Relationship of Soil Erosion On Land Use Type and Water Quality in Han-River Basin.

The relationship between land use practices and soil erosion in relation to water quality was investigated in Han-river Basin, Korea.  An assessment of annual soil loss rates was carried out using the empirically based universal soil loss equation (USLE).  Information on the area as land use type was estimated by Geographic Information Systems (GIS), which includes paddy, field, orchard, forest, and land for house from 6 watersheds (CCD, EAD, HCR, SR, CJD, and PHD; 11,172 km²) located in the upstream of Han-river basin.  Nutrient potential index of soil (kg yr^-1) of each land-use area in watershed was estimated from nutrients concentration (kg ton^-1) in soil and the means soil erosion unit each land-use area (ton ha^-1 yr^-1).  4,759 soil samples were collected according to land use types.  Nutrients (TOC, TN, NO₃^-, TP, and exchangeable-P) were determined for soil samples.  Stream water data (N and P concentrations and discharge volumes on biweekly basis) were obtained from 9 stream monitoring site located at the discharge point of sub-watersheds.  The means soil erosion unit each land-use area (ton ha^-1 yr^-1) of field in watershed was in order of CCD (51%) > CJD (41%) > SR (36%) > EAD (24%) > HCR (23%).  For respective land types, soil erosion of orchard land area was higher than other land use types.  Also, cultivated soil had comparatively higher N and P concentrations than the soils used for other purposes.  Therefore, nutrient potential index by soil erosion was highly influenced by agricultural practices area.  And good relationship between nutrient (TOC, TN, TP) potential index and the nutrient load of stream was observed, suggesting nutrient level being a valuable indicator of a watershed’s water quality as influenced by agricultural practice.  Further the results of this study have an influence on basic soil information for water quality management of drinking-water reservoir and estimation of discharge and contribution on land types on water quality.