Effects of Ecological Water Conveyance on the Hydrochemistry of a Terminal Lake in an Inland River: A Case Study of Qingtu Lake in the Shiyang River Basin

Abstract

Along with the growth of the population and economic and social development, water consumption in the upper-middle reaches of inland rivers is increasing, which has resulted in long-term cutout in the lower reaches of the river, shrinkage and drying up of the wetlands around the terminal lakes, and has caused a series of ecological problems at the same time. In order to protect the fragile ecological environment, comprehensive harnessing projects have been carried out in many inland river basins in China, in which adopting ecological water conveyance to rehabilitate degraded terminal lakes and wetlands is an important means. From June 2014 to October 2017, the water in the upper-middle reaches of the Shiyang River Basin and the lake water of the terminal lake after ecological water conveyance was sampled. The effects of ecological water conveyance on the characteristics of surface water and groundwater were analyzed using, for example, the Piper triangle diagram, Gibbs boomerang envelope model, and mixing diagram. After ecological water conveyance, the ion concentration of water in Qingtu Lake was higher overall, and ion concentration of water in the unstable catchment was higher than that of the stable catchment. The time variation was characterized as high in the summer half year and low in the winter half year. The water of Qingtu Lake is of high and large salinity, and its hydrochemical type is Na–SO4 (Cl), which is obviously different from the water in the middle-upper reaches of the Shiyang River Basin. The effects of silicate weathering and evaporation crystallization are the main factors leading to the high ion concentration in the water of Qingtu Lake. Ecological water conveyance and the strong evaporation of arid areas have intensified the salinization of water and soils in Qingtu Lake. Meanwhile, implementing the ecological water conveyance policy in the terminal lake has also led to shortage of water resources for agricultural irrigation in the middle reaches of the Shiyang River Basin. The serial negative ecological effects of the ecological water conveyance should be emphasized.