Assessing SWAT model performance in the evaluation of management actions for the implementation of the Water Framework Directive in a Finnish catchment

The ecological status of Lake Pyhäjärvi may be classified as moderate due to its elevated nutrient concentrations and algal biomass production. Therefore, the Eurajoki river basin, including Lake Pyhäjärvi, has been chosen as the Finnish test catchment in an EU project on benchmarking models for the Water Framework Directive. One aim of the project is to test the suitability of models for the assessment of management options proposed to meet the surface water quality targets. The catchment model SWAT is currently being tested for its applicability for analysing the effectiveness of proposed measures to reduce agricultural and sparse settlement nutrient loading. The model is being applied to the river Yläneenjoki catchment draining to Lake Pyhäjärvi. First results indicate that SWAT can be calibrated for flow and sediment yield using catchment scale parameters. For nutrients, however, parameters describing more detailed catchment processes have to be calibrated. The preliminary essay on measures such as buffer strips indicate that SWAT includes relevant management options that affect nutrient leaching. However, the descriptions of these management options require some modifications in order to describe correctly the reduction efficiency in local conditions.