Sources and health risks of nitrate pollution in surface water in the Weihe River watershed, China

Owing to the significant reductions in streamflow and an increase in human activities in recent years, the quality of surface water in Weihe River continues to pose environmental health concerns. We utilized hydrochemistry and nitrogen and oxygen isotopes to elucidate the status and identify sources of nitrate pollution in the south and north banks for three seasons (flood, dry, and mean-flow periods) in the Weihe River watershed. A Bayesian isotope mixing model was applied to estimate the contributions of four potential N O 3 − sources to river pollution (manure and sewage, soil nitrogen, inorganic fertilizer, and nitrate in precipitation). The U.S. Environmental Protection Agency (USEPA) evaluation model was implemented to evaluate the health risks associated with nitrate pollution in the surface water. Nitrate pollution was most severe during the dry period because the river flow was small. Due to the influence of the topography and land use type of the Weihe River, the pollution in the main stream was greater than that of the tributaries, and the pollution of the south bank was greater than that of the north bank. During the flood and mean-flow periods, δ 15 N and δ 18 O were mainly distributed in the N H 4 + of the fertilizer and soil nitrogen. During the dry period, δ 15 N and δ 18 O were mainly distributed in domestic sewage and manure regions. According to the Stable Isotope Analysis in R (SIAR) model, manure and sewage were the major nitrate sources during the dry period (73%). However, a decrease in the contribution from domestic sewage and manure was observed during the flood period (45%) compared to the dry period, but with a significantly increased contribution from soil nitrogen (23%) and inorganic fertilizer (21%). The health risk value in the dry period was higher than that in the wet and mean flow periods, and children are more susceptible to nitrate pollution than adults. Therefore, reducing the discharge of domestic sewage and manure and improving the utilization rate of nitrogen fertilizers may be effective measures to improve water quality in the watershed.