, ".'

. -.' .; . "

c. ':-,

A Publication of the Savannah River Ecology LaboratoryNational Environmental Research Park Program

United States Department of Energy

, ','

: '.-

-; ,

.' : .. : ,:...' ~,

-~ .' '.

"-:; 7A ,',

, '

'.';

. ~.

. ",' " '~

....;". ',':'

._-~,... : . ....

.~ <:

;:~,~.:,: :r.o·

i • ~' .,'."

.....

, ~'

J;i1'i~'. J~. ,

" ', ' "" ,;; ;t! :':;J 'I1I$):i'iR tt ,WJ,S( ' (~,,!~d;;a~ an , ' account of.WQrk ; '· ';:i!k:;;:; ;\:", '~ ·

'.•~~~i~~~_~~t~~~~i1~f~!~~~· ;. " i':;;' ; ~"~ i(\~•.e. ' it~~,~;!rit~f~~ ~r' ~ssu~es anY : le9 ':; ' . ,': ",' it~;~ 'A,, ' :',\~-: ~II~ t'~~l!rtti~~~ :1()~n~fnf~~~Ultfcj~ . " , ,~rJ~~)1:

:';.: "- , 0:': 'appit-a:tijsl~#r~((~t;;or" 'Pro c;e s,s ' disclos~d, ~ '~r .:.:' :-.- ·;}A~t.~,:,~l;,O'')'" , . r,e~~¥~~t!1at,,~s;o$e wOlJld not Infringe pnvately ", ,',:0t.'t'it::

-' own'entighu- " -', ' ' . ' "

,.C . . .. " A,il~_J:

. ,",' ' .•~ :" ,\ - ~': , '

,~- ';' ~< 'r:.

', '

~.' .

' ..

'~' - '.-

: ' -~-

.:

'.~.'

January, 1988 Copies my be obtained from

Savannah River Ecology

Laboratory

SEASONAL DYNAMICS OF BENTHIC MACROINVERTEBRATES OF

POND B, SAVANNAH RIVER PLANT

AIKEN, SOUTH CAROLINA

APRIL D. WHICKER'

Savannah River Ecology Laboratory

A Publication of the Savannah River National Environmental Research Park

1988

, Present Address: Natural Resource Ecology laboratory

Colorado State University

Ft. Collins, Colorado 80523

TABLE OFCONTENTS

Introduction 1

Study Site 3

Materials and Methods 3

Resu Its 8

Discussion .. . . . . . . . . . . . .. . . .. . . • . .. . . .. . .. . . .. .. . .. . . . . . . . . . . . . . . . . .. 23

SeasonalChanges in Population Densities. . . . . . . . . . . . . . . . . . . . . . . . . . 24

Population Variations with Water Depth 26

Biomassand Diversity 29

Limitations ofthe Data 31

Summary ..... . .. . . .. .. . . ... . .. .. .. . . ... ... . . . . . ... . ... . . .. .. .. .... . • 32

Acknowledgments 33

Literature Cited 35

INTRODUCTION

Invertebrate communities in freshwater lakes and ponds form a complex array

of trophic relationships, life cycles, species compositions, physiological and morpho­

logical adaptations, and habitat utilizations. The benthic invert ebrat es are

undeniably of primary importance in supporting populations of many fish and other

aquatic vertebrates. In a small pond in Indiana, for example, Gerking (1962) showed

that fish were able to consume more benthic invertebrates in one month than were

actually present in the standing crop . Thus, invertebrate production rates must

have been very high, even with heavy predation.

In spite of the importance of these essential faunal components, detailed

studies on communities of benthic invertebrates (those invertebrates associated

with unconsolidated substrate) in standing water are few, perhaps because of

difficulties in species identifications (Brigham et al. 1982, Resh and Unzicker 1975)

and in quantifying abundances (Resh 1979, Cumm ins 1962). However, the

environmental or ecological "health " of a lake is frequently assessed by sampling

invertebrate, especially insect, populations to determine changes in species (or taxa)

composition, as evidence of possible responses to pollution or other perturbations

and stresses (Washington 1984, Resh and Unzicker 1975). The rate of recovery of a

body of water after being impacted is also measured by changes in invertebrate

communities.

The Savannah River Plant (SRP) is a nuclear materials production facility in

South Carolina operated by the U.S. Department of Energy. The site has a number

of reservoirs which are used to store and cool water discharged from nuclear

reactors before the water enters streams, swamps, and/or river systems. These

reservoirs can be impacted by elevated water temperatures, radionuclides, and

chemicals. In the case of one such reservoir, commonly known as Pond B, the input

of radionuclide contamination and thermally elevated effluents ceased in 1964 and

1

since that time, this reservoir has been allowed to recover. It is not known how long

is necessary to achieve a dynamic biotic equilibrium after such stress, but Pond B

currently supports at least 19 species of rooted aquatic macrophytes (Parker et al.

1973).14 species of fish (Bennett and McFarlane 1983).2 species of turtles (Parker et

al. 1973), assorted waterfowl, and alligators. Invertebrate populations have not

been quantitatively studied in this reservoir, since prior aquatic invertebrate

research at the SRP has been focused on other bodies of water which still receive

thermal input: Par Pond, Pond C. and the stream systems.

This study was designed to evaluate the spatial and seasonal distributions.

compositions. and abundances of benthic macroinvertebrates in Pond B after 20

years of postthermal recovery. There are both basic and applied uses for the data

gathered during the study. The examination of species composition and abun­

dances as a function of season and water depth adds to the base of general

knowledge on the benthic invertebrates of lentic systems. The current species

composition also provides an indication of a portion of the postthermal community

succession. An estimate of the biomass of the benthic community permits a calcula­

tion of the radionuclide inventory in th is ecosystem compartment, if average

concentrations are concurrently determined . Suchdata may then be used to predict

food chain transfers to higher consumers and potential export from the ecosystem .

Specific hypotheses tested were : (1) densities of certain benthic invertebrate

communities vary with season, (2)densities of benthic invertebrates vary with water

depth, and (3) the effect of season on invertebrate density depends on water depth

(i .e. there is an interaction between depth and season). Other community

parameters considered were species composition, diversity, and relative biomass by

taxa.

2

STUDY SITE

Pond B isan 87-ha impoundment that was used asa cooling pond from 1961 to

1964 for a nuclear materials production reactor. Since 1964, it has received only

natural subsurface drainage, precipitation, an undetermined amount of subsurface

ground water, and minimal human disturbance. It may be a reasonable model of

other SRP cooling reservoirs twenty years after thermal discharges cease.

The following description of the limnological properties of Pond B is from

Evans et al. (1983). The mean and maximum depths of Pond Bare 4.4 and 12.2 m,

respectively. The impoundment has annual cyclesof thermal stratification, w ith the

summer thermocline occurring at a depth of 6-7 m. The hypolimnion becomes

depleted in oxygen from mid-April until mid-November. The water has a mean pH

of 6.2 and very low concentrations of dissolved nutrients. Large amounts of

dissolved organic matter and high total iron concentration give the system a

" b lackw at er" appearance. Bottom sediments vary from sand and clay

(predominately kaolinite) to organic detritus. At water depths less than 5 rn, there

is a rich assortment of aquatic plants. The more abundant plants include

Nymphoides cordata, Brasenia schreberi, Nymphae odorata, Cabomba caroliniana,

and Utricu/aria itoridene (F. W. Whicker and R. R. Sharitz, pers. comm .). Primary

aquatic vertebrates include fish (largemouth bass, Micropterus salmoides and

yellow bullhead, /eta/urus nata/is), turtles (Pseudemys scripta). the American

alligator (Alligator mississippiensis) (Parker et al. 1973). and numerous species of

waterfowl, the majority of which are winter migrants.

