Title : Nitrate dynamics in groundwater of an intensively cultivated region of eastern India: Hydrogeochemical controls and natural attenuation
Abstract:
Nitrate contamination of groundwater is a major environmental concern worldwide, arising from both natural and anthropogenic sources, particularly the excessive application of nitrogenous fertilizers. Elevated nitrate concentrations in drinking water are associated with methemoglobinemia and have also been linked to chronic health concerns, including colorectal and thyroid cancers and adverse birth outcomes. Despite intensive fertilizer application and agricultural activity in the Kanksa Block of Paschim Bardhhaman District, West Bengal, nitrate concentrations in groundwater remain relatively low, ranging from below the detection limit to 11.53 mg/L. To investigate the hydrogeochemical characteristics and factors controlling nitrate occurrence, a total of 64 groundwater samples collected from tube wells and open wells were analysed for physicochemical parameters, major ions, and trace elements. The groundwater exhibited considerable hydrogeochemical variability, with pH ranging from 4.91–7.47, EC from 3–4535 µS/cm, and TDS from 53–2276 mg/L. Concentrations of HCO??, Cl?, SO?²?, Ca²?, Mg²?, Na?, and K? ranged from 48.8–634.4, 2.37–192.67, 0.053–252.5, 1.81–271.1, 0.078–86, 6.53–473.3, and 0.985–224.5 mg/L, respectively. Fe and Mn ranged from 0.021–4.131 and 0.004–4.147 mg/L, respectively. Hydrogeochemical evaluation indicated that rock–water interaction was the dominant controlling process, with localized evaporation and salinization contributing to groundwater evolution.
The relatively low nitrate concentrations despite intensive agricultural activity suggest substantial attenuation within the soil–vadose zone. At the same time this mechanism can throw light on techniques which may be used to remediate nitrate from groundwater with greater nitrate concentration. To investigate this phenomenon soil column test and soil tank experiments were conducted to evaluate nitrate transport. Breakthrough curve account for the observed low groundwater nitrate concentration. Therefore, another attenuation must be limiting nitrate leaching to the groundwater, with bacterial denitrification being the most plausible process. However, further investigation is required to confirm its role.
Keywords: Nitrate contamination; groundwater; hydro-geochemistry; nitrate attenuation; agricultural fertilizer, denitrification.
