United States        EPA-600/3-81-013
             Environmental Protection    February 1981
             Agency
v>EPA       Research and
             Development
             Sediment Removal as
             a Lake  Restoration
             Technique
             Prepared for

             Office of Water Regulations and
             Standards
             Criteria and Standards Division
             Prepared by
             Environmental Research Laboratory
             Office of Research and Development
             Corvallis, OR 97330

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                                             EPA-600/3-81-013
                                             February 1981
SEDIMENT REMOVAL AS A LAKE RESTORATION TECHNIQUE


                        by
               Spencer A.  Peterson
               Freshwater  Division
   Corvallis Environmental  Research Laboratory
            Corvallis, Oregon  97330
   CORVALLIS ENVIRONMENTAL RESEARCH LABORATORY
       OFFICE OF RESEARCH AND DEVELOPMENT
      U.S.  ENVIRONMENTAL PROTECTION AGENCY
            CORVALLIS, OREGON  97330

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                                  DISCLAIMER
     This  report  has  been  reviewed by  the Corvallis  Environmental  Research
Laboratory, U.S.  Environmental  Protection  Agency,  and approved  for publica-
tion.    Mention  of  trade names  or  commercial  products  does  not  constitute
endorsement or recommendation for use.
                                      ii

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                                   ABSTRACT
     Sediment removal as  a lake restoration technique  is  reviewed  to examine
its  positive and  negative aspects.   The  effectiveness  and longevity  of the
process  is  considered in  terms of retarding eutrophication and reducing the
impacts of toxic sediments.  Freshwater lake sediment removal is  usually under-
taken to deepen  a  lake  thereby increasing  its  volume to enhance fish produc-
tion, to remove nutrient rich sediment, to remove toxic or hazardous material,
or to  reduce the abundance of  rooted  aquatic plants.   Review  of more than 60
projects and  examination  of five  case histories  reveals  that  the first three
objectives  are  usually  met through  sediment  removal.  The effectiveness  of
dredging to control aquatic plants has not been well documented.

     Advantages of sediment  removal  techniques  include ability to selectively
deepen part  of a  lake  basin,  increase  the lake  volume,  recover organically
rich  sediment for soil   enrichment,  and  improve  limnetic  lake quality.  Dis-
advantages  include  high  cost, phosphorus release  from  sediment,  increased
phytoplankton  productivity,  noise,  lake  drawdown,   temporary  reduction  in
benthic fish  food  organisms,  the  potential for release  of toxic materials to
the overlying water  and  for environmental degradation at the dredged material
disposal  site.  High  quality  dredge  material  can be  used  for  beneficial  pur-
poses and may offset  the initial high cost of dredging.

     The technique  is recommended  for deepening and  for  reducing  phosphorus
release  from sediment.   Sediment  removal  to  control  toxic  materials  is  pos-
sible with minimal environmental  impact when proper equipment is used, but it
may  be  extremely  expensive.   Dredging  will  remove  rooted  aquatic  plants,
however,  their re-encroachment rate will be depth, sediment texture, and sedi-
ment  nutrient dependent.   Lack of definitive information  about  the effect of
these factors on the regrowth of various plant  communities prohibits explicit
recommendations on  sediment removal to control  rooted plants.
                                     ill

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                                   CONTENTS
   I.      Introduction 	  1

  II.      Purposes of Sediment Removal 	  1

 III.      Considerations for Sediment Removal  	  5

  IV.      Case Histories of Sediment Removal	20

   V.      Costs of Sediment Removal  	 29

  VI.      Summary	29

 VII.      References	32

VIII.      Appendix:   Status of Lake Sediment Removal Projects  	 42

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                               ACKNOWLEDGEMENTS
     I thank Joanne Oshiro of the Corvallis Environmental  Research Laboratory,
(CERL) USEPA, Corvallis,  Oregon  for  her initiative and persistence in obtain-
ing and assembling the data in the Appendix table of this paper.  I also thank
those  who  assisted  her  in  this task  by  supplying unpublished  information.
They  include  Regional  Environmental  Protection  Agency Clean  Lakes coordina-
tors,  State  personnel  and project managers too  numerous  to  mention.   Thanks
goes  also  to Phil  Larsen of CERL who  offered constructive criticism  of the
manuscript and suggestions for its improvement.
                                     vi

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I.   Introduction

     While control of external pollutant inputs to a lake should be given high
priority  in  any  restoration/protection  plan,  external  controls  alone may be
insufficient  to  produce the  desired changes  in  lake quality  (Emery et aj. ,
1973; Minder, 1948 in Peterson et aj. , 1976: Larsen et aj., 1975).  Where lake
improvement  goals cannot be  met by watershed  nonpoint  source  pollutant con-
trols alone,  sediment removal might be necessary.

     Sediment removal usually  includes  one or more of  four basic objectives.
The first is simply to deepen a  lake to improve boating, fishing, water skiing
and other uses  impaired by the  effects of  shoaling.  A second objective is to
prevent or reduce the internal   cycling of  nutrients.   It  has been shown that
sediment  recycling of nutrients  in lakes may represent a significant fraction
of  the  total nutrient  loading to  the lake (Funk, 1978;  Larsen  ejt al. ,  1975;
Larsen  et aj. ,  1979;  Cooke  e_t afL ,  1977).   A  third  objective might  be to
remove  toxic sediment.   A  fourth  objective,  or  possibly  a fringe benefit of
the  first and  second  objectives,  is to  reduce nuisance  aquatic macrophyte
growths.

     Until  recently   there  was   little documentation  of the  effectiveness of
sediment  removal  for meeting these  goals.   Pierce  (1970)  reviewed  49 lake
sediment  removal  projects  and  concluded that none provided sufficient data to
determine the  effects  of  lake   dredging on the  total  lake environment.   Four
years  later, Dunst  et   aj.  (1974)  reported  on  50 world-wide  lake  sediment
removal projects,  again pointing  out a general  lack of  documented  effects.
Since  1974,  additional   lake  sediment removal  projects have  been initiated.
Some  are  complete  with  documented results  while others  are  ongoing.   The
purpose of this paper is to review and update information on the effectiveness
of  sediment  removal  as  a lake restoration  technique.   Personal communications
are referenced liberally where documented results are unavailable and lakes of
the  United   States are  emphasized.   The effectiveness  of  different  types of
sediment  removal  techniques  and various  objectives  are  illustrated  by five
case histories.
II.  Purposes of Sediment Removal

     1.   Deepening

     Sediment  removal  for maintaining navigation  channels  has  been practiced
for years.  These  deepening  projects  generally have been successful (Herbich,
1975).   However, most  have  failed to  address the source of the problem in the
watershed, thus they necessitate  rather frequent routine maintenance work.  In
small  lakes,  sediment  removal  may become necessary when  uses  such as boating
are  impaired  as  a  direct result  of shoaling.  Other considerations pertaining
to deepening are that lake volume must be sufficient to offset loss by seepage
and  evaporation.   The  U.S.  Department of Agriculture  (1971)  recommends  small
lake and  pond depths  ranging  from 1.5  m to  4.5  m for various  parts  of the
country  to  compensate  for  water  loss  via  these  mechanisms.    Toubier  and
Westmacott (1976)  indicated that  lakes  in  colder parts of  the  United  States
must be  at least 4.5 m  deep to  avoid winter  fish kills.  Each  of these con-
siderations addresses sediment removal strictly from the standpoint of need to

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deepen the  lake basin.  Pierce1s  (1970)  survey of upper  Midwestern  dredging
projects  showed that projects undertaken for the purpose of deepening  were all
successful.   The  conclusion  is  not  surprising,  for  who  can  argue that  if
sediment  is  removed  from a lake basin,  that the lake will be  deeper?


2.    Nutrient Removal

     Nuisance algal  growth  and  nutrient relationships in lakes  are well  docu-
mented; phosphorus is most frequently cited as the limiting nutrient (Bartsch,
1972; Porcella  et a_L ,  1974;  Schindler, 1977).   Uptake of nutrients  from the
water  and  sediment  by plants  ultimately  results  in  deposition  of  organic
materials into  the  lake  basin.  Table 1 shows the total phosphorus content of
sediments in  selected lakes  in  North America.   A portion of this phosphorus
may be released during spring and fall lake  circulation in  dimictic  systems.
In shallow polymictic  lakes,  sedimentary  phosphorus  release may be more fre-
quent, constituting a greater  nuisance by periodic  infusion of  nutrients  to
overlying water during  summer recreation  periods.    The  periodic influx  of
nutrients  in  this  manner  usually  results  in  an   over-abundant  growth  of
unwanted phytoplankton  causing reduced water transparency,  undesirable  green
water color, and  in severe cases  a serious  depletion of dissolved oxygen and
fish  kills.   Livingston and  Boykin  (1962)  estimated  that sediment-regenerated
phosphorus amounted to approximately  45%  of the phosphorus loading to Linsley
Pond, Connecticut.  Welch et  a]_.  (1979) estimated the phosphorus  loading from
sediments in Long Lake,  Washington to be 200-400  kg  yr-1  or about 25%-50% of
the  external  loading.  Jones  and  Bowser (1978), citing  a  personal  communica-
tion  from Callender (1978),  reported  that sediment phosphorus regeneration in
White  Lake,  Michigan  constituted  approximately 40% of that  lake's phosphorus
loading.   Larsen  and Schults  (1978)  stated  that, "the supply of  phosphorus
from  sources  within a  lake can be  several  times the supplies from  external
sources for  periods of time on the order of months."  Shagawa Lake, Minnesota
experiences  internally  recycled  summer  phosphorus  pulses  of  approximately
2000-3000 kg during June, July and August.  This compares to an  annual loading
of phosphorus to the lake from wastewater (before advanced  waste treatment) of
5000-5500 kg, and current loading of about 1000-1500  kg (Larsen, 1980).   Thus,
internal  phosphorus  loading  to  Shagawa Lake prior to advanced waste treatment
(AWT) was about 28-35% of the total loading.  Following implementation of AWT,
internal  phosphorus loading constituted approximately 66% of the  total  load-
ing.   Continued internal  nutrient loading to the lake has been responsible for
the apparent slow recovery rate.

      It  is  evident  that  internal  phosphorus loading  to a  lake can,  in some
instances,  amount  to  major  portions  of  the total   loading.   Thus,  sediment
removal  to  prevent internal   loading  should be  weighed  against  alternative
treatment  techniques  and  given  serious  consideration  where  it  might  be
expected to  produce  significant loading reductions.


