4. Impacts of Nutrient Enrichment on Water Uses a) uses limited to
freshwater portions of estuaries.
Level of
Nutrient
Enrichment
0
10
Public Drinking
Water Supply
Acceptable
Minor
Purification
Required
More
Extensive
Treatment
Needed
Marginally
Acceptable
and
Sometimes
not
Acceptable
Not
Acceptable
LivestocK
Drinking
Water
A
C
.c
E
P
T
A
B
L
E
Algae
May
Clog
Intake
Pipes
Marginally
Acceptable
Not
Acceptable
Irrigation
Acceptable
Increased
Nutrient
Levels
Could
Enhance
Usefulness
Generally
Acceptable
But
Algae
Could
Clog
Pipes and
Pumps
and
There
Could be
Nitrate
Build-up
in
Ground
Water
Freshwater
Aquatic
Life
Acceptable
(oligotrophic)
(mesotrophic)
Problems
Arfse
Periodically
(eutrophic)
Marginally
.Acceptable
Generally
Not
Acceptable
21
-------
Level of
Nutrient
Enrichment
0
1C
Impact of Nutrient Enrichment on Water Uses b) uses which apply to
brackish portions of estuaries.
Marine
Aquatic
Life
Acceptable
(oligotrophic)
Problems arise
Infrequently
or due to
Local
Conditions
(mesotrophic)
Marginally
Acceptable
(eutrophic)
Marginally
Acceptable
Generally
Not
W \J L.
Acceptable
Recreation
and
Aesthetics
Acceptable
Infrequent
Episodes
when
not
Acceptable
Frequent
Episodes
when
Acceptable
Not
Acceptable
Industry
A
C
C
E
P
A
B
L
E
Algae
May
Clog
Intake
Pipes
Not
Acceptable
for some
Purposes
Commercial
Shipping
A
C
C
E
'£$.&' P
T
A
B
L
E
Problems
May
Arise
with
Hydrogen
Sulfide
22
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CONCLUSIONS AND RECOMMENDATIONS
It is clear that there is great variability in the nutrient levels
observed in estuaries and that when enrichment is excessive, beneficial uses
are impaired. Our colleagues working with lake ecosystems have been able to
correlate system responses (average chlorophyll concentrations, water clarity,
and the rate that oxygen is depleted in bottom waters) with environmental ;
conditions (total phosphorus loading rates or total phosphorus concentrations
in the lake). This knowledge has permitted engineers to design programs which
reverse the eutrophication process and ameliorate its negative effects. We
can be hopeful that in the future our efforts in estuaries will be fruitful
and we can provide similar guidance to managers.
Perhaps the greatest need is to make our 'analyses more quantitative.
The first step is to determine the estuarine analog-.to Total Phosphorus in
lakes ecosystems. Then system responses (such as plant biomass, species
shifts and the presence, absence, density and relative abundance of organisms)
-should be correlated with this measure of nutrient enrichment.
i Another tool which could prove to be useful to managers is an index
'of estuarine enrichment which incorporates all of the major aspects of enrich-
ment and its effects. Such an index would summarize environmental conditions
lin a simple fashion and provide a means to chart the decline or improvement I
,in water quality conditions. | ;
i Additional scientific studies are needed to determine and quantify :
;the rates and routes of nutrient transfer in estuaries. Field work is needed
especially, since the observations made during field studies often provide j
.insights which cannot be obtained from paper exercises or laboratory studies. !
When field measurements are made, it is recommended that sufficient analyses :
be performed so that the total amounts of nutrients in the water column can be
calculated. Since many estuary segments have long residence times and the j
jrates of biochemical transformation are often rapid, it is important to know ;
jthe entire nutrient supply rather than only those portions which are readily :
available to the phytoplankton. j |
j A number of scientists or scientific organizations have recommended
^criteria relative to nutrient enrichment; some of these are listed in Table 5.
iThe limits recommended by Ketchum and by the National Academy of Sciences- ]
National Academy of Engineering are similar, since they are based on the same
analysis, namely relating nutrient concentrations to the amount of oxygen
available in the water column. For relatively well-mixed water bodies these
[levels probably are conservative since they assume no oxygen renewal from the
atmosphere. On the other hand, the criteria may not be low enough for systems
with vertical stratification that persists for periods of a week or more.
