Isotopic evidence of denitrified nitrate in groundwater beneath intensive agriculture and exchange with estuary (Godavari, India)
Date
2024Author
Kumar, B.S.K.
Sridevi, B.
Sarma, V.V.S.S.
Cardinal, D.
Sebilo, M.
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Nitrate is accumulated in the groundwater, modified through nitrification/denitrification, and exchanged with coastal/estuarine water bodies. To examine the sources and modifications of nitrate, the concentrations and isotopic composition of nitrate (? 15N and ? 18ONO3) in the groundwater was monitored at 5 locations along the bank of Godavari estuary and in the estuarine waters for 7 months during wet (August-November) and dry (March-May) periods. Though the concentration of nitrate (NO3-) was higher during the wet than dry periods in both the groundwater and estuary, insignificant seasonal variability was observed in ?15N and ?18ONO3 indicating homogenization through mineralization-immobilization turnover of NO3-. The range of ?15N to ?18O of NO3- indicates soil, manure, and septic waste may be the major source of NO3-. The mean ratio of ?15N/?18O of 1.1 0.3 indicates the occurrence of denitrification in the groundwater. Concentrations ?15NNO3 and ?18ONO3 of NO3- displayed a significant relation between groundwater and estuarine water suggesting that NO3- is possibly denitrified. This study suggests that denitrified NO3- (enriched ?15N and ?18O) reported in the Godavari estuary may be contributed through submarine groundwater discharge than it is hypothesized to flux from the watershed.
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