Past and future trends in grey water footprints of anthropogenic nitrogen and phosphorus inputs to major world rivers

Abstract

The grey water footprint (GWF) is an indicator of aquatic pollution. We calculate past and future trends in GWFs related to anthropogenic nitrogen (N) and phosphorus (P) inputs into major rivers around the world. GWFs were calculated from past, current and future nutrient loads in river basins using the Global NEWS model. We present water pollution levels (WPLs), deduced from GWFs for more than 1000 rivers. The calculated GWFs and WPLs of the different river basins show a large variation among different periods. WPL values generally increased between 1970 and 2000. For the year 2000 about two-thirds of the basins have WPL values exceeding 1 for N or P, indicating that the pollution assimilation capacity has been fully consumed. Even though the other rivers have a WPL<1, this does not guarantee that at sub-basin level or within particular periods of the year no eutrophication exists. High WPLs are generally found in rivers in tropical–subtropical areas. For dissolved organic N and P, the problems are located mostly in the southern hemisphere. The results indicate that many rivers may become more polluted with dissolved N and P in the future.