Spatial variability of source contributions to nitrate in regional groundwater based on the positive matrix factorization and Bayesian model

Groundwater nitrate (NO3-) pollution has attracted widespread attention; however, accurately evaluating the sources of NO3 - and their contribution patterns in regional groundwater is difficult in areas with multiple sources and complex hydrogeological conditions. In this study, 161 groundwater samples were collected from the Poyang Lake Basin for hydrochemical and dual NO3 - isotope analyses to explore the sources of NO3 - and their spatial contribution using the Positive Matrix Factorization (PMF) and Bayesian stable isotope mixing (MixSIAR) models. The results revealed that the enrichment of NO3 - in groundwater was primarily attributed to sewage/ manure (SM), which accounted for more than 50 %. The contributions of nitrogen fertilizer and soil organic nitrogen should also be considered. Groundwater NO3 - sources showed obvious spatial differences in contribu-tions. Regions with large contributions of SM (>90 %) were located in the southeastern part of the study area and downstream of Nanchang, which are areas with relatively high population density. Nitrogen fertilizer and soil organic nitrogen showed concentrated contributions in paddy soil in the lower reaches of the Gan and Rao Rivers, and these accumulations were mainly driven by the soil type, land use type, and topography. This study provides insight into groundwater NO3 - contamination on a regional scale.