Source apportionment and quantification of nitrogen transport, and retention, in the River Rhine

One of the first steps needed to allow efficient measures for a reduction of the riverine input of nutrients to surface water and the sea, is apportionment of the total load to its origin (either diffuse or point sources). The objective of the investigation carried out in 1990-1995 was to determine source apportionment of the observed nitrogen load (to the source, either point or diffuse) and to quantify nitrogen transport, emission and retention in the supranational River Rhine and its main tributaries. This overall objective comprised investigating the differences between 30 sub-catchments for the contribution of diffuse or point sources of nutrients, and the (area-specific) emission of these sources and nutrient retention. Furthermore, two fundamentally different types of approaches to source apportionment, riverine and input-output, were investigated with respect to concept, results and applicability. This was done as well for nutrient load analysis. A qualitative source apportionment and a retention calculation based on mass balances were also carried out