Nutrient.docx

Nutrient.docx

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Nutrient

NUTRIENTTRANSPORTDURINGBIOREMEDIATIONOFCRUDE

OILCONTAMINATEDBEACHES

BrianA.Wrens'（EnvironmentalTechnologies&Solutions,Rochester,NY）

MichelC.BoufadelandMakramT.Suidan（Univ.ofCincinnati,Cincinnati,OH）

AlbertD.Venosa（U.S.EPA,Cincinnati,OH）

ABSTRACT:

Theeffectofwaveenergyontransportofdissolvednutrientsintheintertidalzoneofsandybeacheswasstudiedbycomparingthewashoutratesofaconservativetracer（lithium）ontwobeachesinMaine.Thephysicalcharacteristicsofthetwobeachesweresimilar,andtheyweresubjectedtothesametidalinfluences,butthewaveenergieswereverydifferent.ScarboroughBeachisahighenergybeachthatfacessoutheasttowardtheAtlanticOcean,whereasFerryBeachisinaprotectedharbor.ThisdifferenceinwaveenergycausedlithiumtobewashedoutofScarboroughBeachmuchmorerapidlythanfromFerryBeach.ThehigherwaveenergyatScarboroughBeachalsoappearstohaveincreasedtheamountoflithiumthatwasdiluteddirectlyintothewatercolumn.Thesedifferencesintransportrateandmechanismhaveimportantimplicationsforthefeasibilityofbioremediationforcleanupofoilcontaminatedshorelines.

INTRODUCTION

Thegrowthrateofoildegradingbacteriaoncontaminatedshorelinesisoftenlimitedbytheavailabilityofnutrients,suchasnitrogenandphosphorus（PritchardandCosta,1991;Braggetal.,1993;Leeetal.,1993;Venosaetal.,1996）.Effectivebioremediationrequiresnutrientstoremainincontactwiththeoiledbeachmaterial,andtheconcentrationsshouldbesufficienttosupportthemaximalgrowthrateoftheoildegradingbacteriathroughoutthecleanupoperation.Contaminationofcoastalareasbyoilfromoffshorespillsusuallyoccursintheintertidalzone,wherethewashoutofdissolvednutrientscanbeextremelyrapid.Lipophilicandslowreleaseformulationshavebeendevelopedtomaintainnutrientsincontactwiththeoil（AtlasandBartha,1992）,butmostoftheserelyondissolutionofthenutrientsintotheaqueousphasebeforetheycanbeusedbyhydrocarbondegraders（Safferman,1991）.Therefore,designofeffectiveoilbioremediationstrategiesandnutrientdeliverysystemsrequiresanunderstandingofthetransportofdissolvednutrientsintheintertidalzone.

Transportthroughtheporousmatrixofabeachisdrivenbyacombinationofthreemainfactors:

tide,waves,andtheflowoffreshwaterfromcoastalaquifers.Thefocusofthisresearchwasontheeffectsoftideandwaveactivity.Tidalinfluencescausethegroundwaterelevationinthebeach,aswellastheresultinghydraulicgradients,tofluctuaterapidly（Nielsen,1990;Wrennetal.,1997）.Waveactivityaffectsgroundwaterflowthroughtwomainmechanisms.First,whenwavesrunupthebeachfaceaheadofthetide,someofthewaterpercolatesverticallythroughthesandabovethewaterlineandflowshorizontallywhenitreachesthewatertable（RiedlandMachan,1972）.Wavescanalsoaffectgroundwatermovementinthesubmergedareasofbeachesbyapumpingmechanismthatisdrivenbydifferencesinheadbetweenwavecrestsandtroughs（Riedletal.1972）.

Therelativeeffectsoftideandwavesonnutrienttransportintheintertidalzoneofsandybeacheswasinvestigatedbycomparingthewashoutofaconservativetracer,lithium,ontwobeachesinsouthernMaine.ScarboroughBeachisahighenergybeachthatfacestheAtlanticOcean,whereasFerryBeachisinashelteredharboratthemouthoftheScarboroughMarsh.Lithiumtransportat

FerryBeachwasdrivenalmostexclusivelybytidaleffects,whereastideandwavesbothaffectedtransportatScarboroughBeach.

EXPERIMENTALDESIGN

SiteDescription.Thetwobeachesusedinthisstudyaresubjectedtoverydifferentwaveenergies,butinotherrespectstheyarequitesimilar.Botharecomposedprimarilyofmediumtofinesandwithrelativelynarrowparticlesizedistributions.DifferencesinthecompositionofthetwobeachessuggestthatthehydraulicconductivityofScarboroughBeachmightbeslightlylargerthanFerryBeach,butthesmallpermeabilitydifferenceswereexpectedtohavemuchlessinfluenceonsolutetransportthanthedifferencesinwaveenergy.Thetidewasidenticalatbothsites.

