三峡水库营养状态评价标准研究

采用一维水力学模型和30年的系列水文数据,计算了三峡库区干流及其主要支流在不同来水条件下的月滞留时间和月平均流速,通过统计不同类型滞留时间和流速的发生概率,综合计算了库区的富营养化敏感指数,对三峡库区水体的敏感类型进行了划分,将库区水体分为河流型、过渡型和湖泊型3种.根据三峡水库营养状态调查结果,统计分析了过渡型和湖泊型水体的营养指标分布概率、富营养化阈值及其与叶绿素a的回归关系,确定了库区过渡型和湖泊型2种水体的营养指标分级标准值,提出了三峡水库营养指标指数值的确定方法和权重大小,对三峡水库不同类型敏感区的营养状态进行了综合评价,分析了评价结果与同期监测的浮游植物密度的相互关系,从而对三峡水库的评价标准和评价方法的科学性进行了验证.结果表明,三峡水库富营养化敏感程度从库尾至库首逐渐增加,三峡库区长江在银杏沱以上江段为河流型水体,在银杏沱至坝前江段为过渡型水体,位于丰都县以下的支流的回水区以湖泊型水体为主.分别制定了三峡水库过渡类型区和湖泊类型区的营养状态标准值,依据该标准所开展的营养状态综合评价结果与浮游植物数量具有显著的相关性,其中湖泊类型区的营养化程度高于过渡类型区,与三峡水库的现实状态相符合.

On the assessment standards for nutrition status in the Three Gorge Reservoir

It is a challenge to determine the assessment standards for nutrition status for environmental management and protection of the Three Gorges Reservoir. Monthly resident time and mean flow speed were simulated with 30 years hydrological data using an one-dimention hydrodynamics model. Sensitivity indite to eutrophication were calculated from probability statistics of resident time and flow speed. The Three Gorges Reservoir was zoned to river type regions, transitional type regions and lake type regions according to the sensitivity indices. With to analysis of nutrition indicator statistics, regressive relationship between nutrition index and nutrient concentration, and threshold values of nutrition status indicators, grading standards for nutrition status indicators were determined synthetically for transitional type and lake type regions in the Three Gorges Reservoir. Nutrition index approach is applied to assess nutrition status in different type of regions with the standards proposed. The rationality of the standards and its weighting factors were examined. The relationship between nutrition index and density of phytoplankton were analyzed for verification of standards system and assessment method. Results indicate that the sensitivity increases from the upstream to the downstrem of the Three Gorges Reservoir. The reach upper Yinxingtuo of Yangze River is river type region, and the reach from Yinxingtuo to the dam belongs to transition type. Tributaries lower Fengdu County belongs to lake type. Standard values for nutrition index assessment in transition type and lake type regions were set for the Three Gorge Reservoir. It is concluded that the nutrition status closely related to density of phytoplankton. Nutrition level in lake type region is higher than that in transition region, which is consistent with actual situation of the reservoir.