|
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
(50 000 km2). 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%).
|
