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An ecosystem service approach was used to study the water purification service exemplified by impacts of land management scenarios. Nitrogen retention was calculated in two agricultural catchments by the dynamic Integrated Nutrients in Catchments (INCA)-N model. The monetary valuation was based on purification efficiency of artificial wetlands. The set of scenarios were based on existing agricultural water protection measures, and greening of the Common Agricultural Policy proposal. Scenarios were: wintertime crop cover on fields, increase in area of set aside land, decrease in nitrogen fertilization, crop diversification and nutrient recycling in organic farming. Nitrogen retention provided more value in the Yläneenjoki catchment where the main production line was animal husbandry. In the slowly flowing river Lepsämänjoki, the N retention was more effective than in the fast flowing river Yläneenjoki. When comparing measures some proved to have no value or even a negative value. Set aside had a high positive value when calculated per area, but on a catchment scale the value remained low because of the small area of implementation. Nutrient recycling and winter time vegetation cover were the scenarios that reduced N leaching from fields close to targets set in current political decisions. None of the scenarios increased greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Process-based nutrient models are increasingly used to determine the impact of future changes in land use, agriculture production practices and climate on the quantity and timing of nutrients reaching surface waters. Calibration of catchment-scale models to observed conditions can be difficult due to parameter uncertainty and the heterogeneity of catchment processes. Soft data, i.e. knowledge of processes gained through experimentation, have been suggested as one method of reducing uncertainty and producing a more accurate model of the processes that occur in a catchment. In this work, the Integrated Catchment model for Nitrogen was calibrated and validated for the Yläneenjoki catchment in south-western Finland by incorporating soft data. The calibration for 2003-2008 produced an adequate model of the in-stream nitrate concentrations (R² = 0.45, NS=0.42). However, model validation using data from 1997-2002 showed that the simulated in-stream nitrate concentrations were above the observed concentrations throughout the entire period (R² = 0.34, NS< 0). These results show that soft data can be used to constrain model parameters, resulting in a more accurate model of the catchment, but do not guarantee the best validation results as the simulated processes may not occur at the same time and rate as they did in the catchment. [ABSTRACT FROM AUTHOR]