简介：AsoneofthedevelopingcountriesChinahasanarablelandpercapitafarbelowtheworld'saveragelevel.Withahigh-densitypopulationanthequickdevelopmentofeconomyandurbaniztion,theYangtzeRiverDeltashowsthetypicalcharacteristicsoflanduseindevelopedregionsofChina,whichare:highlandreclamationrateandlowarablelandpercapita;intensivelanduseandhighoutputvalue;andrapidincreasingofconstructionlandareaandfastdiminishingofarableland.TheanalysisindicatesthattheprocessofthearablelandchangesintheYangtzeRiverDeltacouldbedividedintofourdifferentchangestagesoverthepast50years.

简介：ThereasonsfortheYangtzeRiverfloodcalamityin1998arebrieflyintroduced.Theauthorsbelievethatusinga'soilreservoir'conceptisanimportantmeanstohelpcontrolfloodingoftheYangtzeRiver.A'soilreservoir'hasalargepotentialstoragecapacityanditswatercanberapidly'discharged'intotheundergroundwaterinatimelyfashion.Theeroded,infertilesoilsoftheYangtzeRiverWatershedarecurrentlyanobstacletoefficientoperationofthe'soilreservoir'.Thestoragecapacityofthis'soilreservoir'hasbeenseverelyhamperedduetointensivesoilerosionandtheformationofsoilcrusts.Therefore,possiblemeasurestocontrolfloodsintheYangtzeRiverWatershedinclude:rehabilitatingthevegetationtopreservesoilandwaterontheerodedinfertilesoils,enhancinginfiltrationofthedifferentsoiltypes,andutilizingthelarge'soilreservoir'oftheupperreachesoftheYangtzeRiver.

简介：Thirteensedimentcoresamples(0-10cm)weretakenfromthesevenlakesinthemiddleandlowerreachesoftheYangtzeRivertodeterminethecontentsanddistributionsoforganicphosphorus(P)fractionsinthesedimentsoftheshallowlakesinthearea.TheorganicPfractionsinthesedimentswereintheorderofmoderatelylabileorganicP(MLOP)>moderatelyresistantorganicP(MROP)>highlyresistantorganicP(HROP)>labileorganicP(LOP),withaverageproportionalratiosof13.2:2.8:1.3:1.0.LOP,MLOP,andMROPweresignificantlyrelatedtothecontentsoftotalorganiccarbon(TOC),water-solubleP(WSP),algal-availableP(AAP),NaHCO3-extractableP(Olsen-P),totalP(TP),organicP(OP),andinorganicP(IP).However,HROPwassignificantlyrelatedtoOPandweaklycorrelatedwithTOC,WSP,AAP,Olsen-P,TPorIP.ThissuggestedthatorganicP,especiallyLOPandMLOPinsediments,deservedevengreaterattentionthanIPinregardstolakeeutrophication.IntermsoforganicP,sedimentsweremorehazardousthansoilsinlakeeutrophication.AlthoughOPconcentrationswerehigherinmoderatelypollutedsedimentthanthoseinheavilypollutedsediment,LOPandMLOPwerehigherintheheavilypollutedsediment,whichindicatedthatheavilypollutedsedimentwasmorehazardousthanmoderatelypollutedsedimentinlakeeutrophication.