洪泛型通江湖泊水环境对水情条件变化的响应研究——以鄱阳湖为例

The large Yangzte-connected floodplain lakes are characterized by great hydrological condition variations and complex water quality processes, the latter of which are greatly influenced by hydrological conditions changes and corresponding changeover between inundation and emersion of wetland. Poyang Lake, a typical Yangzte-connected floodplain lake in China, feeds the Yangtze River with water of relative desirable quality and plays important roles in the development of the Yangtze River economic zone and maintaining ecosystem services. However, in recent years, Poyang Lake suffered abnormal water level fluctuations and increasing pollutants input, which have arisen enormous concerns about the water quality decline in Poyang Lake. The proposed study mainly focuses on the associated relationship between water quality and hydrological conditions. Based on simultaneous monitoring of water quality and hydrological variables, multivariate techniques, functional data analysis, random forest and physical-process based model are proposed to be used to : (1) dynamically evaluate the water quality variations in Poyang Lake; (2) determine the concordance between integrated pollutant degradation coefficient and hydrological variables according to water balance and pollutant flux balance; (3) quantatively modeling the effects of discharge changes from the basin and the Yangtze River on hydrological conditions and associated variations of water quality in Poyang Lake. The proposed study will shed light on water quality management, eutrophication control and will also provide the basis for the possible water quality responses of the Poyang Lake Project.

洪泛型通江湖泊具有水情波动剧烈的特征，其水环境变化过程复杂且很大程度上受到湖泊水情条件变化及其导致的湿地淹没变化的影响。鄱阳湖作为典型洪泛型通江湖泊，以相对优质的水源补给长江，对长江经济带发展和生态系统服务的提供都有至关重要的作用。然而近年来鄱阳湖存在水位异常波动、入湖污染物逐年递增等问题，引起人们对其水环境质量走势的担忧。本项目针对鄱阳湖水环境与水情条件变化响应机制相对缺乏这一现状，开展水文水环境同步监测，运用多元统计、函数型数据分析、随机森林、物理过程模型等方法，对鄱阳湖水环境变化态势进行评估，在考虑湖泊水量平衡与污染物通量平衡的基础上，解析鄱阳湖污染物存量、降解量，构建污染物综合降解速率与水情要素的响应关系，定量解析五河与长江干流来水变化等水情变化情景对鄱阳湖水环境的影响。该研究能够为鄱阳湖水环境管理、富营养化控制提供理论依据，并为可能的水利枢纽工程的水环境效应提供前期基础。

洪泛型湖泊剧烈的水文情势变化强烈影响着湖泊水环境变化。本项目以长江中下游典型通江洪泛型湖泊鄱阳湖为研究对象,综合运用模糊物元可拓评估模型、多元统计方法、随机森林算法、二维水动力水质模型等技术方法，对鄱阳湖近40年来水环境变化态势进行评估，构建了湖泊污染物通量平衡，基于经验模型阐明了其氮磷滞留速率近40年的变化，揭示了五河与长江来水变化导致的湖泊水情条件变化对鄱阳湖水环境的影响。结果表明：鄱阳湖综合水环境质量呈现明显的年内、年际和空间差异特征，且主要受到水位波动变化和赣江与乐安河子流域来水水质的影响。此外，鄱阳湖营养条件与物理环境均已发生深刻变化，且对于浮游植物生长存在明显的营养盐限制期和物理条件限制期，给鄱阳湖富营养化控制带来了新的挑战。伴随着2003年后水文情势深刻变化，鄱阳湖的氮磷滞留速率均发生不同程度的显著下降。在长江干流来水一定的前提下，同污染物通量下，流域来水的增加对湖泊污染物具有明显的稀释作用；就长江干流来水变化的影响而言，其对水文情势与水环境的影响主要集中在丰水期和退水期，其中三峡蓄水期影响最大，退水加快导致同期湖泊水环境容量减少，造成湖泊水环境一定程度恶化，对于典型枯水年的影响最大。本项目研究成果能够为鄱阳湖乃至其他大型洪泛型湖泊富营养化控制与可能的水环境生态调控提供基础。