Modelling of the nutrient load in the Sula River basin using the MONERIS

Abstract

The results of modeling of the load of nitrogen and phosphorus compounds in the Sula River basin using MONERIS are discussed. The MONERIS model is a semi-empirical conceptual model for quantifying N and P emissions from point and diffuse sources in a drainage basin, which allows for separate calculation of nutrient pathways and sources. The modelling period is based on the residual mass curve and the flow duration curve; dry and wet years are identified. For the MONERIS model, the runoff was calibrated by applying a correction factor that depends on the hydrological link between the analytical units. It was established that the total emission of nitrogen of the Sula River basin over a long-term period and under average conditions is 1809.8 t/year and phosphorus emission is 196.2 t/year. It appears that diffuse sources supply 91 % of the total nitrogen, including 57 % from groundwater, due to the predominance of groundwater supply to the river and its tributaries. Anthropogenic sources contribute to 90 % of nitrogen emissions in the Sula River basin, with agriculture being the main source (55 %). Therefore, the highest values of nitrogen emissions are observed in the analytical units with the predominance of arable land. It was revealed that 71 % of phosphorus enters the Sula River basin through diffuse sources, of which groundwater (39 %) and urban areas (22 %) contribute the dominant share. Anthropogenic sources were estimated to contribute 87 % of total phosphorus emissions, with urban sources contributing 50 %. As a result, the highest values of phosphorus emissions were identified in the analytical units with the highest level of urbanization. The efficiency of the modelling was determined additionally and the modelled nutrient emissions were compared with the results obtained by other methods.