Application of GIS for soil erosion and nutrient loss modelling in a small river catchment

This paper aims to describe and compare different possibilities to model soil loss in Sipe River catchment (8.87 km(2)) based on GIS (Geographical Information Systems) application and principles of USLE (Universal Soil Loss Equation) model. The Sipe River catchment is situated in Northern Europe in South Estonia. Different methods and equations were used to calculate USLE factors and soil loss. Nutrient losses are partly determined by the erosion process, an especially strong correlation is found between soil loss and phosphorus runoff. A significant part of nitrogen lies in topsoil and therefore besides leaching erosion also has a major influence on organic nitrogen loss. Nutrient loss due to erosion leads to lowered soil fertility rate and eutrophication of streams and lakes. Calculated erosion amounts in Sipe catchment reached 5 t ha(-1) yr(-1) Average potential soil loss calculated by different methods remained between 0.04 - 0.08 t ha(-1) yr(-1). Modelling results were compared with each other and evaluated by soil-loss measurement results carried out at nine locations with different land use and slope. Calculated and measured erosion values were similar. For grasslands, pastures and forests average differences between easured and calculated erosion rates did not exceed 0.1 t ha(-1) yr(-1)r. Differences between measured and calculated soil loss rates were small also for croplands but variability between different fields was higher than in grasslands. The main differences between measured and calculated erosion were found in fields where potatoes and vegetables were cultivated (up to 1 t ha(-1) yr(-1)). Soil samples were taken in each measurement plot to determine soil properties, phosphorus and nitrogen content. It was calculated that the average phosphorus loss due to erosion in Sipe catchment is 4.5 g ha(-1) yr(-1) and nitrogen loss is 0.1 kg ha(-1) yr(-1).