Using 222Rn 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 222Rn in April and September 2021, and the 222Rn mass balance model was used to quantify the groundwater discharge rates and derived nutrient fluxes to these lakes. The results showed that the 222Rn activity and the groundwater recharge rate of lake water both present a positively correlated with lake water depth. The hot points of high 222Rn activity in the lake water were consistent with the locations of groundwater discharge areas. According to the 222Rn 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) x 107 m3/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) x 105, (3.8 +/- 0.5) x 104, (7.9 +/- 1) x 105, (7.2 +/- 0.9) x 105, (2.5 +/- 0.3) x 104 kg/a, respectively. This study provides a reference for quantifying of groundwater discharge rates into salt lakes in other arid regions.

Automated summary

Groundwater discharge rates and nutrient input were quantified using the 222Rn mass balance model in ten lakes in the Badain Jaran Desert. The results showed a positive correlation between 222Rn activity and lake water depth, indicating the presence of groundwater discharge areas. The annual mean groundwater discharge amount received by lakes in the entire BJD was estimated to be (5.6 +/- 0.7) x 107 m3/a, with significant inputs of dissolved inorganic nitrogen, phosphorus, and silicon.