Using Rn temporal and spatial distributions to estimate the groundwater discharge rate and associated nutrient fluxes into high salinity lakes in Badain Jaran Desert, Northwest China.

Groundwater is the main source of water and salt recharge for to lakes in arid regions. Quantifying the groundwater discharge and its nutrient input is important in the evolution of lake environments in the Badain Jaran Desert (BJD), Northwest China. In this study, ten BJD lakes were sampled for Rn in April and September 2021, and the Rn mass balance model was used to quantify the groundwater discharge rates and derived nutrient fluxes to these lakes. The results showed that the Rn activity and the groundwater recharge rate of lake water both present a positively correlated with lake water depth. The hot points of high Rn activity in the lake water were consistent with the locations of groundwater discharge areas. According to the Rn temporal and spatial distributions, the mean groundwater recharge rates for the ten lakes in April and September were 5.4 ± 0.6 and 7.7 ± 1 mm/d, respectively, and the annual mean groundwater discharge rates varied between 1.1 ± 0.2 and 14.6 ± 1.6 mm/d, with a mean of 7 ± 0.9 mm/d. Given that all the perennial lakes in the BJD have the same groundwater recharge rate as the mean recharge rate of the ten studied lakes, the annual mean groundwater recharge amount received by the lakes in the entire BJD is (5.6 ± 0.7) × 10 m/a. According to the groundwater recharge amount, the inputs of dissolved inorganic nitrogen, dissolved inorganic phosphorus, dissolved inorganic silicon, total nitrogen, and total phosphorus to the BJD lakes from groundwater were (4.7 ± 0.6) × 10, (3.8 ± 0.5) × 10, (7.9 ± 1) × 10, (7.2 ± 0.9) × 10, (2.5 ± 0.3) × 10 kg/a, respectively. This study provides a reference for quantifying of groundwater discharge rates into salt lakes in other arid regions.