Gray Water Footprint and Pollution Levels Related to Anthropogenic Nitrogen Loads to Fresh Water
Global Gray Water Footprint and Water Pollution Levels Related to Anthropogenic Nitrogen Loads to Fresh Water
Mesfin M. Mekonnen and Arjen Y. Hoekstra
Twente Water Centre, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
This is the first global assessment of nitrogenrelated water pollution in river basins with a specification of the
pollution by economic sector, and by crop for the agricultural sector. At a spatial resolution of 5 by 5 arc minute, we estimate anthropogenic nitrogen (N) loads to freshwater, calculate the resultant gray water footprints (GWFs), and relate the GWFs per river basin to runoff to calculate the N-related water pollution level (WPL) per catchment. The accumulated global GWF related to anthropogenic N loads in the period 2002−
2010 was 13 × 1012 m3/y. China contributed about 45% to the global total. Three quarters of the GWF related to N loads came from diffuse sources (agriculture), 23% from domestic point sources and 2% from industrial point sources. Among the crops, production of cereals had the largest contribution to the N-related GWF (18%), followed by vegetables (15%) and oil crops (11%). The river basins with WPL > 1 (where the N load exceeds the basin’s assimilation capacity), cover about 17% of the global land area, contribute about 9% of the global river discharge, and provide residence to 48% of the global population.
Mekonnen, M.M. & Hoekstra, A.Y. (2015) Global gray water footprint and water pollution levels related to anthropogenic nitrogen loads to fresh water, Environmental Science and Technology , 49 (21): 12860−12868