Evolution of Water Chemistry and the Associated Desalination in Jiyun River, Tianjin, China

In order to clarify the characteristics of the water chemistry changes in the rivers entering the sea in the Haihe River Basin after the establishment of estuarine tide gates, this paper took the Jiyun River as the research object, and investigated the main ion sources, the evolution process of the water chemistry types and the controlling factors of the Jiyun River by collecting and analysing water samples in the rainy season and the non-rainy season. The results showed that: (1) The water body of the Jiyun River basin was weakly alkaline in general, and the seasonal variation of acidity and alkalinity (pH) was large, which generally showed that pH value in the rainy season3 type to Ca·Mg‒Cl type in the rainy season, and from Ca·Mg‒HCO3 type to Na·Mg‒Cl type in the non-rainy season. (3)There are significant spatial and seasonal differences in the saturation indices of dolomite, calcite, and hard gypsum in surface water and groundwater in the basin, which control the hydrochemical composition of surface water in the Jiyun River. (4) The Na+/Cl– ratio of surface water in the Jiyun River ranged from 0.86 to 1 in the rainy season, while it was greater than 1 in the non-rainy season, suggesting that the surface water was mainly influenced by rainfall in the basin and incoming water from the upstream during the rainy season, whereas evaporation from the river channel, recharge of groundwater from the riverside and human activities were more significant in the non-rainy season.(5) The establishment of the estuarine tide gates facilitated the freshwaterization of the river and changed the course of the river′s hydrochemical evolution.