Catchment scale modelling of point source and non-point source pollution loads using pollutant export coefficients determined from long-term in-stream monitoring data

This paper presents a framework to estimate pollutant export coefficients from commonly available in-stream water quality monitoring data and using these pollutant export coefficients for catchment scale modelling of pollution loadings. A case study is presented to illustrate the framework in the Fuji River catchment, Japan. The total pollution loading was estimated by constructing an empirical source contribution model. The estimated pollutant export coefficients were used to estimate non-point source pollution loadings and point source loadings were estimated using the data collected from major wastewater treatment plants within a catchment. The non-point source loadings, especially from forest and agriculture, were found to be the major contributor whereas the point source loadings were found to be a minor contributor of total organic matter and nutrient loadings in the study catchment. These results are encouraging especially given the pressing need to identify appropriate management practices to improve the water quality within the Fuji River catchment. It is recommended to investigate further the required number of water quality monitoring stations, sampling frequencies and sampling duration of water quality constituents to enhance the robustness and usefulness of the proposed methodology.