3.    Toxic Substances Removal

      Sediment  contaminated  with  toxic and hazardous  materials  poses  a  poten-
tially   severe  problem  for  highly  industrialized  countries  throughout the

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Table  1.   Total  phosphorus content  of sediments
          America (from Larsen and Schults, 1978)
                                                   in selected  lakes  in North
Lake
Total Phosphorus
  (mg/g dry wt)
                                        Core Depth
Reference
Sammamish, WA

Lower St.  Regis, NY

Huron
         Great
Ontario  Lakes

Erie
                          2 - 5

                        0.5 - 1.4
                       M.2 - *3.i
                       0.19 - 2.9
Monona, WI


Washington, WA


Shagawa, MN
                            - >6
                          1 - 5
                    40 cm core

                    35 cm core

                    50 cm core


                    50 cm core

                    50 cm core

                     top 3 cm
                    from 48 sites

                    100 cm core


                    40 cm core


                    160 cm core
Welch (1977)

Fuhs et al_. (1977)

Kemp et al_. (1972)


Kemp et al_. (1972)

Kemp et a].. (1972)

Williams et al.
     (1976)

Bortleson and Lee
     (1975)

Shapiro et al.
     (1971)

Bradbury and
Waddington (1973)
world -- "potential" because in many cases these problems simply have not been
recognized.   This picture is changing, however, as more thorough and sophisti-
cated  lake  sediment  surveys  are conducted  (Matsubara, 1979;  Sakakibara and
Hayashi, 1979;  Horn  and Hetl ing, 1978; Bremer,  1979; Mackenthun et al_. , 1979).

     Theoretically,  toxic materials  in  sediment might be controlled by cover-
ing  or in-place  detoxification.   These  treatment procedures  are  relatively
untested.   The  obvious  alternative  is  to remove  the polluted sediment.   The
question is  how to  remove  it without reintroducing  toxicants  into the water
column and without causing secondary pollution problems at the disposal sites.
Turner and Fairweather  (1974)  stated that "Once  a body of water is polluted,
the most effective  means  known to man to remove bottom sediment pollutants is
an efficient,  hydraulic  dredge".   Emphasis  here should be placed on  the  word
"efficient".   While  hydraulic dredges are the workhorse of the dredging indus-
try,  and are effective  in moving large volumes of dredged material  with mini-
mal energy input, they are not always effective in minimizing the resuspension
of bottom sediment.   The  key  to removing polluted sediments  is in  minimizing
sediment-water  interface  disruption,  containment  of  polluted dredge materials

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and treatment  of  decant water.   Several  mechanisms for attaining  these goals
have been described  (Peterson  and Randolph,  1977,  1978,  1979;  Peterson, 1979;
Barnard,  1978) and  will  be discussed  later  in  this paper  under  sediment.
removal methods.
4.    Rooted Macrophyte Removal

     Rooted  aquatic  plants  in the  littoral   zone  of  lakes  often  interfere
directly with  recreational  uses.   Fishing,  boating  and swimming become diffi-
cult or  nearly impossible;  further,  an over-abundance of rooted plants may be
aesthetically  displeasing to  some  persons.   Any one of these problems  may be
sufficient justification for  removing  part of the aquatic plant beds.  Dredg-
ing  is  but one  of  several  approaches,  however,  due to  cost  and convenience
differences,  harvesting  and  chemical  treatments  are  more  commonly  used to
"solve" these direct use impairment problems (Robson,  1974).

     While  direct use  impairment  problems  may justify  the  removal  of  some
macrophytes  from  lakes,  there  is  an increasing literature on  the  effects of
macrophytes  on internal  nutrient  cycling.   Their  role in this process,  with
its effect on algal  dynamics,  may be an even more important reason for attempt-
ing to  control  macrophytes  by removing them from a lake.  Wetzel (1975) indi-
cates that most of the organic matter found in small  lakes may be derived from
their littoral  zone.   Reimold  (1972) showed that salt marsh plants (Spartina)
act  as  nutrient  pumps,  extracting sediment nutrients,  translocating them to
stems and  leaves  and  excreting them to the  surrounding water on each succes-
sive tidal  cycle. Other researchers have documented that various  species of
freshwater  aquatic  plants  extract  nutrients  chiefly  from  the  sediment  and
translocate  them  to the  surrounding water (Schults and Malueg,  1971; Twilley
et aj_. ,  1977; Carignan  and Kalff, 1980).

     There is  now considerable evidence that healthy freshwater aquatic macro-
phytes  do  not excrete large quantities of  nutrients  to the  surrounding water
while  in  the  active   growth  phase.    They  do,  however,  tend  to concentrate
sediment  supplied nutrients in their tissues.  Some  loss  is  incurred through
plant part  sloughing,  but  major amounts of nutrients are recycled to the lake
when plants  fruit and during  senescence and plant  decay  (Lie,  1979; Welch et
a]_. ,  1979;  Barko and Smart,  1980).  Barko and  Smart (1979)  estimated  that
in-lake  mobilization  of  phosphorus by Myriophyllum  in  Lake  Wingra, Wisconsin
might amount  to approximately 60% of the  annual external  phosphorus loading.
Welch et  aj_.  (1979)  indicated that  much of  the "sediment"  phosphorus loading
in Long Lake, Washington was probably due to rapid plant die-off and decay.

     While macrophyte  removal  may be incidental to the objectives of many lake
deepening and  nutrient control projects, it appears likely that the removal of
these  plants may be  far more important to  reducing  in-lake  nutrient cycling
than had  been suspected  previously.   Current evidence  indicates that any long
range  lake restoration project concerned with  in-lake  nutrient controls  will
need to focus on both the  macrophyte  and  sediment  compartments (Carignan and
Kalff,  1980; Barko, 1980).

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III.  Considerations for Sediment  Removal

     Currently there  is no  single,  off the shelf,  commonly  accepted problem
assessment procedure,  remedial  action  plan,  preferred piece  of  equipment or
even agreement about  when,  for  what reason, or  how  to remove sediment from a
freshwater lake.   Nevertheless,  there  are  a  number of factors which must be
weighed  when  considering  lake   remedial  action.  Some  are more  critical  to
plans  for sediment  removal  than  they  might  be for  other types  of action.
Factors  which must  be considered  for any sediment  removal  project  are:  1)
determination of problem sources; 2) characterization of sediment; 3) determi-
nation of sediment removal  depth;  4)  environmental  problems  associated with
sediment  removal;  5)  sediment  removal  methods; 6) sediment disposal area; and
7) lake conditions  most  suitable for sediment removal.

     Clear-cut,  definitive  statements  about each of  the  above  factors cannot
always be made.  In  some  cases  this may be due  to  basic lack of information.
In others it will depend on individual lake circumstances such as the intended
use of the lake,  the geographic and socioeconomic setting of the area, and the
project completion time-frame.   The following discussion addresses each of the
above factors.
1.   Determination of Problem Sources

     Lake problems  generally are  identified  as a result of  some  use impair-
ment.  The use  impairment  problem  may be identified by  nothing  more than the
casual  observation  that  the lake  becomes excessively  green with  algae  or
choked with  rooted  aquatic plants  at various times  of  the  year.  In the case
of over-abundent  algal  growth  the  problem is  most frequently traced to exces-
sive amounts of phosphorus.  Chapra and Tarapchak (1976) presented a cause and
effect  sequence  of  events  related  to  phytoplankton  problems  in  eutrophic
lakes.  The approximate sequence is that increased phosphorus loading produces
increased  mean  annual  phosphorus  concentrations  in   water which  lead  to
increased mean summer concentrations of chlorophyll a,  which lead to increased
water  turbidity,  increased  Secchi  depths, and  finally to  reduced  dissolved
oxygen  levels  when sedimented  organic material  decomposes.   Macrophytes pre-
sent a similar problem with regard to dissolved oxygen depletion  and potential
for  fish kills.  They differ, however, with respect to nutrient supply sources
since most are  derived from the sediment (Carignan and Kalff, 1980; Barko and
Smart, 1980).

     While casual  observations  of  lake  conditions may  serve  as the catalyst
for  action,  they  are  insufficient  for the  development of  lake  restoration
plans.  More quantitative  data  are required to  determine causes of perceived
problems.   One of the  most common  and useful  approaches is  a determination of
nutrient  budgets  because  algal   and  associated problems   have  been  shown
repeatedly to correlate with the  nutrient level of lakes (Vollenweider,  1968;
Vollenweider, 1976; Dillon, 1975;  Larsen and Mercier, 1976;  Dillon and Rigler,
1974).  Reckhow (1979)  critically  reviewed a  number of  nutrient mass balance
approaches and concluded  that  several  will perform satisfactorily in predict-
ing  trophic  state  for  a  given set of lakes.   However,  Vollenweider1s  (1975)
loading criteria  have  been most generally used  due  to  ease  of application in
assessing the susceptibility  of a lake to  altered  phosphorus loading.

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     Mass  balances  focus  on  methods  to  account for  surface  and  subsurface
nutrient inputs and outputs.   They do not  account  directly  for  internal  nutri-
ent recycling,  but can be used to  estimate the  relative  importance  of  internal
nutrient supplies.  The  internal  gain  or  loss  of nutrients can be  calculated
as the difference between  the algebraic  sum of the inputs and outputs  of  the
lake and the change  in  nutrient concentration  in the lake over the same time
frame.    Figure  1  illustrates  the potential importance  of internal  nutrient
cycling  in shallow lakes  and  indicates how nutrient washout model  predictions
of lake recovery might vary from measured in-lake results.
                                OBSERVED
                                HYDRAULIC  WASHOUT  MODEL
                                PHOSPHORUS  WASHOUT MODEL
               1973
1974
1975
Figure 1.  Comparison of hydraulic and phosphorus  washout models with  observa-
          tions in  Shagawa  Lake, 1973-1974.  Total phosphorus concentrations
          are the  averages  for  the entire  lake  (updated  from Larsen et  al. ,
          1975).

