Small But Important: The Role of Small Floodplain Tributaries to River Nutrient Budgets

The fertile Indo-Gangetic floodplain contains numerous small, rain-fed rivers. These rivers contribute to the river water chemistry of the Ganges River; however, these small floodplain rivers are never studied nor monitored owing to their smaller size with reference to catchment area (similar to 1000-10000 km(2)) and volume of discharge (similar to 10-100 m(3)/s). Here we quantify the role of a small flood plain river, the Pandu River, in terms of dissolved inorganic nitrogen (DIN) and phosphate export to Ganges River. We present results from time series sampling campaigns over 2015 and 2016. Our result shows that Pandu River exports 793 +/- 128 t/yr of DIN and 177 +/- 29 t/yr phosphate to the Ganges River, which accounts for 0.1% and 0.42% of the total DIN and phosphate fluxes, respectively, that Ganges River exports into Bay of Bengal. Furthermore, we show that the small floodplain rivers in the Indo-Gangetic floodplain could collectively contribute,--15% and similar to 61% of the DIN and phosphate fluxes, respectively, that Ganges River delivers into Bay of Bengal. Therefore, runoff from small floodplain rivers is an important flux that could contribute to the dissolved nutrient budget of large river systems, and they must he better monitored to address future challenges in river basin management.