PlotSetupandSampleCollection.Thetracerwasappliedtothebeachindiscreteareascalled"plots."Eachplotwas5mwide（i.e.,paralleltotheshoreline）,andtheywereeither10m（FerryBeach）or12m（ScarboroughBeach）long（i.e.,perpendiculartotheshoreline）.AlthoughtheplotsonFerryBeachwereshorterthanthoseonScarboroughBeach,thedifferenceinelevationbetweenthetops（i.e.,thelandwardedges）andthebottoms（i.e.,theseawardedges）oftheplotswasapproximatelythesameonbothbeaches.Theplotsweresetupsuchthatthelandwardedgeswereattheelevationthatwasexpectedforthehighesttidethatwouldoccurduringthestudy.

Atransectconsistingofsixmultiportsamplewellswasinstalledperpendiculartotheshorelinethroughthecenterofeachplot.ThelayoutofthesetransectsandtheelevationsofthetopsandbottomsoftheplotsonbothbeachesareshowninFigure1.Threeofthesixsamplewellswereinstalledinsidetheplots,onewellwasinstalledlandwardoftheplots,andtwowereinstalledseawardoftheplots.Figure1alsoshowsthelocationsofthesampleportsforeachwell.

Sprinklerswereusedtoapplythetracertothebeachsurfaceinsidetheplotboundariesatlowtide.Lithiumnitrate（>99.7%;CyprusFooteMineralCo.,KingsMountain,NC）wasdissolvedin100gallonsoffreshwatertoafinalconcentrationof33g/L,whichgaveitadensityapproximatelyequaltothelocalseawater.Watersampleswerecollectedfromthemultiportwellsperiodicallyforabouttwoweeks.

WaterLevelMeasurement.Thewaterlevelsinthebeachesweremeasuredwithtransectsofsixpiezometerwellsthatwereinstalledperpendiculartotheshoreline.Piezometerwellswereinstalledatthetop,bottom,andmiddleoftheplots.Onewellwaslandwardofthetop,andtwowereseawardofthebottomoftheplots.Themostseawardwell,whichwasscreenedoverafourfootintervalabovethebeachsurface,wasusedprimarilytomeasurethelevelofthetidewheneveritwashighenoughtosubmergeanypartofthesamplewelltransects.Vibratingwirepiezometers（RocTest,Inc.,Plattsburgh,NY）wereusedtomeasurethewaterlevelateachwellposition.Threereadingswereusuallytakenforeachpiezometerevery15minutes.Thesethreereadingswereaveragedtosmoothouttheeffectofwavesonthewaterlevelmeasurements.

RESULTSANDDISCUSSION

HydraulicGradients.Thetwomainforcesthatdrivesolutetransportinsandybeachesarewavesandtidallyinducedhydraulicgradients.Althoughnoquantitativemeasurementsofthewaveactivityatthetwobeachesusedinthesestudiesareavailableatthistime,aqualitativecomparisoncanbemadebyinspectionofFigure1.WhereasthewaterlevelchangedfairlysmoothlyatFerryBeachin

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FIGURE1:

Beachprofilesshowingwellpositionsandtheelevationsofthetopsandbottomsoftheexperimentalplots（i.e.,theareastowhichthetracerwasapplied）.Thecirclesoneachwellmarkthedepthsofthesampleports.Allelevationsweremeasuredrelativetoabenchmark,buttheabsoluteelevationsofthebenchmarksonthetwobeacheswerenotthesame.Thetidemeasurementsshowthattheabsoluteelevationsoftheplotsweresimilaronbothbeaches.Timeismeasuredrelativetothebeginning

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responsetothetide,theresponsewasquitejaggedatScarboroughBeach.Althoughmultiplereadingsweretakenwheneverwaterlevelmeasurementsweremade,itwasnotpossibletocompletelyeliminatevariationsduetowavesfromtheScarboroughBeachdata.

TheeffectsofwavescanalsobeseeninFigure2,whichshowsthehydraulicgradientsinthebottom（seaward）halfoftheplotsforbothbeaches.TheresponseatFerryBeachwasrelativelysmooth,whereasthegradientfluctuatedrapidlyatScarboroughBeach.Waverunupandsubtidalpumpingprobablybothcontributedtotheseabruptchangesinthehydraulicgradient.Ingeneral,theresponsesofthehydraulicgradientstothetideweresimilarinbothbeaches.Forexample,landwarddirected（i.e.,positive）hydraulicgradientsdevelopedonlybrieflyinthisregionofbothbeaches.（Landwarddirectedgradientspersistedmuchlongerinthetophalfoftheplots,however.）Mostofthetime,thehydraulicgradientsweredirectedseaward（i.e.,negative）,whichisconsistentwithpreviousobservations（Nielsen,1990;Wrennetal.,1997）.

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FIGURE2:

HydraulicgradientsinthebottomhalfoftheplotsatFerryandScarboroughBeaches.Positivevaluesindicatelandwarddirectedgradientsandnegativevaluesindicategradientsthataredirectedseaward.Thetimeismeasuredrelativetothebeginningoftheexperiment,andthetimescalesforthetwobeachesareoffsetby

6hourstoimprovereadability.

TracerWashout.LithiumwasremovedfromScarboroughBeachmuchmorerapidlythanfromFerryBeach.AtScarboroughBeach,lessth