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Larsen et  a\_.  (1979)  used  a modified  form of the  phosphorus  residence time
model to account  for  and accurately describe periodic summer pulses of inter-
nal  phosphorus  loading  in  Shagawa  Lake, Minnesota.   Application  of modeling
techniques  or  direct  measures  of  nutrient release  rates from sediment  and
calculation of the  sediments'  nutrient contribution to the  lake  is an impor-
tant step  toward  determining the  relative importance of the sediment compart-
ment to the overall  loading of the lake.  Scheider et a]I.  (1979) have summar-
ized methods for using hydraulic and nutrient budgets to assess lake problems.
A more recent  and comprehensive review of  the  subject is  presented by Reckow
(1980).
2.    Characterization of Sediment

     If sediment  removal appears  to  be a  reasonable  lake  restoration option
after  an  initial  analysis,   it  may  become necessary  to further  refine  the
sediment  information  base.   It  would  be useful to  determine  various physical
characteristics  such  as  sediment  depth and  distribution,  particle  size  and
organic content, bulk density, and other factors critical to sediment removal.
Chemically one might want to know if the sediment contains toxicants, what the
nutrient content  is  and what the rate  of  release, of nutrients from the sedi-
ment might be.  A  number of the physical and chemical variables can be deter-
mined on  a one time analysis basis, however, where chemical release rates are
involved the  estimate must  be made from more  than  one analysis.   In the case
of nutrients,  these  estimates may be made "directly" via time series analysis
using two different  approaches:   1)  i_n situ isolation of portions of the lake
bottom and overlying  water  suspected  of contributing nutrients, or 2) incuba-
tion of  sediment samples  in the  laboratory  under simulated  lake  conditions
(i.e.,  time,  temperature,  oxygen  content,  and  pH).   In  either case, sediment
nutrient  release  is measured as  change in nutrient  content  of the overlying
water with  time.   The  following  is a  brief discussion  of  factors  considered
important to   the  description and  analysis of phosphorus  in sediments  as  a
plant  nutrient source.   Much  of  the  same rationale  could  be applied  to  an
assessment of sedimented toxic materials.

     Table 2  indicates  considerable variation  in anaerobic  and aerobic phos-
phorus  release rates  for sediment  from  different  lakes  under  J_n  situ  and
laboratory conditions.   Anaerobic  and aerobic  phosphorus  release  rates  are
both important  since  they  represent conditions common to the two major sedi-
ment compartments  of concern to  the  lake  manager.   These  components  are the
deep water (profundal) sediments (Mortimer, 1941, 1942; Livingston and Boykin,
1962; Delfino et al. ,  1969) and  the  shallow water (littoral) sediments with
associated plant  communities  (Lie,  1979;  Cooke et a!. , 1977; Barko and Smart,
1979).   The  profundal  sediments may  alternate between  anaerobic and aerobic
conditions depending  on  lake stratification,  while  the  littoral  zone will
usually remain aerobic.

     Holdren and Armstrong (1980)  evaluated the effects of mixing, redox, tem-
perature,  bioturbation,  and sediment type on phosphorus release from profundal
sediment.   They found that  bioturbation by tubificids and emerging chironomid
larvae  had  the  greatest effect  on  phosphorus release  rates.   This  may  be
associated with Lee's (1970) observation that the sediment mixing zone extends
5 to  10 cm  below the  sediment-water  interface in lakes with a  well  defined
interface.  In  general,  Holdren and  Armstrong (1980) found  that raising the

                                       7

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          Table 2.   Measurements  of  phosphorus  release  (modified  from  Holdren  and .Armstrong,  1980)
Sediment
Doboy Sound
Baldeggersee
Clear Lake 1
Clear Lake II
San Joaquin Delta
Lake Mendota
Lake Norriviken
Lake Trummen
Lake of Tunis
Lake Erie
Simulated Benthal
Deposit
Ursee
Lake Ontario
Fures
Lake Esrom
St. Gribso
Grane Langso
Lake Mendota
Buzzards Bay
Eel Pond
Lake Sodra Bargundasjon
Muddy River
Lake Warner
White Lake
White Lake
Lake Mendota
Lake Wingra
Lake Minocqua
Little John Lake
Experimental
System
Intact Core
In Situ
Laboratory3
Laboratory3
Laboratory
Laboratory
Laboratory3
Laboratory3
Laboratory3
In Situ

Laboratory
Laboratory
Intact Core
Intact Core
Intact Core
Intact Core
Intact Core
In Situ
In Situ
In Situ
Intact Core
Laboratory
Laboratory
Intact Core
In Situ
Intact Core
Intact Core
Intact Core
Intact Cone
Temp °C


27
27
27
27



11

22
10-15
4-10
7
7
7
7
7-13
1.5
20
8
20-30
20-30


2-23
4-21
3-18
4-16
Release Rate
Aerobic
0.031
-9.3
9.7
7.4
13
49
5


0.68

3

0.03-0.8
-2.0
-1.4
0.2
0.6

3.2
4.9-16.0

9.6
1.2


-1.9-33
-0.56-3.4
<0. 02-0. 37
<0. 02-1.1
mg m-2 day-1
Anaerobic

9-10
8.7
7.3
11
53
10
15b
25-30b
7.6

154
6-16

17.3
12.3
1.2
0.8
7-11


36
96
26
27.2
19.0
0.67-65C
0.95-2.9°
0.03-3.1C
0.02-3.8C
Source
Pomroy et al_. , 1965
Vollenweider, 1968
Porcella et al_. , 1970
Porcella et al_. , 1970
Porcella et a]_. , 1970
Porcella et aj!. , 1970
Ahlgren, 1972
Bjork, 1972
Bjork, 1972
Burns and Ross, 1972













Fillos and Molof, 1972
Tessenow, 1972
Kemp-Nielsen, 1974
Kemp-Nielsen, 1974
Kemp-Nielsen, 1974
Kemp-Nielsen, 1974
Kemp-Nielsen, 1974
Sonzogni , 1974
Rowe et a_[. , 1975
Rowe et al_. , 1975
Bengtsson, 1975










Fillos and Swanson, 1972
Fillos and Swanson, 1972
Freedman and Canal e,
Freedman and Canal e,
Holdren and Armstrong
Holdren and Armstrong
Holdren and Armstrong
Holdren and Armstrong
1977
1977
, 1980
, 1980
, 1980
, 1980
  Columns containing dredged sediment and water.
  Not designated as either aerobic or anaerobic.
c N2-treated cores with 2-3 mg I-1 dissolved oxygen in overlying water.
  Complete citations in Holdren and Armstrong, 1980.

-------
temperature or  lowering the oxygen concentration  in  overlying  water also led
to higher  rates  of nutrient release.  Suspending the sediment or lowering the
water  temperature tended  to  remove phosphorus  from the  water  column.   They
also reported that sediment type affected the relative importance of different
incubation conditions.  One example of this was that redox had more effect on
noncalcareous sediments while  temperature had more effect on calcareous ones.
Most of Holdren  and Armstrong's (1980) experiments  ran for 10 days.  Some were
continued  for  20-30  days.   In most cases,  phosphorus  equilibrium was reached
in 2 to  10 days.  In some cases,  the  phosphorus levels increased slowly over
the  whole  incubation  time.   They  concluded  that,  given  the  proper environ-
mental   conditions, lake  sediments can  release  significant amounts  of  phos-
phorus  to  overlying  water,  even  when  those waters  are  aerobic.    Stauffer
(1980a)  provides  detailed  comments   and   interpretation   of  Holdren  and
Armstrong's results.

     It is  important  to note  that  not all sediment phosphorus is exchangeable
or  biologically  available.   Some  forms  are  tightly  bound  to sediment  or
actually  incorporated  as  part of the  structural  matrix (Jones  and Bowser,
1978).   Therefore, total sediment phosphorus (bulk analysis) is of limited use
in determining the potential for nutrient release.  The phosphorus most likely
to exchange readily with overlying water is that dissolved in the interstitial
zone (pore water).  Because dissolved interstitial phosphorus is often present
at high concentrations  (up to 5 mg/1  in Shagawa Lake, Minnesota according to
Larsen  and Schults,  1978) in  relation  to the  overlying water, there  is  a
strong gradient  for  diffusion of the interstitial phosphorus to the overlying
water.   As this  phosphorus moves  to the water column it must be replaced by a
repartitioning  of particulate  phosphorus.   Some  partitioning  forms  undergo
transition more  readily than  others, thus they more readily replace liberated
interstitial phosphorus and are  therefore more important in terms of internal
phosphorus recycling.

     Williams et a]_.  (1976) suggested that sediment phosphorus be divided into
three components  based  on  chemical  extraction techniques (Figure 2):  "apatite
phosphorus"  (A-P),  "organic  phosphorus"  (0-P),   and   "nonapatite  inorganic
phosphorus"  (NAI-P).   The  NAI-P  is particularly  important  in  lake sediment/
water nutrient exchanges  because  it is thought to be strongly associated with
iron as  a  ferric-oxide-orthophosphate complex  under aerobic conditions.   The
iron complex  dissociates   under  anaerobic conditions  releasing  phosphorus  to
interstitial  water or  directly  to the  overlying  water.   For  this  reason,
Larsen and Schults  (1978)  have suggested that the amount of NAI-P in sediment
might be  a more  valid measure of the  readily  available  sediment phosphorus
reservoir  than   either  total  phosphorus  or  pore  water phosphorus.   This  is
substantiated by Williams  and Mayer's  (1972) conclusion  that  an  increase  in
apatite (phosphorus incorporated as part of the apatite crystalline structure)
with depth in Lake  Ontario sediments was  a product  of diagenesis  of  other
forms of phosphorus to  apatite with time.  This transformation process and its
relationship to  more  readily  exchanged phosphorus forms is shown in Figure 3.
Jones and Bowser (1978) indicate that processes  of  organic phosphorus minerali-
zation and the  release  of  sorbed phosphorus under reducing conditions in lake
sediment  can provide  resolubilized  phosphorus  through  diffusion   from  pore
water,  but that  this process will be offset by apatite formation.  The process
may be responsible  for the commonly observed phenomenon of decreasing quanti-
ties of soluble  reactive  phosphorus with increasing  depth  in  lake  sediments.

