Mercury Concentration in Fish as a Function of Change in Reservoir Size

Mercury Concentrationin Fishas a Functionof

Changein ReservoirSize

ThomasWayneTherriault

A thesis submitted tothe SchoolofGraduateStudies in partial fulfilment of the requirementsfor the

degree of Masterof Science (Biology)

Department of Biology Memorial Universityof Newfoundland

51. John's,Newfoundland

1996

.+.

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ABSlRACT

Increased fish mercuryconcentrationsare often observedfollowing impoundment of a reservoir.Followingimpoundment, there is a fluxof organic matter and nutrients from theflooded soil,providing foodto bacterial communitieswhich methylate inorganic mercury. Based on the hypothesisthat mercury enters a reservoirvia theflooded soil, I investigatedwhether the changein fish mercury concentrations couldbe predictedfrom the change inreservoir size. Mercurymonitoring data for three fish species,northern pike(&ox (ucius),walleye(Slizostedionvitreum),andlake whitefish(Coregonus clupeqfonnis)from reservoirsin northernManitoba and northern Quebec wereused to derive parameterestimatesfor four models. Models were evaluated ontheirability to predictcasesnot used in(he modeldevelopment. Models wereappliedfor predictive purposes to assess the impact of creating a reservoir and to assess the impact of altering the sizeofanexisting reservoir.Skill(closenessof predicted and observedvalues) and explainedvariance were alsousedto assess themodels. The preferred models consisted of a singleenrichment term (a measure of changeinflooded area)that successfully predictedthe mercury ratio.This study alsodemonstratedthat parameterestimates for onespeciescould be appliedsuccessfully 10predict themercury ratio for species with comparable food habits.

ACKNOWLEDGEMENTS

To DavidSchneider,my supervisor,noneofthis wouldhavebeenpossible without his guidance .Iwouldalso like to thank himforfinanc ialsupportthat allowed me10 attendthe ASLOIPSAJointMretinginMiami,FloridaandtheConferenceon Mercury as a GlobalPollutantinWhistler .British Columbia.These conferenceswert a valuable learningexperience.

My committeememb ers, Chris ParrishandRoyKucec hel,whoseinsight aided inthepreparation of thisthesis.

Datausedforthedevelopme nt and evaluation of themodelsin this studywere released,and providedby , a numberof people. DavidWindsor of ManitobaHydro agreed to release data collectedfrom Manitobareservoirs . Drew Badalyfrom the Department ofFisheriesand Oceans, CentralRegion,kindlypro videddataforreservoirs impounded aspartoftheSouthern Indian LUe'ChurchillRiver Diversio nProject in northern Manitoba .TomJohnston, alsofro m FisheriesandOceans,providedthefish mercurydatafrom controllakes thatwere usedtodetermineprcimpoundmcnt fish mercuryconcentrationsfor theManitoba reservoirs. Don Steelfrom North/South ConsultantsInc.also provided datafor otherManitobareservoirs. Claude Langloisfrom HydroQuebecagreedtoreleasefishmercurydata collected in conjunction with monitori ngeffortsintheLaGrandeComplexin northern Quebec.Julie Sbegen pro vided backgro undinformationwhile FrancoisDoyon ofGroupe EnvironnementShoonerinc.

iii

providedthe raw data forLaGrandeComplex reservoirsin additionto fish mercurydata collectedfromcontrol lakes in and aroundtheLa Grande Complex.Thesefish mercury concentrationswere used to determinepreimpoundmentmercuryconcentrations forLa GrandeComplex reservoirs.Datausedforthe Newfoundlandpredictionswereprovided byEdHillandLarryLeDrew fromNewfoundlandand Labrador Hydro and Dave Scrutonfrom the DepartmentofFisheries and OCeans, NewfoundlandRegion.Dueto timcconstraints govcrning the submission of this thesis,fish mercury datacollectedfor reservoirs impounded in BritishColumbia,providedby Tom Watson of Triton Environmental Group (formerlywith B.C. Hydro)was notused. However,Iwould like tothank him forhistimeandefforts.

To all NICOSians,both past and present,who madework bearable, ifnot enjoyable,for thetwo years necessary to completethisthesis.Aspecialthanksto Lynn Busseywho aided inthe preparationof the appendixandthethree W.I.S.E.students, Hilary Baikie,TaraMartin,and Shanna O'Reilly,who assistedin the preparation of mapspresentedinthis thesis.

ToJen, who providedme with continualsupport andencouragement.

iv

TABLE OFCONTENTS

Abstract .•• • ••.... .. .. . . ... . •.••. • • • • • • . . • • • .••• ..••.ii

eckncwtedgemenu•••••••• • •••• •••• • ••••• • •••• •• •• ••. . .• iii

Table ofContents••••.• .•• .• • •.••.•... • .•.• • • •. ..•• •.• •..v

Listof Tables .• •..• ••.•• .•..••.• ... ... ••...•. . . . .viii

ListofFigures . . . . .• • . . . ...•,•.. . . ,

1.0Introduction

2.0Background

tx

2.1 Po.fercuryChemistry ••.•.• . ••• • • • . •....• • •••.• • •• 2 2.2 Toxicology..••• • • •. .• • ••.••. • ••.. .••• ••.• .•• 3 2.3 Remediation .••.•... .. . .•••••• •.•. ....•... 6 2.4 BiogeochemisU'y ••••••.••••.•.•.••• •.•.•.• .• . . 8 2.5 Methylation ••• • . •.• • • • •• • ••.••••• .. ..•. .•. . . 10 2.6 BioaceumulationandBiomagnification •••••.••... 12 2.7 AutogenicMercury Loading .•..•.•.• • •.• • •.•. ... 18

3.0 Effectsof ReservoirImpoundment •.•.• .. . .•.• • ••.. •.. •...•21

4.0 ModelDevelopment •.• • .•• •. .•....• • •.•....••... ..• 34 4.1 ModelEvaluation .• .. .. •• . • ••.. . • . .. . •. •.. ... 39

5.0MethodsandMaterials

5.1 Locationof ReservoirsUsed in thisStudy••.. . . ... .•.... 41

5.1.1 SouthernIndian Lake/ChurchillRiverDiversionProject•• NorthernManitoba ... .... . •.•...• • • • . •. • 43

5.1.2 LaGrande Complex•• NorthernQuebec .••. . ...• 49

5.1.3 Newfoundland •..•.•. . ..•..••. ..• • . . . .... 53

5.1.4 Summary .... . . ...•. • ..•... ... .. ...56

5.2 MercuryData Usedin theAnalyses ..•.• . .... ... •. . • • 57

5.3 ModelValidation ... ..•• . ....•.•... ••. . • •59

5.3.1 DefinitionoftheResponseVaribale.•..• . . . . .... . 59

5.3.2 ValidationProcedure .• ... .. •.•...••..•• 60

5.4 Applicationof theModels.- Newfoundland Predictions ...• 61

5.4.1 DifferentSpecies_. CalArmSalmonids ...•...•... 61

5.4.2 DifferentReservoirs ••TheLong PondPrediction . 63 6.0Available DataonFish MercuryConcentrations ...•.• .. ....• . 65

6.1 Manitoba ... ... . • • •. ... .• •.• . . •.• •. .. •... ... 65

6.2 Quebec ... ... .•.. . . . ...•... . .. . ...67

6.3 Newfoundland .. •.... .. •.• ..• •.• ...•• •.. ••• •.• 69

7.0Results 7.1 TheModels ...•... . . .•. . • . .•.... . . ...87

7.1.1 Model I (Equation12) ...•.•... •.•...•87

7.1.2 ModelH(Equation13)•••.••.•.• ••...••.. .• . 90

7.2 EquationswithParameterEstimates••ModelIandII (Equations12 and l3) ... ..• •. •• ..• •• ••.•... • ••••93

7.3 NewfoundlandPredictions .•.•..• •.•• •..•• •. ..••.. 98

7.3.1 DifferentSpecies- Cat Arm Salmonids •.. •... 98

7.3.2 Different Reservoirs••TheLongPond Prediction .•••. 99 7.4 RevisionofModel I and II .••.• •. .•. •.. . •••.• • ... 100

7.5 The RevisedModels •••.. .. . .... ••.•..•.•.•.••. 101

7.5.1 ModellU (Equation50) .••.•..•.•.• •. • .•.•. 101 7.5.2 Model IV(Equation51) .•.. •...• •. .• . • • • . . . 104

7.6 EquationswithParameterEstimatesc-ModelIIIand IV (Equations50 and 51)•••.•••..•..•.•••••.•.•..• 107 7.7 Newfoundland PredictionsUsingModelIII andIV 113

vi

7.7. 1 DifferentSpecies--CalArm Salmonids ..• ... 113

7.7.2 DifferentReservoirs--TheLong Pond Prediction 114 8.0 Discussion 8.1 ModelI,II,III,IV(Equations 12,13,50,51) .• . .. . . .. .. 152

8.1.1 Modell ...•. . .. ... .. .. . .152

8.1.2 Model 11..•... . . . .. . . .• • . . .•. •. • . . •.154

8.1.3 ModelIII .•.•. .. .. . . . •... . . .... .. ... . . ISS 8.1.4 ModelIv IS7 8.1.5 Comparison of the Four Models ... .... ... . . . •. IS8 8.2 SourcesforImprovement •....•. . . .. . . . • •...•.. 160

