Modelling Nutrient Load Changes from Fertilizer Application Scenarios in Six Catchments around the Baltic Sea.

The main environmental stressor of the Baltic Sea is elevated riverine nutrient loads, mainly originating from diffuse agricultural sources. Agricultural practices, intensities, and nutrient losses vary across the Baltic Sea drainage basin (1.75 x 10⁶ km², 14 countries and 85 million inhabitants). Six "Soil andWater Assessment Tool" (SWAT) models were set up for catchments representing the major agricultural systems, and covering the different climate gradients in the Baltic Sea drainage basin. Four fertilizer application scenarios were run for each catchment to evaluate the sensitivity of changed fertilizer applications. Increasing sensitivity was found for catchments with an increasing proportion of agricultural land use and increased amounts of applied fertilizers. A change in chemical fertilizer use of ±20% was found to affect watershed NO₃-N loads between zero effect and ±13%, while a change in manure application of ±20% affected watershed NO₃-N loads between zero effect and -6% to +7%. [ABSTRACT FROM AUTHOR]