combined effects of short term rainfall paterns an

eScholarshipprovidesopenaccess,scholarlypublishingservicestotheUniversityofCaliforniaanddeliversadynamicresearchplatformtoscholarsworldwide.LawrenceBerkeleyNationalLaboratoryPeerReviewedTitle:Combinedeffectsofshort-termrainfallpatternsandsoiltextureonnitrogencycling--AModelingAnalysisAuthor:Gu,C.PublicationDate:07-13-2010PublicationInfo:LawrenceBerkeleyNationalLaboratoryPermalink::LBNLPaperLBNL-3338EPreferredCitation:JournalofContaminantHydrology,112,1-4,141-154,2010CombinedEffectsofShortTermRainfallPatternsandSoilTextureonSoilNitrogenCycling-------AModelingAnalysisChuanhuiGu1andWilliamJ.Riley21BerkeleyWaterCenter,UniversityofCalifornia,Berkeley,CA2EarthSciencesDivision,LawrenceBerkeleyNationalLaboratory,Berkeley,CAAbstractPrecipitationvariabilityandmagnitudeareexpectedtochangeinmanypartsoftheworldoverthe21stcentury.Weexaminedthepotentialeffectsofintra-annualrainfallpatternsonsoilnitrogen(N)transportandtransformationintheunsaturatedsoilzoneusingadeterministicdynamicmodelingapproach.Themodel(TOUGHREACT-N),whichhasbeentestedandappliedinseveralexperimentalandobservationalsystems,mechanisticallyaccountsformicrobialactivity,soil-moisturedynamicsthatrespondtoprecipitationvariability,andgaseousandaqueoustracertransportinthesoil.Here,wefurthertestedandcalibratedthemodelagainstdatafromaprecipitationvariabilityexperimentinatropicalsysteminCostaRica.Themodelwasthenusedtosimulateresponsesofsoilmoisture,microbialdynamics,nitrogen(N)aqueousandgaseousspecies,Nleaching,andNtrace-gasemissionstochangesinrainfallpatterns;theeffectofsoiltexturewasalsoexamined.ThetemporalvariabilityofnitrateleachingandNO,N2,andN2Oeffluxesweresignificantlyinfluencedbyrainfalldynamics.Soiltexturecombinedwithrainfalldynamicsalteredsoilmoisturedynamics,andconsequentlyregulatedsoilNresponsestoprecipitationchanges.Theclayloamsoilmoreeffectivelybufferedwaterstressduringrelativelylongintervalsbetweenprecipitationevents,particularlyafteralargerainfallevent.SubsequentsoilNaqueousandgaseouslossesshowedeitherincreasesordecreasesinresponsetoincreasingprecipitationvariabilityduetocomplexsoilmoisturedynamics.Forahighrainfallscenario,highprecipitationvariabilityresultedinashighas2.4-,2.4-,1.2-,and13-foldincreasesinNH3,NO,N2OandNO3-fluxes,respectively,inclayloamsoil.Insandyloamsoil,however,NOandN2Ofluxesdecreasedby15%and28%,respectively,inresponsetohighprecipitationvariability.OurresultsdemonstratethatsoilNcyclingresponsestoincreasing1precipitationvariabilitydependsonprecipitationamountandsoiltexture,andthataccuratepredictionoffutureNcyclingandgaseffluxesrequiresmodelswithrelativelysophisticatedrepresentationoftherelevantprocesses.1IntroductionAnthropogenicinputsofreactivenitrogen(N)toecosystemshaveledtosignificantenvironmentalconsequences(Aberetal.,2003;Gallowayetal.,2008).AlterationofthenaturalNcyclehasadirectimpactonwater(NO3-)andatmosphericpollution(N2O,NO,NH3)(Gallowayetal.,2003).GroundwaterNO3-concentrationsexceeddrinking-waterstandardsinmanyareasasaresultofinputsfromfertilizedagriculture,resultinginpotentialhumanhealtheffects(PowerandSchepers,1989;SpaldingandExner,1993;Squillaceetal.,2002).ElevatedNO3-concentrationsinleachateandsurfacewatercanalsoleadtoeutrophicationoflakesandestuaries(Lowranceetal.,1997).Nitrousoxide(N2O)isanimportantgreenhousegasandisinvolvedinthedestructionofstratosphericozone(IPCC,2001).Nitricoxide(NO)emissionscontributetotroposphericozoneformationandaciddeposition(McTaggartetal.,2002).NH3emissionsaffecttheenvironmentintheformofwetanddrydepositionofNH4NO3and(NH4+)2SO4salts,causingacidificationofpoorlybufferedsoilsandeutrophication(vanderWeerdenandJarvis,1997).TheseconcernshavestimulatedstudiestoidentifypotentialfutureclimatechangeeffectsonNleachingandemissionsfromecosystems(Skibaetal.,1997).PrecipitationandtheresultingsoilwaterdynamicsstronglyregulateNcyclinginterrestrialecosystems(Aranibaretal.,2004)viaeffectsonphysicaltransport(Brooksetal.,1999)andsoilmicrobialNtransformations(Correetal.,2002).Nitrificationanddenitrificationarethermodynamicallyfavorableredoxreactionsmediatedbysoilmicrobecommunities(Hedinetal.,1998).Redoxstatusis,therefore,aprimarycontrollingfactoroftheseprocessesinsoils(BollmannandConrad,1998).Further,Nlossesinsoilsareepisodicinnature.PulsesofNgasproductionassociatedwithtransientchangesinsoilmicrositeenvironmentshavebeenshowntoaccountforsignificantsurgesofNemissionstotheatmosphereinrelativelyshorttimespans(Guetal.,2009;Lietal.,1992;Maggietal.,2008;Riley&Matson,2000).Consequently,themagnitudeandextentofN2biogeochemicalprocessesvarywidelywithchangesinsoilwaterdynamics,whicharelargelydeterminedbysoil(e.g.,clayandsoilorganicmattercontent)andrainfallcharacteristics.Manygeneralcirculationmodelsforecastahigherfrequencyofextremerainfallevents,alowerfrequencyofrainfalldays,andlongerintervalsofdryperiods(Easterlingetal,2000;IPCC,2007).Itiswellknownthatchangesinprecipitationdirectlyaltersoilwatercontentandelementcycles.Anexperimentalstudyhasdemonstratedthatincreasedtempor