Landform sedimentary contributed to groundwater nitrate vulnerability in multi-alluvial fan aquifer systems in a watershed

Groundwater nitrate vulnerability in alluvial plains in agricultural areas is characterized and controlled by the distribution, sources, and fate of nitrate, which are influenced by a combination of land use and landform sedimentary types. Determining the relative importance of factors and understanding the combined action of multiple land uses and sedimentary types are important for controlling groundwater nitrate pollution in such areas. The Baiyangdian watershed has a variety of landform types (proluvial/alluvial fans and plains, river belts, etc.) and land use types (agriculture, woods, residential, etc.) and was selected as the study area. Water chemical analyses and stable isotopes were used to identify the distribution characteristics and sources of nitrate, and the Depth to water table, net Recharge, Aquifer media, Soil media, Topography, Impact of the vadose zone, and hydraulic Conductivity (DRASTIC) model was used to assess the vulnerability. The results show that nitrate concentrations are highly variable. 19.1% of nitrate concentrations exceeded the WHO drinking water limit, having a mean of 30.3 mg/L. Nitrate concentrations vary greatly across landform sedimentary types under the same land use. The results of the relative weight calculations showed that the contribution of landform and land use type to groundwater nitrate concentration was 67.4% and 32.6%, respectively. The distribution, source and fate of groundwater nitrate are mainly controlled by landform types. Proluvial and alluvial-proluvial fans has very high and high vulnerability and nitrate levels, with chemical fertilizers being the main source. Alluvial and flood plain has low and very low vulnerability and nitrate levels, where manure and sewage are the major sources. River belts, lakes and depressions are in the medium vulnerability class, where wastewater discharges result in high local nitrate levels and reduction environment are conducive to avoiding nitrate pollution. The study contributes to the management of land and water resources in similar environments.

Automated summary

Groundwater nitrate vulnerability in alluvial plains in agricultural areas is influenced by land use and landform sedimentary types. The distribution, sources, and fate of nitrate are mainly controlled by landform types. Proluvial and alluvial-proluvial fans have high vulnerability and nitrate levels, while alluvial and flood plains have low vulnerability and nitrate levels. River belts, lakes, and depressions are in the medium vulnerability class. The study contributes to the management of land and water resources in similar environments.