MATERIALS AND METHODS

Pond B was sampled for benthic macroinvertebrates during winter

(February 7-10), spring (May 1-2), and summer (July 3D-August 7) of 1984. A random

sampling, stratified by depth, is considered an efficient and satisfactory mean s of

3

assessing benthic populations (Cummins 1962, Gerking 1962, Cuff and Coleman

1979), and therefore was used to sample Pond B. A map of the shoreline was

marked with numbered points 10 m apart, from which 20 locations were randomly

chosen for sampling (Fig. 1). Four depth zones (strata) were chosen for sampling at

each location (0.5-1.5 m, 2.0-3.0 rn, 3.5-5.5 m, and> 6.0 m). Water levels fluctuated

within the year, so to insure that the sampled substrate would always be under

water, depths less than 0.5 m were not included. A 0.5 m difference between the

boundaries of contours minimized the chance of overlap during sampling. These

sampling intervals roughly corresponded to changes in vegetation distributions

(0.5-3.0 m, littoral; 3.5-5.5 rn, sublittoral ; and > 6.0 m, profundal). Other

comparable studies have used similar depth zones (Ferraris and Wilhm 1977,

Gerking 1962). Additionally, proportional areas in each contour could be

determined from topographic maps made at the time the impoundment was

created .

A numbered stake was placed at each designated location and all sampling

was done on a transect extending toward deeper water, perpend icular to the

shoreline at the stake. Although all 20 locations were used each season, the exact

position of the sampling station, therefore depth within each zone , var ied . This

further randomized sampling within a zone and made it possible to position the

boat at any depth falling within an appropriate contour interval. Although

potentially 80 stations (20 locations, 4 depth zones) could be used, some locations

were in bays, the maximum depths of which did not exceed the shallow zones.

Therefore, only 52 stations were routinely sampled (Fig. 1).

Samples were taken with a Ponar grab, measuring 1S x 15 em. Sampled

substrates varied between sand, sand-clay, and silt. A Ponar grab tends to be an

efficient sampler in most bottom substrates, excluding mud (Downing 1984,

Flannagan 1970, Howmiller 1971). In w inter, two drops of the grab were made at

4

.00

100..0 00

00 0..

0

O'N

POND B. SAVANNAH RIVER PLANT

SOUTH CAROLINA

Figure 1. Sampling locations on Pond B, Savannah River Plant, South Carolina .Tics indicate 20 randomly selected stations, and solid circles representapproximate sampling locations with in depth zones. The first circle is inthe 0.5-1.5 m depth zone (l ittoral), the second is in the 2.0-3.0 m zone(l ittoral), the third is in the 3.5-5.5 m zone (subl ittoral), and the fou rth is> 6.0 m (profundal) .

5

each station; but because the variability between locations within a zone was

greater than the variability between drops, only one drop was made in subsequent

seasons. When the number of samples that can be processed is restricted, use of a

single sample per location is generally considered adequate for estimating density,

especially of abundant organisms (Cuff and Coleman 1979, Deevey 1941). Density

of macroinvertebrates was expressed as numbers per square meter of benthos

sampled.

Vegetation and benthic material brought up in the Ponar were immediately

washed through a No. 30 (590 micron) U.S. Standard Sieve. The U.S. Environmental

Protection Agency (EPA) has defined macroinvertebrates as those organisms which

are reta ined by this size sieve (Weber 1973). Washed material was placed into a

polyethylene bag and covered with 80% ethanol. 8ags were stored for later

sorting, which was completed within two months. In the laboratory, benthic

material was again washed and the remaining material was sorted by hand for

organisms. Invertebrates were stored in vials w ith ethanol for counting and ident i­

fication . Taxonomic keys used for identification were primarily those of Brigham et

al. (1982), Pennak (1978), Usinger (1956), and Wood (1982). Identifications were

made to "reasonable" taxa, considering the availability and completeness of keys,

ages of instars, and sample preparation that would be necessary to further refine

the classifications .

Estimates of mean dry mass per individual were made for most taxa for each

season. All invertebrates were oven-dried 24 h at 60°C before weighing. Weights

were obtained using an analytical balance and recorded to the nearest 0.1 mg.

Depending on size of the animal and availability of specimens, members of a taxa

were either weighed individually or composited . A composited sample could

represent two to several hundred individuals for which a mean mass per ind ividual

was calculated . Frequently, several composited samples could be obtained per ta xa;

6

for these, a weighted mean mass was calculated from the proportional number of

animals in each composited sample. Both shells and soft parts were included in snail

weights. Masses of some uncommon taxa, represented by a very few small

individuals (such asOrthrotrichia), could not be estimated.

From the above information on invertebrate density and mass and the area of

the lake in each depth zone, biomass could be estimated for each depth zone, as

well as for the entire lake. In making these estimates, the 0.5 m increments that

were not included in the sampling were accounted for in biomass estimates of the

lake.

Diversity was calculated using the Shannon-Wiener formula:

H' = -E(Pi)(1 n Pi)

where Pi indicates the proportion of total samples belonging to the ith taxa (Krebs

1978). Although the Shannon-Wiener index may not be considered by some to be

the best measure of diversity for aquatic systems (Washington 1984), it is widely

used and generally understood, and the EPA recommends using a modified

Shannon-Wiener to estimate mean diversity in aquatic stud ies (Weber 1973). In this

paper, the index is being used only to investigate patterns of diversity within one

system.

Two-way analyses of variance (SPSS: MANOVA, Hull and Nie 1981) were used

to test for differences in mean abundances by depth and season for total

invertebrates and for the most common taxa (Chaoborus, Ceratopogonidae,

Chironimidae, and Amphipoda) . The following were investigated : main effects of

depth and season, interactions of depth with season, simple effects of density

changes within a season by depth zone, and changes w ith in a depth zone across

each season. The data required natural logarithmic transformations to reduce the

nonhomogeneity of variances before analyses were conducted . Statistical

significance is reported using p < 0.05.

7

RESULTS

Forty taxonomic groups of macroinvertebrates representing 10,400 indiv iduals

were identified during the three seasons of sampling in Pond B (Table 1).

The abundances of benthic macroinvertebrates var ied both among depth

contours and seasons (Tables 2, 3, and 4). In general, the densities of individuals

in a taxon declined with increasing water depth w ithin a season, asdid the number

of taxa found. A summary of density estimates by major taxa (Table 5) shows clearly

the changes w ith season and depth. In winter, although 33 taxa were identified at

0.5-1.5 m, only the annelids, amphipods, and dipteran larvae were found at the

deepest contour (Tables 2, 5). By spring, amphipods were no longer found in the

deep water (Tables 3, 5), and by summer, only dipterans occurred in the deep water

zone (Tables 4, 5).