8.3 Applications . . . ...•. . . ...•....•...•. •. • . 164

LiteratureCited .. ....•.... . . . .•... .. ... . .. 165

AppendixA: RawDatafor Mercuryin Fish ..• .... . .•...••.. . . 220

vii

Table

LIST OF TABLFS

Page Comparisonof morphometric,hydrologic, limnological,and biological factorsfor four Southern Indian Lake regionsbefore and after impoundment ..••. ....•. .•.. .• .•.. ..• .•.•.•.. .••.46 Changes in waterlevel and surface area ofseverallakes affected by the ChurchillRiver DiversionProject ... . • •• • •. ... ... ... 48 CharacteristicsofLaGrande ComplexReservoirs.• . . . .. •... SI Characteristicsof Reservoirsand Controllakes in Newfoundland.. .. 55

viii

Figure

LIST OF tlGURES

Page

Themercurycycle 10

Locationofthethreemainareas of study.•. .... . . ... . •..•.. 42 Locationofreservoirsimpoundedasaresultofthe Southern

Indizn Lake/Cburchill River DiversionProject •... . ...•..•. ..• 47 Location ofreservoirsimpoundedin theLaGrandeComplex located in northernQuebec .... .• .•...•• •..•.. • • •....•.•.•• S2 Location ofCatArmReservoir ...••.. .... ...•.. ... S6 Meanmercuryconcentrationsof northern pikesampledfromlakes i~poU~dedas,partofthe Southern Indian Lake/Churchill River Diversion Project•••...• . .•.•.• .•••.•... . .••....•.,11 Mean mercury concentrationof northernpikesampledfromlakes impounded aspartof NotigiReservoir •..• .••... ••. .••.•.•. 72

Meanmercury concentrationsof walleyesampledfrom lakes impounded aspartof theSouthernIndianLake/ChurchillRiverDiversion Project •••. • ....•• ••••• .• •.••• •• ••. ...• •.• •• •••73 Mean mercuryconcentrations ofwalleyesampledfrom lakes impounded aspartof Noti&iReservoir •••...•••.•. ..• . . .• . . . •• 14 10 Mean mercuryconcentrationsoflake whitefish sampled fromlakes

i~pou~dedas.part of the SouthemIndianLakcJChurchiliRiver DiversionProject••.•• .••...• • . ..•. ••. . •.• • • •.•••.• 1S 11 Mean mercuryconcentrationsof lake whitefishsampledfromlakes

impoundedas partofNotigi Reservoir ..•.•.• .•.. •.. .•.•... 16 12 Meanmercury concentrationsofnorthern pikesampled from La Grande

Complex reservoirs .• • •• • • . ..•• . ... • ...• • ..•.•.• Tl

ix

Figure Page 13 Meanmercury concentrationsofwalleye sampledfromLa Grande

Complex reservoirs ••• •••..••• • • ••••. .• • ••.. •• •• . •.78 14 Mean mercuryconcentraucnsoflakewhitefish sampledfromLaGrande

Complex reservoirs •.••.•. . • ••••• ••. •.•••• . . • •••••.79 IS Plots of meanmercuryconcentrations fornorthernpike,walleyeand

lake whitefish forCaniapiscau;LaGrande2;LaGrande3;La Gra.nde4;

and OpinacaReservoirs ••••.•.••.. .•.• .••••.•• .•. .• •• 80 16 Meanmercuryconcentrationsplottedagainstreservoiragefornorthern

pike,walleyeandlakewhitefish for Caniapiscau:LaGrande 2;La Grande 3;LaGrande4;and OpinacaReservoirs ..• •. • . . ....• • 81 17 Mean mercuryconcentrationsof Arcticcharand brooktrout sampled in

Cal Arm Reservoir .•... ..• . . ••..•.••... ••.. .• .•82 18 Mercury concentrationsplottedagainstforklength,byyear, forArctic

char sampledat cal Arm Reservoir •.•••.•••.. • •• .• •••.•. 83 19 Mercuryconcentrationsplottedagainst forklength,byyear.for brook

troutsampled atcat ArmReservoir ••• •• • •.• •. . ....•• •.. . 84 20 Mercury concentrationsploUedagainstweight, byyear.forArcticchar

sampledatCatArm Reservoir .•• • .•.• •• • ••. • •• ••..••.•. 8S 21 Mercuryconcentrations plotted againstweight,by year,forbrook trout

sampled at Cat Arm Reservoir ••.••• •.•.•.•. ••••..• • •• •• 86 22 Predictedand observedvalues ofthe mercuryratio for northernpike

for Modell .• .•.•• • ••.. •••••••••••••.•••• •. •• .• liS 23 Predicted andobservedvaluesofthemercuryratioforwalleyefor

ModelI •••.• • • . • •.•.•• ..•. ..• •••.•• •• • • • ...• • 116 24 Predicted and observedvaluesofthemercury ratio for lake whitefish

for Modell ..• • • • ••. •.••.• •.• •• ••.• •. . •..••• • • • 117

Figure Page 2S ExplainedvarianceofModelI fornorthern pike.walleye.andlake

whitefishploued byrese rvoir .•••.• • • • ••.•••.• ••••. • • • 118 26 Explained varianceofModelIfornorthern pike. walleye.andlake

whitefish plottedbyregion ••• . ••• ..•• .••• ..•.•...•..• 119 27 Predictedandobserved values ofthenaturalk>garilhrnorthemercury

ratiofor nonheropike using ModelII .•...•. . . ..•...•. . 120 28 Predicted andobserved valuesof the naturallogarithm of the mercury

ratiofor walleyeusingModelII .• ...• . .. • •.. ..•... .. 121 29 Predicted and observedvaluesofthe naturallogarithm orthemercury

ratioforlakewhitefish using ModelII. . ... .... .. 122 30 ExplainedvarianceofModelHfor northern pike.walleye,andlake

whitefishplaitedbyreservoir ... • • ... • • • . . ••... . . 123 31 Explainedvarianceof Model IIfornorthernpike,walleye. andlake

whitefish plaitedbyregion.. •. • •.•..•. • •.. .•.... •. ..• 124 32 Predicted andobservedvalues of themercury ratiofor brook troutin

CatArmReservoir usingModell .••• •.•••• • •• • ••• .•... 125 33 Predicted andobserved valuesofthemercury ratio for Arctiecharin

CatArmReservoirusingMooell .•. ..•.• •.•.•. •••.•. •. 126 34 Predictedandobservedvaluesof the naturallogarithm ofthe mercury

ratiofor brooktroutin Cat Annusing ModelII .• • • • • ••..•. .. 127 35 Predictedand observedvaluesofthenaturallogarithmof the mercury

ratiofor Arctic char in Cat Annusing Model II ••..•• • .•• • . • • 128 36 Mean mercuryconcentrationsof ouananicheand brooktrout sampledin

LongPondafter reimpoundment •.. • •..•.. .•....•.•. •.. 129 37 Predictedandobservedvalues ofthe mercuryratioforLongPond

brooktroutusing ModelI .•.•...•.. • ••• •....•...• 130

xi

Figure Page 38 Predicted and observed valuesof the mercury ratioforLong Pond

ouananicheusing ModelI .. .... .... .. .. • . .. ... ... 131 39 Predictedandobserved valuesof thenaturallogar ithmofthemerc ury

ratio forLongPond brook trout usingModelII ... ..•.. ... . 132 40 Predictedandobserved valuesof the naturallogarithm ofthe mercury

ratio for Long Pod ouananicheusingModelII 133

41 Predictedand observed valuesofthe mercury ratio for northernpike for Mode1111 ,... . .... ... . .. ... ... . . ... . 134 42 Predictedandobserved valuesofthemercuryratiofor walleyefor

ModelIII ••.. . . .•••.•••...• . .•••••••••••••••,. 135 43 Predictedand observed valuesofthe mercuryratio for lake whitefish

forModelIII .•• .... . .. .. . .•. . .•.... •..••. . . • .. . 136 44 Explained varianceofModelIIIfornorthernpike, walleye,and lake

whitefishplotted byreservoir .. . . ..•. .. . . . .•.•. •. . •. .. 137 45 Explainedvarianceof ModelIIIfor northernpike,walleye,and lake

whitefish plotted by region ... . •. .• •...•. • . •..• ... 138 46 Predictedandobserved valuesof the naturallogarithmofthe mercury

ratiofor northern pikeforModel IV .•.•. • ••....•• . . ... 139 47 Predictedand observed valuesof thenatural logarithm of the mercury

ratio for walleyeforModelIV .. . ..• . ..•. . .. ••... .... • 140 48 Predicted and observed valuesof thenaturallogarithm of the mercury

ratiofor lake whitefishforModelIV ...• . •.•.•...••• .• 141 49 Explainedvariance of ModelIVfor northernpike,walleye,and lake

whitefish plottedby reservoir •. . .•.. ... .•.• ...••• ., 142 50 Explainedvariance ofModtIIV fornorthernpike,walleye,andlake

whitefishplotted by region .•. ....•. •.. ..• ••. . .•. •••.• 143

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Figure Page 51 Predicted and observedvaluesofthemercury ratiofor brook trout in

Cat ArmReservoirusing Modcl lII ... .. .. . . ...•• 144 52 Predictedand observedvalues of the mercuryratio for Arctic char in

Cat ArmReservoirusingModelIII

.... ... ...

