AREVIEWOFTHESCIENTIFICLITERATURE ONRIPARIANBUFFER WIDTH,EXTENTANDVEGETATION SethWenger forthe OfficeofPublicService&Outreach InstituteofEcology UniversityofGeorgia RevisedVersion•March5,1999 InstituteofEcology,UniversityofGeorgia,Athens,Georgia,30602-2202 [email protected] 1 TheOfficeofPublicServiceandOutreachatthe InstituteofEcologyprovidesscientificandlegalex- pertisetothecitizensofGeorgiainthedevelopment ofpoliciesandpracticestoprotectournaturalheri- tage.Thegoalsoftheofficeareto: • Developandimplementaresearchagendatomeet communityneeds; • Provideanopportunityforstudents,facultyand stafftoworkwithotherdisciplinesinintegrated environmentaldecisionmakingandproblem- solvingtoimprovetheirabilitytounderstand, communicatewith,andinfluenceother disciplines; • Buildcapacityforservicelearninginthesciences byprovidingstudentsanopportunitytoapply skillslearnedinthetraditionalclassroomsetting topressingcommunityconcernsandproblems; • SupporthighqualityscienceeducationinK-12 schoolsbyprovidingprogramsforstudentsand instructionalsupportandtrainingforteachers; • Increaseawarenessoftheimportanceof addressingenvironmentalissuesproactively withintheuniversitycommunityandthegreater community. Thepublicationofthispaperwasmadepossible bysupportfromtheTurnerFoundation,R.E.M./ Athens,L.L.C.,andtheUniversityofGeorgiaOffice oftheVicePresidentforPublicServiceandOutreach. FormoreinformationabouttheOfficeofPublic ServiceandOutreachattheInstituteofEcology,please contactLaurieFowlerat706-542-3948. 2 EXECUTIVESUMMARY ManylocalgovernmentsinGeorgiaare buffersshouldbesufficientundermanycondi- developingriparianbufferprotectionplansand tions.Itisespeciallyimportanttopreserve ordinanceswithoutthebenefitofscientifically- wetlands,whicharesitesofhighdenitrification basedguidelines.Toaddressthisproblem,over activity. 140articlesandbookswerereviewedtoestablish Tomaintainaquatichabitat,theliterature alegally-defensiblebasisfordeterminingriparian indicatesthat10-30m(35-100ft)nativeforested bufferwidth,extentandvegetation.Thisdocu- riparianbuffersshouldbepreservedorrestored mentpresentstheresultsofthisreviewand alongallstreams.Thiswillprovidestream proposesseveralsimpleformulaeforbuffer temperaturecontrolandinputsoflargewoody delineationthatcanbeappliedonamunicipalor debrisandotherorganicmatternecessaryfor county-widescale. aquaticorganisms.Whilenarrowbuffersoffer Sedimentistheworstpollutantinmany considerablehabitatbenefitstomanyspecies, streamsandrivers.Scientificresearchhasshown protectingdiverseterrestrialriparianwildlife thatvegetativebuffersareeffectiveattrapping communitiesrequiressomebuffersofatleast100 sedimentfromrunoffandatreducingchannel meters(300feet).Toprovideoptimalhabitat, erosion.Studieshaveyieldedarangeofrecom- nativeforestvegetationshouldbemaintainedor mendationsforbufferwidths;buffersasnarrow restoredinallbuffers. as4.6m(15ft)haveprovenfairlyeffectiveinthe Areviewofexistingmodelsforbufferwidth shortterm,althoughwiderbuffersprovide andeffectivenessshowedthatnoneareappropri- greatersedimentcontrol,especiallyonsteeper ateforcounty-levelbufferprotection.Models slopes.Long-termstudiessuggesttheneedfor werefoundtobeeithertoodata-intensivetobe muchwiderbuffers.Itappearsthata30m(100 practicalorelselackedverificationandcalibra- ft)bufferissufficientlywidetotrapsediments tion.Potentialvariablesforuseinabufferwidth undermostcircumstances,althoughbuffers formulawereconsidered.Bufferslopeandthe shouldbeextendedforsteeperslopes.An presenceofwetlandsweredeterminedtobethe absoluteminimumwidthwouldbe9m(30ft). mostimportantandusefulfactorsindetermining Tobemosteffective,buffersmustextendalongall bufferwidth. streams,includingintermittentandephemeral channels.Buffersmustbeaugmentedbylimitson Threeoptionsforbufferguidelineswere impervioussurfacesandstrictlyenforcedon-site proposed.Allaredefensiblegiventhescientific sedimentcontrols.Bothgrassedandforested literature.Thefirstprovidesthegreatestlevelof buffersareeffectiveattrappingsediment,al- protectionforstreamcorridors,includinggood thoughforestedbuffersprovideotherbenefitsas controlofsedimentandothercontaminants, well. maintenanceofqualityaquatichabitat,andsome minimalterrestrialwildlifehabitat.Thesecond Buffersareshort-termsinksforphosphorus, optionshouldalsoprovidegoodprotectionunder butoverthelongtermtheireffectivenessis mostcircumstances,althoughseverestorms, limited.Inmanycasesphosphorusisattachedto floods,orpoormanagementofcontaminant sedimentororganicmatter,sobufferssufficiently sourcescouldmoreeasilyoverwhelmthebuffer. widetocontrolsedimentshouldalsoprovide adequateshort-termphosphoruscontrol.How- ever,long-termmanagementofphosphorus OptionOne: requireseffectiveon-sitemanagementofits • Basewidth:100ft(30.5m)plus2ft(0.61m) sources.Bufferscanprovideverygoodcontrolof per1%ofslope. nitrogen,includenitrate.Thewidthsnecessary forreducingnitrateconcentrationsvarybasedon • Extendtoedgeoffloodplain. localhydrology,soilfactors,slopeandother • Includeadjacentwetlands.Thebufferwidth variables.Inmostcases30m(100ft)buffers isextendedbythewidthofthewetlands, shouldprovidegoodcontrol,and15m(50ft) whichguaranteesthattheentirewetlandand anadditionalbufferareprotected. 3 • Existingimpervioussurfacesintheriparian Foralloptions,buffervegetationshould zonedonotcounttowardbufferwidth(i.e., consistofnativeforest.Restorationshouldbe thewidthisextendedbythewidthofthe conductedwhennecessaryandpossible. impervioussurface,justasforwetlands). Allmajorsourcesofcontaminationshouldbe • Slopesover25%donotcounttowardthe excludedfromthebuffer.Theseincludecon- width. structionresultinginmajorlanddisturbance, impervioussurfaces,loggingroads,mining • Thebufferappliestoallperennialand activities,septictankdrainfields,agricultural intermittentstreams.Thesemay fields,wastedisposalsites,livestock,andclear cuttingofforests.Applicationofpesticidesand OptionTwo: fertilizershouldalsobeprohibited,exceptasmay ThesameasOptionOne,except: beneededforbufferrestoration. • Basewidthis50ft(15.2m)plus2ft(0.61m) Allofthebufferoptionsdescribedabovewill per1%ofslope. providesomehabitatformanyterrestrialwildlife species.Toprovidehabitatforforestinterior • Entirefloodplainisnotnecessarilyincluded species,atleastsomeripariantractsofatleast inbuffer,althoughpotentialsourcesofsevere 300ftwidthshouldalsobepreserved.Identifica- contaminationshouldbeexcludedfromthe tionoftheseareasshouldbepartofanoverall, floodplain. county-widewildlifeprotectionplan. • Ephemeralstreamsarenotincluded;affected Forriparianbufferstobemosteffective, streamsarethosethatappearonUS somerelatedissuesmustalsobeaddressed.These GeologicalSurvey1:24,000topographic includereducingimpervioussurfaces,managing quadrangles.Alternatively,buffercanbe pollutantson-site,andminimizingbuffergaps. appliedtoallperennialstreamsplusall intermittentstreamsofsecondorderorlarger OptionThree: • Fixedbufferwidthof100ft. • Thebufferappliestoallstreamsthatappear onUSGeologicalSurvey1:24,000 topographicquadranglesor,alternatively,all perennialstreamsplusallintermittentstreams ofsecondorderorlarger(asforOption Two). 4 Contents EXECUTIVESUMMARY .............................................................................................................................1 I.BACKGROUNDANDINTRODUCTION ................................................................................................4 Acknowledgments ..................................................................................................................................6 ScopeofReview .....................................................................................................................................6 WhyAnotherLiteratureReview?............................................................................................................7 BackgroundonRiparianZones ..............................................................................................................7 II.SEDIMENT..............................................................................................................................................9 Effects ....................................................................................................................................................9 Sources ...................................................................................................................................................9 LiteratureReview .................................................................................................................................11 SedimentinSurfaceRunoff ..................................................................................................................12 ChannelErosion ...................................................................................................................................16 SummaryandRecommendations ..........................................................................................................18 III.NUTRIENTSANDOTHERCONTAMINANTS ..................................................................................19 A.PHOSPHORUS................................................................................................................................19 Effects ............................................................................................................................................19 Sources ..........................................................................................................................................19 LiteratureReview ...........................................................................................................................19