The primary exception to declining densities w ith depth was among the

dipterans. In each season, densities of Chaoborus (phantom midges) increased

significantly by factors of 15-80 with increasing depth (Table 6). An overall increase

in total invertebrate numbers with increasing water depth (Fig. 2, Table 5) was

primarily due to sign ificant increases in Chaoborus in all seasons. However,

Chaoborus did not show significant changes in densities in the shallowest and

deepest water zones across seasons (Table 6). Densities of Ceratopogonidae (biting

midges) did not change significantly with water depth in any season (Table 6), but

did show significant seasonal decreases. Bysummer, this group was nearly absent at

all depths (Table 4). Although chironomids (nonbiting midges) did not change

significantly with depth in w inter (Table 6), they showed a fourfold increase in

density with depth by spring. Chironomids also exhibited significantly declining

densities from winter through summer.

8

Table 1. Summary of taxonomic classifications of macroinvertebrates identifiedduring the benthic sampling of Pond B during 1984.

PHYLUM PLATYHELMINTHES

Class Turbellaria

PHYLUM ANNELIDA

Class Oligochaeta

Class Hirudinea

PHYLUM MOLLUSCA

Class GastropodaFamily Planorbidae

Helisoma ancepsHelisoma trivolvisMenetus

Family PhysidaePhyse/la heterostropha

PHYLUM ARTHROPODA

Class Amphipoda

Class Hydracarina

Class InsectaOrder Diptera

Family CeratopogonidaeFamily Chaoboridae

ChaoborusFamily ChironomidaeFamily Tabanidae

ChrysopsOrder Coleoptera

Family CurculionidaeFamily Oytiscidae

CelinaHydroporus-HygotusI/ybius

Family HydrophilidaeBerosus

Family ChrysomelidaeDonacia

Family HaliplidaeHaliplus

9

Table 1. Continued

Order TrichopteraFamily Polycentropodidae

PolycentropusFamily Leptoceridae

OecetisFamily Hydroptilidae

OxyethiraOrthrichia

Family PhryganeinaeAgrypnia

Order LepidopteraFamily Pyralidae

EoparargyractisParapoynx

Order EphemeropteraFamily Leptophlebiidae

ParaleptophlebiaFamily Caenidae

CaenisOrder Odonata

Suborder ZygopteraFamily Lestidae

LestesFamily Coenagrionidae

ArgiaEnallagmaIschnura

Suborder An isopteraFamily Corduliidae

EpicorduliaTetragoneuria

Family LibellulidaeCelithemisErythemisPerithemisPachidiplaxLadona

10

Table 2. Winter densi~je~ (number of. individualslm2 of substrate) of majortaxa of benthic Invertebrates 10 Pond B. Numbers in parentheses areone standard error of the mean.

DEPTH (m) 0.5-1.5 2.0-3.0 3.5-5.5 >6.0NUMBER OF STAnONS (N) 20 16 9 7

Turbellaria 8 (4) 0 0 0Oligochaeta 77 (42) 6 (3) 7 (5) 6 (6)Hirudinea 23 (13) 4(3) 0 0Helisoma anceps 33 (13) 76 (31) 15 (5) 0Helisoma trivolvis 4 (4) 0 0 0Menetus 1 (1) 1(1) 0 0Physella heterostropha 30(11) 25 (14) 2 (2) 0Amphipoda 600(111) 114 (22) 37 (11) 3 (3)Hydracarina 1(1) 13 (6) 15 (10) 0Ceratopogonidae 217(78) 104 (26) 106 (37) 114 (55)Chaoborus 141(128) 635 (276) 600(163) 2203 (776)Chironomidae 2210 (226) 1808 (304) 1654 (290) 2168 (432)Chrysops 37 (9) 1(1) 0 0Curculionidae 12 (9) 0 0 0Celina 31(20) 0 0 0Hydroporus-Hygotus 0 4 (2) 0 0lIybius 2 (2) 0 0 0Berosus 12 (6) 0 0 0

Donada 9 (5) 0 0 0

Haliplus 0 1 (1) 0 0

Polycentropus 221(58) 50 (20) 2 (2) 0

Oecetis 66 (18) 32 (12) 12 (10) 0

Oxyethira 3 (2) 0 0 0

Orthrichia 0 0 0 0

Agrypnia 1 (1) 0 0 0

Eoparargyractis 8 (4) 22 (10) 2 (2) 0

Parapoynx 2 (2) 0 0 0

Paraleptophlebia 14 (5) 0 0 0

Caenis 7 (4) 1 (1) 0 0

Lestes 1 (1) 6 (3) 0 0

Argia 1 (1) 0 0 0

Enallagma 33 (12) 25 (8) 0 0

Ischnura 0 0 0 0

Epicordulia 0 0 2 (2) 0

Tetragoneuria 1 (1) 3 (2) 0 0

Celithemis 80 (12) 15 (5) 15 (6) 0

Erythemis 1 (1) 0 0 0

Perithemis 0 0 0 0

Pachidiplax 32 (9) 1 (1) 0 0

Ladona 0 0 0 0

11

Table 3. Spring densities (number of individualslm2 of substrate) of majortaxa of benthic invertebrates in Pond B. Numbers in parentheses areone standard error of the mean.

DEPTH em) 0.5 -1.5 2.0-3 .0 3.5-5.5 >G.ONUMBER OFSTATIONS IN) 20 16 8 7

Turbellaria 0 0 0 0Oligochaeta 33 (24) 14 (5) G(G) 19 (B)Hirudinea 9 (7) 3 (3) 0 0Helisoma anceps 13 (7) 22 (10) 11 (7) 0Helisoma trivolvis 2 (2) 0 0 0Menetus 0 0 0 0Physel/a heterostropha 7 (4) 19 (8) 0 0Amphipoda 87 (28) 94 (31) 78 (37) 0Hydracarina 0 0 0 0Ceratopogonidae 42 (13) 39 (19) 22 (17) 25 (19)Chaoborus 29 (20) 194 (99) 289 (78) 1048 (321)Chironomidae 480{11G) 331 (GO) 822 (35G) 19G8 (5GO)Chrysops 9 (5) 3 (3) 0 0Curculionidae 7 (4) 3 (3) 0 0Celina 1G (7) 0 0 0Hydroporus-Hygotus 0 0 0 0I/ybius 0 0 0 0Berosus 2 (2) 0 0 0Donacia 7 (4) 3 (3) 0 0Haliplus 0 0 0 0Polycentropus 100 (35) 56 (21) 0 0Oecetis 11 (5) 8 (6) 11 (7) 0Oxyethira 9 (G) 0 0 0Orthrichia 2 (2) 0 0 0Agrypnia 0 0 0 0Eoparargyractis 2 (2) 0 0 0Parapoynx 0 0 0 0Paraleptophlebia 0 0 0 0Caenis 4 (3) 3 (3) 0 0Lestes 2 (2) 0 0 0Argia 0 0 0 0Enal/agma 7 (4) 3 (3) G(G) 0Ischnura 0 3 (3) 0 0Epicordulia 0 0 0 0Tetragoneuria 0 0 0 0Celithemis 33 (14) 39 (12) G(G) 0Erythemis 0 0 0 0Perithemis 0 0 0 0Pachidiplax 2 (2) 0 0 0Ladona 0 0 0 0

12

Table 4. Summer densities (number of individualslm2 of substrate) of majortaxa of benthic invertebrates in Pond B. Numbers in parentheses areone standard error of the mean.

