Agriculture releases nutrients and accelerates erosion processes, which threatens the good quality status of surface waters, proposed by the European Water Framework Directive (2000). The purpose of the masters thesis was to define agricultural land management scenarios and to evaluate them, according to their impact on surface water quality. For this purpuse we used Agricultural Policy/Environmental eXtender (APEX) model, which has not yet been tested under Slovenian pedological and climatic conditions. For the experimental area we chose Kožbanjšček watershed site in Goriška Brda region, that covers 14.6 km2. Using the previously calibrated and validated APEX model, we examined the impact of two alternative management scenarios on the water pollutant content. We found that the replacement of 66.3 ha of forested areas with new vineyards, would increase the content of suspended solids, nitrate and total phosphorus by 24.8%, 17.1% and 10.7% respectively, which is not in accordance with the Water Framework Directive goals. With the implementation of vegetation buffer strips as a mitigation measure, we could reduce the water concentration levels of suspended solids, nitrate and total phosphorus by 17.9%, 11.1% and 3.1% respectively, regarding the baseline scenario. The results confirm our hypothesis that we can reduce water pollution by choosing different types of land management, but we must take into account the uncertainty that comes from the model structure, setting of the input parameters and the manner in which the watershed is represented.
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