Evaluation of RUSLE and spatial assessment of agricultural soil erosion in Finland

Agricultural soil erosion has negative effects on surface water quality and aquatic ecosystems. A major imped-iment to agricultural erosion management in Finland has been the lack of high-resolution country-scale data on the spatial distribution of erosion. As a result, erosion mitigation measures have been targeted with limited information. Therefore, we evaluated the performance of the widely used RUSLE model against measurements from experimental fields, used the model to produce a two-metre resolution crop and management independent erosion estimate for all agricultural lands of Finland, and analysed erosion over different spatial scales. RUSLE showed skill (R2 = 0.76, NSE = 0.72) in estimating the observed erosion at experimental fields (55-2100 kg ha- 1 yr- 1) but with large errors (mean:-134 kg ha- 1 yr- 1, 90% range:-711 and 218 kg ha- 1 yr- 1). The evaluation, however, suggests that RUSLE performs similarly in Finland as elsewhere. The analysis of the developed country -scale data, in turn, revealed high erosion regions, and it showed how erosion varies between sub-catchment and between and within field parcels. For example, high-erosion areas concentrated in the proximity of water bodies were identified at the sub-catchment and within-field parcel scales. Altogether, the results demonstrate the predictive skill of RUSLE in high-latitude conditions, fill the earlier data gap in country-scale erosion, provide information for targeting erosion mitigation measures, and considerably improve the understanding of the spatial distribution of erosion in Finland.