Assessing the Effects of Agricultural Change on Nitrogen Fluxes Using the Integrated Nitrogen CAtchment (INCA) Model

The INCA (Integrated Nitrogen CAtchment) model is a semi-distributed, dynamic nitrogen model which simulates nitrogen fluxes in catchments. Sources of nitrogen can be atmospheric deposition, the terrestrial environment or direct discharges. The model can simulate nitrogen processes in six land use classes. There are three components included; the hydrological model, the catchment nitrogen process model and the river nitrogen process model. The aim of this study is to compare the effects of three different agricultural policy scenarios on inorganic nitrogen flux to the sea from Finnish catchments. Target years of these scenarios are 2010 and 2020. The changes in agricultural production in different scenarios of agricultural policy are evaluated using the DREMFIA model (Dynamic Regional Model of Finnish Agriculture). DREMFIA is a dynamic dis-equilibrium model based on an evolutionary scheme of technology diffusion which considers farm investments, evolving farm size structure and technological change explicitly. In the first phase of the study the INCA model is applied to the Simojoki river basin in northern Finland, where main anthropogenic influences are agriculture, atmospheric deposition and forestry. At the Simojoki river basin agriculture is mainly animal husbandry and grass cultivation. The river Simojoki discharges to the Bothnian Bay. The predicted changes in agricultural production and land use at Simojoki river basin prove to have more effect on inorganic nitrogen flux to the sea than changes in forestry practices or atmospheric deposition. This result stems from the specific location, ecosystem type and characteristics of farm land in Simojoki basin. Next the INCA model will be applied to a river basin in southern Finland, where the main land use form is agriculture.