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,SiO2Phytoplankton

Averagedailyprimarygrossproduction Biomass Chlorophylla

Acomprehensiveevaluationofstatusofeutrophication: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: N 323.2t/a（60.3%oftotalinput） P 67.7t/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: 27-949 ind/ml1960s: 156-4662 ind/ml1970s： 1000-35000 ind/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: CyanophytaChlorophyta

MicrocystisAphanizomenonAnabaenaetc.

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）Aggravationofexogenicpollutionthroughthedischargeofurbanhouseholdsewageaswellasindustrialwastewaterinanimmenseamount;Thedisappearanceofaquaticmacrophytesreducedthecompetitionfornutrients,causingtheluxuriantproliferationofphytoplankton;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 Impactsonlakeecosystemsaredifferentwhendifferentfishspeciesarestocked

Grasscarpstockingresultedinthedisappearanceofmacrophytes

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，不论哪种对象，都要衡量其放养后的生态影响就水体中氮、磷的负荷而论，只要输出水体的渔获物中氮、磷的含量大大超过输入水体的全部“鱼种”的氮、磷含量加上这些“鱼种”生长代谢过程中所排泄的氮磷总量，那么这种放养对延缓富营养化的进度还有积极意义Theimportantpointis:whatevertheanimalmaybe,weshouldgiveheedtoitsecologicalimpactfollowingthestocking.TakingtheloadingofNandPintoconsideration,solongasthecontentofNandPinthefishcrop(i.e.,theoutput)plustheNandPexcretedbythestockedfishduringtheirstayinthelakeexceedsenormouslythosecontainedinthestockedfingerling(i.e.,theinput),thensuchstockingwillbeofpositivesignificanceforretardingtheprocessofeutrophication.

5．放养鲢、鳙的生态影响 Ecologicaleffectsofthestockingofsilvercarpandbig-headcarpBothsilvercarp(Hypophthalmichysmolitrix)andbig-headcarp(Aristichthysnobilis)areplanktonfeeders

鲢鱼（Hypophthalmichthysmolitrix）和鳙鱼（Aristichthysnobilis）都是吃浮游生物的鱼类，前者食譜以浮游植物为主，杂有少量浮游动物；后者主要也吃浮游植物，但其肠道中浮游动物的数量多于鲢鱼肠道中的数量。这两种鱼都是我国“四大家鱼”的成员，其人工繁殖的技术也已经普及，所以在我国的湖泊、水库里广泛放养，产量较大，缺点是产值不高。西方国家（不产鲢、鳙）的水生生物学家受传统“食物链”的影响，长期以来把控制藻类过盛的希望寄托在浮游动物身上，所以认为，为了遏制藻类水华，应该保护浮动物，这样就需要清除吃浮游动物的鳙和鲢。实际上，鲢、鳙控制大型浮游藻类（如微囊藻）所形成的水华的本领，比起浮游动物来要高强得多鲢鳙滤食大型浮游藻类小型藻类发展旺盛小型藻类水华Carpsarecapableoffilteringmedium-sizedandlarge-sizedphytoplankton

Small-sizedalgaeincreasesWaterbloomofsmall-sizedalgaeappears6．在东湖里进行的围隔实验Enclosureexperimentsinsidethelake

什么导致了东湖蓝藻“水华”的消失？

营养盐的变化？

牧食浮游动物的变化？

滤食性鱼类的变化？自1985年夏季，蓝藻水华消失ThediappearanceofMicrocystisbloomfromLakeDonghuin1985Whatisthecauseofthedisappearanceofwaterbloom?

Nutrients？

Predator？

Filteringfishes？Enclosureexperimentinthesummerof1989EightcubiformenclosureswereinstalledwithinthelakeTheenclosureswithbottomandsidesweremadeofimpermeablepolyethylenecloth,eachmeasuring2.5msquareatthefourverticalsidesandatthebottom.Theenclosuresarefilledwithlake-watertothedepthof2m;thuseachenclosureheld12.5m3oflake-water.Thelake-waterwasfilteredthroughaplanktonnetbeforebeingintroducedintotheenclosuresinordertopreventtheunintendedintroductionoffishfry.