145 53 Predicted andobserved valuesof thenaturallogarithmofthemercury

ratio for brooktroutin Cat Arm usingModelIV

.. ...

146 54 Predicted and observedvalues ofthenaturallogarithmof the mercury

ratiofor Arctic charin CalArm using Model IV

...

147 55 Predicted and observedvaluesof the mercuryratio for Long Pond

brook troutusingModelIII

... ... .... ... ...

¹⁴⁸

56 Predicted and observedvalues ofthe mercury ratioforLong Pond ouananic heusingModelIII

.... .. ... .. ... ... ... ..

¹⁴⁹

57 Predicted and observed values ofthe natural logarithm ofthe mercury ratio for LongPondbrooktrout usingModel IV

.... ... .. ..

150 58 Predicted andobserved valuesof the natural logarithmofthemercury

ratio for LongPond ouananicheusinl .Model IV

... ... .

¹⁵¹

xiii

1.0 INTRODUCT ION

'Mercury and mercurycompounds havereceived a great deal of attentionover the last two decades becauseof environmentalandhealth concerns. Methylmercury poisoning canbelethal to humansand wildlife.Historically,mercurycontamination has been associatedwithsources ofindustrialor agriculturalpollution. More recently it has been linked to naturalphenomena. Becauseofthesehealth concerns, mercury concentrations need to be monitored as well as modeled.Beforequantitativemodels arc developed,the systembeing modeled mustbe understoodas completelyas possible,includingthe natureof and relationbetweenbiological,chemical,and geological components.

The modelsdevelopedlater in this thesisare based ona biological understanding of processesaffectingfishmercuryconcentrations followingreservoir impoundment.Beforethe modelswere developed,a review of the literaturewas undertaken.This includedgeneralbackground informationabout mercurychemistry (Section2.0)andthe effectsof reservoirimpoundment (Section3.0). A detailed development oftwo modelsis presentedin Section4.0.The locationof reservoirs usedinthis study,the data used inthe analyses,the validationprocedureand the applicationofthe modelsare presentedinSection5.0.Data availablefor this study arepresented in Section6.0.Resultsfromthis study are presentedinSection7.0and discussedin Section 8.0.

2.0 BACKGROUND

2IMerellrvChemistry

Mercuryis ubiquitous,mostlyin traceamounts(Huckabee etaI.,1978).

Mercuryis a grouplIB heavy metal with oxidationstates 2 and 1, nn atomicnumber 80, and atomicweight200,59.Itishighly volatile, aliquidat roomtemperature, and certaincompoundscan be toxic.In water,mercurialions aregenerallyassociated withchloride ions(CI- )or hydroxideions(OH-) .The mercuricion(Hg1+) is a typical class-b" acceptor(Ahrland,1966;Pearson,1968a,1968b) and readily forms covalent compounds,preferringsulfur(5) andselenium(Se)donoratoms (Ramamoorthy andBlumhagen,1984). In natureitoccurspredominately in its sulfideform, cinnabar(HgS),whichcan be minedandroastedto yieldmetallic mercury(Bligh,1970\Itis introducedto theenvironmentthrough fumaroles,hot springs, magmaticsources(Siegel and Siegel,1975), andas a resultof evaporation fromthe earth'scrust.Itisthen distributedby aerialcirculationand precipitation (Stochand Cucucl,1934).

Thesameproperties thatmakemercuryaunique element also makeitvery economically....aluable.Mercuryhasbeen used since thetime of the RomanEmpire, andits compoundsarefoundin cosmetics,medicinaltreatments,dentalamalgams, paints, electricalequipment,thermometers, and batteries(Fitzgeraldand Clarkson,

1991). At one time, mercurywasusedextensivelyin therecovery of gold and silver from are.This use has beendecliningfor years(Bligh,1970),with thenotable exceptionof the Amazon regionof Brazil. FollowingWorldWaIIIthe industrialuse of mercuryincreased,primarilybecauseof chlor-alkali plantsand electricalindustries (Bligh,1970). Thepulp and paperindustryused organic mercurialssuch as phenylmercuric acetate as slimicidesto preventfoulingofmill equipment(Bligh, 1970;Nuortevaet al.,1979;Lodenius, 1991).Ethylmercuryphosphatehas been used forthetreatmentofbacterialinfectionsinhatcheryfish and has ledtoincrewed body burdensof mercury inthese fish (RuckerandAmend,1969).The major fluxes of mercuryinto the atmospherecanbelinkedto oilandcoal combustion,incineration ofsolid wastes,andsmeltingprocessesassociatedwiththe productionofcopperand zinc (Nriaguand Pacyna, 1988).

22 Toxicology

Despitethe widespreaduse of mercuryand mercury compounds,the severity ofmercurypoisoningwas not realized untilthelate1950' s at MinimalaBay,Japan where IIIdocumented casualtiesoccurredfromthe consumptionof fish and shellfish contaminatedby mercury(Lofroth, 1969). Thetoxic agents were foundtobe methylmercurycompoundsoriginatingfromchemicalplants using mercury-based

catalysts;eithermercuricoxideinpreparation of acetaldehydeor mercuricchloride in preparation of vinylchloride(Bligh, 1970). Foliowingthe Minimatadisaster,and dueto concernsforhumanwelfare,mercury becamea closelymonitoredsubstance.

Canada,alongwithmanycountriesaround the world, has imposedrestrictions regulatingmercuryconsumptionby humans (Royal Societyof Canada,1971).

The concernaboutelevatedfishmercurylevels is duetothe propensityof fish to accumulate mercury,thus producinga potential hazard to humansifconsumed (Nriagu,1979).At present, the most effectiveindicatorofboth thedegree of mercurypollutionandthe potential haza rdstohumans and wildlifeisthe mercury contentof fish. Crayfishare also goodindicatorsofmercurycontaminationin variouswaterbodies (Vermeer,1972). Elevatedlevels of inorganicmercuryand methylmercuryinhumanshave been linkedto fishconsumption(Berglundetal.•

1971;Suzukiel ot.,1971;Yamaguchiet01. ,1971).Simpsonetal.(1974)showed that fish is man's primary exposure pathwayto mercury;theconsumptionof fish and fishproductsis essentially the onlypathwayforhuman exposureto methylmercury (WorldHealthOrganization,1976).Researchersin Finland found mercury concentrationsof upto3Sppm inthe hairofpeopleconsumingfishfromFinnish reservoirs(Lodeniuset al.,1983;Alftanet al.,1983).Nativepeopleconsumingfish from BallLake(Wabigoon-English-WinnipegRiverSystem)andother pollutedlakes are known tohave elevatedblood-mercurylevels (Anon.,1973).

Manygovernmentshave imposed restrictionson mercury contaminatedfish,

In Sweden,areaswhere fish are caughtwith mercury levelsgreater than 1.0ppm are

"black-listed"(Bjorklund et01.,1984).These fishcannot be sold or distributed for thepurposeof consumption (Statenslivsmedelsverks forfattningssamling,1983).In Finland,the NationalBoardof Healthrecommended a decrease in consumption of reservoirfish with mercuryconcentrations greater than 0.5 ppm.The Boardforbade the sale of fishwith mercurylevelsgreaterthan 1.0 ppm (Yettaet01.,19800). In Canada,the mercuryconsumptionguidelinefor fishor fishproductshas beenset at 0.5ppm.Products containinghigher than0.5ppmmercurycannotbe sold within Canadabut maybesold on the world marketto ccuutries with highermercury tolerances. In the UnitedStates, based on findings from acidifiedJakesin Wisconsin, a health advisory was issued by both theWisconsin Departmentof NaturalResources and the Wisconsin Divisionof Health(1988) for people consumingsport fishfrom certainareas linked to high mercurylevels.

Globally,fish withmercuryconcentrations less than 0.5 ppm have been accepted as representative of naturalmercurylevelsfor unpollutedwater systems (Holden, 1972).Conversely, fishhavingmercurylevels greater thanO.Sppm indicateevidenceof industrialpollution or allogenicloading. Like Canada,Finland had a problemwith industrialpollution andfish withelevatedlevels of mercury (Hasl!nen and Sjoblom, 1968).A ban on the use of mercurycompoundshasled to reduced mercurylevels in fish from manylocations(Nuortevaet al.,1979; Lodenlus, 1991). However, manyinvestigatorshavefoundelevated mercurylevelsin fish from

pristine lakes and otherremoteareas unaffected byindustrial sourcesof mercury.due toautogenicloading (Korityohannetat.,1974: Wobeserer al.,1970; lohnelsetal., 1967:Bodalyet of.,1984a;Holden,19TI;Kleinertand Degurse,1972;Surma-Abo et01. ,19800;1986b; Lodenluset al.,1983:Mannioet01.,1986;Rask andMetsll.lA, 1991).