DEPTH (m) 0.5-1.5 2.0-3.0 3.5-5.5 >6.0NUMBER OFSTATIONS (N) 20 16 8 6

Turbellaria 0 0 0 0Oligochaeta 0 17 (9) 0 0Hirudinea 4 (3) 0 0 0Helisoma anceps 7 (4) 19 (10) 0 0Helisoma trivolvis 2 (2) 3 (3) 0 0Menetus 0 0 0 0Physella heterostropha 7 (7) 8 (6) 0 0Amphipoda 82 (26) 58 (26) 0 0Hydracarina 0 0 0 0Ceratopogonidae 2 (2) 0 11 (7) 0Chaoborus 27 (8) 186 (44) 1055 (293) 2103 (867)Chironomidae 233 (88) 81 (21) 56 (25) 259 (35)Chrysops 7 (4) 3 (3) 0 0Curculionidae 29 (10) 0 0 0Celina 49 (23) 0 0 0Hydroporus-Hygotus 0 0 0 0lIybius 0 0 0 0Berosus 0 0 0 0Donacia 4 (3) 0 0 0Haliplus 0 0 0 0Polycentropus 16(11} 0 0 0Oecetis 2 (2) 0 0 0Oxyethira 2 (2) 3 (3) 0 0Orthrich ia 0 0 0 0Agrypnia 0 0 0 0Eoparargyractis 0 0 0 0Parapoynx 4 (3) 0 0 0Paraleptophlebia 0 0 0 0Caenis 0 3 (3) 0 0Lestes 0 3 (3) 0 0Argia 0 0 0 0Enallagma 13 (7) 22 (8) 0 0Ischnura 0 0 0 0Epicordulia 0 0 0 0Tetragoneuria 0 0 0 0Celithemis 9 (5) 8 (8) 0 0Erythemis 2 (2) 0 0 0Perithemis 2 (2) 0 0 0Pachidiplax 0 3 (3) 0 0Ladona 2 (2) 0 0 0

13

Table 5. Summary of densities (number of individualslm2) of the major groups ofbenthic invertebrates in Pond B. Numbers in parentheses are onestandard error of the mean.

DEPTH em}

TAXON SEASON 0.5-1.5 2.0-3.0 3.5-5.5 >6.0

Annelida Winter 100 (43) 10 (3) 7 (5) 6 (6)Spring 42 (25) 17 (6) 6 (6) 19 (13)Summer 4 (1) 17 (9) 0 0

Gastropoda Winter 69 (21) 103 (44) 17 (5) 0Spring 22 (8) 41 (14) 22 (17) 0Summer 16 (9) 31 (13) 0 0

Amphipoda Winter 600 (111) 114 (22) 37 (11) 3 (3)Spring 87 (28) 94 (31) 78 (37) 0Summer 82 (26) 58 (26) 0 0

Diptera Winter 2605 (269) 2548 (435) 2385 (315) 4485 (632)Spring 560 (127) 564 (103) 1117 (343) 3041 (580)Summer 269 (88) 270 (54) 1122(313) 2362 (861)

Coleoptera Winter 66 (25) 10 (6) 0 0Spring 32 (12) 6 (4) 0 0Summer 82 (24) 0 0 0

Trichoptera Winter 282 (66) 82 (24) 15 (12) 0Spring 122 (37) 64 (21) 11 (11) 0Summer 20 (11) 3 (3) 0 0

Lepidoptera Winter 10 22 2 (2) 0Spring 2 0 0 0Summer 4 0 0 0

Ephemeroptera Winter 7 1 (1) 0 0Spring 4 3 (3) 0 0Summer 0 3 (3) 0 0

Odonata Winter 151 (20) 51 (12) 17 (7) 0Spring 44 (14) 45 (12) 12(11) 0Summer 28 (12) 39 (17) 0 0

14

Table 6. Results of two-way analyses of variance for changes in densities(number/m2) of total invertebrates and several major taxa from Pond B.Main effects of depth zone and season, interactions, and simple effects ofdifferent zones within one season and of one zone across seasons areconsidered. Significance levels are indicated for p < 0.05 as ", p < 0.01 as**, and not significant (p > 0.05) asns.

TAXA OF BENTHIC INVERTEBRATES

SOURCE OF Total Amphi- CeratfJ- Chaoborus ChironomidaeVARIATION poda pogomdae

Main effects:

Depth zone ** ** ns ** **Season ** ** ** ** **

Interaction:

Zone by season ** ** ns ns *

Simple effects:

Change in number byzone within season :

Winter ns ** ns ** nsSpring ** ns ns ** **

Summer ** * ns ** **

Change in number byseason within

a zone:

Zone 0.5-1.5 m ** ** ** ns **Zone 2.0-3.0 m ** * ** ** **Zone 3.5-5.5 m ** ns ** ** **Zone> 6.0 m ** ns **ns ns

15

SUMMER

± I SE

SPRING

2 3 4

WINTER

o

N~ 5000

!13~

~4oo0IIIUl~

0:Ul

~ 3000o0:

~:E

2000II.a

>- jlJIIIIIII 11!::~ 1000

DEPTH ZONE

Figure 2. Changes in density of all benthic macroinvertebrates in Pond B during1984. Depth zones are 1: 0.5-1.5 m, 2: 2.0-3.0 m, 3: 3.5-5.5 m, and4: > 6.0 m.

16

Densities of total invertebrates showed significant differences due to the

combined effects of season and water depth (Table 6). When the data were

analyzed for simple effects, the densities were not significantly different among

zones in winter and the densities in the deepest zone did not change significantly

with season. However, densities decreased in the other zones w ith season and

differences in densities occurred among zones in spring and summer.

Among the insects, the dipterans were most abundant in all seasons, followed

by: (1) the Trichoptera (caddisflies), represented by Polycentropus and Oecetis, (2)

the Odonata (damsel- and dragonfl ies), primarily Enallagma and Celithemis,

respectively, and (3) the Coleoptera (beetles), primarily Celina. The decrease in

abundance with depth was obvious within these groups (Tables 2-5). From winter

to summer, trichopterans and odonates showed major declines in population

numbers; however, beetles appeared to maintain more stable population numbers

across seasons. Other major invertebrate groups (Annelida, Gastropoda, and

Amphipoda) followed patterns of population change similar to those of insects

other than dipterans. Snailswere the only molluscs found . Britton and Fuller (1979)

recorded Anodonta asthe only clam occurring in Pond B.

Not only did densities of individuals in a taxa usually decl ine by season and

with depth, but the number of taxa represented in the sampling declined (Table 7).

Because the winter collection had two samples taken at each station (104 samples),

the number of taxa in each set of 52 samples is shown separately. Combin ing

sample sets increased the taxa represented by 0-3 taxa per depth because the

doubled sample effort only slightly increased the probability of encountering very

rare species.