1989年夏季的实验围隔用不透水的聚乙烯材料制成2.5m见方上面敞开、下面有底的水箱，湖水2.0m深（湖水容积12.5m3）湖水用浮游生物网滤过，以避免把小鱼苗带进围隔。

Purpose:Howdoesthestockingofsilvercarpandbig-headcarpinfluencethecommunitystructureofphytoplanktonintheenclosure?Canthedensestockingoffisheliminatewaterbloom?

目的：1）鲢和鳙的放养如何影响围隔内浮游植物的群落结构？2）鱼的密集放养能否消灭水华？Fig.藻类体积(Algalvolume(mm3L-1)1989年5-10月各围隔中和周围湖水中浮游植物总量、蓝藻生物量和鞭毛藻生物量变动情况Changesinthebiomassoftotalphytoplankton,cyanobacteriaandflagellatesintheenclosuresandthesurroundinglakewaterintheDonghuLakeduringMay-Oct.1989(afterSheiandLiu,1991)E3E5E7Lakewater1989年5-10月各围隔中和周围湖水中浮游植物总量、蓝藻生物量和鞭毛藻生物量变动情况Changesinthebiomassoftotalphytoplankton,cyanobacteriaandflagellatesintheenclosuresandthesurroundinglakewaterintheDonghuLakeduringMay-Oct.1989(afterSheiandLiu,1991)Thefluctuationofchlorophyll-acontentandthebiovolumeofthetotalphytoplanktoninthethreeenclosureswassimilarinpattern,butinthefish-free#7,thevaluesweremuchhigherthanintheenclosuresstockedwithfishandintheambientlake-water.Theintroductionoffishbroughtaboutmarkedchangesnotonlyinthebiovolumeoftotalphytoplankton,butalsointhecompositionofthedominantgroup.Intheenclosuresstockedwithfish,theproportionofCyanophyceaewasmeager.Intheenclosureswithoutfish,largecolony-formingMicrocystiswaspredominant(SheiandLiu,1991).

三个围隔中叶绿素a的含量和浮游植物总体积的波动情况相似，但在无鱼的#7中，数值要比有鱼的围隔和周围湖水中高的多，鱼的引入，不仅给浮游植物的总体积而且对优势类群的组成带来了明显的改变。养了鱼的围隔中，蓝藻的比例很小，没有鱼的围隔，微囊藻属（Microcystis）的大型群体独占优势（SheiandLiu,1991）Experimentinthesummerof1990Thepurposeofthisexperimentwas:1)torestorewater-bloominmoreoftheenclosures;2)tointroducesilvercarpandbig-headcarpintothoseenclosurescoveredalreadywithwater-bloom,toseeifthebloomcanbeconsumedbythefish;3)tomonitorthechangeinthesizestructureofphytoplanktoncommunityinenclosuresaftertheintroductionoffish.

1990年夏季的实验目的：1）使更多的围隔里重现水华；2）在水华已覆盖水面的围隔里引进鲢和鳙，看水华能否被鱼吃掉；3）监测围隔中引入鱼以后浮游植物群落在大小结构方面的变化。

#1Silvercarp,6(averagebodyweight148g),totalstockingdensity71g/m3

#2Big-headcarp,6(averageweight176g),totalstockingdensity64.5g/m3#3Silvercarp,4(average21g),big-headcarp,2(averageweight32g),totalstockingdensity12g/m3#4Silvercarp,4(average23g),big-headcarp2(averageweight32g).totalstockingdensity13g/m3#5Silvercarp,3(average152g),big-headcarp,3(averageweight172g),totalstockingdensity78g/m3#6Nofish

用了6个围隔，围隔的位置和大小与1989年相同，各围隔放养鱼类的情况如下：

#1鲢鱼6尾（平均体重148g）

#2鳙鱼6尾（平均176g）

#3鲢鱼4尾（平均21g）

#4鲢鱼4尾（平均23g）

#5鲢鱼3尾（平均不152g）

#6不放鱼Luxuriant

Microcystis

bloomoccurredinenclosures#l,#2,#5and#6.Inenclosures#1,#2and#5,thebiomassofphytoplanktonwassubstantiallyreduced.Intheenclosureswithoutfish(#6),thebloom,onceformed,persistedtotheendoftheexperiment.Inenclosures#3and#4,totalchlorophyll-aamountremainedlowthroughouttheexperiment,andontheaverage,morethan80%ofthetotalphytoplanktonwascomposedofthosesmallerthan30μ(SheiandLiu,1992).微囊藻水华大量出现在#1、#2、#5和#6围隔里。养了鱼的第1、2、5号围隔里，浮游植物的生物量大为减少在没有养鱼第６号围隔里，水华一经出现，就持续到实验终了（SheiandLiu,1992）

