2012Floatingwetlandmesocosmassessmentofnutri

ORIGINALPAPERFloatingwetlandmesocosmassessmentofnutrientremovaltoreduceecotoxicityinstormwaterpondsN.B.Chang•M.K.Islam•M.P.WanielistaReceived:21July2011/Revised:15October2011/Accepted:21December2011/Publishedonline:12April2012CEERS,IAU2012AbstractAgroupedmesocosmstudywasconductedwithdifferentwaterholdingcapacitiesandconditionstodeterminenutrientremovalefficiencyusingfloatingwet-landmacrophytes.Differentscenarioswerecreatedbychangingwaterdepth,littoralvegetation,sorptionmediaandareacoveragetoobservehowtheyaffectnutrientremovalefficiencies.Plantspecieswerescreenedandselectedbasedontheliterature,localavailabilityandpre-viouslyperformedmicrocosmstudies.Sorptionmediawerewarpedusinggeotextilefilterfosteringmicrobialcolonizationintherhizosphericzonetoenhancedenitrifi-cationandplantgrowth.Waterqualityparametersincludedtotalnitrogen,totalphosphorus,orthophosphate,nitrate–nitrogenandammonia–nitrogeninadditiontoinsituparameterssuchaspH,dissolvedoxygen,temperatureandchlorophyll-a.Compositesamplesacrossseverallocationswerecollectedperiodicallytounderstandthespatialdis-tributionoraggregationofnutrients.After3monthsofwaterqualitymonitoring,plantswereanalyzedfortissuenutrientconcentrations,andtheaverageuptakeratewascalculatedas36.39and1.48mgm-2day-1fornitrogenandphosphorus,respectively,bythefloatingtreatmentwetlandsystem.Finally,consideringthehighernutrientaggregationintherhizosphericzone,theremovalratewith5%areacoverageandwaterqualityimprovementbylit-toralzone,theoptimizeddesign,placementandmainte-nanceofthewholesystemwererecommended.KeywordsBestmanagementpracticeLittoralzoneNutrientaggregationRhizosphericzoneSorptionmediaIntroductionNutrients,suchasammonia,nitrite,nitrate,andphospho-rus,arecommoncontaminantsinwaterbodiesthatdirectlyorindirectlyaffectpublichealthandecosystemintegritywithacuteandchronicharmfuloutcome.Forexample,withoutpropertreatment,ammoniainwastewatereffluentscanstimulatephytoplanktongrowth,exhibittoxicitytoaquaticbiota,andexertoxygendemandinsurfacewaters(Beutel2006).Undissociatedammoniaisextremelyvola-tileinaqueoussolutionifammoniacannotbeionized;however,ionizedammoniaisverytoxicforfishspecies(Tarazonaetal.2008).Fishmortality,health,andrepro-ductioncanbeaffectedbythepresenceofminuteamountsofammonia-N(ServiziandGordon2005).Nitratecancausehumanhealthproblemssuchasliverdamageandevencancers(Gabeletal.1982;Huangetal.1998).Nitratecanalsobindwithhemoglobinandcreateanoxygendeficiencycalledmethemoglobinemiaininfants(Kim-Shapiroetal.2005).Nitritecanreactwithamineschemi-callyorenzymaticallytoformnitrosaminesthatarepotentcarcinogens(Sawyeretal.2003).Stormwaterrunoffishighlyvariableinbothintensityanddurationduetotheerraticnatureofstormevents.Theuseofconstructedwetlandsthatusevariousaquaticplantstopurifyandremediatenutrient-richstormwaterrunoff(Iamchaturapatraetal.2007)hassignificantlyincreased(Whiteetal.2009;Baldwinetal.2009;BelmontandMetcalfe2003).Thefloatingwetlandtechnologyisoneofthebestmanagementpractices(BMPs)forstormwatertreatmentbywhichmacrophytesremovepollutantsN.B.Chang(&)M.K.IslamM.P.WanielistaDepartmentofCivil,Environmental,andConstructionEngineering,UniversityofCentralFlorida,Orlando,FL32816,USAe-mail:[e-mail].(2012)9:453–462DOI10.1007/s13762-012-0061-7directly,providingasuitableenvironmentformicroor-ganismsandassimilatingthemintotheirtissuetotransformpollutantsandreducetheirconcentrations(Breen1990;Billoreetal.2008).Sediment-rootedplantsforconven-tionaltreatmentofwetlandsexperiencearangeofwaterdepthsandperiodsofinundation(GreenwayandPolson2007).Thedurationofinundation,thedepthofwater,andthefrequencyoffloodingordroughtaffectplantgrowth,establishmentandsurvival.Longperiodsoffloodingarestressfultosomebottom-rootedwetlandplants(Ewing1996;Headleyetal.2006).Tomanagethisissue,wetlandareamightbeincreasedtobufferagainstextremesduringwaterlevelfluctuations,orthehighflowscanbebypassed.Inthelattercase,asignificantportionofincomingstormwaterisuntreated(Headleyetal.2006).Inaddition,thelargelandarearequiredforinstallationisadefinitelimitationtotheirapplicability.Floatingtreatmentwet-lands(FTWs)areaninnovativevariantofthesewetlandsystemsandapossiblesolutiontothisproblem.Plantsgrowonfloatingmatsratherthanrootedinthesediments(Fig.1);therefore,waterdepthisnotaconcern,andthematsareunlikelyaffectedbyfluctuationsinwaterlevels.Biologically,anaquaticmacrophyte-basedwastewatertreatmentsystemisfarmorediversethanpresent-daymechanicaltreatmentsystems(Hammer1989;Moshiri1993).Free-floatingmacrophytesshadethewatercolumn,resultinginacoolerhabitatforfishandmacroinvertebrates(NahlikandMitsch2006).Thehangingrootsprovidealargesurfaceareafordenitrifyingbacteria,creatingananaerobicenvironmentthatcanremovenitratebythedenitrificationprocess(Govindarajan2008),andentrapfinesuspendedparticulatesthatwouldotherwiseremaininsuspensioninaconventionalpondsystem(Headleyetal.2006).Microbesthatliveonthesurfaceofplantrootsinawetlandremove10timesmorenitratethandotheplantsthemselves(Adams1992).Thesemicrobeschangenitrate–nitrogen(NO3–