Impact of changing atmospheric deposition chemistry on carbon and nutrient loading to Ganga River: integrating land–atmosphere–water components to uncover cross-domain carbon linkages

Abstract

Terrestrial contribution of dissolved organic carbon (DOC) to riverine carbon transport remains relatively uncertain despite recent research highlighting its importance. Here we present data on changing state of atmosphere–land–water transfer and associated shift in DOC build-up in Ganga River (India) for a period of 6 years (March, 2007–February, 2013). Although the N:P stoichiometry of atmospheric deposition (AD) showed a declining trend, there was over 1.4 to 1.6-fold increase in AD-NO3 −, 1.5 to 1.8-fold increase in AD-OC and, over 1.5 to 2.2-fold increase in AD-NH4 + and AD-PO4 3− input over time. Water soluble organic carbon and microbial activity in sub-catchments and, DOC and nutrient concentrations in runoff increased consistently over time along the gradient of AD-input. We found a variable but strong linkage between atmospheric deposition and hydrological control of terrestrial carbon and nutrient input to the river. The results showed that the increasing input of AD-nutrients enhance primary production whereas, such input in sub-catchment enhance DOC in runoff and, the coupled effect of these favor DOC build-up in Ganga River at Varanasi. The study that forms the first report establishing trans-boundary drivers of DOC in Ganga River suggests that future climate model should consider large scale inter-regional time series data on changing atmosphere–land–water transfer and associated shift in carbon balance of major rivers for more accurately predicting cross-domain carbon linkages and planning for integrated river basin management.