Phosphorus losses at the catchment scale within Europe: an overview

Quantifying P losses to surface waters at different scales and partitioning of the loads into P losses from point sources and diffuse sources are significant future challenges for river basin managers. The agricultural share of P losses to surface waters is, in many river basins, increasing and therefore becoming more important to quantify and analyse. The importance of phosphorus losses from agricultural land was analysed using monitoring data and two different models for 35 micro-catchments (< 30 km(2)) in the Nordic-Baltic region of Europe, 17 European macro-catchtnents (250-11 000 km(2)) and 10 large European river basins (> 50 000 km(2)) Average annual phosphorus loss from agricultural land in the micro-catchments varied from 0.1 to 4.7 kg P ha(-1) and showed no relationship with the short-term P surplus on agricultural land. The average annual total P loss from agricultural land showed equally large variation in the 17 macro-catchments (0.1-6.0 kg P ha(-1)), but the range was less for the 10 larger river basins (0.09-2.0 kg P ha(-1)). The annual P loss from the 35 micro-catchments was greatest in the micro-catchments characterized by soil erosion and a high proportion of surface run-off as in the Norwegian catchments. The same pattern was true for the 17 macro-catchments where the model-simulated total P loss from agricultural land was greatest in the catchments in northern and southern parts of Europe. The main diffuse pathways for total P loads in the 17 macro-catchments were simulated with the MONERIS model. On average, soil erosion and surface run-off was estimated to have contributed 53% (4.1-81%), groundwater 14% (0.2-41.7%) and tile drainage water 3% (0-14.0%).