-------
              (
                      IN No OH

                      I6H

                      85 C

                      _ EXTRACT
(
                SAMPLE
                                              0.22M No CITRATE /

                                              OHM  No BICARBONATE /
                                              I.OM.  No DITHIONITE (COB REAGENT)

                                              I5MIN

                                              85C

                                              _    EXTRACT
                                          RESIDUE
                                              IN No OH

                                              16 H

                                              25C
                                               __   EXTRACT
               (^RESIDUE J
                      0.5N HCI
                      I6H

                      25C

                        EXTRACT
            HCI04
          DIGESTION

          FOGG AND
          WILKINSON
   HARWOOD
    etol
    AFTER
   CLARIFICATION
            HARWOOD
              etol
C ORTHOPHOSPHATE
 IN COMBINED
   EXTRACT)
              HARWOOD
                 et al
                                                                   WATANABE
                                                                      AND
                                                                     OLSEN
                                                     CORTHOPHOSPHATE\ /toRTHOPHOSPHATE\
                                                      EXTRACTED BY   J I  EXTRACTED BY  )
                                                     NoOH REAGENT) y \j:DB REAGENT) ^/
Figure 2.  Outline  of analytical  procedures  used to  determine apatite-P, NAI-P,
           and organic P (modified from Williams et a].,  1976).
                                            10

-------
          CONCENTRATION  IN OVEN-DRY  SEDIMENT
                                          ORGANIC
                                          PHOSPHORUS

                                     SORBED
                                     ORTHOPHOSPHATE
                                      TOTAL
                                      PHOSPHORUS
Figure 3. Distribution  of  phosphorus  in  a sediment  profile  from  Lake  Erie
         (from Williams and Mayer, 1972)  hypothetical!;/  depicted and illus-
         trating  the  diagenesis  of mineral  phosphate  from  amorphous  to
         crystalline  form.  Percentage of each form  is given by area fields
         (modified from Jones and Bowser, 1978).
One objective of sediment  removal for nutrient control purposes might, there-
fore,  be to skim the upper nutrient-rich layer of  sediment off  to reveal a
strata  containing a  less readily  exchangeable nutrient  form.  Characterization
of pore water and solid phase  sediment profiles  from representative areas  of
the lake will  permit the  development of maps  to locate the horizontal and
vertical distribution of the relatively  nutrient-poor  strata. For phosphorus
limitation  planning  these  maps  should be  based  on  the  component phosphorus
contents of the sediments  as proposed by Williams et a\_. (1976).  Methods for
measuring  these  components are  described by  Sommers  et  a^. (1972)  and  by
Williams  and  Mayer  (1972).    Interstitial   water  extraction  methods are
described by Holdren  et aJL (1977).   Sediment  characterization  data coupled
with time series temperature and oxygen  profiles can be used to calculate the
potential rate of nutrient release from sediments.
                                  11

-------
     Determination  of  sedimentation  rates  of  organic  detritus and  nutrient
elements  is  important  in  providing  estimates of  how  rapidly sediment  has
accumulated,   or  is  accumulating,  in the  lake basin,  and  how  rapidly  the
effects of sediment removal  might be expected  to deteriorate if the  sedimenta-
tion rate remains high.  A common technique  for estimating sedimentation rates
in the  United  States  involves  determining the ragweed pollen (Ambrosia) hori-
zon  in sediments  and  measuring  the  depth  of  accumulation above  that  known
horizon (Bortleson and Lee, 1972; Craig, 1972).  Another method for  estimating
sediment  accumulation  rates  employs  the  isotopes  210Pb (Koide £t  al. ,  1973)
and 137Cs  (Pennington et al_. , 1973).

     Jones and  Bowser  (1978) point  out that pore fluid chemistry,  solid phase
chemistry  and  sedimentation  rate  may be  used to  calculate  the  fluxes  of
solutes (thus  nutrients)  into  and  from the  sediments.  Close  examination of
sediment  data  in  conjunction with physical-chemical  data for  the lake  should
be  useful to  the lake manager in  determining  the  significance of  internal
nutrient  release  and  thus the  advisability  of  removing sediment  to  control
internal  cycling.  For example,  if  one has  determined from the literature, j_n
situ,  or  laboratory studies that the phosphorus release  rate  from anaerobic
sediments is  on the order  of 5 to 10 mg m-2 day-1,  and that 50 percent of the
lake basin in  question  is  intermittently anaerobic for  approximately  20 days
during the summer, then the potential  phosphorus loading to the lake from this
source  would  be:   5 to  10  x 0.50 x  20 = 50  to 100 mg  m-2  summer-1.   If the
overlying water column was  10  m thick the resultant  phosphorus loading to the
water  might  amount to 5  to 10  mg  m-3  summer-1.  A  comparison of the above
phosphorus release rates with  those  of  surface  input  to  the lake and with
those  of  deeper sediment  strata might assist in making a decision about sedi-
ment removal.   For  example,  if  it could be demonstrated that  deeper sediment
released  phosphorus at a  much  slower rate,  say 2.5 to 5 mg  m-2  day-1, the
loading  to  the overlying  water column  from  the strata  might be  reduced to
approximately  2.5 to 5 mg m-3 summer-1, or about a 50 percent reduction.  This
could  translate to a  similar  magnitude  reduction for  chlorophyll a  in the
lake.

     A  similar approach  could  be used to assess the impact  of vegetated and
non-vegetated  aerobic  littoral  sediments, taking into  consideration  the per-
centage of lake basin covered by each.  In the case of vegetated areas (macro-
phytes) one  should keep  in  mind that seasonal variation  in  nutrient  release
may be critical (Barko and Smart, 1980; Carignan and Kalff, 1980).

     The  above  mentioned  analytical  approach  provides a simplistic  example of
how  a   quantitative estimate of  the  effectiveness  of  sediment  removal  for
nutrient  control might be compared to other  major loading sources  to the lake.
It also provides  an  idea of how  long the effects  (minus sedimentation rates)
might  be  expected  to  last.   Not all of the  phosphorus released from the sedi-
ment is recycled to overlying water, so the  potential  impact is probably over-
estimated.   Stauffer  and  Lee   (1973),  however, have  shown  that  significant
amounts  of   hypo!imnetically released phosphorus do  reach the epilimnion in
shallow lakes  as the thermocline  is eroded by  strong winds.  One might improve
the accuracy of estimates for sediment-released phosphorus impacts on the lake
by  applying  Stauffer  and  Lee's mixing model  approach, or  by application of
Stauffer1s (1980b)  "LAKETRANS"  model  which  predicts  thermal diffusivities and
                                      12

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solute  transport  in   stratified  lakes.   A thorough  discussion  of  internal
nutrient  loading  in lakes  and methods  for assessing their  significance  was
completed recently by Stauffer  (1980a).


3.   Determination of Sediment  Removal Depth

     When  deepening a lake  to  improve  it  for  sailing,  power  boating  and
associated  activities, the  deepening  requirements  are  relatively straight-
forward.   Projects  aimed  at  controlling  internal   cycling  of  nutrients  may
focus  on  open water area sediments  or on littoral  sediments  and associated
macrophyte beds.  Sediment  removal  requirements  in  these cases are not always
clearly defined.

     Lake  Trummen,  Sweden,  is perhaps the  most thoroughly  documented  case
history of  a  lake subjected to sediment  removal  to  control  internal  nutrient
cycling.  Sediment removal  depth  in Lake Trummen was  determined  in a fashion
similar to  the example  given  previously.  Sediment  was  characterized chemi-
cally   and  physically,   both   horizontally  and  vertically,  in  the  lake.
Digerfeldt (1971)  as referenced by Bjork (1972) determined that sedimentation
rates  in  the  lake increased dramatically during the period from 1940 to 1965.
About  40  cm of  loose  FeS-colored (black)  fine sedimeni  was  deposited during
that time.  Aerobic  and  anaerobic  release  rates  of P04-P and  NH4-N  from  the
black  sediment  layer and  the underlying brown layer were shown to be markedly
different.  Based on   these differences  a  plan  was  developed to  remove  the
upper  40 cm of sediment.  Results of the project are presented as case history
#1 in a later section of this paper.

     Another approach  to  determining  sediment removal depth  has  been used by
Stefan  and Hanson (1979)  and by Stefan  and  Ford (1975).  Their approach was to
use  a  lake temperature model  to  predict the lake depth  necessary to prevent
summer  destratification.   The  model uses air temperature,  dew  point  tempera-
ture,  wind  direction,  solar radiation,  and wind  speed inputs at 12-hour time
step intervals, plus a consideration  of lake morphology,  to produce an output
of temperature prediction with depth.   The approach used by Stefan and Hanson
(1979)   is similar to that developed by Stauffer and  Lee (1973) which shows  how
windpower  erodes   the   thermocline  of  northern  temperate  lakes.  The  major
difference is  that Stefan and Hanson (1979) used their model  output to predict
to what depth  a  lake  must be  dredged  to  maintain a stable summer stratifica-
tion,  thus  preventing  enriched hypolimnetic waters  from  mixing  into  the  epi-
1imnetic zone.

     Use  of  the  Stefan  and  Hanson   (1979)  model   for  determining  sediment
removal depth  assumes  that a stable  summer  stratification  is  necessary to
prevent enriched  hypolimnetic  waters  from  mixing into the epilimnion.   Based
on that assumption, Stefan and Hanson (1979) indicated that Hall Lake (one of
the  Fairmont,  Minnesota  lakes) would require dredging to a  maximum  depth of
8.0 m.   Other data presented by Stefan and Hanson (1979)  indicate that dredg-
ing to  8.0  m   may require the removal  of  4.0  to  6.0  m of sediment.  There is
no reference to the sediment volume involved.  However,  it would be  sizable.
Hall  Lake  has  a  surface  area  of  2.25 km2  and  a mean depth of  2.1  m.   Lake
profile data presented  by Stefan and Hanson indicate an accumulation of 2.0 to
10.0 m of sediment in  the  lake basin  overlain  with about 0.5  m  of "boundary

                                      13

-------
layer limnetic material".  There  is  no  apparent chemical  or physical  distinc-
tion between this layer and the deeper sediment.  In fact,  their core  analyses
show relatively uniform  phosphorus  concentration  in sediment from the surface
to a depth of 8.5 m (737 to 1412 mg kg-1 for 37 samples,  with a mean of 1097).
There is no indication, however, of phosphorus release rates for sediment from
different depths.   It  is  possible  that  the release rates  from deeper  sediment
might be  less  than  that of the surface sediment.   Furthermore, it is  possible
that reduced nutrient  release  from the  deeper sediment could be sufficient to
significantly  reduce  the adverse  impact  of nutrients on  the  overlying  water
even though stratification was  not stable (Bengtsson, et al. , 1975).   If that
were the  case, it argues  for  removal  of much  less  sediment  at significantly
less cost and  perhaps  fewer  disposal problems.  Therefore, it seems advisable
to  examine  phosphorus  release  rates for sediment  from various  depths before
adopting a lake temperature modeling approach to determine dredging depth.

     Where  sediment  removal   is contemplated  to  control   nuisance  macrophyte
growths and  associated nutrient  cycling,  it is necessary  to  know  what  depth
must be attained to  prevent the  nuisance.   Guidelines  for determining this
variable are even  less definitive than  those for controlling nutrient cycling
from limnetic zones.