2 3 Remedia tion

Of greatpublic concernishow quicklyandeffectivelyapollutedor contaminated site can be cleanedand restoredto its formeruses.Becausethe removalofall formsof mercuryfrom an aquaticsystemis virtuallyimpossible, BisogniandLawrence(1975)suggestreducing or eliminatingmethylmercury formation. They present three possibleremedial procedures10reducethe amountof mercuryavailablefor methylation:(I)changethe mercurybindingcharacteristicsof the sediments:(2)eliminateorreducethe amountof organicor nutrientinputto the benthicregion;and(3) reducethe total inorganicmercuryconcentration.Fitzgerald et of.(1991)suggesllhatthe in-lakeproductionof metallic mercury(HgO)would reduce the amountofmercuric(Hg2+)substrateavailabletothemicrobial community for mercury methylation.RamamoorlhyandBlumhagen (1984)concludedthat increasedlevels of organic matterdecreasedthe uptakeofmercuryby fish.Verta

(984)hypothesized that decreased fish mercurylevelscould beattainedbyremoving methylmercuryfrom Utefish biomass,therebyreducing the amountof mercury available forcycling,In an extensivelyfishedlake, Verta (1990) founddecreased mercurylevels in fish as aresult of fastergrowthratesand reduceddietary intakeof methylmercury. Verta(1990) indicates thatforsmall lakes,overfishingmaybea reasonable way to reducethemercurylevels intop predatorsto an allowed marketing levelasayoungerage structurewouldlikelybecreated. Billenet al.(1974) suggest thatmethylmercury-degrading bacteriacan existin locationswithhigh methylmercury concentrationsthereby reducing the amountofmethylmercuryinaparticular environment.Biodegradationcould take placethroughthe use ofthe pollutant(for energy andcarbon requirements)orthroughenzymaticmodification tothepollutant withouta nutritional benefitfromthe toxin (Billenet al.,1974). Foracidifiedlake systems,Winfreyand Rudd (1990)suggestthatfishmercury levels could be decreasedthroughareductionina lake'sacidity.Ruddetat.(1980b)and Turnerand Rudd(1983)suggestedthatlow-level additionsofselenium to thewater column may alsoreduce fishmercurybody burdens.This suggestion was tested and was foundto reduce fish mercurylevelsfor a Swedishsystem(Bjornberget al.,1988) and a pollutedCanadiansystem, the English-WabigoonRiver System innorthwestern Ontario (Ruddand Turner,1983a; 1983b;Turnerand Rudd,1983).In addition, Turnerand Swick (1983)indicated seleniumadditionsto the watercolumnwere not as effectiveatreducing afish's mercuryburdenas seleniumadditions10 food

organisms.lemel3vand Lann (1973) discuss the feasibilityofrestori ngmercury contaminatedecosystemsand the methods employed,suchas the removal ofmercury deposits through drtd ging.Theyindicate thatthere are bothtechnical andeconomic problemswhich mustbeovercome beforetheprocessescanbepractical lyapp lied. In addition , theyprovideevidencethat the disturbancecausedbydrro ging wouldserve toresuspendparticulatematterand could actuallyincreasemercury meth ylation.

2 4 Bjopeochemjs!l:)'

The processesby whichmercury compounds are assimilated, stored and eliminatedfrombiota constitute asmallfraction of thetoW mercurycycle.Winfrey andRudd (1990)present afigure ofthe biogeochemicalcyclingof mercuryspecies withinafreshwaterlakc (Figure1). Biota add complexity to the mercurycycl edue to thedynamics of,andinteractions between,variousfood webcomponen ts. As showninFigureI,theorganicmethylmercu ry ion(CHIHg· )is the pri marymercury compoundbioaccumulatedinfish.Methylme rcury hasrecentlybeen detectedinrain (Bloom and Watras,1989) and waterfrom catchment areas(LeeandHullbcrg,1990) but itis rarelydepositedinlarge quantitiesdirectlyintolakes(Winfreyand Rudd, 1990). Itis probable that the methylmercuryisformedeither in lhecatchmentarea orin the lakefromthemethylation ofinorganicmercury(Hg^h).

The bioavailabilityof mercuryspeciesis alsoof concern.Suspended sedimentsarebelieved to be important in the bioavailabiIity(Ramamoorthyand Blumhagen, 1984) andthe bloconceruraticnof toxicsubstances (Gibbs,1973 ; Hem, 1976: Karickho ffandBrown, 1978: Poppand Laque r,1980:Tessiererof., 1980).

Studies have shown that the mercuricion(HgH)isreadily absorbedbyorgan ic and inorganicparticulates(Bene!andHavlik,1979;Rudd and Turner,1983; Rogerset af.,19 84; Cranstonand Buckley,1972; Hannan and Thompson,197 7) and by dissolvedorganic carbon,DOC (Miller, 1975).These processesma y limitthe amountof mercuryavailableformethylatio n(Ruddand Turner,1983; Miskimmin, 1989). Inthepresence of hydrogensulfide(H:S)the mercu ricion(HgH)precipitates as mercuricsulfide,HgS (Winfreyand Rudd, 1990). JernelOv (1968) suggested that mercuricsulfide wouldonly becomemobilizedafter oxidation to mercuricsulfate (HgSO~). FurutaniandRudd (19 80) showed thatmercurycould bemethylated inthe water columnandin thepresenceof mercuricsulfide.Therefore,the mercury was not beingcompletely sequesteredinto the sedimentsas mercuric sulfi de(Furutaniand Rudd, 1980). Gillespie and Scott (1971) showedthat underaerobicconditions, mercuricsulfidein the sediments could bemobilized and absorbedbyfish.

10

.,R Hf-Hgt

^{CH3 ,H3}

WATER

I I 1" ^I

Hf-HIIIIl

~CH1H9+

.

^CH',CH]

SEDIMENT

H~O _HgtO.

^I

^CH!Hg+ CH)~H3

ORGANIC "'"^COMPLEXES

~",,"'\s

Figure1Mercurycycle (afterWinfreyand Rcdd,1990).

2 S Methylatio D

Methylation ofmercury is a smallpartof thetotal mercurycyclebut has a critical influenceon fish mercuryconcentrations. Methylmercuryis producedin both the sedimentandthe watercolumn(Westoo. 1966;JensenandJeme16v,1969;

Jemelcv,1970)and in soils(Van Faassen, 1976;YamadaandTonomura,1972).

Methylation mayoccur abiotically(Rogers,1977;Nagase et aJ.,1982; 1984;Leee/

1l al.•1985)orbioticallythrough bacterialmediation(Jensen andJemelev,1969). The mercuricion(Hg²⁺⁾maybeformedthrough photocatalytic reactions (Lindqvist and Rod lle, 1985;Brasset,1987;Iverfeld tandLindqvist,1986)of elemental mercury (Hg~,whichisthe predominantatmospheric mercury compound(Lindqv istand Rodhe,19 85; Slemrttal.,1985).Ramamoort hy and Blumhagen(1984)alsodetected photochemical met hylationof mercury.

Avarietyof organismsmethyla te mercury(Robinson and Tuovinen,1984;

Gilmourand Henry,1991). Wooder01.(1968) first showedthatmethanogenic bacteria couldproducemethyl mercury.Landner(1971)showedthatNeurosporasp.

was capableof methylation whileYa mada andTonomura(1972) demonstratedthat Clostridium cochleariumcoulddothesame. Anumberof aerobicgram-negativerods andgram-positivecoccithatHamdy and Noyes (1975)isolated from riversediments also provedable(0methylatemercury.Aswell, sulfate-reducingbacteria can methylate mercury;their metabolism maybeenhancedby sulfate-deposition(Gilmour andHenry,1991). Methylati on ofinorganic mercury and mercurycompoundsoccurs rapidlyviamicrobialactioninaquatic environ ments (BisogniandLawrence,1975;

Ra mlal etal.,1987 ; WilliamsandCoffee, 1975; Sommersand Floyd,1974).Most ofthemerc uryentering anaquaticecosystem is inorganicandisstrongly adsorbed onto organicandinorganicparticulates in thewater(Bene!and Havlik,1979;Rudd

e r

al.,1980b) orreversiblyboundtohum ic acid(StrohalandHuljev,1971;Miller, 197 5;Bendaal., 1976;Jackson etat.,1980) . Organicparticulates,notably

12 phytodetritus,undergodecomposldonthatfreespreviously boundinorganic mercury for methylation(Ranllaltf01.,1987).Methylmercuryisproducedby microorganismsthaImetabolizethemercuric(Hgl")ionto detoxifytheirenvi ronment (Pan-HcuandImura,1982)oras aresult oflITOn inthesynlhesis oforganic moleculessuchasaminoacids(Woodtr01.,1972).Somebacteria caneliminate methylmercuryby convertingit10methane (CH.) andelementalmercury. HgO (fonomuraand Kanzaki,1969;Tonomuraet01.•1972). Mercurymust bepresentin itsmercuric ionform to undergobiological methylation(DeSimoneet af.,1973),

Methylation ratesarc influencedbyorganiccontent(Olsonand Cooper,1976:

Rudder01.•1983);pH(Ramlalet01.,1985;Xuntt01.,1987);theconcentrationof inorganicmercury(YamadaandTonomura,1972);thebacterialspeciespresent (Vonk 2J:dKaanSijpesteijn,1973);the growth rate ormethylatingmicrobes(Bisogni andLawn...'ce,J975);andlheoxygenconcentration in thewater(Bisogni and Lawrence,1975). Consequently,methylationratesaresitespecificanddifficulllO generalize.

~'C!l m !!!aljQnandBjornagnjficaljon

The literatureon uptake and accumulationofessentialand nonessentialmetals in fishisbothconfusingandconflicting(McFarlaneandFranzin,1980).Tovarying

13 degrees,livingcreatures possessthe ability10accumulate,withintheirtissues, substancesthat are only slightlybiodegradable(Boudouet01.,1979).

Bioaccumulationoccurs naturallywhen the assimilationrate ofa specific compoundis greater thanthe excretion rete.Thiscontrasts with biomagnification,the processby whicha slightlybiodegradablecompound is magnifiedthroughthefoodchain.

Mercury, when dissolvedin the watercolumn, is at itslowest concentration. Each successivelevel of thefood chaindisplaysahigher concentrationthan the previous level.Biomagnificationcontinuesto the topof Utefoodchain wheretop predators displaythehighest concentrations.The accumulationof mercury in fish due to biomagnificationwas generallyassociatedwilhindustrialdischargesofmercuryto natural waters(D'ltri,1972;Kleinert and Degurse,1972;Rajet al.,1992).More recently,increasedfish mercuryconcentrationshave beenfound innaturallakes withoutindustrialor pointsourcesofpollution(WrenandMacCrimmon, 1983;Sloan and Schofield,1983;McMurtryetal.1989; Griebet a1.,1990;Wieneretal. , 1990;

Bodalyetal.,1993). Globally,humanactivitieshaveraised the mercury concentrationintheenvironment well above naturallevels (Jchnels

a

al.,1967)and these increasedmercurylevels mightbe detectedinaquaticbiota.

Biomagnificationoccurspredominatelywithlipidsolublecompoundssuch as DDT(1 ,1~bis(4~chlorophenyl)·2,2 ,2·trichloroethane)andmethylmercury.Fishshow increasedmercurylevels intheir tissuesdue to thisprocess(Stock and Cucuel, 1934;

Raederand Snekvik,1941;RankamaandSaharn, 1950).The retentiontime of

I' lipophilic substancesin fish fleshcanbeyears .Thispartly accountsfor the effect of size and age on tissue concentrations(Lelander ot.,1976:Hasselrct, 1974). In general, largefish have greater white musclemercury concentrations both within species and within populations(Scott, 1974).However,the relationshipbetween mercuryconcentration and lengthis not consistentwithinspecies(SCOItand Armstrong,1972; Scott, 1974), II is welldocumented that fish mercurylevels increasewithfish size (Scottand Armstrong,1972;Scott.1974; Huckabee et al., 1979).However, the increases in mercury body burdens of fishfrom newly impoundedreservoirs in northern Manitobawere not a resultof changes in the average size of fish sampled(Bodalya01., 1984a).In addition, Bodalyet01.

(1984a)found that duringthe sametime period and at thesamelocation,Ihere were no increasesin fish mercuryconcentrations from undisturbedlakes.Phillips(1976) showedthat themercuryconcentrationspresent in fish representingthe sameyear class from a contaminated reservoirwereindependent of size.

Methylmercury(CH}Hg-+)is the mosthazardous mercury species.IIis more toxic and more easily bioaccumulaledthaninorganicformsbecauseit can easily penetratemembranebarriers,facilitating the absorptionof thecontaminant in organisms and its transportand fixationin differenttissues (u.Judouer0/. ,1979).

This mercurycompoundis readilybound10 thiolor sulfhydralgroups, SH- (fakahashi and Hirayama,1971),whichare associatedwithneurons.Consequently, methylmercuryis a neurotoxin and, if exposureis high,cancause Minimata disease

IS (methylmercury poisoning).Methylmercuryalso demonstruesa highcapacityfor intracellularstorage,thusincreasing the biologicalhalf-life of the toxicant in the organism(Boudouer01.,1979).Wcstoo (1966) first demonstratedthat most of the mercuryfoundin fishisin the methylated form.Recently,thk, finding has been confirmed byBloom (1992)and Lasorsaand Allen-Gil(1995).Olsonetal.(1973) suggestedthat the rateof methylmercuryaccumulationisgreater than the rate of inorganic mercury accumulationas demonstratedbythe anomaloustissuedistribution of thesetwo mercurials, suggestinginorganicmercury doesnotrequiremethylation prior to entry intothe fish. Gavis and Ferguson(1972)concludedthat aquatic organismscan extract methylmercurycompoundsfromthe waterin preference to inorganicmercury.However,morerecentexperimentshaveindicatedthe overwhelmingimportance of foodas theprimary mercury uptake pathwayforfish (e.g.Hall et01.,1994). Potter el aJ.(1975) suggested that the patternsof mercury uptake,accumulation,and eliminationin fishwere speciesspecific. Thebiological half-lifeof methylmercurymayalsobe speciesspecific(Fribergand Vostal,1972).

Reportedvalues range from aboutfive monthsfor bluegills,Lepomis macrochirus (Burrowsand Krenkel,1973),to over 200 day' forrainbowtrout,Oncorhynchus myklss(GiblinandMassaro, 1972),to nearly700 days innorthernpike,Esox lucius (Lockhartet01.,1972), andto more thanI,OCO days inflounder, (1arrenpaa el01., 1970).TI,e reporteddifferencescouldbe partly size related.

Methylmercury enters fish throughtwo differentpathways: either direct

16 adsorptionfrom the watercolumnacross the gill membraneor absorptionof methylmercuryfrom ingested food items. Predictingtherelativeimportance of methylmercuryfromfood or wateris complicatedbygeographical and seasonal variationsin methylmercuryavailabilityand by seasonal changesin prey availability andpredatorfeeding habits(PhillipsandBuhler,1978).Mercury uptakeviathegills is directlyrelated to metabolicrate, whichis determinedprimarilybyfish size and secondarily by watertemperature and the concentrationof dissolvedoxygen (Phi11ips and Buhler,1978).Ribeyereet aJ. (1991) foundthat both pH and temperatureaffect mercurybloaccumulation. Norstromer al.(1976)reported a 12% efficiency for respiratoryassimilationof methylmercurywhileFagerstrOmand AscII(1973)reported a14%efficiencyforassimilationof dietary methylmercury.The netefficiencyof methylmercuryassimilationrangesfrom 67%- 94%(Hannen, 1968; deFreitaset 01.,1974;Suzuki and Hatanaka,1975jMatidaet01., 1971jdeFreitaset01., 1977).

Therehasbeen somedebate over the primary pathwayfor mercury accumulationbyfish. Exposingpond animal communitiestomethylmercury, Hannen(1968) foundthat the tissueconcentrationsin the organisms were not related totrophiclevel,suggestingthat direct adsorption from thf. watercolumnwas the majorroute formethylmercury accumulation.Armstrong and Hamilton (1973) found that, in amercury contaminatedsystem, mercury concentrationwasrelated to food selection.Their studyindicatedthat omnivorousorganisms,detritusfeeders, and bottomdwelling invertebrates had considerablyhigher mercury levelsthan either

17 herbivorous organismsor zooplanktivores. Phillipset al. (1980)foundthe rate of mercuryaccumulation was fasterin pisclvorcus species(i.e.northernpike, walleye Sliz.ostedionvitreum,and saugerStlzostedlon canadense) than in planktivores(i.e.

blackcrappiePomoxis nlgromaculatus,and whitecrappiePomoxis annular/s).Wren and MacCrimmon(1986) found significantlyhigher mercurylevels in predatory species than in otherspecies of comparableage. Small yellow perchPerea jIavescens arecommonprey items for walleyes(Colbyer01.• 1979)and other piscivorous speciesand presumably playa primaryrole in the trophictransferof mercuryup the foodchain (Copeet al.,1990).Jemelovand Lann (1971) attributed 60% ofthe mercury presentin northern pikefrom 3 Swedishrivets to mercury inthe fish's food.

The percentage of organic-to-totalmercuryhas been foundto increasewith positionin the foodchain (Gardneret al.,1975;Hildenbranderol.,1975; Lelandet at., 1976;

Meisteret al••1979)with top predatorshaving the greatestconcentrationsof toxic methylmercury.deFreitaset al,(1977)suggestthat an organism'slifespan and growthrate are importantdeterminantsof pollutantconcentrationsin tissues.

Recently,field experiments relatingmercuryconcentrationsinthe water to mercury concentrations in fish (HaIlel al.,1994) demonstrated that in lakesthe primary methylmercuryaccumulationpathwaywasthe food.This impliesthatthequantityof mercuryaccumulated directlyfromthe watercolumnis negligible whencomparedto the quantityaccumulatedviathe foodchain.

Regardlessoftheuptake path,mercuryhas toxiceffects on wildlife. Spryand

18 Wiener (1991)presenta critical reviewof bioavailabilityand toxicityof mercury compoundstofish.Mercurypoisoninginits final(irreversible) stageisdetectable fromsensory-motordysfunctionsasmercury accumulateswithinthecentral nervous system (Carleyaal.,1971; Putman, 1972).Hartman(1978)foundthat.whentrout were givenfoodwithmoderateto highdosesof mercury.deficiencies in conditioned avoidance performanceresulted. However,RuckerandAmend(1969) and Amend (1970) foundno prolongedeffectsoforganicmercurypoisoningin fish asfish growth rates dilutedthe initial mercuryburden.Burrowsand Krenkel(1973)suggestthat demethylationcouldbe occurring in theliver and kidneys.Trouthave beenobserved to have increasedmucus production in the presenceofsublethalconcentrationsof mercuricchloride(Lock and Van Ovcrbeeke,1981). Vamasiet al.(1975)suggest that the structuralproperticsofthe mucus covering the gill epitheliumchanges, resulting inincreased permeability tomethylmercury.

