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Easternoyster(Crassostreavirginica)filtration,biodeposition,andsedimentnitrogencyclingattwooysterreefswithcontrastingwaterqualityinGreatBayEstuary(NewHampshire,USA)TimothyJ.Hoellein•ChesterB.Zarnoch•RaymondE.GrizzleReceived:29January2014/Accepted:4September2014/Publishedonline:17September2014SpringerInternationalPublishingSwitzerland2014AbstractBenthicdepositionofcarbon(C)andnitrogen(N)-richoysterbiodepositsmayincreasedenitrification,oranaerobicrespirationofnitrate(NO3-)todi-nitrogengas(N2).However,environ-mentaldriversofCandNdynamicsinoysterbiodepositsandreef-adjacentsedimentsrequireclarification.InJuly2012,wecollectedintactsedimentcoresadjacenttoand15–20mawayfromtwooysterreefs(Crassostreavirginica)inGreatBay,NewHampshire,USA:onereferencesiteandonesitewithculturaleutrophication.Wealsomea-suredseston,chlorophylla,andinsituoysterfeedingandbiodeposition.Coreswereincubatedincontin-uous-flowchamberswhereinflowwaterreceived15N-ammonium(NH4?),15NO3-,ornoisotopes(control).Wequantifiedfluxesofdissolvednutrientsandgasses(oxygen,28N2,29N2,30N2,andargon)after24h.Finally,wemeasuredsize-fractionatedsedimentorganicmatter.Attheeutrophicsite,abundantphytoplanktoninthe5–28lmsizerangewascorrelatedwithenhancedoysterfeedingratesandbiodepositquality(lowerC:N).Thissitehadgreaterdenitrificationratesinreef-adjacentcoresrelativetodistalcores.Lowproductionof29,30N2in15NH4?amendedcoressuggestedwatercolumnorbiodepositNH4?wereunlikelytobeconvertedtoN2.Atbothsites,reef-adjacentcoreshadmoreshellandhigher29,30N2productionwith15NO3-additionrelativetodistalcores,suggestingdirectdenitrifica-tionenhancementnearreefs.OysterslikelyincreasedsedimentN2productionviahighqualitybiodeposits(eutrophicsite),andNO3-diffusionviastructuralcomplexityofreef-adjacentsediment(bothsites).Overall,resultssuggestoyster-mediatedecosystemsservicesmaybeexpectedtovarywithenvironmentalconditions.KeywordsBiodepositsClearancerateDenitrificationEutrophicationPhytoplanktonResponsibleEditor:LeilaJ.Hamdan.ElectronicsupplementarymaterialTheonlineversionofthisarticle(doi:10.1007/s10533-014-0034-7)containssupple-mentarymaterial,whichisavailabletoauthorizedusers.T.J.Hoellein(&)DepartmentofBiology,LoyolaUniversityChicago,1032WSheridanRd,Chicago,IL60660,USAe-mail:[e-mail]alSciences,BaruchCollege,CityUniversityofNewYork,BoxA-0506,17LexingtonAve,NewYork,NY10010,USAe-mail:[e-mail]aboratoryandDepartmentofBiologicalSciences,UniversityofNewHampshire,85AdamsPointRoad,Durham,NH03824,USAe-mail:[e-mail]123Biogeochemistry(2015)122:113–129DOI10.1007/s10533-014-0034-7IntroductionOysterreefshavesuffered[80%reductionfromglobalhistoricranges(Becketal.2011),attributedtoharvest,disease,andenvironmentaldegradations(Becketal.2011).InNewHampshire,similardeclineshaveoccurredwiththemostdramaticrecentlossessincethemid-1990s(Barberetal.1997;PiscataquaRegionEstuariesPartnership2013).Healthyoysterreefsprovidevaluableecosystemservices(Coenetal.2007;GrabowskiandPeterson2007)includingfishhabitat(Coenetal.1999),waterfiltration(Grizzleetal.2008b;Plutchaketal.2010),andincreaseddenitrification,ortheanaerobicmicrobialrespirationofnitrate(NO3-)todinitrogengas(N2)(Kelloggetal.2013).Althoughhistoricallyoysterrestorationpro-gramshavefocusedonoystersasaharvestableresource,documentationoftheircontributiontoecosystemservicesandecologicalcommunitieshascausedashiftinemphasisinmanyareas(BrumbaughandCoen2009;Coenetal.2007;Luckenbachetal.1999;ZuErmgassenetal.2013).Developingbestpracticesforrestorationandconservationofoysterreefsasatooltoaddressculturaleutrophicationrequiresdocumentationofmultipleoyster-mediatedecosystemservices(CercoandNoel2007),acrossvariableenvironmentalconditions(HoelleinandZar-noch2014).Oysterscouplebenthicandpelagiccomponentsofecosystemsthroughfiltration(i.e.,clearance)andexcretion(Dame2012;NewellandLangdon1996).Particlescapturedbyoystersaresortedtomaximizetheingestionofnutritiousmaterial.Excessandnon-nutritiousparticlesarerejectedaspseudofeces.Oys-tersingestthepalatablecomponentofthefiltrate,digestthefood,andreleaseunabsorbedmaterialasfeces.Bodysizeandtemperaturearewellstudieddriversofoysterfeedingbehavior(Cranfordetal.2011;NewellandLangdon1996).Sestonconcentra-tionandnutritionalqualitycanalsoaffectoysterfiltrationandrelativeproductionoffecalandpseu-dofecalbiodeposits(Newell2004).Forexample,Ryther(1954)demonstratedthatoysterstocksinGreatSouthBay(NY,USA)werenegativelyaffectedbyextensivebloomsofpicoplanktonalgaewhichwerestimulatedbyhighlevelsofammoniaanduricacidfromagriculturalrunoff.Oystersretainanddigestfewerphytoplanktonfromthesesmallestsizeclasses(i.e.,below5to6lm)(Riisga˚rd1988).Conversely,eutrophicconditionsinthePeconicEstuary(NY,USA)favoreddiatomsandautotrophicnanoflagellateswhichwerepositivelycorrelatedwithoystergrowth(Walletal.2013).Theinfluenceofeutrophicationonoysterfiltrationandbiodepositionviachangesinsestonisimportanttostudyasmanyreefconservationandrestorationprojectsoccurinsiteswithculturaleutrophication(Ho