Diversity declined with depth in all seasons, but spring and summ er diversities

exceeded that of winter in the shallower zones (Fig. 3). The greatest changes in

diversity with depth occurred in summer, when only dipterans were found in the

17

Table 7. Numbers of taxa of benthic macroinvertebrates identified in each depthzone in Pond B. Two numbers in winter indicate numbers of taxa fromeach of two drops of the dredge.

DEPTH (m)SEASON 0.5-1.5 2.0-3.0 3.5-5.5 >6.0

Winter 33,26 17,20 11, 13 4,5

Spring 24 17 9 4

Summer 21 14 3 2

deepest zones. Therefore, although both numbers of individuals and taxa were

higher in winter, by spring and summer there was a more even distribution of

ind ividuals among those taxa, especially in the shallower zones.

The mean estimate of mass per individual animal for each taxa (Table 8) was

multiplied by the appropriate density estimates (Tables 2, 3 and 4) and the results

summed across taxa by season and depth to obta in estimates of biomass per unit

area (Fig. 4). In winter and summer, biomass declined by over 40 % from the

shallowest to the deepest water. Within a zone, biomass decl ined approximately

75% from winter through summer. Biomass estimates in the shallow zones were

similar in spring and summer; however, biomass increased in the deepest zone in

spring. Although total density increased somewhat in the deeper water (Fig. 2), the

animals causing th is increase were very small (Chaoborus and chironomids; Table 8)

and thus did not greatly increase biomass in deep water (Fig . 4).

Although some groups of animals were relatively abundant (e.g. trichopterans

and amphipods; Table 5), their contribution to the biomass at any particular time

was very small (Fig. 5). Two groups of animals, snails and odonates, had small

18

2.0

1.8.... 1.8...c

~ ~4..c..!i 1.2

Ic0c 1.0ca.c:I/)

.8-)-

t: .6I/)a::w

A>is

.2

0234

WINTER234

SPRING

DEPTH ZONE

234SUMMER

Figure 3. Changes in macroinvertebrate d iversity among seasons (1984) andwater depths in Pond B. Depth zones are 1: 0.5-1.5 rn, 2 : 2.0-3.0 m,3: 3.5-5.5 m, and 4: > 6.0 m.

19

Table 8. Estimates of dry mass (mg/individual) by taxa of benthicinvertebrates from Pond B. "T" Indicates traceamounts, but not enough mass or individuals to obtainestimates of weight.

TAXONOMICCLASSIFICATION

TurbellariaOfigochaetaHirudineaHelisoma ancepsHelisoma trivolvisMenetusPhysella heterostrophaAmphipodaHydracarinaCeratopogonidaeChaoborusChironomidaeChrysopsCurculionidaeCelinaHydroporus-HygotuslIybiusBerosusDonaciaHaliplusPolycentropusOecetisOxyeth iraOrthrichiaAgrypniaEoparargyractisParapoynxParaleptophlebiaCaenisLestesArgiaEnal/agmaIschnuraEpicorduliaTetragoneuriaCelithemisErythemisPerithemisPachidiplaxLadona

WINTER0.270.611.658.03

31.601.552.060.090.200.220.070.234.670.210.100.33

17.45.67

7.76T

0.160.26

To

12.350.370.700.780.091.203.051.19o

11.107.771.59

19.801.50.93o

20

SPRINGo

0.691.386.022.00o

2.680.09o

0.170.120.301.630.230.17ooT

0.50o

0.190.11

TToTooT

3.60o

1.083.10oo

3.00oo

1.70o

SUMMERo

0.35T

5.2519.50

o1.780.07oT

0.080.10

35 .330.480.19ooo

0.10oTTTTooToT

0 .40o

0.58ooo

0.23T

0.601.401.80

2.0

1.8

1.6

~

N 1.4E<,0 1.2>..."0 1.0-(J)(J) .8<l:~0 .6Ul

.4

.2

02 3 4

WINTER234

SPRING

DEPTH ZONE

2 3 4

SUMMER

Figure 4. Estimate of biomass of ben thic macroinvertebrates per unit area inPond B. Depth zones are 1: 0.5-1.5 rn, 2: 2.0-3.0 m, 3: 3.5-5.5 rn, and4 : > 6.0m.

21

WINTER

Cl'llronomldo•

e e.c1.0-10

SUMMER

'1.0

Otl'llf Dipt.,o

O.S.Ul

2.0->.0 5,S·D.II

DEPTH ZONE 1m)

100

.0

eo

<0

20

0'''0

Ctlironom ldll.

..!lIOO...

~OOIii

110.,.,..,.~40..0...z'" 20u

'"'t0

0.5-1.15

SPRING

DEPTH ZONE (m) OEPTH ZONE (m)

Figure 5. Changes in relative composit ions of macroinvertebrate biomass duringdifferent seasonsand at different depths in Pond B.

22

populations, but comprised 30-60% of the biomass (per unit area) in all but the

deepest zone . The snails showed proportionally high biomass becauseboth the soft

body tissue and the external shell were used to estimate mass. Odonates, especially

dragonfly larvae, while perhaps not as heavy as beetle or larger caddisfly larvae

(Table 8), were much more abundant. At the deeper stat ions, Chaoborus and

chironomids dominated in both numbers and biomass. The 40-60% of biomass

shown as "other dipterans" in summer (Fig. 5) was due exclusively to the presence

of several large deerfly (Chrysops) larvae. Although Chrysops had been present in

greater numbers in winter and spring (Tables 2 and 3), its mass increased by a factor

of7 in summer.

Biomass estimates per unit area were combined by area of the lake within

individual depth contours. These values were then weighted by the proportion of

the lake comprised by that contour and summed to estimate total biomass for the

entire lake (Table 9). For the lake as a whole, the littoral zone had the greatest

biomass, followed by the profundal zone. The sublittoral usually showed declines in

density and biomass of most major invertebrate groups that were common in

shallow water (Table 5), but did not show the increases in density and biomass of

dipterans that characterized the greatest depths. Biomass declined from winter

through summer over the entire lake .

DISCUSSION

Deta iled studies on communit ies of benthic macroinvertebrates are

uncommon in lentic ecosystems, but compared to the few studies conducted in

various locations of the United States, Pond B is fairly typical in terms of animal

density, biomass,spatial distributions, and representative taxa .

23

Table 9. Biomassestimates of benthic macroinvertebrates from Pond B. Theareas between zones were included in the biomass estimates.

