三峡水库河流生境评价指标体系构建及应用

摘要

三峡水库建成蓄水后,库区支流因水位调度导致河流生境发生了剧烈的变化,消落带的形成使库区河流具有同自然河流截然不同的河流生境,新形势下库区河流生境评价十分必要.国内外现有的评价指标体系及评价方法不能够很好地适应这种特殊生境状况,急需建立或改进并形成新的评价指标体系和评价方法.基于此,分析了大量国内外河流生境评价方法,根据大型水库影响下的库区河流的生态环境特点,构建了包括水文情势、河流形态和河岸带生境3个方面18个指标的库区河流生境评价指标体系,并利用层次分析法(主观赋权法)和熵值法(客观赋权法)结合组合赋权法计算得到了各指标权重.使用新建立的指标体系和方法,以三峡库区支流东溪河、黄金河、汝溪河为例,进行河流生境质量评价发现,52.6％的样点河流生境质量处于优等或良好等级;42.1％为一般等级;5.3％为较差等级;没有最差等级的样点.结果表明,该评价指标体系适合库区支流河流生境状况的特殊性,得到的评价结果能较直观的反应河流生境状况,且操作便捷,数据易获得,具有较强的科学性和可操作性.%After the completion of the Three Gorges Reservoir,regulation of the water in the reservoir tributaries caused drastic changes in the river habitat,including a greatly reduced flow of water and formation of a 30 m deep water-level fluctuation zone.With such drastic changes,it is not clear whether the river habitat can play a positive and important role in the ecosystem health of the Three Gorges Reservoir and the maintenance of the normal functions of the reservoir ecosystem.However,existing evaluation methods cannot be easily adapted to these special habitat conditions;therefore,a new or improved evaluation method is urgently needed.Based on the analysis of a large number of domestic and international river habitat assessment index systems and the characteristics of the ecological environment of the rivers in the reservoir area,a new river habitat assessment index system,including 18 indicators that relate to river hydrology,river morphology,and the water-level fluctuation zone habitat,was constructed.The combination weighing method,which is based on the game theory and combines a subjective weighing method (the analytic hierarchy process method) and an objective weighing method (the entropy method),was used to calculate index values.We conducted river habitat quality assessments for the Dongxi River,Huangjin River,and Ruxi River,all tributaries of the Three Gorges Reservoir.The majority of the habitats scored within the range of " excellent" or "very good".This ranking corresponded with 52.6％ of the sampling sites.However,42.1％ received a score within the range of "average",whereas the remaining 5.3％ received a "poor" score.No site within this catchment received a score of "very poor".Our research suggests that this index system can be used to efficiently detect the status of river habitats,as it is feasible to operate and it allows easy access to scientifically sound data.