长江中游大型通江湖泊鄱阳湖水生态健康诊断及时空分异研究

The changes of lake aquatic ecosystem is very complicated with great uncertainties, particularly for those large lakes which are naturally connected with the large River where the relationship between the lakes and rivers are complex and ecological conditions have obvious variation across space and time. Being the largest freshwater system connected to the Yangtze River, Poyang Lake plays a vital role in global ecological environment and shows great temporal and spatial heterogeneity of hydrological characterization. Due to the dual impact of climate change and human activities, Poyang Lake has experienced drastic hydrological changes, water quality decline and aquatic ecological function degradation in recent years. And it attracted wide public attention on the aquatic ecosystem health of the Poyang Lake. However, few studies exist regarding the ecological health status. In this study, the index system for ecological assessment is put forward based on the analyses of the variation characteristics of water level, water environmental factors and aquatic organism of Poyang Lake. And the assessment indicators thresholds are determined based on empirical method, frequency analysis, specification standards and so on. Then the extension method is used to assess the ecological status temporally and spatially and the influence mechanism of ecological health status of Poyang Lake was analyzed. The study could provide theoretical basis for identifing the causes of the lake ecological health degeneration and protecting the environment of the Poyang Lake.

湖泊生态系统变化复杂且具有很大不确定性，尤其是河湖关系复杂、湖区差异显著的大型通江湖泊。鄱阳湖是具有重要国际地位的高水情变幅通江湖泊，水情动态呈时空异质性。近年来，受气候变化和人类活动的双重影响，鄱阳湖出现水文情势大幅波动、水环境恶化和水生态功能退化等问题，引起人们对鄱阳湖生态健康走势的担忧。本项目针对从健康角度认识鄱阳湖水生态状态缺乏这一现状，拟选取鄱阳湖典型湖区，运用多元统计学方法分析梳理鄱阳湖水生态变化过程，遴选通江湖泊水生态健康关键表征指标，确定指标阈值，运用可拓评价方法诊断鄱阳湖水生态健康状态，探索水生态健康时空分异特征及机制。该研究可为鄱阳湖水生态健康退化原因识别以及湖泊水生态的保护提供理论依据。

本研究针对具有高水情变幅，湖区分异显著的大型自然通江湖泊水生态变化的复杂性和重要性，以鄱阳湖为例，进行水生态健康评价研究。本研究监测搜集鄱阳湖水文、水环境以及水生态数据并分析鄱阳湖水生态变化过程；结合界定的湖泊水生态健康的内涵和水生态变化分析结果，遴选鄱阳湖水生态健康关键表征指标，构建鄱阳湖水生态健康评价指标体系，利用多种方法确定评价指标阈值,基于可拓评价方法揭示鄱阳湖水生态时空分异特征及影响机制。研究结果表明：（1）鄱阳湖水文、水环境、水生态时空差异显著。鄱阳湖水位年内、年际均波动明显，近年来水位呈现不断下降趋势；不同湖区水环境空间差异显著，且整体呈现不断恶化的趋势；相应地湖泊生物多样性锐减，生态系统功能不断退化。（2）构建以水生生物为主，水文、水环境生境要素为辅的大型自然通江湖泊水生态系统健康评价指标体系，具体包括蓝藻硅藻生物量比值、底栖动物多样性指数、底栖动物耐污指数、枯水期最低水位距平、涨水期平均水位距平、综合营养指数6个指标。确定鄱阳湖水生态系统健康评价指标阈值，把鄱阳湖水生态系统健康分为三个等级，健康、临界状态（亚健康）、不健康。（3）鄱阳湖水生态系统整体呈健康的状态，亚健康的趋势，且时空差异显著。时间上，丰水期水生态系统健康状态优于枯水期，涨水期水生态系统健康状态与退水期状态基本持平，季节差异年际变化也较为显著；空间上，蚌湖、赣江等河流入湖口以及东部的撮箕湖区域相对不健康，大湖面湖区相对健康。（4）鄱阳湖水生态系统健康影响机制较为复杂，受入湖污染物、湖泊水文水动力条件、鄱阳湖与长江的江湖关系、人类活动等共同作用。其中，入湖污染物是影响鄱阳湖水生态系统健康的关键因素，湖泊水文、水动力条件以及人类活动等因素导致其生态系统健康状态时空分异，时间上主要受水文条件影响较大，空间上主要受人类活动、水动力条件等作用。