Hydrochemical zoning: natural and anthropogenic origins of the major elements in the surface water of Taizi River Basin, Northeast China

Discriminating the hydrochemical origins in the polluted rivers is a challenge work due to multiple sources contributing to the river’s chemical composition. The Taizi River, as an important tributary of the Liao River, in Northeast China, is flowing through an urban-, industry-, and agriculture-intensive area, and its hydrochemistry has been disturbed by human activities especially in the lower basin. In this study, an extensive analysis has been conducted to evaluate the natural and anthropogenic origins of the hydrochemistry in the Taizi River Basin. Three hydrochemical zones are determined based on hydrological connectivity, land use types and lithology, and the hydrochemistry pattern has changed from Ca-HCO3 type to Ca-HCO3-SO4 type from the upper basin to the lower basin due to increasing areas of agriculture and residence land. Six end members including the rain inputs, sewage discharge, mine drainage, carbonate, silicate and evaporate weathering are discriminated in the study area by applying a two stage stoichiometric method. The first stage is used to separate the anthropogenic inputs (sewage discharge and mine drainage) by an inversion technique, and the second stage is evaluating the rock weathering contributions from carbonates, silicates and evaporates by a forward method. Chemical budget calculation shows that carbonate weathering and anthropogenic inputs are two important factors controlling the hydrochemistry with contributions of about 52 and 27 % of the TDS, respectively. In addition, the contribution of anthropogenic inputs increases from 20 % in the upper basin to 30 % in the lower basin.