NutrientWord下载.docx
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NutrientWord下载.docx
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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
oftheexperiment(i.e.,whenthetracerwasapplied).
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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
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