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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-
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).
Sources: UNEP-GPA, 2004.
Adapted from a map by Ahlenius, H.,
http://maps.grida.no/go/graphic/ratio-of-wastewater-treatment
Mediterranean
Untreated
Treated
Caribbean
West and
Central Africa
Southern
Asia
East
Asia
Caspian Sea
Central and East Europe
Baltic Sea
North
Atlantic
Western
Europe
Ratio of wastewater treatment