DEPTH AREA INVERTEBRATE BIOMASS(DRY KG)ZONE (m) (ha) WINTER SPRING SUMMER

Littoral 0-2.0 26 458 120 104

Littoral 2.0-3.5 15 192 72 50

Sublittoral 3.5-6.0 19 116 74 17

Profundal > 6.0 27 184 197 46

TOTAL 87 950 463 217

Seasonal Changes in Population Densities

Documentation of complete seasonal cycles of benthic macroinvertebrate

populations is rare. Of the few comprehensive studies done on the composition and

abundance of invertebrates, most have been carried out on a single lake and only

during spring and summer (Mittelbach 1981, Gerk ing 1962, Ferraris and W ilhm

1977), although the most extensive study (Deevey 1941) was conducted on 36 lakes

over a period of three years. However, even in that study, only one lake (Linsley

Pond) was sampled monthly for 14 months, and sampling was only done in the

sublittoral and profundal zones. Deevey states that, "In all lak es which have been

carefully studied, maximum populations have been observed in the winter, ...

minimum in the spring or early summer." Invertebrates of Linsley Pond generally

followed th is pattern. Mittelbach (1981) and Ferraris and Wilhm (1977) found both

declining numbers and biomass from spring through August. In an Ok lahoma

reservoir with similar depths and Iimnological characteristics of Pond B, Ferraris and

24

Wilhm (1977) estimated population ranges of 144-16,639 organismslm2 in March

and 114-4686 organisms/m2 in July and August. Over a two-year period in a shallow

pond in Minnesota, Dineen (1953) found densities of benthic invertebrates to be

300-500 organismslm2 in spring to 800-4200 organismslm2 in fall and winter. In

South Carolina at Par Pond on the Savannah River Plant, Thorp and Bergey (1981)

found seasonal population densities of 14,000 organismslm2 in December, 6000

organismslm2 in April, and increasing to 12,000 organisms/m2 again in August.

Macroinvertebrate densities of Pond B declined dramatically by season and

were well within these published ranges with winter densities of 3000 to 4500

organisms/m2, spring densities of 900-3000 organisms/m2 and summer densities of

400-2300 organismslm2. Similar values for Pond B have been recent ly reported by

Kondratieff (1985) . These numbers are considerably lower than estimates of

benthic invertebrates in Par Pond (Thorp and Bergey 1981). That study, however,

was only conducted at depths less than one meter and included much smaller

organisms than are usually included in other such studies.

The decline in numbers by season is commonly attributed to the emergence of

overwintering larvae of aquatic insects (M ittelbach 1981, Deevey 1941) . Many

aquatic insects have a one-year life cycle and overwinter as larvae, and then emerge

as adults in spring and/or summer. Adults then become reproductively active, lay

eggs, and the larvae emerge. The tiny larvae may start appearing in mid- to late

summer and fall, but they may be difficult to find when sampling. As the larvae

grow, larger ones are likely to be sampled. thus fall and winter densities increase.

Another factor in seasonal sampling is the change in water temperature and

chemistry (Jonasson 1978). Most southern lakes achieve a very distinct thermal

stratification during the summer. This results in little mixing between the shallow

warm water and the deeper cooler water. Oxygen depletion usually occurs at the

deeper depths and water at those depths may become hypoxic. Some organisms

25

will not be able to survive such low oxygen levels or chemical changes and thus will

migrate or die (Deevey 1941). After an artificial thermal and chemical

destratification was conducted in summer on an Oklahoma reservoir, densities and

diversities of invertebrates actually increased in the deep water (Ferraris and Wilhm

1977). Pond Bhas been shown to stratify thermally and exhibit oxygen depletion at

deeper depths (Evan et al. 1983).

Gerking (1962) attributed a decline in bottom invertebrates from July to

August to predation by fish . Bluegills in this Ind iana pond were considered to be

highly efficient at cropping invertebrates, and seasonal changes in bluegill

population dynamics and foraging behavior heavily impacted the bottom fauna.

Mittelbach (1981) offered some support for this hypothesis with studies on prey size

and seasonal util ization by blueg ills in a Michigan pond. However, Thorp and

Bergey (1981) did not find appreciable differences in invertebrate populations

between control sites and experimental sites from which fish and turtles were

excluded.

Other factors that could influence benth ic population sampling are changes in

aquatic plant biomass and structure. Increased plant abundance in summer may

decrease the substrate collection efficiency and also prov ide protection for

escaping, mobile invertebrates, thus lowering apparent densities.

Population Variations with Water Depth

In his description of the vertical distribution of organisms along depth

gradients, Deevey (1941) described a "sublittoral minimum" condition in which the

number of organisms was least in the middepth zones (sublittoral) and greatest in

the shallow (littoral) and deeper water (profundal) zones. Deevey suggested that

the sublittoral minimum may be caused in part by predation by fish because (a) the

vegetation in the littoral provided invertebrates with protection from fish and (b)

26

the oxygen depletion and depth of the profundal excluded fish . Therefore, the

heaviest predation occurred in the sublittoral, severely reducing the invertebrates.

Gerking (1962) also found the greatest numbers of animals at the 0-2 m and> 6 m

depths, and fewer animals in the 2-4 m and 4-6 m depths. He felt this was a

"sublittoral minimum" and described it as a zone in which the habitat provided by

the flocculent plants was not as favorable asthat of the littoral or profundal zones,

and thus was not capable of supporting dense populations. Ferraris and Wilhm

(1977) observed that 3-5 m depths were less densely populated than either the

littoral and profunda!. For a Danish lake, Jonasson (1978) reported a decrease in

invertebrate densities in the transition zone between littoral and sublittoral, and

then an increase in densities from the sublittoral to the profunda!.

In Pond B,the minimum number of animals was at a middepth zone, and then

increased again at the deepest stations. In winter, the minimum was at the 3.5-5.5

m depth, and in spring and summer at the 2.0-3.0 m depth . Analyses of variance

indicated that, unlike spring and summer densities, winter densities did not differ

across zones. The greatest densities were clearly in the profundal zone, but it was

not clear whether or not the littoral was more productive than any sublittoral zone

in Pond B. Gerking (1962) similarly failed to find statistically significant differences

in populations by depth (almost identical depths used in Pond B), but he believed

that "the similarity in the quantities of bottom fauna in the littoral and profundal

zones masked the effect of the sublittoral in the analysis of variance" and that real

differences did occur among the four depth zones. This might also be true of the

winter densities in Pond B.

Pond Bshowed depth-faunal relationsh ips typical of similar lakes. However, as

observed by Thorp and Diggins (1982), this is not a simple inverse relationship

between density and depth. There are some differences in behavior among taxa.

27

In general, changes in macroinvertebrate densities in Pond B with depth could

be attributed to the declining numbers of individuals, and the eventual elimination,

of most taxa with depth. New taxa (at least at the resolution level used in this

study) did not appear at depth; rathe r populations there were extensions of

populations occurring in shallower zones. Only a few taxa are adapted to live in the

profundal zone, but those animals that can seem to flourish . At about 6 m,

Chaoborus increased dramatically, thereby increasing total density. Chaoborus was

the only group of organ isms that significantly increased by depth in each season

studied. This increase of Chaoborus, and usually only Chaoborus, in deep water has

been observed in several other locations (Ferraris and Wilhm 1977, Deevey 1941,

Thorp and Diggins 1982).

An earlier study (Thorp and Diggins 1982) conducted on Par Pond, SRP, during

the winter and spring and at similar depths, found very similar trends at their

control sites for the major taxonomic groups. The dominant odonates (Celithemis

and Enallagma) in Par Pond were also those of Pond B and all odonates had greater

densities at depths <2 m. Dens ities of the Ceratopogonidae were evenly

d istributed across depth, aswas also observed in Pond B.

