Quantitative sources of nitrate in typical plain river network areas by a combined PMF and MixSIAR approach

Abstract

Nitrate nitrogen (NO₃⁻) pollution has become a severe issue in the plain river network areas with the intensification of human activities, leading to environmental problems such as eutrophication. Therefore, it is imperative to trace the sources of NO₃⁻ in rivers. This study performed stable isotope sampling on samples collected from two main rivers of the Yubei Plain river network based on different land-use types, with sampling focused on aquaculture and industrial areas. A combination of positive matrix factorization models (PMF), isotope tracer and mixed stable isotope analysis in R (MixSIAR) was used to quantify the sources of NO₃⁻ in the typical plain river network in China. NO₃⁻ concentrations in the river network of the Yubei Plain ranged from 0.62 to 1.54 mg L⁻¹ and showed an increasing trend downstream. NO₃⁻ accounted for over 70% of the total nitrogen (TN) concentration. PMF and MixSIAR results showed that industrial, agricultural, domestic and aquaculture wastewater were the main drivers of NO₃⁻ in the river network. The results from both the PMF and MixSIAR models were similar, confirming the validity of the analysis. The results showed that industrial wastewater contributed more than 40% of NO₃⁻, which was the main driver affecting NO₃⁻ pollution in the river network. In addition, nitrification was significant in the plain river network, while denitrification was negligible. The results of this study provide valuable insights into the pollution control of nitrate nitrogen in plain river network areas.