Co-evolution mechanism of groundwater and wetland ecosystem in a typical inland watershed in northwest China

Wetland restoration projects represented by ecological water conveyance have been widely used in the inland watersheds in northwest China. The interaction between groundwater and wetland vegetation under the ecological water conveyance determines the evolution of wetland ecosystems. In this study, the Qingtu Lake Wetland of the Shiyang River Basin in northwest China is taken as the research area, and the groundwater dynamic change and wetland vegetation restoration under the condition of the ecological water conveyance are analyzed based on a multi-element integrated monitoring network of groundwater-wetland ecosystem, combining with technologies of stable isotopes and satellite remote sensing. The purpose of this work is to reveal the co-evolution mechanism of groundwater and wetland ecosystems from the perspective of hydrogeology. The results show that the lake water recharges groundwater and the soil moisture increases during the ecological water delivery in late summer and autumn (the maximum soil moisture of observation sites is 0.45 m³/m³). In winter, this recharge decreases with the freezing of lake and surface soil. The thawing of frozen soil and lake in spring leads to a slight recovery of groundwater and an increase in soil moisture. In summer, the lake surface and the groundwater level are the smallest before the next ecological water delivery (the minimum surface area is about 1 km², and the maximum groundwater depth of observation sites is 3.6 m). Meanwhile, the surface soil moisture is also the lowest (the minimum soil moisture of observation sites is 0.01 m³/m³), and the groundwater recharges the lake in some areas. The ecological water conveyed in late summer and autumn can act on vegetation recovery and growth in the following year by storing the water in groundwater and soil. Increasing the lake surface area formed by ecological water is helpful in upgrading vegetation coverage (the average correlation coefficient is 0.655). The soil water environment formed by the interaction of surface water-soil-groundwater is the main factor affecting vegetation types, root distribution and water use strategy. It is mainly controlled by the groundwater depth. With the increasing groundwater depth, the vegetation types and root depths increase, and the vegetations tend to use deep soil water. The research results can provide a scientific basis for the restoration of wetland ecosystems and efficient use of water resources in the northwestern inland basins.