Of the macroinvertebrates, the Chironomidae were usually numerically

dominant at all depths sampled in Pond B and also in lakes at other geographic

locations, such as Oklahoma (Ferraris and Wilhm 1977), New York and Connecticut

(Deevey 1941), and South Carolina (Thorp and Bergey 1981, Thorp and Diggins

1982). The Chironomidae exhibited uniform population densities in winter across

depths, but in spring and summer generally increased with depth. Because of the

different generation times of the chironomids, even population data taken at

monthly intervals could show widely fluctuating patterns of densities with depth

(Deevey 1941); therefore, to accurately describe the chironomid populations of

Pond B, more frequent sampling would be necessarythan was possible in this study.

28

Biomass and Diversity

Productivity (mass per area over time) is an important parameter for under­

standing trophic relationsh ips and consumer dynamics of a lake (Gerking 1962,

Jonasson 1978). However, because secondary productivity is difficult to measure,

many studies have relied on the more easily measured parameter of standing crop

(biomass, or mass/area) as being indicative of productivity levels. Biomass

comparisons among lakes can thus be made even with single season samples,

although very productive lakes with high turnover rates could exhibit standing

crops similar to those of less productive lakes. Biomass estimates of benthic inverte­

brates of Pond B, averaged over the entire area, ranged from 2.5 kg dry wtlha in

summer to 10.3 kg dry wtIha in winter. Since the samples were preserved in alcohol

before drying and weigh ing, there may have been some loss in mass due to the

preservative (Howmiller 1972, Stanford 1973, Down ing 1984). However, most other

studies also share this problem. Gerking (1962) found an average of 11 kg dry wtlha

in July and 6 kg dry wtlha in August for a lake in Indiana. This lake was only 3 ha

and fairly shallow, and would be expected to be more productive on the average

than Pond B. For 36 lakes, Deevey (1941) reported summer values of 11 to 348

kg/ha, wet weight. Assuming water contents of 80-90 %, these values are probably

5-10 times higher than the equivalent dry weight. Mittelbach (1981) summarized

biomass estimates for vegetated littoral zones from several studies as 4-36 kg dry

wtIha and reported his own estimates as rang ing from 15 kg dry wtIha in May to 8

kg dry wtlha in August. The littoral area of Pond B ranged from 4 kg dry wtlha in

summer to 15 kg dry wtIha in winter. In a similar study on Pond B and Par Pond,

Kondratieff (1985) reported seasonal mean bio mass of 5 kg/ha and 34.9 kg/ha,

respectively, averaged over all depths.

29

As with some other lakes (M ittelbach 1981, Ferraris and Wilhm 1977), Pond B

generally showed decreasing biomass with increasing depth (Fig . 4). Even though

invertebrate density was greater in the deepest waters, it was comprised of very

small organisms which did not contribute greatly to the biomass. However, when

the area of the lake in each zone was considered, the profundal contained more

biomass than the sublittoral (Table 9). A different pattern of biomass with depth

has been shown with Jonassen's (1978) work on a Danish lake in which biomass

increased with depth from 0-10 m, then decreased at depths >10 m.

Diversity (Shannon-Wiener Index) is a combined measure of the number of

species or taxa and their relative contributions to the total number of individuals.

Communities comprised of many species but with only one or two species

representing the vast majority of ind ividuals are not very diverse. However, a more

diverse community has many specieswith a good representation of individuals from

many taxa (higher "evenness" ). Since the diversity index is a relative measure,

patterns can be compared across communities, with respect to t ime (season) and

space (depth). Ferraris and Wilhm (1977) found decreasing diversity with depth

over the range of 1-8 m in late summer which they attributed to a decrease in the

number of species and an increase in Chaoborus. Similarly, in Pond B, diversity

declined w ith depth for all seasons (Fig. 3) (also, Kondratieff 1985), because an

increasingly larger proportion of the individuals were from only one or two taxa .

Chaoborus increased w ith depth as did chironomids, except in winter, but most

other taxa d isappeared at depths. However, in the shallow water «3.0 m)

diversity generally increased from winter through summer. Although density

decreased in these contours through time (Fig. 2), the proportion of individuals per

taxa became more balanced (Tables 1,2,3) because the Chironomidae showed such

marked declines from w inter through summer. Hence diversity increased.

30

Related to diversity, but not accounting for abundance in any way, was the

number of taxa represented in an area. This could be a simple and straightforward

measure of change in a system. Pond B clearly showed fewer different kinds of

animals in progressively deeper water and from winter through summer. Similar

trends were found in an Oklahoma reservoir (Ferraris and Wilhm 1977), and in a

Danish lake (Jonasson 1978) in which 300 specieswere identified in the littoral zone,

50 species in the sublittoral, and less than 20 in the profunda!.

Limitations of the Data

This study provides baseline information on the structure and distribution of

benthic invertebrates in Pond B. However, these data were taken at three-month

intervals, and some changes in community structure could have been overlooked.

The estimates of density and biomass are point estimates in time and the decline

between winter and summer may not have been linear; rather, maxima and minima

may have occurred between sampling periods. However, because processing

benthic samples is so labor intensive, increasing the number of sampling periods to

detect such changes would have been prohibitive. If the goal of the study had been

only to identify which animals were present and how their populations changed

through time, all the sampling could have been concentrated in the most

productive shallow waters. More experimental w;ork could also have allowed

production estimates to be made. These estimates would be important for nutrient,

chemical, or radionuclide cycling studies, and for trophic level and food base

considerations, as large year-to-year variations may occur in benthic populations.

There were a number of sources of potential error and variability in the

estimates of the parameters presented in this paper. In addition to the statistical

error that is inherent in all sampling schemes, there was also error (or bias)

associated with the sampling device, animals' avoidance behavior and spatial

31

distributions, the handsorting of the animals, the estimates of dry mass per

individual (single samples, composite samples), the measurement of the surface

area of the lake, the measurement of the contours of the lake, and potential loss of

mass during preservation in alcohol. There was no way to accurately estimate the

magnitude of these errors ; however, most of these sources of error would be

expected to remain relatively constant across sampling depths and dates.

Therefore, comparisons could still be made across sample groups while observing

trends in the data. It was these trends in the data that were most important to this

study. Comparisons to other studies should also be made with some caution ,

because sampling and sorting methods used among investigators, and physical and

limnological properties of the lakes, may vary.

SUMMARY

Pond B, an 87-ha, 20-yr postthermal reactor cooling impoundment on the

Savannah River Plant , South Carolina, was sampled during three seasons (winter,

spring, and summer, 1984) to measure temporal and spatial variations in density,

biomass, and divers ity of benthic macroinvertebrates. The benthos at 52 stations,

representing four depth zones, were sampled using a Ponar grab. Some 100400

ind ividual organisms were hand-sorted and ident ified to forty taxa, and the mean

dry mass pe r ind ividual was est imated.

The densities of invertebrates generally declined from winter through summer

within each depth zone. In each season, the greatest total densities occurred in the

deepest zone due to the large number of Chaoborus. Standing crop of dry biomass

also decreased from winter through summer. Biomass generally declined with

depth in winter and summer, but not in spring. Major contributions to the total

biomass were shared by many taxa at depths less than 3 m, but the biomass in

sublittoral and profundal was dominated by Chironomidae and Chaoborus.

32

Diversities (Shannon-Wiener Index) decreased markedly with depth in all seasons.