2 7 AutogenicMercuryLpadjng

In addition to industrialsourcesof mercury, there areanumber of environmentalstressesthat resultinincreased mercuryconcentrationsinbiota.

Recently,there have beenmercuryproblemsassociatedwith"pristine'environments.

Many of theseareas are remoteand isolatedfrompointsourcesofmercurypollution

19 suchas mining, chlor-alkali plants,orpulp and paper mills.Research.has shown that thecauseof increased mercurylevels in fishandwildlife may be acid stress, atmospheric deposition,reservoir impoundment.or some combination of these.

Acidificationwas thought 10aggravate the already harmful ecological impacts of mercury contaminationthrough the productionof methylmercury(Iemelilvand Lann, 1973: Brouzeser 01.•1977).Elevatedfish mercurylevels havebeen observed in poorlybuffered.low pHlakesin areasremote from point sourcesof emissionsfor lakes onthe CanadianShield(Wrenand MacCrimmon. 1983);inthe Adirondalcs (Sloan and Schofield, 1983);in Maine (AkielazekandHaines, 1981), Michigan (Griebet a!••1990),andWisconsin (Wieneret al. ,1990; Wiener, 1983); inSweden (BjOrklundet a!.•1984; Llndqvistet at••1984)and Finland(Vertaelal.,1986);and inOntario(Scheideret al.,1979: Sunset01.,1980).However, severalresearchers foundthat, in acidifiedwaters,mercurywas methylatedmoreslowly than waterat neutralpHlevels (Bakeret01.,1983;Furutanietat.,1984; Ramlalet at. 1985).

Mercuryconcentrationsin waterhavebeencloselyassociatedwithcolor, possiblydue to the concentration of humicand fulvicmatter andthe corresponding complexationsbetweenmercuryand humicmaterial(Mierleand Ingram,1991).

Jacksonet of.(1980)foundthatmercury was rapidlyremovedfrom the water column at pH 6.7 - 6.8due to its strong eJectronegativitybutwasremoved moreslowlyat pH5.1due to itslarge ionicradius.Jacksonet at.(1980)foundthatmercury formed exceptionallystrongcovalentbondswithhumicmatter. Rask and MetslUi (1991)

20 found a trendtowards highermercury levelsinnorthernpike fromareaswhichwere either acidicorhumic as compared touncolored andnearlyneutra11akes.Driscolla at.(1994)found a strong,positiverelationshipbetweenfish mercuryconcentrations and dissolvedorganiccarbon (DOC) to a maximumof about 8 mg ClL,afterwhich fishmercury concentrationsbeganto decline.Otherresearchershavereponed elevatedmercury bodyburdens for fishinhabiting natural,unpollutedJakeswith humic,brown water (HultbergandHasselror, 1981;Bjorklund,1982;Paasivirtaet al.,1983;vertaetaJ. ,1986b; Driscolletal. ,1995),

Increasedfish mercury concentrations have alsobeen observedfor newly impoundedreservoirs acrossCanadaand aroundthe world.Onceareservoiris impounded.mercurylevels in fish begin to rise beyondthe Canadianconsumption guidelineof0.5ppm mercury.The effectsof reservoirimpoundmentonfish mercury concentrations are reviewedin thenext section,before quantitativemodels aredeveloped.

3.0 EffECTS OF RFSERVOlR L\U'OUNDMF.NT

Followingreservoir impoundment,speclesshifts and rearrangements are commonasafluvialsystemis convertedinto alotic one (Lindstrom, 1973). Reservoir formation severelyalterstheexistingchemical andphysical characteristics ofan aquatic ecosystem. ImpoundmentofSouthern IndianLakeand the diversion of theChurchillRiverin northernManitobaaffeetedthe optical,thermal, andbiological regimes(Reeky,1984).Afterimpoundment, laketemperatures,light availablefor photosynthesis (PAR)andSecchidisk transparenciesalldecreased (Reeky,1984).

Primaryproductionin anew reservoirwill change in avarietyofwaysdepending on the specificlocation(Rodhe, 1964;Funk andGaulin, 1971;Chamberlain,1972;

Soltero andWright,1975;Duthie and Ostrofs1cy,1975:Pyrina,1979;Reeky and Guildford, 1984).Heeky andOuildford (1984)foundthat phytoplanktonincreased the efficiencyoflightutilizationduringphotosynthesiswhenmean light intensitywas loweredas aresultof impoundment.Given decreasedtemperaturesand Secchidisk transparencies(Hecky,1984),Patalas andSaIki(1984) concluded that compositional changes in thezooplanktoncommunity were a result of decreasedprimaryproduction.

However, in regionsof SouthernIndianLakewhereno changesin phytoplankton productionhadoccurred (Hcekyand Guitdford,1984),standingcrops of zooplankton decreased (patalasandSaIki,l')i~)while zoobenthosincreased (Wiensand Rosenberg,1984).

22 The drasticchangein the distributionof fishpopulations after floodingcoutd affect exposure to mercury.After SouthernIndian Lakewas flooded,therewas an observed dispersion of lake whitefish out of the lake and into thediversion channel.

This mayhave resulted from the decreasein light penetration as a resultof shoreline

erosionandincreased levelsofsuspended sediment(BOOalyetal.,1984b:Newbury and McCullough,1984).The lightintensities onthe bottomduring the day (Heck)', 1984)werebelowthoserequiredforeffectiveschooling andfeedingfor mostspecies (Blaxter,1970).

Increased fish producti vityhasbeen observedin new reservoirsat all trophic

levels (Ellis,1936;Stroud, 1967; Nilsson,1973;Bodalyand Lesack,1984).One species forwhichimpoundmen t effects havebeen studied isthe northern pike

(Hassler,1970;June,1970; 1971;Cooper, 1971).BodalyandLesack (1984) found thatWupawBay (SouthernIndianLake)produced a verystrongyear class of northern pike during the first year of impoundment. This trendhas been observed in olher reservoir systems whereterrestrial vegetationbecomescoveredby water, providing increasedspawning habitat(Gasaway,1970;Beckman and Elrod,1971;Suman and Westman,1969;Holcik,1968; Domanevskii, 1957;Hassler,1969:1970).

Theproblemofincreased mercuryconcentrationsinreservoirfish populations has beenknownforsome lime (Smithet01.,1974;Abernathyand Cumbie,1977;

Lodeniusel 01.,1983:Bodalyet 01.,1984a; Boucheret 01.,1985).Typically,fish mercurylevelsrise rapidlyinafew yearsfollowingimpoundment. Theythen

23 graduallydecline, remainingabove the normalbackgroundlevelsobserved for natural environments(ormanyyears (Johnston et 01.• 1991).The observedrate ofdeclinein fish mercuryconcentrationsisvariable.Initial investigators suggested a returnto baselinemercury concentrationswithinfiveyears (Abernathyand Cumbie,19TI;Cox

es01.,1979).More recentlyBodalyet01.(198430)predicted a slower decline with fishmercurylevelsremaining elevatedfor decades.Even aftermercuryfoundin lake sediments has beendepicted, biomagnirkationinhigherorganismsisexpectedto continuefor some time (Hildenbrandet01.,1975;Pfister,1978). Verta (1984) proposed thaielevatedfishr-ercurybodyburdens can occurevenifthemercury

loading islow duetoan efficient recycling ofmethylmercurythroughlacustrinefood webs.Ramsey(1990) estimatedthatfishmercurylevels wouldremainelevated bya factorof 2 - 3for atleast50 years andmercury concentrationscould remain elevatedabove thebaselinelevelforaslong as 150years. Coxer al,(1979) note that if impoundmentsare used forfisheries,there needsto beclose monitoringof mercury levels inpredatory fish.

Afterimpoundmentthe source of mercurytofishisnot apparentbecause excessive mercurylevelsarenottypically present inthewater (Meisteretat.,1979).

The primary sourceof mercuryto newimpoundments is not anthropogenic.Meister etat.(1979)identified inundatedsoil as the sourcebut othersources are possible (Coxet al.,1979). Smithelat.(1974) suggestedthatthe mercurysource to a Utah reservoirwaseitherinsolublemercury salts or sulfidesfoundin the mud.Meisteret

24 01. (1979) hypothesized thatmercurywas beingassimilatedthrough foodsources ratherthandirectlyfromthewater column.These authorseliminatedpointsource pollutantsas the mercurysourcebecause fishshowedno unusua11evclsofotherheavy metals or pesticides.

Theflooding ofterrestrialsoil andvegetation duringimpoundmentaddsboth inorganicmercuryandorganicnutrientsto the aquaticsystem.Thebottom of the reservoirisdisturbedbywashoutsandflooding,resultinginareleaseof organic matterandnutrients from decomposition (Grim!! ,1965).Also,nutrientsarereleased from cleared land aroundnewreservoirs(Ramell,1967).These additionscan acceleratemicrobialmethylation(Rudderal.,1980a;Wright andHamilton,1982;

BodaIyetat,1984a).Substantialmethylation occurredin thethree yearsfollowing impoundment ofLaGrAnde 2ReservoirinnorthernQuebec(Verdont!l al.,1991).

The decomposition oforganicmatter (i.e.inorganiccarbon,total phosphorous) peaked afterthreeor four years (Schetagne, 1990).

