Precipitation patterns of nitrogen and phosphorus in reservoirs: A study in typical sand-source area of Inner Mongolia using PMF-HYSPLIT model

Abstract

Analyzing the sources of nitrogen and phosphorus pollution in atmospheric deposition is crucial for protecting the surface water environment in vulnerable areas. This study focused on the Dahekou Reservoir, Shayuan District, Xilin Gol League, Inner Mongolia, China. It established 12 monitoring sites, conducted one-year monitoring, and collected 144 samples. The concentrations of nitrogen, phosphorus, and water-soluble ions in atmospheric wet sedimentation were measured. This study identified atmospheric precipitation types, revealed seasonal variations in nitrogen and phosphorus concentrations, assessed the contribution of atmospheric wet sedimentation to reservoir water quality. Utilizing the air mass backward trajectory (HYSPLIT) model and PMF model, the main pollution sources were analyzed. The results were as follows. 1) During the observation period, the atmospheric precipitation types were nitric acid rain in spring, sulfuric acid rain in winter, and mixed acid rain in summer and autumn. 2) The monthly concentrations of nitrogen and phosphorus of various forms varied significantly, with NH₄⁺-N peaking in spring, NO₃^--N and DOP in autumn, and DIP and DON in summer. Annual pollution loads of atmospheric nitrogen and phosphorus precipitation into the reservoir were 35.77 and 4.17 t/a, respectively, severely impacting reservoir water quality. 3) Precipitation was negatively correlated with TN concentration, particularly with the NO₃^--N/TN ratio, and positively correlated with TP and DIP concentrations. 4) The analysis of pollution sources indicated that the sources of atmospheric nitrogen and phosphorus wet deposition pollution in the study area included agricultural, anthropogenic, dust, and coal sources, with contribution rates of 32.4 %, 25.6 %, 21.0 %, and 21.0 %, respectively.