东湖富营养化的成因分析和治理对策

东湖富营养化的成因分析和治理对策EutrophicationofLakeDonghu:CauseAnalysisandRemedyStrategy刘建康JiankangLIU中科院水生生物研究所InstituteofHydrobiology,theChineseAcademyofSciencesSeriouseutrophicationinLakeDonghu东湖富营养化十分严重1．二十年前东湖富营养化的综合评价和氮磷收支ComprehensiveevaluationofDonghu’seutrophicationinthe1980sanditsN,PbudgetsEutrophicationofthelakebeganinthemid-1950sandproceededratherfast.东湖的富营养化开始于五十年代中期，进程颇为快速。Early1980s:NO3-N,NO2-N,NH4-N,TN,PO4-P,TP,SiO2PhytoplanktonAveragedailyprimarygrossproductionBiomassChlorophyllaAcomprehensiveevaluationofstatusofeutrophication:onthewayoftransitionfromeutrophictohyper-eutrophic(Cai,1993)八十年代初期NO3-N,NO2-N,NH4-N,TN,PO4-P,TP,SiO2浮游植物:日平均初级生产量生物量叶绿素a东湖当时已处于富营养化向超富营养化过渡的阶段（蔡庆华，1993）氮的总输入量:536t/a总负荷量:19.22g/m2磷的总输入量:87.8t/a总负荷量:3.15g/m2输入-输出差:总氮323.2t/a（占总输入量60.3%）总磷67.7t/a（占总输入量77.1%）（张水元等，1984）Ninput:536t/aTotalloading:19.22g/m2Pinput:87.8t/aTotalloading:3.15g/m2Differenceininputandoutput:N323.2t/a（60.3%oftotalinput）P67.7t/a（77.1%oftotalinput）（Zhangetal，1984）AbundanceandspeciescompositionofphytoplanktoninLakeDonghuduring1956－1975,andthedynamicsofprimaryproductivity2．1956-1975年东湖浮游藻类数量和种类组成情况，和初级生产力的演变Theaverageannualtotalnumberofphytoplanktonwassteadilyontheincrease1950s:27-949ind/ml1960s:156-4662ind/ml1970s：1000-35000ind/ml浮游藻类年平均总数不断增加50年代：27-949个/ml60年代：156-4662个/ml70年代：1000-35000个/ml（饶欽止、章宗涉，1980）（JaoandZhang，1980）Pronouncedchangeoccurredinthespeciescompositionofphytoplankton1956-1957:PyrrophytaBacillariophyta1960s:CyanophytaChlorophytaMicrocystisAphanizomenonAnabaenaetc.种类组成明显改变1956－1957:甲藻硅藻60年代：蓝藻绿藻（饶欽止、章宗涉，1980）微囊藻（Microcystis）束丝藻（Aphanizomenon）鱼腥藻（Anabaena）等（JaoandZhang，1980）Primaryproductivityofphytoplanktonincreasedrapidly浮游藻类初级生产量急剧增加1963－1990年:最高生产层日产量平均每年增长0.256mgO2/天水柱最高日产量平均每年增长0.243gO2/m2﹒天1973－1985年:水柱日产量平均每年增长0.554g/m2﹒天（戎克文等，1995）1963-1990:Averagedailyproductionatthelayerofmaximumproductionincreasedby0.256mgO2perday,Maximumdailyproductionofwatercolumnincreasedby0.243gO2/m2perday.1973-1985:Dailyproductionofwatercolumnincreasedby0.554gO2/m2perday.（Rongetal.，1995）1)Aggravationofexogenicpollutionthroughthedischargeofurbanhouseholdsewageaswellasindustrialwastewaterinanimmenseamount;2)Thedisappearanceofaquaticmacrophytesreducedthecompetitionfornutrients,causingtheluxuriantproliferationofphytoplankton;3)DikeconstructionwithinthelakediminishedtheexchangeofwatermassbetweenGuozhenghuareaandotherlakeareaswithlowerloadingofNandP.(Rongetal.,1995)1）城市生活污水和工业废水大量排入，外源污染加剧；2）水草的消失减轻了对养料的竞争，促使浮游藻类大量繁殖；3）湖内人工堤的修筑，减少了郭郑湖区与其他氮磷含量较低的湖区之间的水团交流（戎克文等，1995）Thedistinctionbetween“fish-stocking”and“intensefish-farming”3．