[Hydrochemical Characteristics of Shallow Groundwater and Identification of Water Quality Types in the Dawen River Basin].

Abstract

Groundwater chemical characteristics and water quality are affected by both natural geological conditions and human activities. Taking the Dawen River Basin as the research object, we analyzed the hydrochemical characteristics and their influencing factors through field investigation and sampling, evaluated the water quality by applying the entropy-weighted water quality index （EWQI）, distinguished the degree of influence of human activities on the groundwater quality by applying the method of identifying hydrochemical anomalies, and then coupled the two evaluating methods to identify the types of groundwater water quality. The results showed that the anions and cations of groundwater in the Dawen River Basin were dominated by HCO₃^- and Ca²⁺, respectively, and the exceedance rates of TH, TDS, SO₄^2-, and NO₃^- concentrations in the groundwater were high； the groundwater chemistry types were dominated by HCO₃·SO₄-Ca, HCO₃·Cl-Ca, and HCO₃·SO₄·Cl-Ca types； and the chemical components of the groundwater were affected by the interaction between the water and rocks. The chemical components of groundwater were affected by water-rock interactions and human activities. The EWQI results showed that the proportions of groundwater quality classes I and II were 10.71% and 36.91%, respectively； the proportion of groundwater quality class III was 41.67%； and the proportions of class IV and V water were 5.95% and 4.76%, respectively. The water quality condition from the upstream to the downstream of the basin was getting worse, and the quality of fissure water and karst water was better than that of pore water. The areas where water chemistry identified a greater degree of anthropogenic influence were mainly located in the downstream Dongping County and Dongping Lake, in the middle reaches of the river in Ningyang County and Wenyang Town, and in the upper reaches of the river in Quangou and Yucun Towns, where human activities were mainly concentrated in the watershed's low-lying terrain. The above two evaluation results had a strong positive correlation, with a correlation coefficient of 0.588. Combining the two evaluation methods of EWQI and the degree of influence of human activities, the state of groundwater protection and management was classified into three categories： protection, prevention, control and management, which could make up for the fact that the single evaluation method was incomplete in identifying the type of water quality. Moreover, it is useful to differentiate between poor-quality water under natural geological conditions and poor-quality water caused by human activities.