FinalEvaluationMemorandum StrategiesforResolvingLowDissolvedOxygenand MethylmercuryEventsinNorthernSuisunMarsh ACollaborativeProjectby: WetlandsandWaterResources BachandandAssociates SuisunResourceConservationDistrict CaliforniaDepartmentofFishandGame CaliforniaDepartmentofWaterResources UniversityofCaliforniaatDavis UnitedStatesGeologicalSurvey Fundedby: StateWaterResourcesControlBoard ProjectNumber062835520 May2011 FinalEvaluationMemorandum StrategiesforResolvingLowDissolvedOxygenand MethylmercuryEventsinNorthernSuisunMarsh May2011 PrimaryContributors StuartSiegel,Ph.D.,P.W.S.,DanGillenwater WetlandsandWaterResources PhilipBachand,Ph.D. BachandandAssociates StevenChappell,BruceWickland,OrlandoRocha SuisunResourceConservationDistrict MarkStephenson,WesleyHeim CaliforniaDepartmentofFishandGameMossLandingMarineLaboratory ChrisEnright,P.E. CaliforniaDepartmentofWaterResources/DeltaStewardshipCouncil PeterMoyle,Ph.D.,PatrickCrain UniversityofCaliforniaatDavis BrianDowning,BrianBergamaschi,Ph.D. UnitedStatesGeologicalSurveyCaliforniaWaterScienceCenter GrantManager NaomiFeger RegionalWaterQualityControlBoard,SanFranciscoBayRegion SuggestedCitation: Siegel,S.1,P.Bachand2,D.Gillenwater1,S.Chappell3,B.Wickland3,O.Rocha3,M.Stephenson4, W.Heim4,C.Enright5,P.Moyle6,P.Crain6,B.Downing7.B.Bergamaschi7.2011.FinalEvaluation Memorandum,StrategiesforResolvingLowDissolvedOxygenandMethylmercuryEventsin NorthernSuisunMarsh.PreparedfortheStateWaterResourcesControlBoard,Sacramento, California.SWRCBProjectNumber062835520.May. Availablefordownloadat:www.swampthing.orgorcontactWetlandsandWaterResourcesat (415)4570250. 1. WetlandsandWaterResources,Inc.,www.swampthing.org 2. BachandandAssociates,Inc.,www.bachandassociates.com 3. SuisunResourceConservationDistrict,www.suisunrcd.org 4. CaliforniaDepartmentofFishandGame,MossLandingMarineLaboratory,www.mlml.calstate.edu 5. DeltaStewardshipCouncil,www.deltacouncil.ca.gov 6. UniversityofCaliforniaatDavis,DepartmentofWildlife,Fish,andConservationBiology,wfcb.ucdavis.edu 7. UnitedStatesGeologicalSurvey,CaliforniaWaterScienceCenter,ca.water.usgs.gov Coverphotograph:DanGillenwater(WetlandsandWaterResources),Nov28,2007 EXECUTIVESUMMARY Thepurposeoftheprojectistoimproveourunderstandingaboutbestmanagementpractices thatcanbeutilizedondikedmanagedwetlandsinSuisunMarshforreducingtheoccurrenceof lowdissolvedoxygen(DO)andhighmethylmercury(MeHg)eventsassociatedprimarilywithfall flooduppractices.LowDOeventsareofconcernbecausetheycanleadtounduestressand evenmortalityofsensitiveaquaticorganisms.ElevatedMeHglevelsareofconcernbecause MeHgisaneurotoxinthatbiomagnifiesupthefoodchainandcancausedeleteriouseffectsto highertrophiclevelconsumerssuchaspiscivorousfish,birds,andmammals(including humans). Thisstudyinvolvedtwoyears(20072008)ofintensivefielddatacollectionattwomanaged wetlandsitesinnorthwestSuisunMarshandtheirsurroundingtidalsloughs,anareawithprior documentedlowDOevents.Inaddition,thestudycollectedlimitedsoilsandwaterqualityfield dataandmappedvegetationforthreemanagedwetlandsitesinthecentralinteriorofSuisun Marsh,forthepurposeofexaminingwhetherwetlandsatotherlocationsexhibitcharacteristics thatcouldindicatepotentialforsimilarconcerns.InYear1ofthestudy,theobjectivewasto identifythebaselineconditionsinthemanagedwetlandsanddeterminewhichphysical managementconditionscouldbemodifiedforYear2toreducelowDOandMeHgproduction issuesmosteffectively.TheobjectiveofYear2wastoevaluatetheeffectivenessofthese modifiedmanagementactionsatreducingproductionoflowDOandelevatedMeHgconditions withinthemanagedwetlandsandtocontinueimprovingunderstandingoftheunderlying biogeochemicalprocessesatplay. ThisFinalEvaluationMemorandumexaminedatotalof19BMPs,14involvingmodifiedwater managementoperationsandtheremainingfiveinvolvingmodifiedsoilandvegetation managementpractices.SomeoftheseBMPswerepreviouslyemployedandothershavenotyet beentested.ForeachBMPthisreportassessesitsefficacyinimprovingwaterquality conditionsandpotentialconflictswithwetlandmanagement.Itmakesrecommendationsfor furtherstudy(eitherfeasibilityassessmentsorfieldtesting)andwhethertoconsiderforfuture use.CertainpreviouslyusedBMPswerefoundtobeimportantcontributorstopoorwater qualityconditionsandtheircontinueduseisnotrecommended.SomeBMPsthatcould improvewaterqualityconditionsappeardifficulttoimplementinregardstocompatibilitywith wetlandmanagement;theseBMPsrequirefurtherelaborationandfeasibilityassessmentto determinewhethertheyshouldbefieldtested.Inpracticeforanygivenwetland,thereislikely acombinationofBMPsthatwouldtogetherhavethegreatestpotentialtoaddressthelowDO andhighMeHgwaterqualityconcerns.Consequently,thisreportmakesnosweeping recommendationsapplicabletolargegroupsofwetlandsbutinsteadpromotesacareful FinalEvaluationMemorandum:StrategiesforResolvingLowDissolvedOxygenand MethylmercuryEventsinNorthernSuisunMarsh