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During recent years, the treatment of municipal and industrial sewage has been improved significantly, such that the release of phosphorus loads to aquatic environments has been reduced. Improvements achieved in cleansing of sewage has led to a new focus on phosphorus loads from agriculture. Phosphorus adsorbs strongly to the soil and therefore normally does not leach. It does, however, reach the aquatic environment adsorbed to fine soil particles eroded by wind and particularly water. It seems that the extended growth of winter wheat, grown to alleviate the problem of nitrate leaching, simultaneously has increased water erosion and thereby the loss of phosphorus from arable land. As opposed to losses of nitrate from agriculture, no estimates exist on the agricultural loss of phosphorus to aquatic environments.

6.2 Material Information on the size of the area grown with various arable crops was taken from the Danish agricultural statistics of 1994. In the statistics, the level of aggregation is the county, an administrative (and geographical) unit comprising a number of municipalities. Since we intended to calculate the risks of erosion and nitrate leaching at the level of municipalities two assumptions had to be made. Firstly, that all municipalities within a county had a distribution of crops similar to that of the county as a whole. Secondly, that crops were distributed equally within the municipality regardless of soil type. This is of course a simplification since eg potato are predominantly grown on the more sandy soils. Due to lack of detail in the statistics and the fact that some crops grown in Denmark were not included in the joint Nordic simulations …