Fig.lChangesinchlorophyll-aamountinbothtotalphytoplanktonandthosesmallerthan30μmintheenclosureandsurroundinglakewaterinDonghuLakeduringApril-August,1990.Arrowindicatestheintroductionoffish(afterXie1996)

Enclosureexperimentinthesummerof1992Thisexperimentwasaimed:1)toascertaintheroleofsilvercarpandbig-headcarpintheeliminationofMicrocystisbloom,2)tofindoutwhetherthestockingofgrasscarphadthesameeffect.

1992年夏季的实验目的：１）证实鲢、鳙在消除微囊藻水华中所起的作用；２）找出放养草鱼是否有同样效应。#1and#2Blanktest,nofishwasstockedin.#3Grasscarp,3(averagebodyweight187g),totalstockingdensity45g/m3

#4Grasscarp,3(average229g),totalstockingdensity55g/m3#5Silvercarp,3(average137g),totalstockingdensity33g/m3#6Silvercarp,2(average133g),totalstockingdensity21g/m3#7Big-headcarp,4(average233g),totalstockingdensity75g/m3#8Big-headcarp,4(average216g),totalstockingdensity69g/m3

实验用了８个围隔，在七月份至九月份进行，８月21日，各围隔养入鱼类如下：#１和#２ 空白试验，不放入鱼类#3 草鱼 ３尾（平均体重187g）#4 草鱼 ３尾（平均229g）#5 鲢鱼 ３尾（平均137g）#6 鲢鱼 ２尾（平均133g）#7 鳙鱼 ４尾（平均233g）#8 鳙鱼 ４尾（平均216g）EnclosuresTherewasnowater-bloominalltheseenclosureswhentheexperimentstartedonJuly6th.Twoweeksafterwards,athinlayerofbloomoccurredinmostoftheenclosures;thedominantphytoplanktonlaterturnedtobe

Microcystis

inallcases.BytheendofJuly,therewasthicklayerofwater-bloominmostoftheenclosures.Inmid-Augustallenclosureswerecoveredwithathickbloomlayer.７月６日开始时所有围隔都没有水华两星期后，大多数围隔出现一层薄薄的水华后来，优势浮游植物成为微囊藻７月底，大多数围隔里有厚层水华８月中旬全部围隔都有稠密水华层Intheenclosuresstockedwithbig-headcarp(#7and#8,withstockingrateof63-75gfishpercubicmeterofwater),thetotalbiomassofphytoplanktondiminishedrapidly.

Waterbloominthesetwoenclosuresdisappearedtwoweeksaftertheintroductionoffish.Grasscarpstockedintoenclosures#3and#4didnotreducethebiomassofphytoplanktonatall,andthewater-bloom,onceformed,lastedtotheendoftheexperiment(Sheiletal.,1993).放入鳙鱼的7号和8号围隔（放养密度为每立方米水含鱼65－75克）克，导致浮游植物总生物量迅速减少。这两个围隔在鱼放入两星期后水华全部消失。第3号和第4号围隔里放养的草鱼，完全没有减少浮游植物的生物量，水华一经形成，就持续到实验终了（Sheietal.,1993）。Withbig-headcarp,water-bloomwascompletelyeliminatedatthestockingdensity(biomass)of69－75g/m3;withsilvercarp,theamountofwater-bloomintheenclosureswasmateriallydiminishedatthestockingdensityof21－33g/m3,buttherewasremnantbloompersistingtotheendofexperiment.Accordingly,theeffectivebiomassofsilvercarpandbig-headcarpforthecontrolofwater-bloomshouldbe33－69g/m3.Effectivestockingdensity(biomass)forsilvercarpandbig-headcarpshouldbe46－50g/m3(LiuandXie,1999)

当鳙鱼的放养密度（用生物量表示）为65－76g/m3时，水华全部被消灭；当鲢鱼的放养密度为21－33g/m3时，围隔中水华的量大为减少，但直到实验终了仍有少量群体残留。因此，鲢、鳙控制水华的有效生物量应在33－65g/m3的范围内。有效放养密度（生物量）应该是46－50g/m3

(刘、谢1999)。7．为什么微囊藻水华17年来没有在东湖重现？ WhyMicrocystisbloomdidnotrecurinLakeDonghuinthepast17years?

