湖岸带地下水与湖水作用关系——以鄱阳湖为例

Interactions between Groundwater and Lake Water of Riparian Zone in the Typical Area of Poyang Lake

依托野外地下水位与湖水位观测、地下水流速与流向测定、地下水与湖水水化学离子测试分析等研究方法,探析了鄱阳湖湖岸带地下水与湖水之间的作用关系。结果表明:湖岸带地下水和湖水偏弱酸性,SO_2^(4-)、Ca^(2+)和Mg^(2+)是湖水和地下水的主要阴阳离子。此外,湖岸带地下水中出现了较多NO_3^-,可能受到当地农业施肥及化粪池泄露等影响。研究区地下水流向主要是由周边丘陵地区向下游地势相对平坦的湖区流动,该地区潜水面为由补给区向排泄区倾斜的曲面,地下水总体上向河流和湖区方向流动。监测数据表明:所测得的研究区地下水位由上游向下游地区呈减小趋势,地下水位呈明显的动态变化,但水位变幅基本<2 m。地下水流速较大的区域主要分布在远离湖区和河流的上游丘陵地区,最大流速可达19.5 m/d,而下游湖区附近地下水流速较小,平均流速约5.1m/d。地下水位和流速的空间分布特征与地形变化基本一致,比较符合地形影响下的地下水流动规律。水化学证据指示了地下水和湖水之间存在一定的水力联系,而地下水流场特征以及地下水与湖水之间的季节性动态水位梯度表明了地下水可能以不同的排泄强度补给湖泊。

Study of the interactions between groundwater and lake water is helpful to improve the understanding of water resource management, hydrogeochemistry, biogeochemistry and eco-hydrology in lakes. Hydraulic relationship between groundwater and lakes has become an important topic for the scientific and decision-making communities. Poyang Lake, the largest freshwater lake in China, has significant seasonal lake water level variations. This will cause the groundwater level changes in the riparian zone of the lake, and hence affect the water resource characteristics in the local area. This paper selected riparian zone of Poyang Lake （China） as the typical study area. We used groundwater and lake water level observations, groundwater velocity and flow direction measurements, and hydrochemistry signatures to identify the recharge and discharge between groundwater and lake water. Results show that SO2-4 , Ca2＋ and Mg2＋ are the major anion and cation in both the groundwater and lake water. The flow direction of the riparian groundwater is mainly from the upstream mountainous areas to the downstream plain areas, indicating an inclined surface from the recharge area to the discharge area. Generally, the riparian groundwater flows to the river and the lake in the study area. Field observations also indicate that the spatial distributions in groundwater level have a decreasing trend from the upstream to the downstream areas. Although the riparian groundwater exhibits obvious dynamic changes, the magnitude of groundwater level variations is generally less than 2.0 m. Additionally, groundwater velocities are distinctly large （up to 19.5 m/d） in the upstream mountainous areas, which are far from the lake zone, and those are relatively small with a mean value of 5.1 m/d close to the lacustrine area. The spatial pattern of groundwater level and groundwater velocity coincides with the surface topographical changes, suggesting an important effect of the topography on the local groundwater flow. The evidences of hydrochemistry indicate that the lake water and groundwater have a hydraulic link. In addition, the groundwater velocity field and seasonal dynamics for both the groundwater level and the lake water level demonstrate that the riparian groundwater may discharge to the lake with different water fluxes. Our study is the first attempt to perform a field work on the interactions between groundwater and lake water, which can provide scientific knowledge for the water resource management and environmental assessment in Poyang Lake.