Impact of water diversion practices on spatiotemporal changes in hydrologic and hydrochemical landscapes of surface and groundwater

Water diversion activities in lakes and the associated hydrological landscape ’diverted rivers/estuaries’ alter the lake's spatiotemporal dynamics of hydro-environmental characteristics. However, only a few studies have focused on these complex effects in large lakes. We report here the results of an investigation conducted on the natural river estuary, diverted river estuary, and unchannelized lakeshore (blank control) within Hongze Lake. This lake is the largest on the eastern route of the South-to-North Water Diversion Project in China. Stable isotopes (δ¹⁸O, δ²H), major ions (Na, Mg, K, Ca, HCO₃, SO₄, Cl), trace elements (Sr, Pb, Al, Zn, Cu, As, F), and nutrients (NO₃, TP) of the lake water and shallow and deep groundwater were analyzed for samples taken during the water diversion and drainage periods. The data indicate that water diversion and drainage activities accelerate the infiltration and recharge of lake water, involving dilution and enrichment of major ions in groundwater, respectively. However, the diverted river landscape induces the contribution of hydrology and hydrochemistry from deep groundwater to lake water and shallow aquifers during water diversion activities. The impact of these processes persists for approximately a month after the end of the water diversion period. Additionally, increased water temperature and acidity during the water diversion period release more trace elements from sediment into the lake and shallow groundwater. This process also enriches nutrient concentrations in the lake water. The results and the proposed model provide insights for the management of water quantity and quality during the implementation of water diversion practices in lake systems.