2011Performanceofafloatingtreatmentwetlandfo

WETLANDRESTORATIONPerformanceofafloatingtreatmentwetlandforin-streamwaterameliorationinNEItalyG.DeStefani•D.Tocchetto•M.Salvato•M.BorinPublishedonline:18May2011SpringerScience+BusinessMediaB.V.2011AbstractFloatingtreatmentwetlandsareinnova-tivesystemsandtheirprocessesarestillscarcelyknownwithinthetraditionalmethodsofphytodepu-ration.Togaininitialinformationontheirperfor-manceandpotentialinremovingpollutants,twoexperimentshavebeenconductedinnortheastItaly,inaNaturalParkwithresurgentwater.Barriersformedbyanewpatentedfloatingelementweretestedinrealclimaticandwaterflowconditions.Oneexperimentwasconductedinachannelreceivingaquacultureeffluents,whiletheotherwassetintwocleanerchannelstotesttwoinstallationdesigns(twobarrierscomposedoftwolinesofelements—292designandtwocomposedofthreelinesofele-ments—293design).Differentmacrophytespecieswereused(Phragmitesaustralis,Carexelata,Juncuseffusus,Typhalatifolia,Chrysopogonzizanioides,Sparganiumerectum,andDactylisglomerata).Thefloatingsystemswereeasilyinstalledandrequiredfewmaintenanceoperations.Nativeplantsgrewsuccessfully,developingroots90–135cmdeep1yearafterplanting.Conversely,Chrysopogonziza-nioidesshowedscarceadaptationtolocalconditions.Inthefirstexperiment,medianchemicaloxygendemand(COD)inwaterpassingthroughthefloatingwetlandsystemwasreducedby66%,biochemicaloxygendemandby52%,andtotalphosphorusby65%.Inthesecondexperiment,the293designhadaslightlybetterperformancethan292inreducingCOD(38and28%ofremoval,respectively).ThetwodesignsperformedsimilarlyonNO3-N,reducingtheincomingconcentrationsby12%(293design)and14%(292).Thisformofnitrogenrepresentsalmostallthetotalnitrogen,whichwasabatedby13%bythe293designandby29%by292design.KeywordsFloatingtreatmentwetlandRiverwatertreatmentMacrophytesAquacultureeffluentsIntroductionFloatingtreatmentwetlands(FTW)areinnovativewithinthetraditionalmethodsofphytodepuration.Thesesystemsemployrooted,emergentplantsgrowingasafloatingmatonthewatersurfaceratherthaninthesediments(Headley&Tanner,2006).Thistechniquecomplementsnaturalfloatingwetlands,definedbySasseretal.(1991)asamarshofvascularvegetationhavingasignificantmatofliveanddeadroots,peatanddetritus,thatfloatsoveralayeroffreeGuesteditors:DominikZak,RobertMcInnes,Jo¨rgGelbrecht/Restoration,biogeochemistryandecologicalservicesofwetlandsG.DeStefani(&)M.SalvatoM.BorinDepartmentofEnvironmentalAgronomyandCropProduction,UniversityofPadova,Padova,Italye-mail:[e-mail],SpinOffatPadovaUniversity,Padova,Italy123Hydrobiologia(2011)674:157–167DOI10.1007/s10750-011-0730-4water.Duetothefactthatthesystemcanfloat,plantsarenotaffectedbyfluctuationsinwaterlevels,soFTWhaveseveralapplicationsandareusedespe-ciallyinpondsorrivers.Itispossibletousenonfloatingplantshighlyefficientintermsofwaterpurification,withawell-developedrootingsystemandimpossibleforplantstoescapefromtheareaallocatedfortreatmentandcolonizespaceinthewaterbody.Furthermore,FTWcanoperateatgreaterwaterdepththanconventionalwetlands,andarethusabletoachieveahigherleveloftreatment.Innature,floatingwetlandsexistthatconsistofafloatingorganicmatsupportingplantgrowth,wheretheself-buoyancyismadepossiblebytheentrapmentwithinthematrixofgasesgeneratedbyanaerobicmetabolismandthepresenceofairspacesintherootsofcertainplantspecies(Hogg&Wein,1988).Floatingtreatmentwetlandsareartificiallycreatedsystemsusingvariouswaystotrapmacrophytesinself-buoyantmats.Theymaysustainsuitableplants,whichareabletoextendtheirrootsinthewatercolumn,instillorrunningwaters,andperformthetypicalfunctions:physicalfilteringofthewaterflow,dissolvednutrientsuptakeandsupportformicroor-ganisms.Vegetationabsorbsnutrientstransformedintosimpleelementsdissolvedinwatercolumn.Thisactionisperformedbybacterialcommunitieswhichgrowontherootsystemandthatliveinsymbiosiswithplants.Itisthusimportanttousedifferentbotanicalspeciessothatdifferentbacterialcoloniesdevelopthatwillhelporganicmacromolecules’degradation.Purificationefficienciesofphytodepu-rationsystemsdependonthetypesofplantsused,localclimateconditions,thetypeofsystemadopted,maintenanceperformedandseveralothertechnical,ecological,andmicrobiologicalfactors.Floatingsystemsdevelopedaroundtheworldhaveperformedwellinpollutioncontrol(removingsus-pendedsolids(SS),nitrogen(N),phosphorus(P),biochemicaloxygendemand(BOD),chemicaloxy-gendemand(COD),andmetalsinparticular)andinthecreationofnewwaterenvironments.Themainapplicationsintermsofwaterqualityimprovementareforstormwater,sewage,acidminedrainage,piggeryeffluent,poultryprocessingwastewater,andwatersupplyreservoirs(Headley&Tanner,2006).AfamoussystemforstormwaterrunofftreatmenthasbeenoperatingatHeathrowAirportsince1994,toremovemainlyglycolandassociatedBOD.Thetreatmentsystemconsistsofdifferentcomponentsandthefloatingreed-bedsachievedaBODremovalefficiencyof43%(Revittetal.,2001).VanAckeretal.(2005)describeafloatingsysteminBelgiumfortreatmentofcombinedseweroverflowsandgivethesepollutantremovalresults:COD33–68%,SS66–95%,totalP61%andavariabletotalNremovaldueprobablytotheanaerobicconditionofthewaterbeneaththefloatingislan