(剑5Test3ReadingPassage2)DisappearingDelta翻译谁有啊
AThefertilelandoftheNiledeltaisbeingerodedalongEgypt'sMediterraneancoastatanastoundingrate,insomepartsestimatedat100metresperyear.Inthepast,landscouredawayfromthecoastlinebythecurrentsoftheMediterraneanSeausedtobereplacedbysedimentbroughtdawntothedeltabytheRiverNile,butthisisnolongerhappening.
BUptonow,peoplehaveblamedthislossofdeltalandonthetwolargedamsatAswaninthesouthofEgypt,whichholdbackvirtuallyallofthesedimentthatusedtoflowdowntheriver.Beforethedamswerebuilt,theNileflowedfreely;carryinghugequantitiesofsedimentnorthfromAfrica'sinteriortobedepositedontheNiledelta.Thiscontinuedfor7,000years,eventuallycoveringaregionofover22,000squarekilometreswithlayersoffertilesilt.Annualfloodingbroughtinnew,nutrient-richsoiltothedeltaregion,replacingwhathadbeenwashedawaybythesea,anddispensingwiththeneedforfertilizersinEgypt'srichestfood-growingarea.ButwhentheAswandamswereconstructedinthe20thcenturytoprovideelectricityandirrigation,andtoprotectthehugepopulationcentreofCairoanditssurroundingareasfromannualfloodinganddrought,mostofthesedimentwithitsnaturalfertilizeraccumulatedupabovethedaminthesouthern,upstreamhalfofLakeNasser,insteadofpassingdowntothedelta.
CNow,however,thereturnsouttobemoretothestory.Itappearsthatthesediment-freewateremergingfromtheAswandamspicksupsiltandsandasiterodestheriverbedandbanksonthe800-kilometretriptoCairo.DanielJeanStanleyoftheSmithsonianInstitutenoticedthatwatersamplestakeninCairo,justbeforetheriverentersthedelta,indicatedthattheriversometimescarriesmarethan850gramsofsedimentpercubicmetreofwater—almosthalfofwhatitcarriedbeforethedamswerebuilt.I'mashamedtosaythatthesignificanceofthisdidn'tstrikemeuntilafterIhadread50or60studies,'saysStanleyinMarineGeology.Thereisstillalotofsedimentcomingintothedelta,butvirtuallynosedimentcomesoutintotheMediterraneantoreplenishtheCoastline.Sothissedimentmustbetrappedonthedeltaitself.'
DOncenorthofCairo,mostoftheNilewaterisdivertedin
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