武汉东湖渔产量FishyieldinLakeDonghu鲢鳙生物量的稳步增长导致微囊藻水华的消失IncreaseintheyieldofbigheadcarpandsilvercarpresultedinthedisappearanceofMicrocystisbloom

Thestrategyadoptedbytheupholdersofconventional“biomanipulation”is:tostockpiscivorousfishspeciesintothewaterbodytosuppresstheplanktivorousfish,soastoreinforcethezooplanktonpopulation,whichistoberelieduponforwater-bloomcontrol(Starling,1993)

常轨的生物操纵（Biomanipulation）论者用来控制水体富营养化的对策是：在水体中放养食鱼性鱼类（piscivorousfish）以抑制食浮游生物的鱼类（planktivorousfish），借此壮大浮游动物种群，然后依靠浮游动物来控制藻类（Starling,1993）Astothecontroloffilamentousalgaeandlarge,colonialalgaelikeMicrocystis,thenzooplanktonincludingDaphniaareutterlyhelpless.Filter-feedingfisheslikesilvercarpandbig-headcarp,underappropriatestockingdensity,arecapableofsuppressingMicrocystisbloomeffectively(LiuandXie,1999).浮游动物只能摄食细菌、较小的浮游动物、和小型藻类，因而有助于增进水的透明度。控制丝状藻类和像微囊藻之类的大型群体，那么包括Daphnia在内的浮游动物是完全无能为力的。滤食浮游浮生物的鱼类像鲢和鳙，在适当的放养密度下，是能有效地遏止微囊藻水华的（刘、谢，1999）

8.东湖富营养化的治理对策CountermeasuresforthecontrolofeutrophicationinLakeDonghu

Startfromthecentraltreatmentofhouseholdsewage

Onthebasisoftheeffectivenessofsewagetreatment,todecidewhetheraselectivedredgingofthebottomdepositisnecessary.Priortothefulfillmentofcentralsewagetreatment,preventionagainsttheresurrectionofcyanobacteriabloomatpresentcanonlyresorttothestockingofsilvercarpandbig-headcarp.根据东湖富营养化当前情况，治理首先应该从生活污水的集中处理着手，然后视处理的效果而决定是否需要对湖底淤泥进行重点清除。在污水处理尚未到位之前，防止蓝藻水华的暴发目前还只能依赖鲢、鳙的放养措施.Fromalong-termpointofview,therepairoftheecosystem,includingtherecoveryofmacrophytesinthelake,therehabilitationofbenthicinvertebratecommunity,aswellastheconstructionofverticalwetlandsewagetreatmentinstallation(tobeintegratedwithtourismconstruction)inresidentialareabeyondthereachofsewagepipelinesystem,andtheselectiverectificationofthelake’swatershed,soastoreducethesourceofpollution,tolessenthePandNloadingofthelake-water,etc.

从长远来说，生态系统的整治，包括修复湖内水生植被，重建底栖无脊椎动物群落，结合旅游景点建设，在截污管道系统以外的零星居民点建立人工垂直湿地污水处理设施，在东湖流域（汇水区）进行重点整治，减少污染源，以降低东湖湖水中的磷、氮负荷，是治理富营养化的必由之路。?WhatdoesIETC“PlanningandManagementofLakesandReservoirs:AnIntegratedApproachtoEutrophicationAbridgedVersion--AStudent’sGuide”(2000)sayabout“ConstructedWetland”? ConstructedWetlandsThetransitionzonesbetweenlakesandterrestrialecosystemsarecrucialforprotectionoflakesagainstanthropogenicimpacts.Transiti