鄱阳湖洪泛湿地地下水与湖水转化机制及对洪水脉冲的响应研究

Poyang Lake, a topographically open freshwater lake in China, and extensive floodplain wetland surrounding the lake, plays an important role in the protection of biodiversity for the internationally recognized wetland system. The significant drying and wetting characteristics across the floodplain wetland depend mainly on the interdependence between the lake and floodplain wetland. The dynamic processes of groundwater-lake water interactions enhance the transfer and exchange for mass, energy and information in various floodplain wetlands, which is strongly influenced by the flood pulse in rivers or lakes. Additionally, the groundwater-lake water interactions have important effects on the ecohydrology, including the wetland evolution, material cycling and biological growth. In this study, we used field observations, geophysical inversion and tracer technology to focus on the scientific question on groundwater-lake water interactions. We analyze the seasonal variations of water cycle factors in the typical floodplain wetland and the associated responses of groundwater flow field to the flood pulse, and explore the seasonal recharge/discharge relationship between the groundwater and lake water. In addition, the numerical coupling model of surface water-groundwater flow is adopted to quantitatively reveal the affecting patterns and dynamic processes between the floodplain groundwater and lake water. The model is further used to explore the influences of different properties of the flood pulse on the groundwater-lake water interactions. Finally, future climate change and corresponding flood pulse variations are used to assess the responses of groundwater-lake water interactions. The outcomes in this study will contribute to the water resources regulation of the wetland and the lake, their water quality and ecological environment.

鄱阳湖大面积的洲滩湿地在季节性洪泛作用下干湿交替十分显著，归因于湖泊水体与洪泛湿地之间的相互依存与作用关系。在洪水脉冲作用下，地下水与湖水转化的动力学过程促进了洪泛湿地环境系统之间物质、能量和信息的传递与交换，驱动了湿地演变、物质元素循环和生物生长等生态功能的实现。本项目定位于地下水-湖水转化这一基础科学前沿问题，采用原位监测、物探反演与示踪技术等研究方法，分析现状条件下鄱阳湖典型洪泛湿地水循环要素变化，阐明地下水动力场对洪水脉冲变化的动态响应特征，辨析地下水与湖水的季节性补排转化关系。运用地表-地下水流数值模型，从空间尺度上定量揭示洪泛湿地地下水与湖水转化的作用模式与动力学过程，阐明不同洪水脉冲表现形式对地下水-湖水转化的影响机制，结合未来气候变化下的洪水脉冲干扰，评估地下水-湖水转化的响应与趋势。研究成果将直接服务于湖泊湿地水资源时空转换调节与分配、生态环境安全等重大需求。

本项目以鄱阳湖洪泛湿地在生态水文方面所遭受的频繁干扰为背景，以地下水与湖水相互转化的动力学过程为基础，以湖泊洪水脉冲变化为主线，主要开展了鄱阳湖洪泛湿地水循环要素变化与地下水动力场分析，探明了鄱阳湖洪泛湿地的地质环境状况与成因，基于原位试验等技术方法反演了地质结构特征与水力参数。采用同位素与温度示踪、水化学演化与水位动态数据资料，辨析了洪泛区湖水与地下水的季节性转化特点和相互作用。基于上述多源数据集合，构建了洪泛区地表-地下水三维数值模型FEFLOW，揭示了湖水与洲滩地下水作用过程的动力学机制与季节性转化模式。基于IPCC全球气候模式，综合考虑流域和长江来水影响，成功预估了未来鄱阳湖洪水与干旱的变化趋势，评估了湖泊水位变化对地下水与湖水转化的影响程度及态势。项目主要围绕洪泛区碟形湖-地下水作用关系、鄱阳湖主湖区-湿地地下水作用关系以及地下水三维数值模拟等几个方面开展研究工作，研究成果和结论可服务于湖泊湿地水资源调节以及生态环境保护等。