     A  number  of  factors  contribute to  the growth of macrophytes, e.g.,  sedi-
ment type,  nutrient  availability,  temperature and  light level.  The Wisconsin
Department of  Natural  Resources presently uses light  level  (as  determined by
Secchi   disc determination   of  water  clarity) as  the  chief  determinant  of
nuisance  macrophyte  growth.   The method  consists of  determining the average
summer  water  clarity   through  periodic  Secchi  disc  measurements,  and  then
estimating the maximum depth of macrophyte growth.  The estimate is determined
from a  graphic display  of  maximum  plant  growth  depth (m) as  a  function of
Secchi  disc (m).  The straight line relationship is described by the equation:

               Y = 0.83 +  1.22X

     where,    Y = maximum depth of plant growth in meters

               X = average summer water clarity (Secchi disc) in meters.

The  r2  for  this  relationship is 0.53, with N equal to 55.   According to Dunst
(1980b) the  relationship was  derived  from work  done by  Belonger  (1969) and
Modlen  (1970).   Dredging projects designed for macrophyte control in Wisconsin
currently  use  this  technique   as  a guide  to  prescribe  dredging  depths for
macrophyte control (Dunst, 1980b).  However, Dunst (1980a)  also indicates that
dredging depth need  not always exceed the predicted Y-value to achieve effec-
tive rooted  plant control.  Simply  increasing the water  depth  can result in
speciation  changes,  and  in  Wisconsin,  nuisance  surface growths are  uncommon
where depth equals or  exceeds three meters.  Moreover, removal  of soft organic
sediment to  hard  sand  and clay bottom usually results in reduced plant growth
and  density of problem species.  Unfortunately, truly predictive methodologies
are  undeveloped in  these areas.   It should be  pointed out that the objective
of  dredging  for macrophyte  control  is  not  synonymous with macrophyte eradi-
cation.   Any macrophyte dredging plan  must take into consideration  the pre-
servation of  fish spawning  and nursery areas,  waterfowl   feeding  areas, and
other wild!ife  habitats.

                                     14

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4.    Environmental Problems Associated with Sediment Removal

     Peterson (1979) pointed  out  a number of potential environmental problems
associated with  sediment removal.  The  problems generally  can  be classified
into in-lake and disposal site types.   In-lake problems commonly center around
the resuspension  of  sediment  during its removal when dredges, drag lines, and
clam shells  are  employed.   One  of the most common  problems  is the liberation
of  nutrients with  resuspended  fine  sediment.   Phosphorus  is  of particular
concern  due  to  its  high  concentration  in  interstitial  waters  in  eutrophic
lakes and its affinity for finely divided particulate material.  Dredge agita-
tion and wind action tend to move  the  disturbed nutrient-laden  sediment into
the  euphotic zone  of  the  lake,   producing  the  potential for  algal  blooms.
Churchill et a]_.  (1975b) reported  increased phosphorus concentration  in Lake
Herman,  South  Dakota,  coincident  with  dredging but  they noted  no  increased
algal  production.    This  was  presumably  due   to  the  high   turbidity  level.
Dunst  (1980a);  on the other  hand, found increased algal  production in Lilly
Lake,  Wisconsin  when  dredging   began.   This  was   a short  term  phenomenon
associated with the  immediate time  of active dredging.  There were no signifi-
cant adverse  effects.

     Apparently,  the reverse  of increased algal production  problems can also
be  triggered by the  resuspension of sediment.   Reduced light penetration due
to  turbidity will  have  a tendency  to inhibit algal  production.  Lackey et al.
(1959)  indicated  this  problem  may be  further  aggravated by  the tendency of
small phytoplankton  to be  adsorbed to the surface of precipitating fine sedi-
ment  particles.   A  potentially  more  serious  problem associated  with  finely
divided  sediment  in  the  water column  is oxygen depletion.  If the sediment is
highly organic,  the  particles quickly become bacteria-coated.  The tremendous
surface  area of  these  particles  permits  rapid decomposition   and  possibly
oxygen  depletion.  This  factor may pose a problem  in  lake  dredging projects
considering  that  the organic  content  of lake sediment may approach 80 percent
on  a dry weight basis  (Wetzel,  1975).  To my knowledge there is no documenta-
tion of  this problem in  lake dredging  projects,  however,  one should be aware
of the potential  for  it.

     Another  problem associated  directly with  resuspended  sediments  is  the
liberation of toxic substances.   Although small  lake sediment removal projects
for the specific purpose of removing toxic substances are  relatively uncommon,
the concern  is becoming more evident (Matsubara, 1979; Sakakibara and Hayashi,
1979;  Bremer, 1979).  The  major problem associated with  toxicants and resus-
pended sediment centers around the  fine particle sizes.  Murakami and Takeishi
(1977)  have  shown that  when  dredging  in PCB  (polychlorinated biphenyl) con-
taminated sediments, up  to 99.7 percent of the  PCB materials adhere to sedi-
ment  particles  less  than  74 u  in diameter.    This  could be a particularly
perplexing  problem  in   freshwater  dredging  due to  the  increased  particle
settling times  required  for  freshwater over those  required for  brackish or
marine waters.
                                                                    /
     A relatively common concern with  lake dredging  projects  involves destruc-
tion of  the  benthic  community.   If the lake basin  is dredged completely, two
to  three years  may be  required to  reestablish  the  benthic fauna (Carline and
Brynildson,   1977).  However,  if portions  of  the bottom are left undredged the
reestablishment may be almost immediate (Andersson et aj. , 1975) or within one

                                      15

-------
to two  years (Crumpton  and  Wilbur,  1974).   In  any case,  the  effect  on  the
benthic community appears  to  be  of relatively short duration compared to the
longer  term  benefits  derived  from  sediment removal.   The same appears  to be
true for game fish populations (Carline  and  Brynildson, 1977; Spitler, 1973).

     The above concerns  are  associated primarily with dredging as  a sediment
removal technique.  The other major technique for sediment removal  in lakes is
drawdown (lowering  the water  level) to expose the littoral sediments,  or in
some cases (Born  et  aj. , 1973) the entire  lake  basin,  followed by removal of
sediment  with  earth-moving  equipment.   Drawdown  accompanied  by  bulldozer
sediment removal  may  pose  additional  nuisance problems such as  noise,  dust,
and  truck  traffic.   It  should be  pointed  out  that hydraulic  dredging might
produce an unplanned  lake  drawdown  if  the  solid to liquid ratio of the dredge
slurry is  low (typically 5% to 10%) and  the dredge pumping rates are high.


5.   Sediment Removal  Methods

     Once a  lake  has  shoaled to  the degree  that  it no longer serves a useful
lake-oriented recreational purpose, the methods  available for amelioration of
the  problem  are   limited.   In  theory,  there are two approaches.  One  is con-
struction  of an  outlet control  structure  to  raise  the  water  level.   This
approach has limited  practical  application due to problems of  shoreline and
habitat destruction  and flooding  of  private  property.   The  second and most
common alternative is  sediment removal.

     The  drawdown/excavate method  of   sediment  removal  was mentioned above.
The  technique  is summarized by  Born et aj.  (1973).  It can be seen that the
applicability of this method is limited to  lakes with control  structures or to
those where  pumping  rates  above  water  inflow rates can be achieved at reason-
able cost.

     Dredging  is  a  much  more  common   approach  to sediment  removal.   Pierce
(1970)  described  various  types  of  hydraulic dredging  equipment  and provided
guidance on  the engineering aspects of  dredge selection, i.e.,  size of dredge,
pumping rate, pumping distances,  etc.   Barnard (1978) and Peterson (1979) have
described  various grab,  bucket,  and clam  shell  dredges;  hydraulic cutterhead
dredges; and  specialized dredges  to minimize secondary water quality impacts.

     The  conventional  hydraulic  cutterhead  dredge (Turner and  Fairweather,
1974)  is  the most  commonly employed  piece  of dredging equipment.   Hydraulic
dredges have a number  of  advantages  over grab or  bucket  type  dredges.  They
have almost  continuous  operating cycles, allowing removal  of large volumes of
material  in  a short  time.   Production  rates in excess of  1,000  m-3 hr-1 are
not  uncommon.  These dredges can  span virtually any horizontal  reach of water,
due  to  their floating operations  platform and, in general, have the capability
to  be  "environmentally  cleaner"  than  grabs and buckets, due to  their closed
cycle  system of  operation.   This may  not always be the case,  however,  because
by virtue  of their ability to move large volumes of sediment,  they also might
create  large turbidity plumes, with resuspension  of  sedimented  nutrients and
hazardous  materials.   The  turbidity  around the cutter  of  a hydraulic  cutter-
head  dredge  increases exponentially with  the thickness  of the  cut,  rate of
swing,  and cutter rotation rate (Barnard,  1978).   The  latter  three functions

                                     16

-------
            •*>
         400
     o>
     =   300
o
_i
o
     Q
     Ld
     0

     Ld
     Q_
         200
          100
                     (80; 2,628)              (139; 31,002)

                                 (I32;3O,979)
                              REGION OF
                           HIGH TURBIDITY

                                                      J
                                                        LJ
                                                        O
                                                        Q
                                                        LJ
                                                        cr
                                                        Q
                                                        CJ
                                                        =>
                                                        Q
                                                        O
                                                   X
                                                   <
                                 \^™jl^W:*mm&** LJ

                                 !^
            0       20     40      60      80     100

              RELATIVE PRODUCTION (PERCENT)
Figure 4. Relationship between the  concentration of suspended solids 1 m from
        the cutterhead and the  relative  production of a 61  cm  cutterhead
        dredge (from Barnard, 1978).
                               17

-------
are related closely  to  dredge production rate.   Therefore,  production rate is
closely related  to turbidity  around  the dredge cutterhead.  Using  data from
Yagi  et  al.  (1975),  Barnard  (1978)   plotted  the  relationship  of  suspended
solids collected one meter  from the cutterhead, to the  production of a 61 cm
diameter cutterhead dredge (relative to its  apparent maximum production rate).
He concluded  (Figure 4)  that it is possible to  increase  the dredge production
to  the  maximum rate (broken line  in  Figure 4), without  generating  excessive
turbidity levels.  This  involves optimization  of  cutting  depth,  swing rate,
and cutter rotation rate.  Therefore,  minimization  of turbidity  with a cutter-
head hydraulic dredge will  depend  as  much on the  skill  and experience of the
operator  as  on  the  texture  and  particle  size of  the  sediment  and general
operating conditions.

