Application of the dual-isotope approach and Bayesian isotope mixing model to identify nitrate in groundwater of a multiple land-use area in Chengdu Plain, China

• Published in: The Science of the total environment 2020-05, Vol.717, p.137134-137134, Article 137134
• Main Authors: Zhang, Han, Xu, Yi, Cheng, Siqian, Li, Qiling, Yu, Haoran
• Format: Article
• Language: English
• Subjects: Agriculture; Bayesian isotope mixing model; Groundwater nitrate pollution; Land-use; Stable isotopes
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.137134

Nitrate (NO3−) contamination in groundwater is an environmental problem worldwide. Partitioning the pollution into its sources is the key for effective controls. In this study, NO3− dual isotopic compositions (δ15N-NO3− and δ18O-NO3−) were measured in groundwater samples from 28 wells in an area with multiple land-uses, followed by the application of an isotope mixing model (SIAR) to identify the main NO3− sources and their biogeochemical processes. The results showed that denitrification was unlikely occur at significant rates, while nitrification was an important nitrogen transformation processes. Spatial variation of groundwater NO3− and its isotopic compositions was associated with the land-use types. Agricultural areas were characterized by relatively high NO3− concentrations and low δ15N-NO3− values. In contrast, industrial areas were characterized by enriched δ15N-NO3− and δ18O-NO3− values. In crop field, vegetable field and poultry and livestock breading farm, the proportional contribution represented a similar pattern with highest contribution from chemical fertilizer followed by soil organic nitrogen, manure, atmospheric precipitation and sewage in order. Nitrate in groundwater in industrial areas has different pattern of the proportional contribution, in which groundwater NO3− is largely influenced by sewage discharge and atmospheric precipitation. We concluded that the combination of isotopic analysis together with land-use information and chemical analysis was an effective approach for assessing the source apportionment and the fate of nitrate in the aquifer in multiple land-use areas. [Display omitted] •Isotopic analysis was combined with land-use and chemical analysis to identify the main sources of groundwater nitrate in a multiple land-use area.•An isotope mixing model (SIAR) was employed to estimate the proportional contributions of various sources for different land-use types.•Major nitrate sources are chemical fertilizer and soil N in agricultural areas; while major nitrate sources are sewage and atmospheric precipitation in industrial areas.•The results will aid to take measures and strategies to prevent groundwater contamination in the area.