Estimation of organic matter and nutrient loadings from point and non point sources into the Fuji River, Japan: Export coefficient modeling approach

Abstract

A simple export coefficient modeling approach was used to estimate loadings of organic matters and nutrients from both point and non point sources into Fuji River, Japan. First, we estimated land use export coefficients of organic matters (biochemical oxygen demand (BOD) and chemical oxygen demand (COD Mn)), and nutrients (nitrate nitrogen (NO 3-N) and inorganic dissolved phosphorus (PO 4-P)) specific to Fuji river basin. Semi-monthly water quality monitoring data of BOD, COD Mn, NO 3-N and PO 4-P from 8 stations, 6 years stream discharge from 3 stations and land use information were used to estimate land use export coefficients using available hydrological, statistical and spatial tools. A distributed hydrological model, Blockwise use of TOPMODEL with Muskingum-Cunge routing (BTOPMC), was used to estimate discharge for those stations where continuous discharge data was not available. A seven parameter log linear model was used to estimate loadings using historical water quality concentration along with observed and estimated discharge for each sub basins. The annual, seasonal, wet/dry season, high/low flow season and monthly yield as dependent variable and land use proportion in each sub basins as independent variables were used to derive the land use export coefficients through multiple regression technique. These land use export coefficients were used to estimate the total loadings and relative contribution of point and non point source loadings of organic matters and nutrients within the basin by developing an empirical source-contribution model. It was observed that forest is the dominant source of organic matters and inorganic dissolved phosphorus loadings and agriculture is the dominant source of nitrate nitrogen loadings within the basin. Point source organic matters and nutrients loadings represent a much smaller portion of the overall loadings as compared to non point source loadings. Therefore, this study shows that proper management practices has to be developed to reduce organic matters and inorganic dissolved phosphorus loadings from forest and nitrate nitrogen loadings from agriculture to reduce current and future water quality problems in the basin.