     Where minimizing  resuspension of  sediments  is critical to  the progress
and completion of a project (toxic  substances removal), it may be necessary to
take  special  measures  and  perhaps  to  employ specialized  dredging equipment.
Equipment types  and capabilities,  described by Barnard (1978)  and Peterson
(1979), vary  from  modified  grabs and  innovative cutterhead design, the newest
being the disc bottom  cutterhead (Breebot brochure),  to air  driven  pumps.  A
number of the  specialized equipment variations  have been used successfully in
removing  toxic  substances  from Japanese  waterways  (Peterson  and  Randolph,
1977,  1978,  1979).  Suda (1979) compared the  suspended  solids  concentration
around a  conventional  cutterhead  dredge to that  around  specialized Japanese
dredges.   Results  indicated an approximate 10-fold  reduction   in  suspended
solids concentration  around the specialized dredges.   A  serious  drawback to
these results, however,  is that no comparisons of production rates were made.

     Recently,  scientists  at  the   U.S.  Army Engineers  Waterways  Experiment
Station  completed  tests  of  the  "pneuma"  (air driven  pump) dredge  system.
While no mention was made of this system's ability to minimize resuspension of
sediments, it was  indicated that the  system was extremely inefficient because
of  its high  energy input requirements  relative to  dredge  material production
(McNair,  1980).  This may be indicative of the  bid cost differentials between
hydraulic and  specialized dredging equipment reported by Peterson (1979).  In
view  of  this, one must  examine  closely how critical   it might be to minimize
the resuspension  of sediments in any sediment removal project.


6.   Sediment Disposal  Area

     The major non-lake impact of sediment removal  centers around the disposal
site.  High population densities among a myriad  of other things  make it diffi-
cult  to locate suitable  sites.  Another complicating factor is that the indis-
criminate filling  of  low-lying areas  is no longer permitted under Federal Law
(Section 404, Public Law 92-500).  Fill permits  are required under Section 404
for virtually  all  projects  where the  lakes  and any adjacent wetland proposed
for  filling  exceeds  4.0 ha (10  acres) in  area.   Guidelines  for  preparing
Section 404  permit applications are  available   from  District Offices  of the
U.S. Army Corps of  Engineers.

     In upland disposal  areas (where  Federal permits are not required) diking
operations  are commonly  employed.  A major problem  with  upland  disposal  is
dike  failure  (Calhoun,  1979).  Another problem not uncommon  to  dredging pro-
jects  is  underdesign of  disposal  area  capacity.  This  problem  is not always
                                      18

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readily evident, but  may become apparent as the project progresses.  Disposal
of  freshwater  sediments may  be  particularly  troublesome  because of  their
relatively slow settling rates  (Wechler and Cogley, 1977).  As disposal  areas
fill,  their  ponding  depth  is  reduced  and  so  is  their efficiency  to  retain
suspended solids.   Disposal  areas must be designed for the end of the project,
not for some  intermediate point.  Palermo et a_L (1978) have summarized impor-
tant technical  information  and  research projects which will  assist with the
proper  design,  construction,  and  maintenance  of  dredged material  disposal
areas.   Where standards  for discharge  from disposal areas cannot  be  met,  it
may be  necessary  to  treat  the  discharge.   Barnard  and Hand  (1978) describe
when and  how  to treat if it becomes necessary.   Other reports prepared by the
U.S. Army Corps of  Engineers  which are particularly useful  in  handling dis-
posal area problems  include:   Evaluation of Dredged Material  Pollution Poten-
tial  (Brannon,  1978), Confined  Disposal Area  Effluent and  Leachate  Control
(Chen  et  a\_. , 1978),  Disposal  Alternatives  for Contaminated  Dredged Material
(Gambrell  e_t  a_L ,  1978),  and  Upland  and  Wetland  Habitat Development  with
Dredged Material: Ecological Considerations (Lunz et aj. ,  1978).


7.   Lake Conditions Most Suitable  for Sediment Removal

     Obviously,  a lake with a  filled basin might become a prime candidate for
sediment  removal.   How  much sediment  is removed will  depend  not  only  on the
amount of material  obstructing use of the lake,  but also upon the availability
of  suitable sites for disposal.   The latter need  not  necessarily  be a deter-
rent to  sediment removal.   There are various productive use options available
for dredged sediment  (Lunz  et  aj.  , 1978; Walsh and Malkasian, 1978; Spaine et
aK , 1978).   In the case of Nutting Lake,  Massachusetts,  where approximately
275,000 m3 of sediment  were removed, the material is being sold for $1.00 m-3
effectively reducing  dredged material  removal  cost to $0.45 m-3 (Manfredonia,
1980).   This  not only solves  the  disposal problem,  but  reduces significantly
the overall cost of the project

     Due  to the high cost of removing sediment from lakes, $1.00 to $15.70 m-3
as  reported  by  Peterson  (1979),  it would  seem that lake  size  might  play an
important role  in determining lake types suitable  for dredging.  That does not
appear to be  the case.  Surface area of  lakes being dredged range from 2 ha to
over 1,050 ha, and volumes being removed range from a few hundred m3 to over 7
million  m3  (Peterson, 1979).   While  technically  there  is no  reason  a large
lake  cannot  be dredged,  there  are  some serious  economic constraints.   Most
projects, however,  have  not been scrutinized closely from the economic stand-
point.

     Current  information indicates  that lakes with highly  enriched  surface
sediment,  relative  to  underlying  sediment,  would  benefit  from  dredging
(Andersson e_t al. ,  1975;  Bengtsson et a!. , 1975).  Lake Trummen, Sweden showed
marked improvement  when   treated  in this manner.  Similar short term results
were observed when  25-50 cm  of organic sediment was  removed from Steinmetz
Lake, New York  (Snow et  aj. ,  1980).  This project differed significantly from
that at  Lake  Trummen, however,  since  clean  sand replaced almost  all  of the
organic sediment removed  (see case history #4 in  this paper).
                                      19

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     Sediment  removal  will  not be  cost effective  where  nigh  sedimentation
rates prevail.  Sediment removal projects should have reasonable assurance of
extended  longevity.   Generally, the  smaller  the ratio  of watershed  area to
lake surface  area,  the  greater the assurance of a lasting effect due to sedi-
ment removal.  Watershed management  practices  should be encouraged with sedi-
ment removal  projects where  practical.   However, massive watershed management
programs to protect small lakes could be counter productive.  Uttormark et a1.
(1974) have pointed out that where watershed area to lake surface area ratios
greatly exceed 10  to  1, significant nutrient reduction from the watershed may
be impractical.

     Generally speaking, small lakes with organically rich sediment, low sedi-
mentation  rates  and long  hydraulic  residence times  would be  ideal  sediment
removal candidates.
IV.  Case Histories of Sediment Removal

     Sixty-four  pre-implementation,  on-going,  or completed  sediment  removal
projects in the United States are summarized in the Appendix table.  The table
identifies sediment  removal  projects  in 22 states.  There are no doubt others
which have not  been included.   Many lake sediment removal projects are under-
taken  by  municipal   districts,  counties  and  even  state organizations  with
little  or  no documentation  of their  effectiveness.   The summary  attests  to
this  by the  large  number  of data  gaps.   In most  instances,  where  data  do
exist,  they  are  not readily  available.   Published  results are  relatively
scarce  and documented long  term (5  years or more)  effects are  simply  non-
existent.

     The five  case  histories  presented  were  included for one or  more of the
following  reasons:   1)  they  are  examples  of  different  sediment  removal
approaches,  2)  they  have  different  objectives,  3)  they point  out  some
strengths  and  weaknesses of  the  technique, 4) their  results have been rela-
tively well documented.  The  first,  and perhaps best  example of a well docu-
mented sediment removal project is located in Sweden.


1.   Lake Trummen,  Sweden

     Lake  Trummen,  Sweden is  one of the  most  thoroughly documented dredging
projects  in  the world  with  both pre-  and post-treatment  information.   This
project  represents  an attempt to reduce internal  nutrient cycling by skimming
off a thin  nutrient-rich  sediment layer.

     The lake has an  area of 400 ha and, prior to restoration, a maximum depth
of  2 m  and  a mean  depth  of  1.1  m.   By the early  1960s,  domestic waste  dis-
charge  had deteriorated  the  lake to  such  a degree that the citizens of Vaxjo
considered filling the  basin  (Bjork et al. ,  1971).   Diversion of  the major
pollutant  sources  had little effect on the  lake.  Sediment removal  implementa-
tion  in  1970  was preceded by two years of study and project plan development.
In  1970, one-half  meter of  finely divided organic sediment was dredged  uni-
formly  from the  main lake basin (Bjork,  1974).  In 1971, another half meter of
sediment was  removed bringing  the  total   volume  to  about  400,000  m3.   This

                                      20

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deepened  the  lake by  approximately 40 cm.  Dredged  material  was disposed of
partially in three macrophyte-infested, diked off bays.  One large bay, repre-
senting  approximatley  one-third of  the lake surface  area  and overgrown with
macrophytes, was  preserved in total as a  wildlife  habitat.  Dredged material
not  placed  in  diked  embayments was  pumped to  upland diked  ponds  where the
return  flows  were  treated with  aluminum  sulfate  to  reduce  the  phosphorus
concentration  in  dredge  slurry  (M  mg  P liter-1)  to  about  30  ug liter-1.
Dried dredge material was  sold as top soil  for about $2 (U.S.)  m-3.  The total
phosphorus  concentration  in the  lake  prior to sediment removal  was  600 pg P
liter-1.   Following  sediment  removal  the  concentrations   occasionally  have
reached 70 to 110 ug P liter-1  (Bengtsson et al_. , 1975).

     Bengtsson  et al.  (1975)  indicated that phosphorus and nitrogen decreased
drastically (Figure  5)  and that the role  of  the sediment  in  recycling nutri-
ents was minimized.   The  total  and orthophosphate  as well  as the Kjeldahl-
nitrogen  levels have remained  significantly  lower than before or during the
dredging program.

     Biologically, the  Shannon phytoplankton  diversity index increased from
1.6  in  1968 to 3.0  in  1973 (Cronberg et aj_. , 1975).  Secchi disc transparency
increased from  23 to 75 cm over  the  same  period.   Prerestoration mean annual
phytoplankton productivity  was  370  g C m-2 (1968-1969),  declining to 225 g C
m-2  following   restoration  (1972-1973).   More than 60 percent of  the  annual
phytoplankton production  in 1972-1973  was attributed to algae  less than 10 urn
in  size.   Blue-green algal biomass  was drastically  reduced  and  some species
disappeared, notably  Oscillatoria  agardhii.

