Biochemical oxygen demand is an indicator of the organic pollution of freshwater. Alkalinity (concentration of calcium carbonate or CaCO3) is another indicator of freshwater quality. These graphics compare the concentrations of these two factors, in milligrams per litre, in the major regions of the world for the periods 1976 to 1990 and 1991 to 2000. The accompanying text explains the implications of the changes in BOD and alkalinity during these time periods.
From collection: Vital Water Graphics
Philippe Rekacewicz, Delphine Digout, UNEP/GRID-Arendal