Relationship Between Water Quality Formation of Rivers and Land Use in Their Watershed

The relationship between the formation of river water quality and the land use of river watershed at Lake Kasumigaura (Ls. Nishiura and Kitaura) was investigated in this study using measured in situ data and data calculated using a geographic information system (GIS). NO3-N concentrations in river water were high, particularly in L. Kitaura watershed. The NO3-N concentrations increased at a low-water-temperature period and decreased with dilution after rainfall. The relationship between river water quality and land use characteristics in river watershed was examined by principal component analysis. The nitrogen concentrations in river water were correlated with the number of livestock, upland field and forest area in their watershed at ordinary flow. A high correlation was confirmed particularly between the number of pigs and NO3-N concentration. Paddy field and urban area were correlated with phosphorus, organic matter and particulate matter concentrations. During flood due to rainfall, the nitrogen concentrations in small-scale rivers showed a high correlation with only the number of pigs.