     Before  dredging in  Lake Trummen,  the  benthic   fauna was  dominated  by
oligochaetes and  chironomids  (Andersson et al_. , 1975).  A year after dredging
tubificid oligochaetes  and chironomids became much more  numerous.   The total
number  of  benthic   organisms  changed  little.  This was  attributed  to  the
mobility  of chironomid  larvae  and the  fact that the  dominant  species swarmed
all summer,  probably  recolonizing newly dredged areas almost  immediately.

     The  results  at  Lake  Trummen are  highly  encouraging.   Born  (1979) indi-
cated that  today  Lake  Trummen is not only a usable recreational resource, but
that  the lake  ecosystem  has  been  restored.   Figure  5 indicates  that water
quality  has been remarkably good for four years following dredging compared to
that prior  to dredging.  Jorgensen (1980), however,  recently stated about Lake
Trummen  that,  "a  deterioration  of the water  quality  has  been  recorded during
the last 2-3 years (1976-1978),  caused by the phosphorus input  in the mixtures
of  rain and wastewater  discharged  to  the lake during  heavy  rainfalls."  No
data were presented  to  determine what the nature  of  the  deteriorated water
qua!ity might be.


2.   Lake Herman,  South  Dakota

     Lake Herman, South  Dakota  has  a surface area  of 546  ha,  a maximum depth
of  2.4  m and  a mean depth of  1.7  m.   The lake has  a 145  km2  agricultural
watershed.  Row crop and  small  grain farming practices beginning in the early
1900s have  resulted  in the deposition  of  approximately 2  m  of silt over the
entire  lake basin.   In  1970,  1971,  and 1972,  a 4.2 ha area of  one bay in Lake

                                     21

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                                            DREDGED MATERIAL
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         •1.2—  Water Depth (meters)

          (23)    Sediment Depth (meters)

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                LAKE HERMAN, SOUTH  DAKOTA
Figure 6.  Lake Herman, South Dakota (redrawn from Churchill et al., 1975a).
                                23

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Herman was  dredged.   This  work was undertaken to test the effect of hydrauli-
cally  dredging  nutrient-laden  inorganic  silt.   This  project  serves as  an
example of a marginally successful, limited scale hydraulic dredging operation
to reduce  availability  of  nutrients in a shallow, intermittently destratified
lake.

     About 48,000 m3  of silt were  removed from  the  dredge site, deepening it
from 1.7 m to  approximately 3.4 m  (Figure 6).  Dredged material was deposited
in a 3.4  ha area adjacent to  the  lake (Churchill et a_L , 1975a).  At the end
of the dredging project in 1972, drying had reduced the volume of the material
about 50 percent.  No coagulants were added to the dredge slurry.

     Orthophosphorus  concentrations in the  lake increased  dramatically  from
approximately 0.13  mg  P liter-1 to > 0.56 mg P liter-1 shortly after dredging
began  (Brashier et  a!. , 1973).  Phosphorus concentrations in the southeast bay
of the lake paralleled those  of the  main  lake but appeared to  lag behind by
several days (Figure  7).   Despite  the rapid increase in phosphorus concentra-
tions, they were  not  accompanied by major increases  in  phytoplankton produc-
tivity.   This  is  not  surprising,  however,   since  Churchill  e_t aj.  (1975b)
indicated the lake was primarily nitrogen limited and that nitrogen frequently
declined to zero  during algal  blooms.  Orthophosphorus concentrations in Lake
Herman prior to  dredging  were about 0.30 mg  liter-1,  during dredging (summer
1970,  1971,  and  1972)  they were  almost  uniformly 0.17  to 0.50 mg  liter-1,
while  after  dredging  (summer  1973,  1974,  and 1975) they  ranged  form 0.10 to
0.50 mg liter-1  with  a tendency toward the  lower end of the range (Churchill
et aj. ,  1975b).  Churchill  and  associates  were  reluctant to  conclude  that
dredging was responsible  for the increase in phosphorus concentration in Lake
Herman, however,  they  indicated that "there  were no other noticeable environ-
mental changes that could  readily  account for this dramatic increase in phos-
phates".    While  no apparent  increases  in  phytoplankton  production  resulted
from the  increased  phosphorus  concentrations,  the same may not have been true
if the lake was  not  normally nitrogen limited.  If  the large  increases  in
phosphorus were actually attributable to dredging one might conclude that this
particular  dredging operation  was  inefficient in terms  of limiting resuspen-
sion of  sedimented  material.   While  the  project  demonstrated  that nutrient-
laden silt could be removed by hydraulic dredging, thereby reducing the amount
available  for  internal  cycling in  the area dredged,  it  left a question about
the efficiency  of  such operations.


3.   Wisconsin  Spring  Ponds

     The Wisconsin  Spring  Ponds  (Sunshine  and  Krause  Spring  Ponds)  Project
represents another  of the  more thoroughly  documented  records  concerning the
ecological  effects  of  dredging small  lakes.   The purpose  of the  dredging was
to deepen the ponds and increase their area to improve fish production.  Inci-
dental  to  the  deepening was the control of aquatic  macrophytes.  This was an
important plus  for  the  project since Carline and Brynildson (1977)  stated the
belief that aquatic macrophytes played an important,  if not the most important
role,  in  determining  the  rate of  filling  in  spring ponds.   Presumably  this
conclusion might have  implications  for other  types of small closed basin lakes
such  as Lilly Lake, Wisconsin (Wis.  Dept. Nat. Resour. , 1969).
                                      25

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     The physical  characteristics  of  the  two spring  ponds  before  and  after
dredging are shown  in  Table 3.   Sediment removal  from the entire basin repre-
sents the most  severe  short run environmental impact possible.  It completely
disrupts the  benthic invertebrate population  and removes almost  all  aquatic
macrophytes.   In Sunshine Pond  the predredging mean annual  density of benthos
was 5,500 organisms m-2.  Immediately after dredging the number was reduced to
84 m-2.  Five  years after  dredging  the density of  benthic  invertebrates had
increased to 16,000  m-2  in  Sunshine  Pond.   Results for Krause Pond were simi-
lar.   However,  while most of  the invertebrates prior to  dredging  were chiro-
nomid larvae, those five years later  were primarily oligocheates which are not
an important  trout food.

     Carline  and Brynildson  (1977) indicated that after four years the impor-
tant fish food  organisms,  such  as  amphipods and chironomid  larvae were still
in the  process of  reestablishing.   This had  a  temporary,  but statistically
insignificant,  effect on  fish production.   Fish  growth rates declined sharply
in 1971  during  the  dredging operation but by 1975 had returned to predredging
values.

     Chara (a non-rooted, non-vascular aquatic macrophyte) covered 60 percent.
of the  Sunshine Pond  basin prior  to  dredging.  Dredging removed essentially
all of  the plant  material.   Five years after dredging Chara was reestablished
over 28  percent of  the pond.   However, its  biomass  was  only about 10 percent
of the predredging level.

     Lake dredging  frequently is of  concern to fisheries managers because of
the  suspected  adverse  impacts on fish populations.  Destruction  of  fish food
organisms is often  the  focal  point of this  concern.  The above indicates that.
benthic invertebrate reductions  had but a limited impact on the fishery in the
short run.   Carline and  Brynildson  (1977)   indicated that four to five years
after restoration by dredging the average density and biomass of fishable-size
fish were substantially greater than during the pre-dredging period.


4.   Steinmetz Lake, New York

     This case  history is  presented  because of its  relatively unique whole-
lake treatment technique, which  consisted of complete drawdown, bulldozing out
of approximately 25  to  50 cm of organic sediment and replacement of the sedi-
ment with  clean quarry  sand.   Macrophyte  control and  beach improvement were
the objectives.

     Records   indicate  Steinmetz  Lake,  in   Schenectady,  New York was  once  a
quarry  (Snow et aj. ,  1980).  The city acquired the  lake and surrounding pro-
perty for a  park  in 1935.  In  1936,   the  lake  was  drained and  some deep holes
filled  to  improve  swimming.  It has  been  maintained  by the  city since that
time for recreational use.

     The lake  is  1.2 ha in area, with a mean depth of about 1.5m and a maxi-
mum  depth  of 2.1  m.   It has a 28-40 ha naturally  vegetated watershed which
serves  as a public park (Snow et aj.,  1980).  Day use of the swimming and park
facilities declined rapidly since 1971 (over 17,000 users) to a low of approxi-
mately  6,000 in 1975.  The decline was attributed to excessive weed growth and

                                      26

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turbidity due to  algal  production,  caused by nutrient loading from stormwater
drains and surface  runoff,  lawn fertilizing in the watershed, and the in-lake
macrophyte growth/death/decay cycle which  was  rapidly building up the organic
sediment (Snow et  al. , 1980).

     The  restoration  project was  implemented  in  1978.   It  included sediment
removal,  diversion  of stormwater  drains,  and the  construction of  a surface
runoff interceptor  drains.   Bulldozing  2026  m3 of sediment required much more
time  than anticipated (six  weeks)  ,due  to sinking of  equipment in  the  soft
sediment  (Snow et alI.,  1980).   Backfilling with clean sand was much less of a
problem.   About   1843 m3  of sand  was placed  in eight days.   This  technique
results in no net changes of lake bathymetry,  but produces  a completely new,
clean substrate.

     The  short term results of the Steinmetz Project have been dramatic.  Snow
et  aj.  (1980) and  Bloomfield  (1980)  indicate the average summer  Secchi  disc
readings  have improved from  the 1976 and  1977  readings  of 1.25 m and 1.33 m,
respectively to post-treatment  readings  in 1978 and 1979, of 1.47 m and 2.20
m,  (maximum depth of  the  lake).  Average  summer chlorophyll  a levels in 1976
and  1977 were  10.4  ug  liter-1  and  5.8 ug  liter-1,   respectively.   Post-
treatment levels  have  been reduced  to  0.1  [jg  .liter-1   in  1978  and  1.8  |jg
liter-1 in 1979.  Aquatic macrophyte  biomass,  primarily Potamaogeton crispus,
ranged from 30-50 g wet  weight m-2 before sediment removal and was reduced to
virtually zero after  treatment.   Snow et al.  (1980) reported that after sedi-
ment  removal  P.  crispus  was  observed  growing  at  irregular  intervals  in
straight  lines  at  a  density  of  2  to  20  plants  m-2.   Closer  observation
revealed that the  plants were growing where tracked vehicles  had forced incom-
pletely  removed organic  sediment  up  through  the  sand  cover  during the sand
spreading operation.  Snow  et  
-------
     The fish population was dominated by slow growing yellow perch.   Chemical
eradication and restocking with largemouth bass,  sunfish and northern pike was
generally unsuccessful (Wisconsin DNR,  1969).  Winter fish kills were common.
It was concluded that deeper water was required to manage for fish production.
The DNR recommended that at least 10 percent of the lake be dredged to a depth
of approximately 6.0  m.   There  is no indication of  how that particular depth
or area was determined.