鱼类“放养”与“精养”的区别不同养殖类型的划分Differenttypesoffishculture放养密度Density天然饵料Naturalfood精养Intensive半精养Semi-intensive粗养Extensive管理水平投入和回收抗病能力人工饲料Artificialfeed4．放养不同种类的鱼给湖泊生态系统带来的不同影响ImpactsonlakeecosystemsaredifferentwhendifferentfishspeciesarestockedGrasscarpstockingresultedinthedisappearanceofmacrophytes草鱼（Ctenopharyngodonidellus）的放养导致水生植物的消失沉水植物的消失给水生态系统带来了一系列的影响1）水生大型植物能起到净化水质的作用，它的消失直接削弱了水体自净的能力2）水生大型植物是与浮游植物竞争养料的，前者的消失使后者能独享养料资源，导致浮游藻类的大量孳生，反过来通过在养料和光照方面的竞争优势，进一步压制水草的恢复1)Aquaticmacrophytesplaytheroleofpurifyingthewaterquality,theirdisappearanceattenuatesdirectlytheselfpurificationcapabilityofthewaterbody.2)Aquaticmacrophytescompetefornutrientsandlightwithphytoplankton3)Macrophyteisthesubstratumonwhichtheadhesiveeggsofmanyfish,snail,andaquaticinsectspeciesaredeposited;lackingofmacrophyteswoulddeprivetheseeggsofsuchsubstratumanddepressthehatchingratessubstantially;4）Macrophytesalsoserveasasortofrefugeforthefryoffishandlarvaeofaquaticinvertebrates.Themortalityoftheseanimalswouldbemarkedlyincreasedintheabsenceofsuchrefuge,thuswouldfurtheraffectthebiodiversityoftheecosystem沉水植物的消失给水生态系统带来了一系列的影响3）水草是好几种产粘性卵的鱼类、螺类以及水生昆虫卵粒附着的基质，产出的鱼卵、虫卵、和螺的卵囊没有水草可资附着，卵的孵化率大大降低4）水草也是许多幼鱼和水生无脊椎动物躲避敌害的隐蔽场所，少了这样的避难所，这类动物死亡的机率大增，进而影像响到该生态系统的生物多样性。Donghu:团头鲂（MegalobramaamblvcephaiaYih）是草食性鱼类Bluntsnoutbream(Megalobramaamblicephala),alsoknownas“WuchangFish”,islikewiseagrasseater,thoughlessvoracious;itsstockinginlakeisnotrecommended.鲤鱼（Cyprinuscarpio）是生活在水体底层的鱼类。它以螺蚌等底栖动物为食，习惯在底泥中觅食，动辄把水搅浑。鲤鱼在泥底中的掘进习性使它易于从围圈边缘逃逸；鲤鱼的捕捞也比较困难。湖泊放养对象中不包括鲤鱼Thecommoncarp(Cyprinuscarpio)isafishlivingonthebottomofwaterbody,feedingonbenthicanimalslikesnails,clams,andinsectlarvae.Searchingforfoodinthesediment,thefishisverylikelytostirupthebottomdepositandmakesthewaterturbid.Itisalsodifficulttocapture.Itisnotatargetfishforlakestocking.鲫鱼（Carassiusauratus）的食性较广，肉味也较好，但野生的品种生长缓慢，一般不是放养对象，但鲫鱼有些品种生长明显较快，有些品种主食浮游生物，将来有可能发展成为放养对象。Thecruciancarp,i.e.,thewildvarietyofgoldfish(Carassiusauratus),hasawiderfoodspectrum,andtastesbetter,butthewildbreedgrowsupslowly,hencenotachoiceforstocking.鳜鱼（Sinipercachuatsi）是吃鱼的鱼类，肉味好，又少细刺，经济价值较高。现在已有科研部门在小杂鱼类丰多的湖泊中放养鳜鱼，效果看来较好。Themandarinfish(Sinipercachautsi)isapiscivorousfish,feedingonotherfishspecies.Itistasty,devoidoffineskeletalspines,andfetcheshighprice.Certainresearchinstituteshavetriedtostockthisfishintolakeswithplentyoftrashfishes,andtheresultseemspromising.Donghu:河蟹、虾等是有潜力的放养对象Crabandprawnaresomeotherpotentialstockingspecies重要的是，不论哪种对