This study investigated the behaviour of two groups of widespread and different textured soil types, on nutrient (N, P) losses under cold climate conditions. The investigation was conducted in the Norwegian Vansj-Hoblv catchment through the application of a physical model named Soil and Water Assessment Tool (SWAT), taking into consideration the additional aspect of freezing soils during winter, which distinguishes Scandinavian from other European soils. SWAT is a physical river-basin model that was developed for the USDA Agricultural Research Service, by the Blackland Research Center in Texas. In the current modelling approach the catchment was divided into 43 Hydrologic Response Units (HRUs) which consist of different combinations of the existed land cover and soil types. Nutrient losses arising from these HRUs were estimated for the period 1990-2001 through the simultaneous simulation of water and sediment processes that are closely linked to the nutrient processes. The model took into account soil temperature to quantify water and nutrient transport to deeper layers, considering negligible downward movement when the soil temperature was under 0°C. It also simulated the aboveground development of the snowpack and the snowmelt processes on a daily basis. The six different soil types were aggregated in two groups according to their similarity in texture and other physical properties, one group of fine-textured soils and a group of coarse soils. The results were evaluated for different crop cultivations (barley, oats and wheat) of the aforementioned soils. Finally, the model was calibrated and validated by comparing predicted results with measured data. Fine-textured soils caused significant runoff, sediment and nutrient yields to the river system while coarser soils were characterized by high water drainage and nitrates leaching. The first soil group caused a mean of 517 mm of runoff in annual basis, 200 mm higher than this arising from coarse soils. Moreover, 3 tonnes of sediments per hectare, 24.6 kg N/ha and 0.54 kg P/ha were lost annually to surface water from fine soils while the average respective losses originating from coarse soils were only 1.3 tonnes of sediments/ha, 13.6 kg N/ha and 0.17 kg P/ha. The sensitivity ranking of the soil types to nutrient losses was silty-clay-loam > silty-loam > clay > loamy > sandy-loam > sandy. An average of 277 mm of water was percolated annually under the bottom of the soil profile in coarse soils causing the additional leaching of 5.6 kg N-NO 3/ha whereas the losses originating from fine-textured soils were 153 mm and 2.5 kg/ha, respectively. According to their sensitivity in nitrates leaching, the six soil types were ranked in the following order: sandy > loamy > sandy-loam > silty-loam > silty-clay-loam > clay. The results showed that even though under cold climate conditions, with monthly periods of average air-temperatures below zero, the overall amounts of annual TN and TP losses to surface waters as well as nitrates leaching to groundwater were considerable. The results demonstrate the need of considering the soil differentiation in Scandinavian countries similarly to the rest of Europe in order to apply mitigation measures against nutrient losses to surface and groundwater.
