太湖湖滨带生态系统健康评价

根据湖滨带生态系统的特点,运用综合健康指数法建立了湖滨带生态系统健康评价体系,由目标层、准则层、指标层构成,其中准则层由湖滨带水质状况、底泥状况、植被状况、其它生物状况(浮游动物、浮游植物、底栖动物)、岸带物理状况5项组成,指标层由总氮、总磷、溶解氧、挺水植物覆盖率等15项指标构成。采用专家打分法、熵值法分别确定了准则层、指标层的权重系数。对太湖湖滨带33个点位进行了采样分析,并进行无量纲化处理后应用到所建立的评价体系中。评价结果显示33个点位中为"很健康"、"健康"、"亚健康"、"疾病"、"严重疾病"的分别占0%、24.2%、21.2%、51.5%及3.0%,也即超过一半的点位处于"疾病"状态。只有东太湖刚刚超过"健康"分数的下限,东部沿岸、贡湖、南部沿岸均处于"亚健康"状态,而梅梁湾、竺山湾、西部沿岸属于"疾病"状态,且竺山湾的生态健康状态最差。该评价结果与太湖湖滨带各分区的实际调查情况相符合,评价方法可靠性、可行性较强,可为其它湖泊湖滨带的生态系统健康评价提供一定的参照。

The ecosystem health assessment of the littoral zone of Lake Taihu

Lake littoral zone,as a natural protection barrier of lake,is one kind of the most important ecotones between terrestrial and aquatic ecosystem.It plays an important role in diluting pollutant concentration,improving aquatic environment and providing aquatic animals′ habitat for their survival and reproduction.Therefore,ecological restoration of littoral zone is a necessary measure for lake protection and rehabilitation technologies.However,little work has been done on its ecosystem health assessment.Lake Taihu,being a typical large shallow lake,is one of the five famous greatest lakes in the east China plain.Its ecosystem has been deteriorating due to the more and more serious water pollution and eutrophication since 80′s.The environmental problems of Lake Taihu have attracted Chinese government′s careful attention.Many attempts for Lake Taihu′s pollution control have been made by the government.Some progresses have been achieved since the 10th Five-Year period.In the present work,a case study for assessing ecosystem health of lake littoral zones has been conducted in the littoral zone of Lake Taihu. A unique structure of littoral zone of Lake Taihu is its dike,which occupies about 73% of the total lake bank length.The dike blocks the natural material flow between the surrounding land area and the lake water,sequentially the material exchange between them was reduced to a great extent.Therefore,unlike the natural lakes without dike,the littoral zone of Lake Taihu does not cover the land area near the bank.After a careful analysis of the hydrology,geography,and aquatic plant distribution,we defined the littoral zone as the region ranging from dike edges to 50—100m water forward.Among the three common methods for ecosystem health assessment,namely,biological indicator,pressure-state-response(PSR) method and ecological health comprehensive index(EHCI) method,the last one was employed for the lake littoral zone,because it could better reflect the ecological health state from different aspects.According to the characteristic of littoral zone ecosystem,an ecosystem health assessment approach for lake littoral zone was developed based on the method of comprehensive ecological health index.The evaluating system in this approach is composed of objective level,normal level and index level.The normal level consists of 5 factors including water quality,sediment quality,emergent macrophyte conditions,and other biological physical conditions.In the index level,there are 15 factors including total nitrogen,total phosphorous,dissolved oxygen,emergent macrophyte cover and so on.Total 33 sites in the littoral zone of Lake Taihu were sampled.The normalization values of the observed sample data were used for ecosystem health assessment.The assessment results shows that among these 33 sampling sites,the percentages of ’very healthy’,’healthy’,’sub-healthy’,’ill’ and ’serious ill’ ecological situation are 0%,24.2%,21.2%,51.5% and 3.0%,respectively.This result indicates that more than half of the ecosystems in the 33 sampling sites were ’ill’ state.Generally,the ecological health situation of the East Taihu Lake littoral zone was better than others,with an EHCI value just over the low limit score for ’healthy’ situation.The ecosystems in the east lake side zone,Gonghu lake and the south lake side zone were in ’sub-healthy’ state,while those in Meiliangwan,Zhushanwan and the west lake side zone were evaluated to be ’ill’ state.It is shown that the ecosystem in Zhushanwan was in the worst ecological health situation among all of the littoral zones in Taihu Lake.The assessment results were coincident with the real situations.The assessment approach developed in this study is highly workable and reliable.This study may have some implications for the ecosystem health assessment of other lake littoral zones.