Heckyer01.(1991) suggestedthat the organicmatter fromfloodedsoil and vegetationhas agreaterimpactonfishmercurylevels thaneitherinorganicmercury ornutrients. Measures oforganiccontenthavebeen linked 10fishmercury concentrationsInboth naruraiIakes (McMurtryet01. ,1989)andreservoirs (Mannio tl 01.,1986;venaer ai"1986a).When primaryproductionIs stimulated,there are two opposing mechanisms affecting theconcentrationofmercury in fish.In the tirst process,theincreasedsupply of decomposablealgalcarbonstimulatesthemethylating

25 bacteria.eventuallyincreasingfish mercury body burdens at upper trophic levels (Furutani and Rudd, 1980;Ruddet01., 1983; Rudd and Turner, 1983b).In the second process,the stimulationof primary productiontends to reduce the concentration of methylmercuryin fish if the bioaccumulationof mercury is diluted by fasterfish growth rates (Rudd and Turner.1983b;deFrcitasa01.,1974; Beijer and Jerneldv,1979). Thus,the tissue concentration(Ifmercury in faster growing species(l.e.prey)wouldbelower relativeto the slower growingspecies (i.e.

predators). However,in fieldexperiments, Rudd et01. (1983) found that increasing fish.growth ratesthrough.stimulationof primaryproductionresultedin substantial increasesin fish mercurybodyburdens.Undernatural conditions,Abernathy and Cumbie(I9n)foundthat mercury levelsin largemouth bass(Micropterussalmoides) from threereservoirsin the samedrainagebasin of the SoutheasternUnited Stales were highestinyounger, relativelyoligotrophicreservoirsand were significantly lower in older,moreeutrophicreservoirs.

Bioaccumulationof mercury compoundsoccurs at every level in aquatic food chains (Nrtagu,1979). Algaeaccumulateand concentratemercuryfrom the water primarilybysurfaceabsorption and also by adsorption(Hannen ,1968;Glooschenko, 1969).For algae, theuptake of both organicand inorganicmercury is proportionalto the length ofexposureand the concentration(Fang,1973;Mortimerand Kudo, 1975).Since forage fish containmuchhigherconcentrations of methylmercurythan zooplankton (Jemelovand Lann, 1971; Cox e/ al.,1975),ithas been suggested that

26 large, piscivorousspecieJmayingest mostoftheirmercurybodyburden throughthe foodchainwhilelowertrophic feedersmayabsorbmanoftheirmercuryviatheskin or gills(Bruce,1984;Phillips andBuhler.1978;Armstron gandScott, 1979 ; BoCtius, 1960:Hannen,1968: Hasse lrot,1968;Amendtlal. ,1969:Backstrom , 196?;

Ruckerand Amend,1969;Olsonetal•• 1973;Olson andFromm,1973; Utheetal.•

1973;deFrietu

a

at.,1974; Hasselrotand Gothberg, 1974).Somehigherspecies maypossess the abilityto convertinorganic mercury into methylmercury(WestM, 1968;Imuraes01.,1972).Pennachioniet al.(976) could findnoevidenceof methylationinfish.Ruddel al.(198Ga) suggestedmethylmercurywas being producedbymethylatingmicrobesinthe intestines of fish.The cc.nnicti ng reports and disagreement concerning mercury bioaccum ulationinfish arisesbothfromalack ofinformation concerningthespecificmen..airyexposure regimesexperiencedbyfish and from aJacleof quantitativedata relating food uptake10wateruptake(Phillipsand Buhler,1978).

Adsorption ofmercuryfromthewater columnisanotherpathway (or mercury accumulationin fish.Wobesera01.(1970)suggestedtheepitheliawas an important routefor directmercuryaccumulation. Intheiropinion,thismaypartially explainthe lackof specificvariationinfishmercuryconcentrations,evenamongspecieswith different feedinghabits. Someauthorshavesuggestedthat mercuryis taken up througha fish's mucuslayer and/orthrough the skin (McKaneet01.,1971;Burrows etal., 1974). Strangeet al.(I991)suggested that passiveaccumulationof mercery is

27 highestin littoral zone species (e.g. northern pike), which spend a majorityof their timenearshore wheremethylation ratesare highest.

The food chain is a criticalsourceof mercury to fish (Huckabeeetat.•1978;

Huckabeeet al.•1975; Lock, 1975). Huckabeeet ol,(1978)found that about 50% of themusclemercury contentwas derivedfrom thefood.Surma-Altotlof.(19800, 1986b)suggestedthat large amountsof methylmercuryor mercury that was ready to be methylatedare dissolvedinto the water phase and accumulated,particularlyby the zooplanktoncommunity,followingimpoundment. Boudouet al. (1979)demonstrated that,for a simple food chainconsisting of a green algae(Chiarella vulgaris),a eooplankter(Daphniamagna)and first level carnivorous fish (Gambusio affinis), the quantities of the substance bioaccumulated by the consumerfishcorresponded to the amountof mercuryingested.Potteret al.(1975) andLodeniuser al. (1983)found thatspeciesin the highesttrophiclevelshad the highesttissuemercury concentrations.For Labradorfishes, Beuceand Spencer (1979) observed the highest (>0.5ppm) mean mercuryvaluesin the two plsclvorousspeciesstudied (lake trout Sah'e/inl/Snamaycushand northernpike)whilelower mercurylevels« 0.5ppm) wereobservedin the non-plscivorous species(whitefishCoregonusdupeajannis, whitesuckerCatouomus commersom,longnosesuckerCatostomus caMs/amus,and brooktroutSalvelinusfonlinalis). Similarly.Smith et 01. (1974) founda trophiclevel effectfor mercuryconcentrations in fish froma Utah reservoir,with predatorshaving the highestmercurybody burdens.Surma-Ahoelal.(1986a,1986b)showedthat, in

28 Finnishlakes andreservoirs.theconcentrationof mercuryincreasedsubstantially up thefood chain. Phillipsetal.(1980)showed that mercury was accumulatedmore rapidlyinpiscivorous species (nonhem pike, saugerandwalleye)thanin planktivorousspecies(blackandwhite crappies) apparentlydueto the:l!Tlou nlof mercury consumed.Funher evidenceforfoodcbain bloaccumutalonof methylmercurycernesfromlaboratoryexperiments(Kaniaet at., 1974).Fish demonstrated decreasedability toavoidpredatorsas sublethal concentrations of mercuryincreased. This resultindicates that,under natural conditions. predatory fish couldhavehighbodyburdensofmercurybecausemercury enriched preyarc easierto catchand less ene rgyisrequiredto catch them.

Thephysical and chemical characteristicsofan aquaticecosystemmaylimit, enhance,orotherwisemodifyafish'suptakeof mercuryfromthewater (Burkett, 1974).Lathropetal.(199 1)listseveralvariablesthaiinfluence fishmercurylevels.

Brieflytheselnctude:sedimentmercury(Hfunson,1980;H1kansonetal., 1988;

Cope etal.,1990);chlorophyll-a,totalphosphorous,and otherlakebioprodccrlviry indices(H1kanson.1980;Helwig andHeiskary,1985;Latnropet at.,1989);water aluminum(Helwig and Heiskary,1985);dissolvedorganic:carbonorcolor (McMurtry et al.,1989: Copeet 01.,1990:Griebet ot.,1990); sedimentorganicmatter (H!kanson,1980;Vertaetal.,19800; Copeet at.,1990); and lake morphometry (Wrenand lAacCrimmon,1983; Helwig andHeiskary,1985).Increasedtemperature hasbeen srcwnto increasefishmercurylevelsbecausefisharelesstolerantof

29 mercuryat highertemperatures (Amend, 1969;Hasselrot,1968: Boetlus,1960;

Macleod and Pessah, 1973). The rate of methylmercury uptake in fish has been positivelycorrelatedwithmetabolic rate and oxygenconsumptionin natural environments(Rodgers andBeamish,1981) perhapsbecausefish increase their exposureto melhylmercurybyrespiringlarger volumesof water (Ponceand Bloom, 199 1). Generally,factorsthat influencemetabolic rates are the sameasthose that controlmercury kinetics: theamount of mercury 10 whichthe organism is exposed (concentrationin ambientwater,sedimentandfood);temperature;water quality(pH, totaldissolved solids,dissolvedoxygen,degreeof eutrophication,complexing ligands, etc.): sex; breeding status: ingestionrate; species; and metabolic differences (Nriagu, 1979; Forresteretat., 1972; Olsson,1976;Bishopand Neary,1977; Macleod and Pessah,1973).Weight and age also affectmercury accumulationbyfish because large,older fish lend 10havehighermercuryconcentrationsthansmall, youngerfish (VtM and Bligh, 1971;Jemelov and Lann, 1971;Bransonet al.,1975).Scott and Armstrong(1972)founda positivecorrelation between mercuryconcentration and fish length.Similarly,mercuryconcentration wasfoundto increasewith fishlenglhfor allspeciescollected fromthe Tongue RiverReservoirin Montana(phillipset at., 1980).A positiverelationshipwasalso demonstrated between time of exposureto waterborne methylmercury andtissueconcentrations of mercury(deFreitaset al.•

19n ).Wren andMacCnmmon (1986)suggestedthatexposuretimeto waterborne mercuryisless importantthandiettype indeterminingtissuemercury levelsfrcm

30 organismsinhab iting undisturbedlake environments.Variation in fishmercury concentrationsmay be due10altemtionsinformationanddecompositionof melhylmercuryin response\0differences in water chemistry betweenlakes, differences in mercuryloading,watershed 10lake area ratios and retentionof mercury by watersheds (MierleandIngram,1991).

