基岩海岛地下水与海水相互作用研究

Interaction between groundwater and seawater in bedrock islands

中国北方基岩海岛水文地质条件独特,气候变化和人类活动不同程度地影响着海岛地下水与海水相互作用过程,然而对包括海水入侵(SWI)和海底地下水排泄(SGD)的水文过程的定量认识比较缺乏。本研究基于2012—2016年我国北方某基岩群岛降水、地下水水位、水质动态监测数据,运用数理统计、空间插值和水力学方法,分析了基岩海岛地下水与海水相互作用的特征和影响因素。结果表明,降水和开采是影响地下水、海水相互作用的主要因素,地下水水位变化滞后于降水事件约10 d;南岛东北岸、南岸的大部分地区没有发生海水入侵,地下水向海排泄过程较稳定,2012—2016年SGD速率均值为0.2 m/d,向海NO3-N通量均值为81.8 mmol/(m^(2)·d);北岛东南地区是海水入侵的严重区域,地下水水位长期低于海平面且逐年下降,2012—2016年SWI速率均值为0.3 m/d,向陆NO3-N通量均值为69.6 mmol/(m^(2)·d)。分别计算南、北两岛枯水季(2014年4月)、丰水季(2013年9月)SGD水量,北岛SGD水量为3.5×10^(4)~4.5×10^(4)m^(3)/d,南岛SGD水量为0.4×10^(4)~1.1×10^(4)m^(3)/d。相关结果可为基岩海岛地下水资源管理和生态环境保护提供重要参考。

The hydrogeological settings of bedrock islands in northern China are unique. Climate change and human activities can affect the interaction between groundwater and seawater around the islands to varying degrees, but there is a lack of quantitative understanding of such hydrological processes, including seawater intrusion(SWI) and submarine groundwater discharge(SGD). In this study, we analyzed the precipitation,groundwater levels, and water quality data(2012-2016) for identifying the characteristics and controlling factors of the interaction between groundwater and seawater in bedrock islands by using mathematical statistics, spatial interpolation, and hydraulics methods. The results show that precipitation and groundwater pumping are the main factors affecting the groundwater-seawater interaction. The variations of groundwater levels lag behind the rainfall events by about 10 days. There occurred no SWI in most areas on the northeastern and southern coasts of the South Island, with relative stable marine groundwater discharge. The average SGD velocity was 0.2 m/d, and the average NO3-N flux to the sea was 81.8 mmol/(m^(2)·d). The southeast area of the North Island has been seriously threatened by SWI, and the groundwater levels have been below sea level for a long time and falling year by year.The average SWI rate is 0.3 m/d, and the average NO3-N flux towards the land is 69.6 mmol/(m^(2)·d). The SGD rates of the South and NorthIslands were estimated for dry season(April 2014) and wet season(September 2013),respectively. It was 3.5×10^(4)-4.5×10^(4) m^(3)/d for the North Island, and 0.4×10^(4)-1.1×10^(4) m^(3)/d for the South Island.The results can provide important reference for coastal groundwater resource management and ecological environment protection in bedrock islands.