国外关于湿地研究的论文(4)

118W.Shuwenetal./EcologicalEngineering18(2001)115–120

3.1.Designandmanagement

3.1.1.Choosingasite

Investigationsontheplantcommunitysucces-sionsereofYanchengcoastalbeachecosystemsweredonebeforechoosingthemitigationsite(Fig.1).Thedominantplantcommunitiesinthetidalzonecanbeclassi edintothreecategories:(1)theprimarytypesofplantationinsuccessiondominatedbysaltlivingwornwood(Suaedasalsa);(2)thexerarchclimaxwherelalanggrass(Imper-atacylindrica)isdominant;and(3)themarshcommunitywherereed(Phragmitescommunis)prevails.Thesuccessionalseresofreedandlalanggrasspartiallyoverlapanddivergemainlybecauseofwaterconditionsintheirecosystems.Wecanconcludefromthesuccessionhistorythattheenvironmentalconditionsofreedmarshandlalanggrasslandaresimilarexceptforwater;thisisalsocon rmedbytheinterestingphenomenonoftransientclimaxobservedinYanchengtidalland.Insomelowerplacesofthelalanggrassland,reedgrowswhenthewaterisamplebecauseof ooding.Insomeplacesencircledbydikesandshortofwatersupply,thereediseventuallyre-placedbylalangandothergrassesandthereedwetlandecosystemturnsintoagrasslandecosystem.

Analyzedfromsuccessionhistory,wateristhemajorfactorforcreatingareedmarshecosysteminYanchengtidallands.Thewornwoodgrasslandorlalanggrasslandbothhavetheabilitytoturn

intoamarsh.However,alalanggrasslandisbetterforitsclosenesstoreedinasuccessionsere,whichensuresarelativelyshortertimeforcreat-ingareedwetland.Nextcomesthestepofchoos-ingalalanggrassland.Severalaspectswereconsidered.First,thesiteshouldbebetweenthecorezoneofthereserveandhumanareas(farm-landsandarti cial shponds),servingasabridgeforbirdsgatheringtothecorezonefromhumanareas.Second,thereshouldbeacertainareaofreedmarshnearorinthechosenlalanggrassland,whichensuresthepropagulesourcesforcreatingareedwetland.Third,thereshouldbeasourceoffreshwaterforcreatingawetlandonthesite.Takingallofthesefactorsintoconsideration,a240halalanggrasslandattheedgeofthecorezonewaschosentocreateareedwetland.

3.1.2.Creatingawetland

InMarch1994,a240-hagrasslandwasencir-cledanddikeswerebuiltaroundthegrassland.Freshwaterwaspumpedintothegrassland.Theaveragewaterlevelwasabout0.5mandtheconstantwaterlevelwasmaintainedaroundtheyear.Somesmall shandshrimpwereputintothewetlandtoprovidefoodforwaterfowl.Whenwintercame,somewaterwasdischargedtokeepashallowlevelofabout0.3m,providingmoreconvenienceforwaterfowlstoplayandforage.Aftertheprojectwasconstructed,thewetlandwasstrictlymanagedtoavoidinterferencefromhumanactivities.

Table1

PlantprimaryproductivityandpercentcoverofcommunitiesinthelalanggrasslandandreedwetlandatthecreatedwetlandsiteatYanchengBiosphereReserveLalanggrassland(priortocreation)PlantLalangChineseaeluropusReed

Average,entiresiteTotal

Primaryproduction(gm 2yr 1)116032514869982971

100Cover(%)75214

Reedwetland(4yearsaftercreation)PlantAlgaeCattailReed

Primaryproduction(gm 2yr 1)53241453294743399724

100Cover(%)681517

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