This study delved into the origins and transformation processes of nitrate in the groundwater of the Datong Basin, utilizing hydrochemical analysis alongside multi-isotope techniques (δ18O-H2O, δ15N-NO3- and δ18O-NO3-). With the MixSIAR model, we quantitatively assessed the contribution of various pollution sources. Research results are as follows, the mean concentrations of NO3--N, NO2--N and NH4+-N in groundwater were found to be 32.07,0.96和0.61mg/L, respectively, with NO3--N being the most prevalent. Remarkably, the peak concentration of NO3--N soared to 538.61mg/L, surpassing the Class III groundwater quality benchmark (20mg/L) by a staggering 27 times, with a 39.13% exceedance rate. The NO3--N concentration decreased as groundwater depth increased: shallow groundwater averaged at 34.26mg/L, middle groundwater at 22.05mg/L, and deep groundwater at 13.07mg/L. Nitrogen transformation in groundwater was primarily driven by nitrification, whereas denitrification played a minor role. The primary culprits behind nitrate pollution in groundwater were identified as sewage and manure, soil nitrogen and chemical fertilizers. Their respective average contribution rates were as follows: in shallow groundwater, sewage and manure accounted for 33.6%, followed by soil nitrogen at 33.5% and chemical fertilizers at 21.5%. For middle groundwater, the rates were 43.3% for sewage and manure, 34.4% for soil nitrogen, and 18.1% for chemical fertilizers. In deep groundwater, soil nitrogen led with 54.4%, chemical fertilizers followed at 25.1%, and sewage and manure contributed 18.5%. An uncertainty analysis revealed that the contribution rates of chemical fertilizers and soil nitrogen carried significant uncertainty, indicated by their relatively high UI90values. The research results provide a reference for understanding nitrogen transformation and identifying pollution sources in groundwater.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |