Application of radon-222 to assess groundwater discharge and associated nutrients input in the karst wetland
Baxian Lake,located in Huixian Wetland,was taken as the study's object in this paper to investigate the groundwater discharge flux and the associated nutrient input.The samples of lake water,groundwater,sediments,and air collected in December 2021(dry season)and May 2022(wet season)were tested for physical and chemical properties,222Rn and nutrients.The input items of 222Rn in Baxian Lake were 226Ra parent decay,sediment diffusion,and groundwater discharge.The output items included the runoff flux,decay of 222Rn inventory in the lake,and atmospheric diffusion.Then,the 222Rn mass balance model of Baxian Lake was established,and the groundwater discharge rate during the dry season and the rainy season were 110.60±23.75mm/d and 238.04±46.58mm/d,respectively.Based on the average nutrient concentration of groundwater around Baxian Lake,the nutrients flux from the groundwater discharge during the dry season were estimated as follows:(2.24±0.52)×10-3mol/m2×d(NH4+-N),(1.93±0.42)×10-2mol/(m2·d)(NO3--N),(1.20±0.26)×10-1mol/(m2·d)(TN),(1.97±0.42)×10-4mol/(m2·d)(TP).The nutrient fluxes from the groundwater discharge during the wet season were:(1.30±0.25)×10-2mol/(m2·d)(NH4+-N),(2.71±0.53)×10-2mol/(m2·d)(NO3--N),(2.18±0.43)×10-1mol/(m2·d)(TN),(4.51±0.89)×10-4mol/(m2·d)(TP).This study provides important information for water circulation and water ecosystem for the water resource management of Huixian Wetland.
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