Virtual mapping of reference conditions of pollutant load in waterbodies : phosphorus in the Lake Peipsi basin

Our study proposes a novel virtual mapping method to define reference conditions in a water body that is assumed to be not affected by human activities.We applied a modified PolFlow model, a raster-GIS analysis tool, to the Lake Peipsi basin.Running 'reference conditions' scenario revealed that the mean annual reference load comprised 225 t (31%) of phosphorus while the remaining 498 t (69%) originated from anthropogenic sources.Of the total reference load, 77 t (34%) originated from the Estonian part of the catchment, while the remaining 148 t (66%) came from Russia.High variability appeared in key factors that determine the P load to the lake in Estonia and Russia.The management measures in Estonia should prioritize land use issues, such as a reduction of diffuse emissions from agriculture.In contrast, the short-term Russian policy should focus on improved municipal and industrial waste-water treatment.