Spatial and Temporal Variations of Nitrogen and Phosphorus in Surface Water and Groundwater of Mudong River Watershed in Huixian Karst Wetland, Southwest China

Abstract

When considering the factors affecting the spatial and temporal variation of nitrogen and phosphorus in karst watersheds, the unique karst hydrogeology as an internal influencing factor cannot be ignored, as well as natural factors such as meteorological hydrology and external factors such as human activities. A watershed-scale field investigation was completed to statistically analyze spatial and temporal dynamics of nitrogen and phosphorus through the regular monitoring and collection of surface water and shallow groundwater in the agricultural-dominated Mudong River watershed in the Huixian Karst Wetland over one year (May 2020 to April 2021). Our research found that non-point source pollution of nitrogen (84.5% of 239 samples TN > 1.0 mg/L) was more serious than phosphorus (7.5% of 239 samples TP > 0.2 mg/L) in the study area, and shallow groundwater nitrogen pollution (98.3% of 118 samples TN > 1.0 mg/L) was more serious than surface water (68.6% of 121 samples TN > 1.0 mg/L). In the three regions with different hydrodynamic features, the TN concentration was higher and dominated by NO3−-N in the river in the northern recharge area, while the concentrations of TN and TP were the highest in shallow groundwater wells in the central wetland core area and increased along the surface water flow direction in the western discharge area. This research will help improve the knowledge about the influence of karst hydrodynamic features on the spatial patterns of nitrogen and phosphorus in water, paying attention to the quality protection and security of water in karst areas with a fragile water ecological environment.

Spatial difference on nitrogen removal in the water based on different resolutions for Sanhuanpao wetland, Northeast China

“…The wetland areas have been decreasing at an increasing rate; they became an important place to accommodate the retreating farmland when the surrounding wetland areas were occupied by cropland. The function of nitrogen purification in wetland water has faced enormous challenges, and it has become a research hotspot in the study of the spatial heterogeneity of nitrogen concentrations in wetlands (Li, Chu, et al, 2021; Pan et al, 2021). In the Baidugang wetland of Taihu Lake in China, the total nitrogen (TN) concentration was 0.37–5.42 g/kg, with a medium spatial difference (Huang et al, 2011).…”