Likeotherchemical substances inaquaticecosystems,the environmental concentrationof methylmercury isregulated bythe concurrentprocesses ofproduction and degradation (Brosset,1981; Lexmondaal.,1976). Inorganicmercuryand mercury containingcompounds can be rapidly transformedby microbialactionin aquatic environments(Ramlaletal. , 1987). Anaerobicconditionsenhancemicrobial methyltransferwhichoccurs when the methylgroups(CH]")are transferred from methylcobaJamine(CH]-Co·S,6-dimethylbenzimidazolylcobamidc)to the mercuricion (Hg1+) to formmethylmercury(CH)Hg+) using both enzymaticand nonenzymatic reactions(Woodetaf. ,1968; Sorensen, 1991).Bacteria capableof synthesizing a1kylcobalaminesin the presence ofincreasedlevelsof nutrientsalsoenhance methylation (Sorensen, 1991). Meisteret 01.(1979)suggestedthatanaerobic conditionsfavourtheuptake of mercuryfrom the soil through methylationunder conditionspresentin lake sediments. Other bacteria eliminatemethylmercury from aquaticsystemsby convertingit10methane(C~)and elementalmercury,Hg^O (Tonomura and Kanzakl, 1969; Tonomuraa01.,1972),

Inreservoirs,mostmethylationtakesplacein floodedzones(Ramsey, 1989)

31 wherethe mcthylationfdemethylationratiosarehigher thanat deep water sites (Ramsey and Ramla1,1987).In SouthernIndian LakeinnorthernManitoba,the highest mcthylatlon/d emcthylaticn ratios occurred alongtheflooded shoreline (Ramlal et al.,1986). Thisprovides one explanationforincreasedmercurybodyburdensof fishfollowing impoundmentsincemostfish species spend the majorityof theirtime in thelittoral zone where habitat and feeding conditionsare favourable. This observation points to increasedbacterialmethylation under aerobic conditionsdue to the oxygenregimeassociated with thelittoralzone of mostreservoirs. In contrast, Ruddetal.(I983) and Parkset of.(1984)foundthat,forthehighlypolluted Wabigoon-English Riversystem,methylation rates were ordersofmagnitude higher under anaerobicconditionsthan underaerobic conditions.Itappearsthat the observed differencesbetween anaerobicand aerobicconditionsarelikely a functionof themicrobial speciespresent,themicrobialcommunity'sgrowth rate andthe availability of mercuric ion speciesfor methylation,ratherthan due todirecteffects of oxygenconcentrations.

Ingeneral,reservoircreationleadsto elevatedmercurylevels at alllevelsof Ihe aquaticfood chain. especiallyinfish. The ability10predict these levelsprior10 impoundment wouldbeuseful infuture environmental impact assessments(Johnston et al. ,1991). Bodalyet al.(1984a)found that fish mercurylevelsrespondedquickly to impoundment,withsubstantial increases withinthefirst two to threeyears.

Mercuryconcentrations in fish in Manitobareservoirs showedno significantdecline

32 after fiveto eight yearsofimpound ment (Bodaly tl 01••1984a). Assuming thatthe increasein methylmercury prod uctio n is proportional to the amountof organicmatter introducedtothesystem,a relationship betweenthe extentof flooding (te.organic matterinundated)and mercurylevelsin reservoirfish is expected(Bodalyet01., 1984a;Johnston et01.,1991).Thelargest mercuryfluxto fishis seenwherethe rise in lakeleve l and thearealextent offlooding are the greatest(Jackson,19 87).

Modellingfish mercury levelsas a functionofextent offlooding in reservoirs

has been attempted withmixed results.Jonesetal.(1986) relatedfish mercury concentrationsto several physicaland chemical characteristicsof Canadian reservoirs . They foundthat the extent offlooding wasno t a useful predictive variablebyitself.

Johnston etal.(1991) also modeled fish mercuryconcentrationsas an extentof floodingusing twolinear models.Theirstudyincludedwithin-lakeeffects (changein surface level,percent flooding and floodcdarea tovolume ratio)andupstreameffects (upstreampercentfloodingand upstreamflooded area tovolume ratio). Iohnston et al.(1991)demonstrated thatupstream effects had a greaterexplained variancethan within-lake effectsbut indicatedthatdifferences betweenpredictedand observed mean mercury body burdensfor some tcstcases may havebeen causedbythe equal weightinggiven10 with-in lake andupstreameffects.The modelsof Johnstonetat.

(1991) alsoindicated thepresence ofgeographicaldifferencesas some predictions were closerto the observed-predictedline than others. HAkansonaal. (1988)found a weak inversecorrelationbetween lake sizeand mercuryconcentrationin northern

33 pikein Swedishlakes,while McMurtryet al.(1989)found a positivecorrelation between the sametwo variablesforOntariolakes.For naturallakesinnorthwestern Ontario, BlXlalyec01.(1993)founda stronginverserelationshipbetweenfish mercuryconcentrationsandlakesize.Also, fish mercuryconcentrationshavebeen correlated with watershedarea (Vertaet01. ,1986b;McMurtryet al.1989;Sunsand Hitchin,1990).The resultsofthese correlativestudies are conflicting,perhaps becauseofthe dirficultyof isolatingmechanismsinsuchstudies. Experimental studies designedto identifymechanismsof mercurymethylationshowed thatthe

addition of organicmatterincreasedthe rateof microbialactivityand subsequently, therate of mercurymethylation(Ruddel al.,1983). Aspart of the Experimental LakesArea ReservoirProject(ELARP),Heyes et01. (1994)showed that newly floodedpeatis ideal(orsustaining high methylationrates dueto increased temperaturesand carbon and nutrientsfromdecayingvegetation. Basedon experimental studies (e.g.Rudd et01. ,1983; Heyeset01.,1994),and on demonstrated correlations with watershedarea(e.g.Verlaet01.,1986b;McMurtryel 01.•1989; Sunsand Hitchin, 1990).Iinvestigatedwhetherchangein fish mercury concentrationscanbepredictedfromchangein reservoir size.

4.0MODEL DEVEWPl\fENT

Avarietyor factorscaninfluencethe accumulationofmercuryin freshwater biota(Huckabeeaal.•1979).Comprehensivemodelsofthekinetics ofmercuryin naturalaquatic environments have notbeen developed (Bisogni, 1979)aslIteyhave for limitingnutrientssuch asphosphorus (Grimard andJones,1981). One consequence ofthisisthatquantitativeassessmentsofchangein fishmercury levels due to developmentor alterationof reservoirs cannotbemade. Recently, Harrisel al.(1994)have developed a mass-balance mercury modelusing bioenergetics equationsto simulate mercury dynamicsfollowing reservoirimpoundment.

Bioenergeticsequations are commonlyusedtodescribemercuryaccumulation byfish (e.g.Norstromaal.1976;Korhonentl01., 1995).Parameters for Harris'smodel arecurrentlybeingrefined in an ongoing project involving TetraTechInc., Departmentof Fisheries and OceansFreshwaterInstitute,and Hydro Quebec.The predecessorofthecurrentmodel was developedaspartof a Master's thesisin conjunctionwithOnlario Hydro(Harris,1991).

Work.to date onthebiogeochemistryofmercuryin naturalwatershas focused largelyon experimental studiesofsingle factorsunderlaboratoryconditionsalthough morerecentstudieson thebiogeochemistryof mercury have beenfield oriented.

These studiescanprovide someinsightintothekineticsof mercury innaturalsystems butcannotbeusedto evaluatechange in mercury level infish under natural

35 conditions for severalreasons. First,quantitative modelshave beendevelopedfrom some factorsbutnot forothers. Second,therelative contributions of concurrent processesremainunknown. A thirdreasonis that considerableunexplainedvariation exists in those parametersthathavebeenestimated.Giventhecurrentstateof knowledge, itisnot feasible 10constructhighlydetailedmodelsbased on a large number of parametersdescribing important processesleading tomercuryuptakeby fish.

An alternativetohighly detailedmodelsis thedevelopment of aggregate modelsthat summarizethe relationofa variableofinterest (i.e. mercury levels in fish)10 one ormore readilymeasuredenv,.onmental variablesofknownimportance (i.e. changein area).Parametersof highlyaggregatedmodelscanbecompletely empirical(Ryder,1965: Peters,1986), ahybrid of empiricaland rationalparameters (Platter al.•1981), or completelyrational (Lehman,1986). The present study presentstwo hybridmodelsto describe increasein mercury levelsinfishas a function ofchangein reservoirsize.This variable (changein area) was chosenforseveral reasons.First. this variableiseasilyobtainedprior toimpoundmenttherebyallowing forauseful predictionoffish mercurylevels. The area of the lakes tobeflooded can be calculatedand the area of thereservoir has alreadybeen estimatedbythe hydroelectric developer.The evidence from correlationstudies(e.g. Johnstonetat••

1991; Bodalyerat.,1993)indicatesthat thechangeinarea is a key variable. In addition, previous studiesindicatedthat the sourceof mercurytonew impoundments