会仙岩溶湿地地下水主要离子特征及成因分析

Major Ionic Characteristics and Factors of Karst Groundwater at Huixian Karst Wetland,China

以我国最大的低海拔岩溶湿地会仙岩溶湿地为研究区,对该区丰水期、平水期和枯水期共采集的27组地下水样品中常规离子进行检测和分析,在分析会仙岩溶湿地地下水主要离子化学特征和不同时期变化基础上,运用单指标污染标准指数法对不同时期地下水进行污染评价,利用多元统计、Gibbs模型和离子比例关系识别地下水主要离子成因.结果表明,研究区内岩溶地下水主要为弱碱性淡水,Ca^(2+)和HCO^(-)_(3)为优势离子.不同时期地下水主要离子总浓度顺序为:平水期>丰水期>枯水期,枯水期水质优于丰水期和平水期.地下水中K^(+)和NO^(-)_(3)主要受含水层空间分布差异影响,Mg^(2+)、SO^(2-)_(4)、NO^(-)_(2)、NH^(+)_(4)和TDS受时空尺度综合作用,Na^(+)、Ca^(2+)、HCO^(-)_(3)和Cl^(-)为水体中较稳定离子.受碳酸盐岩控制,丰水期、平水期和枯水期地下水化学类型具有高度一致性,HCO_(3)-Ca水占比分别为77.78%、77.78%和88.89%.地下水主要受SO^(2-)_(4)、NO^(-)_(3)和NO^(-)_(2)污染,NO^(-)_(3)出现极严重程度污染样点,SO^(2-)_(4)在丰水期和平水期出现较重污染样点.地下水化学组分主要受水岩作用控制,Ca^(2+)和HCO^(-)_(3)主要来源于方解石风化溶解,少量水点受白云岩、白云质灰岩及硫铁矿控制导致Mg^(2+)和SO^(2-)_(4)浓度偏高,K^(+)、Na^(+)、SO^(2-)_(4)、NO^(-)_(3)和Cl^(-)部分来源于大气降水,Na^(+)和Cl^(-)部分来源于当地居民生活,K^(+)与种植施用的钾肥相关,NO^(-)_(3)主要来源是化学肥料.

To investigate the major ionic chemical characteristics and seasonal variations,27 groundwater samples were collected from the wet season,flat season,and dry season during 2018-2019 in the Huixian Karst wetland,which is the largest low-altitude karst wetland in China.The single pollution standard index was applied to evaluate the groundwater pollution during different periods,and the major ionic factors of the karst groundwater were analyzed using the statistical analysis method,Gibbs diagram,and ion ratio.The results revealed that the groundwater samples were a weakly alkaline fresh water that were rich in Ca^(2+)and HCO^(-)_(3).The average concentrations of the primary ions followed the order of flat season>wet season>dry season;meanwhile,the water quality in the dry season was better than that in the wet and flat seasons.The K^(+)and NO^(-)_(3)in the karst groundwater were mostly affected by the spatial distributions of the aquifers,and the Mg^(2+),SO^(2-)_(4),NO^(-)_(2),NH^(+)_(4),and TDS were related to the space-season scale.Na^(+),Ca^(2+),HCO^(-)_(3),and Cl^(-)were relatively stable ions in the karst groundwater.The hydrochemical characteristics were primarily determined by carbonate rock dissolution and were found to be the HCO_(3)-Ca type,which accounted for 77.78%,77.78%,and 88.89%in the wet season,flat season,and dry season,respectively.The karst groundwater was predominantly polluted by SO^(2-)_(4),NO^(-)_(3),and NO^(-)_(2);particularly,NO^(-)_(3)exhibited serious pollution points,and SO^(2-)_(4)had heavy pollution points in the wet and flat seasons.The chemical composition of the karst groundwater was controlled mostly by water-rock interactions.Ca^(2+)and HCO^(-)_(3)primarily came from calcite dissolution,and the high concentrations of Mg^(2+)and SO^(2-)_(4)in a few number of points were controlled by dolomite,dolomitic limestone,and pyrite.K^(+),Na^(+),SO^(2-)_(4),NO^(-)_(3),and Cl^(-)partly came from atmospheric precipitation,and Na+and Cl^(-)partly came from human activities;K^(+)was related to potash fertilizer,and the main source of NO^(-)_(3)was chemical fertilizer.