tural run-off exacerbating the spreading of dead zones (Diaz and Rosenberg, 2008): current agricultural practices, convert about 120 million tonnes of nitrogen from the atmosphere per year into reactive nitrogen containing compounds (Rock- ström et al, 2009). Up to two thirds of this nitrogen makes its way into inland waterways and the coastal zone, exceeding all natural inputs to the nitrogen cycle. Approximately 20 million tonnes of phosphorus are mined each year for fertilizers, al- most half returns to the ocean – approximately eight times the natural input (Rockström et al, 2009a). Together, this excess nitrogen and phosphorus drive potentially toxic algal booms and changes in biodiversity which can in turn lead to devastat- ing hypoxic events and enhancing dead zones (Tilman, 1998; Rockström et al, 2009b) resulting in huge economic losses across many sectors (Figueredo and Giani, 2001, Hernández-

Ratio of wastewater treatment Baltic Sea Central and East Europe

Western Europe

North Atlantic

Caribbean

Southern Asia

Central Africa West and Untreated

Sources: UNEP-GPA, 2004. Adapted from a map by Ahlenius, H.,

http://maps.grida.no/go/graphic/ratio -of-wastewater-treatment

Treated

Figure 17: The ratio of treated to untreated wastewater reaching water bodies for 10 regions. An estimated 90 per cent of all wastewa- ter in developing countries is discharged untreated directly into rivers, lakes or the oceans (UN Water, 2008).

44 Mediterranean

East Asia

Caspian Sea