太湖北部地区地下水环境同位素组成及其演化分析

Analysis on groundwater environmental isotopic composition and evolution in northern Taihu Lake

太湖北部地区是苏南现代化建设示范区,其地下水资源是区域经济社会发展的重要资源之一。通过地表水、潜水、承压水水样的采集、测试和分析,结合研究区水文地质资料,识别各水体环境同位素(D,18 O,3H,14 C)的组成特征,以揭示研究区地下水的形成和演化规律。结果表明:研究区潜水主要来源于现代大气降水的入渗补给,大气降水补给潜水的过程中经历了明显的强烈蒸发;Ⅰ承压水为无氚水,14 C年龄变化范围为7~9 ka,降水补给时温度范围为12.2℃~13.5℃,主要形成于地质历史时期;Ⅱ承压水为无氚水,年龄变化范围为16.27~27.37 ka,降水补给时温度范围为3.5℃~3.8℃,比现代温度(14.8℃)低约11℃,推断其形成于末次冰期的盛冰期降水入渗补给。潜水、Ⅰ承压水、Ⅱ承压水的D,18 O值在垂向上表现为明显的成层性,且地下各水体之间水力联系较弱。潜水具有一定的更新能力,Ⅰ承压水和Ⅱ承压水处于封闭–半封闭状态,具有不可再生资源属性。研究结果可为研究区正在开展的区域地下水资源调查评价工作提供基础数据支撑。

The northern area of Taihu Lake is the Sunan Modernization Demonstration Area of Urban Agglomeration, its groundwater is one of the important resources for regional economic and social development. Based on collecting, testing and analyzing the samples of surface water, phreatic water and confined water and hydrogeological data, we identified the composition characteristics of environmental isotopes(D,18O,3H,14C) in different water bodies to reveal the formation and evolution of groundwater in the study area. The results as follows: the phreatic water in the study area is mainly from the infiltration recharge of present precipitation and the process of atmospheric precipitation recharging phreatic water has experienced obviously strong evaporation. The I confined water is non-tritium water and mainly formed in the geological history, of which the 14C age is 7-9 ka and the precipitation recharging temperature is 12.2℃~13.5℃.The II confined water is non-tritium water and is inferred to formed from the precipitation infiltration recharge during the Last Glacial Maximum, of which the age is 16.27~27.37 ka and the precipitation recharging temperature is 3.5℃~3.8℃, about 11℃ lower than the modern temperature(14.8℃). The δD and δ18O of phreatic water, I and II confined water show obvious stratification in the vertical direction, and they have weak hydraulic connection. Phreatic water has a certain renewal capacity, and I and II confined waters are in an enclosed to semi-enclosed environment with non-renewable resource attributes. The results can provide basic data support for the investigation and evaluation of regional groundwater resources in the study area.