Biogenic Runoff from the Nizhny Novgorod Area

The methodical approaches to the integral estimation of the biogenic diffuse export from urbanized areas have been developed and tested, using the Nizhny Novgorod area as an example in the absence of direct hydrological observations. The conditionally natural runoff of the Rakhma River, the catchment of which is mostly occupied by the present-day Nizhny Novgorod area, has been reproduced based on the RosHydroMet data on the Sundovik River-analog runoff for 2010-2017. The interannual distribution of the Rakhma River runoff has been analyzed, and the variations in the groundwater and surface runoff components have been estimated with regard to the joint impact of climatic and anthropogenic factors. The surface component of the Rakhma River runoff has been shown to increase twice while the groundwater component, to decrease by 38%. In this case the groundwater runoff value remains rather large (63 mm per year), accounting for 33% of the total river runoff. The calculations of the biogen export by the river into the Cheboksary Reservoir in different seasons, less the biogen input with wastewater, have been illustrated. The present-day diffuse export of biogens from the Nizhny Novgorod area has been roughly estimated. The export of mineral nitrogen (195 kg km(-2)) is maximal in the cold season and that of phosphorus (11 kg km(-2)), during the spring flood, respectively.