Groundwater hydrochemical signatures, nitrate sources, and potential health risks in a typical karst catchment of North China using hydrochemistry and multiple stable isotopes

In this study, hydrochemical compositions, multiple stable isotopes ( δ2H –H2O, δ18Ο–Η2Ο, δ15Ν–ΝΟ3−, and δ18Ο–ΝΟ3−), and Bayesian stable isotope mixing model (MixSIAR) were applied to elucidate nitrate pollution sources in groundwater of the Yangzhuang Basin. The Durov diagram identified the dominant groundwater chemical face as Ca –HCO3 type. The NO3− concentration ranged from 10.89 to 90.45  mg/L (average 47.34 mg/L), showing an increasing trend from the upstream forest and grassland to the downstream agricultural dominant area. It is worth noting that 47.2% of groundwater samples exceeded the NO3− threshold value of 50  mg/L for drinking water recommended by the World Health Organization. The relationship between NO3−/Cl− and Cl− ratios suggested that most groundwater samples were located in nitrate mixed endmember from agricultural input, soil organic nitrogen, and manure& sewage. The Self-Organizing Map (SOM) and Pearson correlations analysis further indicated that the application of calcium fertilizer, sodium fertilizer, and livestock and poultry excrement in farmland elevated NO3− level in groundwater. The output results of the MixSIAR model showed that the primary sources of NO3− in groundwater were soil organic nitrogen (55.3%), followed by chemical fertilizers (28.5%), sewage& manure (12.7%), and atmospheric deposition (3.4%). Microbial nitrification was a dominant nitrogen conversion pathway elevating NO3− level...
Source: Environmental Geochemistry and Health - Category: Environmental Health Source Type: research