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cznMinnesota Pollution Control Agency <br />EnvironmentalOutcomesDivision <br />GroundWaterMonitoring &AssessmentProgram <br />Inabufferarea, groundwaterpassesthroughorunderthe <br />vegetatedarea.Watermustinteractwiththevegetationto <br />beimpactedbyit. Consequently ,vegetatedbufferswill <br />havetheirgreatestimpactinareaswheregroundwateris <br />closetothesurface .Inthediagramonthefirstpageof <br />thisfactsheet, nitratesinfiltratethroughsoilinthe <br />agriculturaluplandarea .Whenthiswateremergesasa <br />springalonganimpermeablezoneorinshallowground <br />water, grassesandtreestakeupsomeofthenitrate. <br />Nitrateisalsobrokendownintheforestedareathrougha <br />processcalled "denitrification." <br />Nitrateistypicallythechemicalofconcerninground <br />water. Riparianforestsretainupto99percentofnitrate, <br />comparedtoabout85percentinazonevegetatedwith <br />grass. <br />Vegetationremovesaboutonethirdofthenitratein <br />shallowgroundwater .Thenitrogentakenupbyplantsis <br />storedintheirtissues .Thisoccursonlyduringthe <br />growingseason. <br />Themostimportantmechanismofnitrateremovalis <br />denitrification. Microorganisms ,suchasbacteria,utilize <br />nitrateduringfoodproduction .Thebacteriatransformthe <br />nitratetonitrogengas ,whichisthenreleasedtothe <br />atmosphere. Microorganismsalsoneedorganicmatter <br />duringthisprocess ,andvegetationisthesourceofthis <br />organicmatter. Organicmatterisreleasedwhenleaves <br />andotherplantpartsdieandreachthesoilsurface .These <br />plantpartsarebrokendownandinfiltratethroughthesoil, <br />intothegroundwater ,wheretheyareusedby <br />microorganisms. Consequently, denitrificationratesare <br />highestandplantshavetheirgreatestimpactinsoilandin <br />shallowgroundwaterthatisinterceptedbyplantroots. <br />Theeffectofdilutiononreducingnitrateconcentrationsin <br />groundwaterissmallcomparedtoplantuptakeand <br />denitrification.Otherchemicals ,suchasherbicidesand <br />tracemetals, maybeaffectedinwayssimilartonitrate. <br />Thefollowingfactorsenhanceremovalofnitrateorother <br />chemicalsinavegetatedbufferzone: <br />• moderatelypermeablesoilsthatallowinfiltrationbut <br />notexcessivelyrapidflow; <br />• groundwaterwithinito3meters (3tolOfeet)ofthe <br />landsurface ,thusallowingforplantuptakeand <br />removalinbothsoilandgroundwater; <br />• uniformflowingroundwater ,suchasoccursinsand <br />andgravelorsandstoneaquifers; <br />February2000� <br />• groundwaterwithhighconcentrationsofreduced <br />sulfur, whichcanbeusedinsteadoforganicmatter <br />duringdenitrification; <br />• increasedplantproduction;and <br />• increasedwidthofthebufferzone ,whichallowsa <br />greaterareafromwhichchemicalscanberemoved. <br />Whataresomeguidelinesforestablishing <br />vegetativebuffers? <br />• Vegetativebuffersshouldbeusedinconjunctionwith <br />landmanagementsystemsthatincludenutrient <br />managementandsedimentanderosioncontrol. <br />• Buffersshouldbe 18.3meters (60feet) ormorewide <br />andcontaintreesandshrubs. <br />• Bottomlandhardwoods ,suchascottonwood,silver <br />maple,willowandgreenash ,aretolerantofwaterand <br />removelargequantitiesofnutrients .Shrubs,suchas <br />dogwoods,ninebark ,chokecherryandviburnum, <br />provideadditionalcoverbeneaththetreecanopyand <br />areeffectiveinremovingnutrientsfromwetzones. <br />Increasingthevarietyoftreesandshrubsprovides <br />greaterdiversityinnutrientuptakeandenhances <br />uptakeoverlongperiods .Someplantspeciesmaybe <br />sensitivetoherbicidespresentingroundwater. <br />• Anadditionalzonetoenhanceinfiltrationofwater <br />mayincludegrasses .Thisgrassystripshouldbeat <br />least6.1 meters (20feet) wide. Recommendedspecies <br />includeswitchgrassorothernativegrasses. <br />• Forestsaresomewhatmoreeffectiveatremoving <br />nutrientsfromshallowgroundwater. <br />• Onpermeablesoils ,utilizeatreedensityofabout35 <br />percentofthetotalvegetativeareatoprovidethemost <br />effectiveremovalofnitrate. <br />• <br />References <br />ThefollowingWebsitesaregoodstartingpointsfor <br />gatheringmoreinformationonriparianbuffersandwater <br />quality. Thesecondsiteprovidesalistofpublications. <br />http : / /ink.yahoo.com/bin /query ?p = riparian +buffer +nitrate +groun <br />d +water &hc= 0 &hs =0 <br />http: / /www.serc.si.edu/SERC web html/pub ripzone.html <br />http : / /affiliate.directhit.com/fcgi <br />bin/DirectHitWeh.fcg? alias = websrch &fmt= html &qry= Riparian. <br />&meta= rs &persrch =iIj <br />Vegetativebuffersforprotectingandim provinggroundwaterquality Page2 <br />