极端洪涝作用下江西乐安河沿岸地下水化学组分特征及来源分析

Characteristics and sources of chemical components in groundwater along the Le’an River of Jiangxi Province under an extreme flood event

为研究极端洪涝作用下乐平市乐安河沿岸地下水化学组分来源及环境健康风险,综合应用图示法、数理统计、主要离子比等方法,对研究区洪涝期间及洪涝后期24组浅层地下水样品的22项指标进行了分析。结果表明:不同时期地下水主要化学组分无显著差异,均属弱酸性的低矿化度淡水,优势阴、阳离子分别为HCO_(3)^(-)、SO_(4)^(2-)、Ca^(2+)、Na^(+)、K^(+)。地下水水化学类型空间差异明显,洪涝期间以HCO_(3)-Ca·Na型和HCO_(3)·SO_(4)-Ca·Na型为主,洪涝后期出现Cl型及NO_(3)型水。地下水主要组分的形成主要受控于水-岩相互作用、硅酸盐矿物溶解、阳离子交替吸附作用,局部地区受农业施肥、污水排放等人为活动干扰。洪涝灾害发生后地下水水质较差,不适宜直接饮用,污染指标主要为氨氮、NO_(3)^(-)、Mn、Cd,污染物来源于地表-地下水混合、洪水对土壤中含锰矿物的溶滤以及乐安河上游采矿活动。

In order to study the sources of groundwater chemical components and the environmental health risks along the Le’an River in Leping City under the effect of an extreme flood event,22 parameters of 24 groups of shallow groundwater samples collected during and after an extreme flood were analyzed by the combination of graphical method,mathematical statistics and main ion ratio.The results show that there is no significant difference in the main chemical components of groundwater in different periods,and all the samples are tested to be weak acidic fresh water with low salinity,with HCO_(3)^(-),SO_(4)^(2-),Ca^(2+),Na^(+)and K^(+)as the dominant anions and cations.The spatial distribution of groundwater chemical types is significantly differntiated,which is mainly HCO_(3)-Ca·Na and HCO_(3)·SO_(4)-Ca·Na types during the flood period,and Cl and NO_(3) types in the post flood period.The formation of the main chemical components of groundwater is mainly controlled by the water-rock interaction,the dissolution of silicate minerals and the cation alternating adsorption.In additon,some local areas are also affected by human activites such as agricultural fertilization,sewage discharge.After the flood,the groundwater quality is degraded,which is no loger suitable for drinking.The main pollutants are ammonia nitrogen,NO_(3)^(-),Mn and Cd,which come from the surface-groundwater mixing,the leaching of manganese-containing minerals in the soil by the flood and the mining activities in the upper reaches of Le’an River.