! If we assume that total phosphates account for about one-half to
two-thirds of the total phosphorus in the water column, then Pritchard's
criterion is roughly equal to Ketchum1s. Similarly, if we assume that the
chlorophyll levels which actually develop in the real world are between one-
: - :V. - : ': 23
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TABLE 5. Enrichment Criteria.
ro
is
Ketchum
(1969)
Pritchard
(1969)
Jaworski,
et al.
(1971)
NAS-NAE
(1972)
Heinle,
et al.
,(1980)
Total Phosphorus
1.7 yg-at/1 (0.054 mg/1)
2.55 Pg-at/1 (0.082 mg/1)
summer
winter
Total Phosphate
0.1 mg-PO^/1 (0.033 mg-P/1)
Chlorophyll a
25 Ug/1
Total Phosphorus
less than 0.05 mg/1
Total Nitrogen
less than 0.36 mg/1
Chlorophyll a
low salinity areas
(less than 8-12 ppt)
Moderate enrichment
Excessive enrichment
30-60 yg/1
>60 yg/1
To maintain oxygen demand forjj
decomposition at or below !
available oxygen supply. ';
Undesirable conditions occur
for higher levels.
To maintain recreational and
aesthetic values.
To limit organic matter so
that oxygen supplies are not
depleted at warmest time of
the year with poor water
circulation.
high salinity areas
(more than 8-12 ppt)
20-40 Vg/1
>40 yg/1
-------
half to two-thirds of that which is theoretically possible, then the upper
limits for chlorophyll set by Heinle et al. are roughly equivalent to the
NAS-NAE criteria for nutrients and Ketchum's criterion for phosphorus.
When one considers the range of salinities and the diverse physical
environments found in Chesapeake Bay and its subestuaries, it is natural that
the effects of nutrient enrichment vary from place to place. The criteria to
avoid problems of over-enrichment must vary somewhat too. In this light, the
relative agreement between those who have suggested criteria related to
enrichment is perhaps more surprising than the fact that they differ slightly.
, Even though much remains to be learned about enrichment problems,
it is possible to set conservative standards which assure that enrichment will
not damage the use of Chesapeake Bay in any serious fashion. As research,
field studies, and analysis provide us with better understanding of estuarine
ecosystems, we can further define where, when, and under what circumstances
additional nutrients can be added without damage or with benefit. It is the ;
author's opinion that the criteria recommended by a number of knowledgeable ;
and competent scientists indicate that these "safe limits" are at about ;
Nutrient Enrichment Level 4, or total nitrogen concentrations at or below i
:0.32 mg/1 and total phosphorus concentrations at or below 0.044 mg/1. !
Between levels 4 and 5, it is likely that there will be brief, -
'periodic episodes when conditions are stressful to aquatic organisms and water
uses will be impaired. This range might be considered the counterpart to the
mesotrophic range for lakes. , :
j It appears that nutrient concentrations above level 5 (TN = 1 mg/1
and TP = 0.14 mg/1) represent a danger signal. Episodes of poor quality water
'and undesirable conditions are likely to occur frequently and persist, at ;
;least in a few local areas. Water uses could be impaired significantly during
!these periods and ecological damage could be great. Given the extraordinary
'value of Chesapeake Bay and its tributaries, it is imperative that we take
;these warning signals seriously. Furthermore, the prudent course of action
.would be to limit nutrient levels to the greatest extent possible until such
jtime as we can be certain that higher levels will not impair uses or result
Jin ecological damage. j
25
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REFERENCES
Bishop, Doyle W. and Robert Aukermann, 1970. "Water Quality Criteria for
: Selected Recreational Uses", University of Illinois, Water Resources
Center Research Report No. 33. ;
Clark, L. J. , S. E. Roesch and M. M. Bran, 1980. "Assessment of 1978 Water 1
; Quality Conditions in the Upper Potomac Estuary", EPA-903/9-80-002.
