In-situ Observation and Nitrate-N Load Assessment in Madhubani District, Bihar, India

Fertilizers may leach through the vadose zone and eventually reach groundwater in agriculturally intensive areas. Thus, the main focus of this study was to investigate Nitrate-N load and vulnerability of groundwater resources using in-situ observed hydrogeological data. Soil water flow and contaminant transport equation was numerically simulated using HYDRUS 1D for constant head and atmospheric top boundary conditions. Subsurface materials were distributed based on the lithologs of the target area. Observed water table locations were considered as bottom boundary condition to respective numerical domain. The time taken by Nitrate-N to reach groundwater table was considered to estimate vulnerability index. The results show that Nitrate-N load is higher in constant head boundary conditions than atmospheric boundary conditions. The eastern part of the study area shows high vulnerability than northern part followed by western part. In-situ observed nitrate concentrations were well matched with simulated results. The high vulnerability in eastern and northern part is due to alluvial sandy lithologs and very shallow groundwater table. These findings are in line with the observed low water table depths, less runoff, and higher hydraulic conductivity of the vadose zone material in these area. In western part, forest cover dominated land use causes low pollution vulnerabilities to groundwater resources. This study may help to frame agricultural and soil-water conservation practices with more sustainable remedial techniques.