     No action was  taken  on the DNR  recommendation  until  1976  when  Wisconsin
received a grant from the U.S.  Environmental Protection Agency for the purpose
of restoring  Lilly  Lake.   The  restoration plan submitted by  the State called
for dredging  about  665  x 103 m3  of  sediment  from the lake, deepening it to a
maximum depth of about 6  m.  The objective of the project was  to deepen the
lake sufficiently so  that plant growth and winter  fish kills would  no longer
be serious  problems  (Wisconsin  DNR,  1975).  The project proposal called for
disposal of most  of the dredge material in  a  nearby abandoned gravel pit.

     Pre-implementation  indications  were  that the sediment would  flow to the
intake  of  a  suction dredge and that cutterhead  swing could  be  eliminated.
However, when dredging began in July 1978  it  was  quickly discovered that the
non-decomposed plant material  in the  sediment formed  a tight matrix  which
resisted flowing.   From  early  July  to October 26,  1978, approximately  360 x
103  m3 of  sediment  were  pumped from  the lake  (Dunst and  Beauheim,  1979).
During  the 1978  dredging  period in-lake 5-day BOD ran about 1-2 mg 02 liter-1
greater than  during the previous year.  Turbidity increased in the same manner
from 1  to 3 formazin  units.  Ammonia concentration increased dramatically from
approximately 0.01  mg liter-1  during most  of  1977  to a high of nearly 5.5 mg
liter-1 when  dredging ceased in October 1978.   Although predredging records of
particulate phosphorus  concentrations were incomplete  it appeared that there
was  a   steady  increase during  dredging.    Chlorophyll  a  levels in  the  lake
during  1977 were steady at about 2.5  to 3.0 |jg liter-1.  In 1978 chlorophyll a
reached a high of approximately 27 |jg liter-1  immediately after dredging began
and  then  decreased  to a  level  ranging  from  12  to  18 (jg liter-1  for the
remainder  of  the dredging season.   Dunst  and  Beauheim (1979)  reported  that
while  productivity  had averaged about 200 mg C m-3 day-1 during the  summer of
1976 and 1977, it increased to an average of  about 750 mg C m-3 day-1 in 1978.

     Dredging  commenced  again  in May  1979  and  was  completed by  September
(Dunst, 1980b).  Sediment  removal actually  exceeded 680 x 103 m3 and the lake
now  has a maximum  depth  of 6.5 m.   Additional Lilly  Lake  dredging  data have
been reported by Dunst (1980c).  The summer of 1980 was the first full growing
season  since  dredging.   Dunst  (1980a)  has  indicated  that  in-lake macrophyte
biomass of 200  to  300 g dry wt m-2 in 1977 was reduced to virtually zero when
dredging ceased  in  September 1979.  Water quality since that time has remained
good  and  local  sponsors  are  generally  pleased with  the outcome (Dunst and
Beauheim, 1980).  It will be interesting to observe over the next few years if
macrophytes and  internal  nutrient cycling remain diminished as a result of the
lake deepening at Lilly Lake.
                                      28

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V.    Costs of Sediment Removal

     Sediment  removal  costs  vary widely  depending on  type and  quantity  of
sediment  being  removed;  type  of  removal method,  i.e.,  bulldozer, mechanical
hydraulic or special purpose dredge,  sediment transport distance and method of
transporting;  availability  of disposal  area;  and ultimate  use  of  dredged
material.   Even  within  the same  geographic  region  using the  same  dredging
equipment,  costs  may  vary widely.  Carline  and Brynildson  (1977) indicated
that cost per cubic meter of sediment removal to increase the volume of spring
ponds in  Wisconsin  ranged  from $0.52 to $2.67.  On a  national  basis the cost
differentials  are  much  greater  (Table  3).   The Army  Corps  of  Engineers has
shown a similar broad  range  in  sediment  removal   costs  on  a  national  basis
(Saucier, 1976).

     Generally speaking,  per  unit volume  costs for sediment removal  will  be
inversely related to the total  volume of material removed when disposal is not
a  problem.   Contaminated  dredged material,  requiring treatment  and  perhaps
upland  containment,  may increase  cost  by  3 to  5  times  (Peterson, 1979).  On
the  other  hand,  sale  of  "desirable"   dredged material  may help  offset the
removal   cost.   Nutting  Lake,  Massachusetts  sediment  is  being  sold for $1.40
m-3 (Manfredonia,  1980).   A portion  of  the sediment from Lake Trummen, Sweden
was  sold for  nearly  $2.00 m-3.   Innovative  disposal  practices  may  signifi-
cantly  reduce  the cost   of  sediment  removal.   Closer  examination  of  cost
figures  is required before  reliable generalizations  can  be  stated.


VI.  Summary

     1.    The purposes for removing  sediment from   a lake  are 1) to deepen it
for  improved boating,  fishing,  swimming  and other recreational  activities,
2)  to prevent or  reduce  the  internal  sediment/water  recycling  of nutrients,
3)  to reduce the  effects of toxicants,  and 4) to remove and reduce the growth
of  nuisance aquatic  plants.   The  expected  results  of these  treatments are
improved  dissolved  oxygen concentrations;   less  sediment  water  nutrient
exchange,  accompanied   by   reduced  algal  biomasses,  increased  clarity,  and
reduced  macrophyte  nuisance problems.   All  of these goals may not be attained
in al1 cases.

     2.    The  technique  is effective   for  deepening,  and when  a lake  has
shoaled   extensively there   may  be no other  practical  method  for restoration.
Sediment  removal  for deepening  is  accompanied  by  nutrient  removal which  no
doubt contributes   to  the overall  improved  lake quality  in  many  sediment
removal  projects.

     The  duration   of  deepening  effectiveness  will   depend  largely  on  lake
sedimentation  rates.  The  one  case history  of  skimming  nutrient-rich  surface
sediments  for controlling internal  nutrient cycling  has been  dramatically
successful  for approximately six  years.   Signs of  reduced water quality after
that  time  were  associated with  external  nutrient  loading, however,  water
quality  has remained better than it was prior to dredging.
                                     29

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     Macrophyte  control   by  sediment  removal  is  usually attempted  through
deepening.   The  effectiveness  of this  approach is  not  clear at  this point.
Sediment texture, nutrient content,  and water temperature may be as important
as light level  in determining if plants  reinvade  a dredged area.

     3.    The  reduction  of  toxic problems  in lakes  by sediment  removal  is
technically  feasible.  This  technique  is  being practiced at a  high  level  of
sophistication  in  Japan.  It  requires  special dredging  equipment,  confined
disposal areas  and  treatment  of dredged material  return  flow  waters.  Costs
are usually double to quadruple those for removing uncontaminated sediment.

     4.    Relatively  unsuccessful  sediment  removal projects  can  usually  be
associated with  extremely  limited sediment removal  (simply too  small  a scale
to be effective), an inefficient dredging operation (poor production of solids
in the dredge slurry, excessive downtime, extreme turbidity problems or inade-
quate disposal areas), or no  attempt to control  external  loading of pollutants
to the lake.

     5.    Any project considered for sediment removal should be  preceded by an
investigation  of nutrient and  sediment  mass  balances.   Mass  balance calcu-
lation  will   provide  information  on  the relative  proportion  of  pollutants
derived  from  the various sources, thus providing  a mechanism to focus on the
critical compartments.   Accurate portrayal of  sedimentation  rates  permit the
extrapolation of sediment  removal  longevity,  thus the comparative cost effec-
tiveness of sediment removal.

     6.    There  are  a number of environmental  concerns  associated  with sedi-
ment  removal  activities.   The  majority of those associated with  the  sediment
removal   phase  (in-lake)  appear to be of  short  duration  and thus limited sig-
nificance  when  compared  to  the  longer range effectiveness of  the treatment.
This  may  not  be the  case  when toxic  substances  are  involved  if  sediment
removal   is  poorly  managed.  The effects of dredged material disposal  may be
longer  lasting.  These effects will be tied directly to the method of disposal
and  the quality  of  the dredged  material.   Filling  of wetlands  (no longer
commonly accepted)  results in  permanent destruction of  that habitat.   Enrich-
ment of agricultural land with non-toxic dredge material  may have a long range
positive effect.  Imaginative disposal plans can reduce the impact of disposal
and the  overall  cost  of a dredging project.

     7.    The  hydraulic  dredge  is  the preferred piece  of  equipment  for most
sediment removal operations.   It is comparatively  efficient  in  terms  of pro-
duction  and  relatively  clean  (resuspension  of  sediments)  in  its operating
cycle.   Special  purpose dredges  reduce  resuspension  of  sediment,   but  are
relatively inefficient in terms of energy expended to remove a given volume of
sediment.  Therefore,  operational  costs  are  usually  higher  than  for conven-
tional  hydraulic  dredges.   Their  use  may be warranted  only when  toxic sub-
stances are being removed.

     8.    An  average unit cost  for sediment  removal  cannot be  stated.   The
variables  associated  with  dredging are so numerous  that an  average unit cost
figure  becomes  meaningless.  About  the only generalized statement that can be
made  about  unit cost is  that it is likely to be inversely proportional to the
amount of sediment removed.

                                     30

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     9.    There are  still  a number of uncertainties  associated  with dredging
as a  lake  restoration  technique.   Among  these are the longevity of effective-
ness, the  relative  effectiveness  of partial compared  to  whole-lake dredging,
how to dredge in order to minimize ecosystem shock and encourage rapid repopu-
lation of  desirable organisms.   In  cases where nutrient control  is of major
interest, more experience is needed with  surface sediment skimming compared to
deepening  as  a restoration  technique.   A clearer picture  of  the comparative
effectiveness of these  two  techniques  could have a  major influence on future
projects.  Costs could  be  reduced  significantly if  it was demonstrated that
surface  skimming of  sediments  might accomplish the same objectives as deepen-
ing.   More sustained  research  and monitoring of the  effectiveness  of diverse
sediment removal methods  is  required.
                                     31

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                                       38

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                                      39

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                                      40

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                                      41

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                                                                                                          1 US  GOVERNMENT PRINTING OFFICE  1961 -757-064/OZ9Z

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