Statistical tests examining differences in the measured parameters among seasons,

sampling depth and their interactions are reported.

These data serve as a measure of the current status of macroinvertebrate

populations in Pond B and as a baseline against which future changes may be

compared as the process of postthermal recovery continues. These data are

probably reasonably representative of other postthermal, softwater reservoirs in

the southeastern region of the United States. The biomass values and trends with

season and depth were, in fact, similar to comparable information from most other

lentic systems reported in the literature. These data from Pond B may also be used

to construct radionuclide inventory estimates for the benthic macroinvertebrate

component of the Pond B ecosystem. Pond B vertebrates such asfish and waterfowl

may depend upon these benthic invertebrates as a food base. Thus, this

information should be useful in the interpretation of ecological and radioecological

studies and in the construction of general energy-flow and radiocontaminant

cycling models for this lake ecosystem.

ACKNOWLEDGMENTS

I would like to thank the people at the Savannah River Ecology Laboratory

who especially encouraged and supported this project: I. Lehr Brisbin, John

Bowling, and John Pinder. Helpful and enthusiastic field and laboratory assistance

were given by Donna Mayer, Yvonne Downs, and Eric Peters. Boris Kondratieff

kindly helped identify the odonate larvae. Jan Hinton typed the final report. A

special and warm thanks go to Barbara Taylor and Ward Whicker. I deeply

appreciate the support that was given to me by James K. Detling during the final

stages of this project.

33

This Pond B project was supported by the Savannah River Ecology Laboratory's

National Environmental Research Park Program, under a contract (DE-AC09­

76SROO-819) between the Institute of Ecology of the University of Georgia and the

United States Department of Energy.

34

LITERATURE CITED

Bennett, D. H. and R. W. McFarlane. 1983. The Fishesof the Savannah River Plant:

National Environmental Research Park. Publication (SRO-NERP-12) of the

Savannah River National Environmental Research Park. Aiken, South Carolina.

Brigham, A. R., W. U. Brigham, and A. Gnilka, eds. 1982. Aquatic Insects and

Oligochaetes of North and South Carolina. Midwest Aquatic Enterprises.

Mahomet,lIIinois.

Britton, J. C. and S. L. H. Fuller. 1979. The Freshwater Bivalve Mollusca (Unionidae,

Sphaeriidae, Corbicul idae) of the Savannah River Plant, South Carolina.

Publication (SRO-NERP-3) of the Savannah River National Enviro nment al

Research Park. Aiken, South Carolina.

Cuff, W. and N. Coleman. 1979. Optimal survey design: lessons from a stratified

random sample of macrobenthos. 1.Fish. Res. Board Can. 36:351-361.

Cummins, K. W. 1962. An evaluation of some techniques for the collection and

analysis of benthic samples with special emphasis on lotic waters. Am. MidI.

Nat. 67:477-504.

Deevey, E. S. 1941. Limnological studies in Connecticut VI. The quantity and

composition of the bottom fauna of thirty-six Connecticut and New York

lakes. Ecol. Monogr. 11:413-455.

Dineen, C. F. 1953. An ecolog ical study of a Minnesota pond. Am . MidI. Nat.

50:349-376.

Downing, 1. A. 1984. Sampling the benthos of standing waters. !D.: A Manual on

Methods of the Assessment of Secondary Productivity in Freshwaters, 1. A.

Downing and F. H. Rigler, eds. Blackwell Scientific Publications, Oxford.

Evans, D. W., 1. J. Alberts, and R. A. Clark. 1983. Reversible ion-exchange f ixation of

cesium-137 leading to mobilization from reservoir sediments. Geochim.

Cosmochim. Acta 47 :1041-1049.

35

Ferraris, C and J. Wilhm. 1977. Distribution of benthic macroinvertebrates in an

artificially destratified reservoir. Hydrobiologia 54: 169-176.

Flannagan, J. F. 1970. Efficiencies of various grabs and corers in sampling

freshwater benthos. J.Fish. Res. Board Can. 27: 1691-1700.

Gerking, 5. D. 1962. Production and food utilization in a population of bluegill

sunfish. Ecol. Monogr. 32:31-78.

Howmiller, R. P. 1971. A comparison of the effectiveness of Ekman and Ponar

grabs. Trans. Am. Fish. Soc. 100:560-564.

Howmiller, R. P. 1972. Effects of preservation on weights of some common

macrobenthic invertebrates. Trans. Am. Fish. Soc. 101:743-746.

Hull, C H. and N. H. Nie. 1981. SPSS Update 7-9. McGraw-HilI. New York.

Jonasson, P. M. 1978. Zoobenthos of lakes . Internationale Vereinigung fOr

Theoretische und Angewandte Limnologie 20: 13-37.

Kondratieff, B. C, M. J. Chimney, and W . B. Painter. 1985. Final report on the

macroinvertebrates of Par Pond and Pond B: January 1984-June 1985 ECS-SR­

21. Prepared by Environmental & Chemical Sciences, Inc. for E. I. du Pont de

Nemours &Co. Aiken, South Carolina.

Krebs, J. 1978. Ecology, the Experimental Analysis of Distribution and Abundance.

Harper and Row, New York.

Mittelbach, G. G. 1981. Patterns of invertebrate size and abundance in aquatic

habitats. Can. J. Fish. Aquatic Sci. 38:896-904.

Parker, E. D., M. F. Hirshfield, and J. W . Gibbons. 1973. Ecological comparisons of

thermally affected aquatic environments. J.Water Poll. Cont. Fed. 45:726-733.

Pennak, R. W. 1978. Freshwater Invertebrates of the United States, 2nd ed. Wiley

and Sons. New York.

Resh, V. H. 1979. Sampling variability and life history features: basicconsiderations

in the design of aquatic insect studies. J.Fish. Res. Board Can. 36:290-311.

36

Resh, V. H. and J. D. Unzicker. 1975. Water quality monitoring and aquatic

organisms: the importance of species identifications. J. Water Poll. Cont. Fed.

47:9-19.

Stanford, J. A. 1973. A centrifuge method for determining live weights of aquatic

insect larvae, with a note on weight loss in preservative. Ecology 54:449-451.

Thorp, J. H. and E. A. Bergey. 1981. Field experiments on responsesof a freshwater,

benthic macroinvertebrate community to vertebrate predators. Ecology

62:365-375.

Thorp, J. H. and M. R. Diggins. 1982. Factors affecting depth distribution of

dragonflies and other benthic insects in a thermally destabilized reservoir.

Hydrobiologia 87:33-44.

Usinger, R. L. 1956. Aquatic Insects of California . University of California Press.

Berkeley, California.

Washington, H. G. 1984. Diversity, biotic and similarity indices: a review with

special relevance to aquatic ecosystems. Water Res. 18:653-694.

Weber, C. I. (ed.). 1973. Biological field laboratory methods for measuring the

quality of surface waters and effluents. EPA-6701/4-73-001. U.' S.

Environmental Protection Agency. Cincinnati, Ohio.

Wood, D. H. 1982, The Aquatic Snails (Gastropoda) of the Savannah River Plant,

Aiken, South Carolina. Publication (SRO-NERP-10) of the Savannah River

National Environmental Research Park. Aiken, South Carolina.

37