Adescriptiveassessmentofthewetlandsofthelakevictor

Resources,ConservationandRecycling20(1997)127–141AdescriptiveassessmentofthewetlandsoftheLakeVictoriabasininTanzaniaG.R.Kassenga*En6ironmentalEngineeringDepartment,Uni6ersityCollegeofLandsandArchitecturalStudies,P.O.Box35176,DaresSalaam,TanzaniaReceived24January1997;receivedinrevisedform15March1997;accepted15April1997AbstractLakeVictoriaisthesecondlargestfreshwaterbodyintheworldbysurfacearea.Itisaveryimportantwaterbodyforthelivelihoodofpeople,particularlythoselivinginitsbasin.Thelakeiscurrentlyfacingmanyproblemssuchasseriousenvironmentaldegradation,pollutionandoverfishing.Mismanagementofwetlandswhichisanotherproblemthreateningthehydrologicalandecologicalbalanceofthelakeisdiscussed.Thisreportprovides:anoverviewoftheLakeVictoriaecosystem;describesmajorwetlandsoftheLakeVictoriabasininTanzaniaandtheiruses;identifieswatersupply,agriculture,fishing,conversionintootheruses(mainlyresidential);andcattlegrazingasmainusesofwetlands;anddiscussesthreatsandchangesfacedbywetlands.Directanthropogenicactivitiessuchasirrationalusesofwetlandsforagriculture,pollutionandconversionofwetlandsintosettlementareasareresponsibleforwetlanddegradationandloss.Problemsofsedimentationasaresultofagriculturalactivities,hydrologicalchangesofwetlandsduetoroadconstructionandsubsidenceofwetlandsduetoexcessiveextractionofwaterareindirectresultsofhumanactions.Droughtisthecommonnaturalcauseforthechangeorlossofwetlandsinthelakebasin.Absenceofwetlandspolicy,conflictingsectoralpoliciesonissuesrelatedtowetlands,deficientplanningconcepts,limitedinformationandawarenessontheimportanceofwetlandsandabsenceofaninstitutiontodealspecificallywithwetlandmanagementcontributetodegradationandlossofwetlands.Anumberofrecommendationsforsustain-ableuseofwetlandsareputforward.FormulationoftheNationalWetlandsPolicyandlaunchingofawarenesscampaignsonwiseuseofwetlandsarerecommended.Thepresenta-*Tel.:2555175004.0921-3449:97:$17.00©1997ElsevierScienceB.V.Allrightsreserved.PIIS091-3449(97)00014-1G.R.Kassenga:Resources,Conser6ationandRecycling20(1997)127–141128tionalsoemphasisescarryingoutofresearchontheproperutilisationofwetlands,monitoringofwetlandusesandprovisionofsustainableexploitationofwetlandresourcesextensionservices.©1997ElsevierScienceB.V.Keywords:Wetland;Loss;Degradation;Policy;LakeVictoria;Basin;Tanzania1.IntroductiontothestudyThemainpartofthispresentationisaresultofa6monthstudy(February–July1995)onwetlandsoftheLakeVictoriabasininTanzania.Methodsusedtocollectinformationaboutthestatusofwetlandsinthelakebasinincludeinterviewswithstakeholders,literaturesurveyandphysicalobservations.2.LakeVictoriaecosystemLakeVictoria,thesecondlargestfreshwaterbodyintheworld(bysurfacearea),isanequatoriallake,locatedbetweenlatitude0°31’N:3°05’Sandlongitude31°35’–34°54’E.WithinTanzaniaitliesbetweenlatitudes1–3°Sandlongitudes31°35’–34°05’E.Itissituatedat1134mabovemeansealevel[1].LakeVictoriacoversasurfaceareaof69000km2,ofwhich51%liesinTanzania.Ithasameandepthof85mandanaverageamountofwaterequalto2.751012cubicm.Thetotalcatchmentareaofthelakebasinisestimatedtobe184000km2ofwhich46%(84640km2)isinTanzania[2].OntheTanzaniasidethelakeismainlyfedbytheKagera,Mara,Mori,Grumeti,Ruwana,Simiyu,Mbalageti,BariadiandIsangarivers.GeologicallyLakeVictoriabasincanbroadlybedividedintotwocategories.ThefirstcategorythatincludestheMara,MwanzaandShinyangaregionshasmainlygraniticrocksintersectedlocallybybandedironstoneridges.LargeflatareasinthesouthofMararegionandcentralandsouthernpartsoftheMwanzaandShinyangaregionsarecoveredwithalluvium.ThesecondcategoryisthatfoundintheKageraregion,onthewestofthelake.ItischaracterizedbytheBukobanformationwhichisdominatedbyquarziticsandstonesandbyKaragwe-Ankoleanformationcomprisedofquartziteandshales.MostoftheMara,MwanzaandShinyangaregionsarecharacterizedbytypicalSukumalandsoilcatena,whereasintheKageraregion,thesoilsaremainlycharacterizedbyshallow,freedrainingsandyloamsandbysandyclaysinthevalleys[2].Therearedifferentclimaticzonesinthelakebasin,dependentonannualrainfallandpotentialevapotranspiration.Theareahasgenerallyabi-modalpatternofrainfall.Thereareconsiderablevariationsinthetotalrainfallthroughoutthezone.Mwanzaregionreceivesanaverageannualrainfallof900–1000mminthewesternandcentral750–900mminthesouthand800–1100mminthecentralareas.G.R.Kassenga:Resources,Conser6ationandRecycling20(1997)127–141129However,rainfallincreasesnorthwardsinhigherareasandTarime,forexam-ple,hasanaverageof1600mmperannum.Kageraregiongetsmorerainfallthantheothers.Onaveragetheregionreceives800–1200mm,butaroundBukobatowntheannualaverageisover2000mm.Fig.1illustratestherain-fallpatterninBukoba,MusomaandMwanzatownsfrom1986to1991[2].Likerainfall,themeanmaximumandminimumtemperaturesdifferfromoneplacetoanother.LakeVictoriawaterisusedfordomesticandindustrialpurposes.Itisalsousedforirrigation,transportandasadepositoryforindustrialanddomesticwastes.MajorlandusesintheLakeVictoriabasinare:(a)Farming:agricultureisamajoractivitywherebycommoncropslikecot-ton,coffee,bananas,maize,cassava,sorghum,potatoes,rice,legumes,etc.,arecultiv