Atmospheric deposition and land-surface runoff driven nutrient flushing in Ganga River (India)

Abstract

Disproportionate addition of nutrients can alter the nutrient stoichiometric balance of surface water bodies. In the present study, we investigated the atmospheric deposition (AD) and runoff-induced nutrient enrichment and N:P stoichiometric shifts in the Ganga River along a 35 km stretch of Varanasi city. The region receives 8–42 kg ha−1 of reactive-N (NO3− + NH4+) and 0.40–3.10 kg ha−1 of PO43- through AD annually. The most polluted Rajghat Site receives ~770.50 tons of reactive-N (Nr) and ~64.50 tons of PO43- annually as AD input in the sub-watershed; and ~25.10 tons of Nr and 2.09 tons of PO43- directly on the water surface. Concentrations of nutrients in surface runoff increased with AD input irrespective of land use. Among land use categories, the runoff nitrate was highest from agricultural catchment while NH4+ and PO43- were highest from urban areas. The study showed that the AD-runoff coupled with additional supplies could substantially alter the overall load and stoichiometric ratios of critical nutrients with a consequent effect on ecological functioning of the river in long-run. © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.