Copeland, B. J. and E. Gus Frah, 1970. "Ecological Studies of XJalveston Bay
1969", Final Report to Texas Water Quality Board. ;
Copeland, B. J. and Donald E. Wohlschlag, 1966. "Eutrophication: "Saline " "1
I Water Considerations", circa 1966, complete citation not known. j
j . : .rr,?.- .,<*:;} \
Cronin, L. Eugene, 1980. Personal communication. . i
Darnell, R. M. , 1967. "The Organic Detritus Problem" in Estuaries, American
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Environmental Protection Agency, 1977. "Eutrophication Work Program for j
i Chesapeake Bay". j j
Environmental Protection Agency, 1980a. "Research Summary: Chesapeake Bay",
! EPA-600/8-80-019, May, 1980. j
i i i ' j
Environmental Protection Agency, 1980b. "Restoration of Medical Lake", EPA- '
\ 625/2-80-025. j j
i ' i i
Environmental Protection Agency, 1980c. "Restoration of Lake Temescal", EPA-
j 625/2-80-026. ! . !
j ! . ! ' 1
Environmental Protection Agency, 1980d. "Lake Restoration in Cobbossee Water-
| shed", EPA-62 5/2-80-027. j j
'Federal Water Pollution Control Administration, 1968. "Water Quality j
1 Criteria". I I
! i i
! - ' '< i
^Ferguson, John F. and David Simmons, 1974. "The Fate of Nutrients in Back |
I River", Chesapeake Research Consortium, Publication No. 32, j
i Annapolis, MD. ; . ]
Flemer, D. A., D. H. Hamilton, C. W. Keife and J. A. Mihursky, 1970. "The --:
~_ ________ ........ Effects of Thermal Loading and Water Quality on Estuarine Primary .:
,: : 26 " :
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Production", Chesapeake Biological Laboratory, University of Mary-
land, Natural Resources Institute Reference No. 71-6.
Gargas, Nielsen and Mortenseu, 1978. "Phytoplankton Production, Chlorophyll-
a and Nutrients in the Open Danish Waters 1975-77", National Agency
for Environmental Protection, Denmark.
Guide, V. and Orterio Villa, Jr., 1972. "Chesapeake Bay Nutrient Input
Study", Annapolis Field Office, EPA Technical Report 47. ;
Harris, Graham P., 1980. "Temporal and Spatial scales in phytoplankton
ecology. Mechanisms, methods, models, and management." Can. J.
Fish. Aquat. Sci. 37:877-900.
Heinle, D. H., C. F. D'Elia, J. L. Taft, J. S. Wilson, M. Cole-Jones, A. B.
Caplins and L. E. Cronin, 1980. "Historical Review of Water Quality
i and Climatic Data from the Chesapeake Bay with Emphasis on the !
Effects of Enrichment". Chesapeake Biological Laboratory Solomons,
: University of Maryland. UMCEES Reference No. 80-15CBL. I
Hydroscience, Inc., 1975. "The Chesapeake Bay Waste Load Allocation Study", :
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i J
Jaworski, N. A., D. W. Lear, Jr., and 0. Villa, Jr., 1971. "Nutrient Manage- !
ment in the Potomac Estuary". Technical Report No. 45, Chesapeake
Technical Support Laboratory, Environmental Protection Agency. j
! i ' . !
Ketchum, Bostwick H., 1972. "Eutrophication of Estuaries" in "Eutrophication:
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Washington, D.C. | j
. ! i
Loftus, M. E., D. V. Subba Rao and H. H. Seliger, 1972. "Growth and Dissipa-
tion of Phytoplankton in Chesapeake Bay. I. Response to a Large j
Pulse of Rainfall", Chesapeake Science 13:4, pp. 282-299. 1
i i i
McErlean, Andrew J. and Gale J. Reed, 1979. "On the Application of Water
Quality Indices to the Detection', Measurement and Assessment "of
Nutrient Enrichment in Estuaries". Reference Number 79-183-
Horn Point Environmental Laboratory, University of Maryland,
Cambridge, Maryland.
National Academy of Sciences and National Academy of Engineering, 1972. 1
| "Water Quality Criteria 1972". Washington, D.C. pp. 594. j
i ' ! ' !
Neilson, Bruce, 1976. "Water Quality in the Small Coastal Basins". Virginia ,
j Institute of Marine Science Special Report #128 in Applied Marine j
| Science and Ocean Engineering. !