ExecutiveSummary considerationoffactorsateachwetlandorsmallgroupsofwetlandsandfromthatassessment toapplythemosteffectivesuiteofBMPs. Thisreportalsoidentifiesanumberofrecommendedfutureactionsandstudies.These recommendationsaregearedtowardimprovingtheprocessunderstandingoffactorsthat promotelowDOandhighMeHgconditions,theextentoftheseproblemsinSuisunMarsh,the regulatorybasisfortheDOstandardsforalargeestuarinemarsh,theeconomicsofBMPs,and alternativeapproachestoBMPsondikedmanagedwetlandsthatmayaddressthewater qualityissues.ThemostimportantoftheserecommendationsisthatfutureBMP implementationshouldbecarriedoutwithinthecontextofrigorousscientificevaluationsoas togainthemaximumimprovementinhowtomanagethesewaterqualityissuesinthediked managedwetlandsofSuisunMarsh. FEM_SuisunLowDOMeHg_1119_2011R0525.docx ES2 FinalEvaluationMemorandum:StrategiesforResolvingLowDissolvedOxygenand MethylmercuryEventsinNorthernSuisunMarsh Contents TableofContents EXECUTIVESUMMARY...................................................................................................................................ES1 1 INTRODUCTION.........................................................................................................................................1 1.1 PROBLEMSTATEMENT...........................................................................................................................................3 1.1.1 HistoryofLowDissolvedOxygenConditionsinSuisunMarsh...............................................................6 1.1.2 PeytoniaandBoyntonSloughsStudyArea............................................................................................8 1.1.3 SpatialContextofStudyAreas.............................................................................................................10 1.1.4 DissolvedOxygenStandardsinSuisunMarsh......................................................................................15 1.1.5 PreviousEffortstoManageLowDissolvedOxygenEvents..................................................................15 1.2 STUDYOBJECTIVES.............................................................................................................................................16 1.3 DATACOLLECTIONAPPROACH..............................................................................................................................1 7 1.3.1 StudyYear1Sampling(Fall2007–Spring2008)................................................................................21 1.3.2 StudyYear2Sampling(Fall2008).......................................................................................................27 1.4 MANAGEMENTACTIVITIESINWETLANDSTUDYSITESYEARS1AND2..........................................................................27 1.4.1 Wetland112........................................................................................................................................27 1.4.2 Wetland123........................................................................................................................................28 2 INTEGRATEDFINDINGSONKEYSTUDYQUESTIONS..................................................................................30 2.1 HYDROLOGICCHARACTERISTICSOFPEYTONIAANDBOYNTONSLOUGHS........................................................................30 2.2 QUALITYOFWATERSUPPLIEDTOTHEMANAGEDWETLANDS.....................................................................................32 2.2.1 TidalSloughs........................................................................................................................................33 2.2.2 FairfieldSuisunSewerDistrictTreatmentPlantEffluent.....................................................................35 2.2.3 Rainfall.................................................................................................................................................35 2.2.4 WatershedOutflows............................................................................................................................35 2.3 WATERQUALITYWITHINTHEMANAGEDWETLANDS................................................................................................36 2.3.1 DissolvedOxygen.................................................................................................................................36 2.3.2 DissolvedOrganicCarbon....................................................................................................................37 2.3.3 Methylmercury.....................................................................................................................................40 2.3.4 Salinity.................................................................................................................................................41