求一篇关于水污染的英文论文

WaterpollutionWaterpollutionisamajorproblemintheglobalcontext.Ithasbeensuggestedthatitistheleadingworldwidecauseofdeathsanddiseases,andthatitaccountsforthedeathsofmorethan14,000peopledaily.Anestimated700millionIndianshavenoaccesstoapropertoilet,and1,000Indianchildrendieofdiarrhealsicknesseveryday.Some90%ofChina'scitiessufferfromsomedegreeofwaterpollution,andnearly500millionpeoplelackaccesstosafedrinkingwater.Inadditiontotheacuteproblemsofwaterpollutionindevelopingcountries,industrializedcountriescontinuetostrugglewithpollutionproblemsaswell.InthemostrecentnationalreportonwaterqualityintheUnitedStates,45percentofassessedstreammiles,47percentofassessedlakeacres,and32percentofassessedbayandestuarinesquaremileswereclassifiedaspollutedWateristypicallyreferredtoaspollutedwhenitisimpairedbyanthropogeniccontaminantsandeitherdoesnotsupportahumanuse,likeservingasdrinkingwater,and/orundergoesamarkedshiftinitsabilitytosupportitsconstituentbioticcommunities,suchasfish.Naturalphenomenasuchasvolcanoes,algaeblooms,storms,andearthquakesalsocausemajorchangesinwaterqualityandtheecologicalstatusofwater.CausesofwaterpollutionThespecificcontaminantsleadingtopollutioninwaterincludeawidespectrumofchemicals,pathogens,andphysicalorsensorychangessuchaselevatedtemperatureanddiscoloration.Whilemanyofthechemicalsandsubstancesthatareregulatedmaybenaturallyoccurring(calcium,sodium,iron,manganese,etc.)theconcentrationisoftenthekeyindeterminingwhatisanaturalcomponentofwater,andwhatisacontaminant.Oxygen-depletingsubstancesmaybenaturalmaterials,suchasplantmatter(e.g.leavesandgrass)aswellasman-madechemicals.Othernaturalandanthropogenicsubstancesmaycauseturbidity(cloudiness)whichblockslightanddisruptsplantgrowth,andclogsthegillsofsomefishspecies.Manyofthechemicalsubstancesaretoxic.Pathogenscanproducewaterbornediseasesineitherhumanoranimalhosts.Alterationofwater'sphysicalchemistryincludesacidity(changeinpH),electricalconductivity,temperature,andeutrophication.Eutrophicationisanincreaseintheconcentrationofchemicalnutrientsinanecosystemtoanextentthatincreasesintheprimaryproductivityoftheecosystem.Dependingonthedegreeofeutrophication,subsequentnegativeenvironmentaleffectssuchasanoxia(oxygendepletion)andseverereductionsinwaterqualitymayoccur,affectingfishandotheranimalpopulations.