I I ' i
Neilson, Bruce and Penelope Ferry, 1978. "A Water Quality Study of the j
i Estuarine James River". Virginia Institute of Marine Science i
1 Special Report #131 in Applied Marine Science and Ocean Engineering.
27
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Neilson, Bruce and Susan Sturm, 1978. "Elizabeth River Water Quality Report".
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Marine Science and Ocean Engineering.
Olinger, Rogers, Fore, Todd, Mullins, Bisterfield and Wise, 1975. "Environ-
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Ott, Wayne, R., January, 1978. "Water Quality Indices: A Survey of Indices
Used in the United States". U. S. Environmental Protection Agency,
EPA-600/4-78-005.
Pearson, T. H. and R. Rosenberg, 1978. "Macrobenthic Succession in Relation
to Organic Enrichment and Pollution of the Marine Environment". j
Oceanog. Mar. Biol. Ann. Rev., 1978, 16:229-311. !
Pritchard, D. W., 1969. "Dispersion and flushing of pollutants in Estuaries".
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Rast, Walter and G. Fred Lee, 1978. ""Summary Analysis of the North American
(U. S.. Portion) OECD Eutrophication Project: .Nutrient.-Loading - j.
\ Lake Response Relationships and Trophic State Indices". U. S. j
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i - : ' . -; i
Reid, G. K. and R. D. Wood, 1976. Ecology of Inland Waters and Estuaries. i
; Van Nostrand Company. 485 pp.
i i $
Rosenbaum, Arlene and Bruce Neilson, 1977. "Water Quality in the Pagan j
; River", Virginia Institute of Marine Science Special Report #132 i
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i . , I i
Sanders, James G. and Edward J. Kuenzer, 1979. "Phytoplankton Population j
j Dynamics and Productivity in a Sewage-Enriched Tidal Creek in j
| North Carolina", Estuaries 2:87-96. ' ' j
I ' ' I j
Sturm, Susan and Bruce Neilson, 1977. V'Water Quality in the York River", i
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i ' i . i
Train, Russell E., 1972. "The Quest for Environmental Indices". SCIENCE
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i ; i
Witherspoon, Balducci, Boody and Overton, 1979. "Response of Phytoplankton
i to Water in the Chowan River System", UNC-WRRI Report No. 129.
i i I
; , i
28
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WILLIAMSBURG SYMPOSIUM PAPERS _ .....
Axelrad, Poore, Arnott, Bauld, Brown, Edwards and Hickman. "The Effect of
Treated Sewage Discharge on the Biota of Port Phillip Bay,
Victoria, Australia".
Darnell, Rezneat M. and Thomas M. Soniat. "Nutrient Enrichment and Estuarine
Health".
Fraser, Thomas and William Wilcos, "Enrichment of a Subtropical Estuary
with Nitrogen, Phosphorus and Silica".
Lee, G. Fred and R. Anne Jones. "Application of the OECD Eutrophication
Modeling Approach to Estuaries".
: ; *?.* .&.&"
McCarthy, James J. "Uptake of Major Nutrients by Estuarine Plants".
McComb, Atkins, Birch, Gordon and Lukatelich. "Eutrophication in the Peel-
; Harvey Estuarine System, Western Australia".
' ! '
McErlean, A. J. arid Gale Reed. "Indicators and Indices of Estuarine Over-
j enrichment".
Myers, Vernon and Richard Iverson. "Phosphorus and Nitrogen Limited Phyto-
plankton Productivity in Northeastern Gulf of Mexico Coastal
Estuaries". j
I ' ! ' 1
Nixon, Scot W. "Remineralization and Nutrient Cycling in Coastal Marine
j Ecosystems". j
I i i
O'Connor, Donald J. "Modelling Eutrophication in Estuaries".
I i "!
Ryther, John H. and Charles B. Officer. "Impact of Nutrient Enrichment on
I Water Uses". j
Schindler, D. W. "Studies of Eutrophication in Lakes and their Relevance to i
j the Estuarine Environment". '
! i I
Webb, Kenneth L. "Conceptual Models and Process of Nutrient cycling in
Estuaries".
29
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