Spatial variability of lacustrine groundwater discharge in the largest urban lake in Asia: Coupled influence from land use and hydrogeology

Abstract Lacustrine groundwater discharge (LGD) has a profound impact on the status of lake ecosystems. The distinct spatial variability of LGD has been acknowledged, but corresponding research has rarely been conducted, especially in urban lakes with changing land use. In this study, the spatial variability of LGD in Tangxun Lake, the largest urban lake in Asia, was quantitatively estimated using the 222 Rn mass balance model. Catchments with different land use and hydrogeological conditions within the study area are divided into five regions. The results revealed three ranges of the LGD rate in five regions: the first range of 25 mm/day (region II: 27.25 ± 8.38 mm/day and region IV: 23.04 ± 7.51 mm/day), the second range of 15 mm/day (region III: 14.16 ± 5.64 mm/day), and the third range of 10 mm/day (region I: 10.61 ± 4.31 mm/day, region V: 9.05 ± 3.60 mm/day). Here, we found that the LGD rate of urban lakes was largely controlled by land use patterns, although it was also inherently affected by hydrogeological conditions, which is consistent with a significant positive correlation between the proportion of impermeable/total surfaces within 1 km of the lakeshore and the LGD rate of the corresponding region. The proposed reason is that the head difference between groundwater and lake water decreases with increasing proportion of impermeable surfaces around the urban lake because of reduced infiltration, leading to the decrease of LGD rate. This study provides new insights into the spatial variability of LGD for lakes in a changing environment.