Surface Water Quality in Relation to Soil Type, Land use and Discharge in a Rural Catchment Area

Abstract

Surface water quality and the factors that influence it were investigated in a rural area that lies between an ice-pushed ridge and river backlands. The influences of soil type, land use and household wastewater on the concentrations of nutrients were studied during base-flow as well as peak-flow periods. Samples were taken in ditches and canals, more frequently as discharge increased. Average values of the base-flow quality in ditches were calculated per soil type and land use and for all measure points in the canals. The fluctuations of water quality were plotted and analyzed in concentration-time and concentration-discharge diagrams. The relative importance for the quality of total discharge in the main canal of the loads coming from several parts of the drainage basin, was investigated with a stepwise multiple variable regression analysis. During base-flow situations sources of nutrients are the intensively cultivated sandy soils. In addition the concentration of orthophosphate is increased by household wastewater. During peak-flows, potassium and nitrate run off from all soil types with all types of land use, resulting in high concentrations in the surface water, in spite of dilution by rainwater. It is concluded that for proper management, intensity of manuring and fertilizing should decrease, especially on sandy soils. Wastewater should be drained outside the basin, to lower the concentration of orthophosphate.