in a Blue World

OCEAN NUTRIENT POLLUTION

Industrially produced nutrient fertilizers (nitrogen, phosphorus) are essential to global food security and have been the main driver of dramatically improved agricultural yields over the last sixty years to feed a growing population. At the same time, excess nutrients from inefficient use in farming and insufficient treatment of nutrients in wastewater, have made their way into rivers, aquifers, coastal areas and oceans, leading to degradation of marine ecosystems and groundwater at a global scale.

Nutrient loads from continents to oceans and the coastal zone have increased roughly three fold from pre-industrial levels, primarily from

Dead zones and fertilizers

agricultural run-off and poorly or untreated sewage. Mainly due to the addition of manufactured nitrogen (from atmospheric nitrogen and natural gas), the amount of reactive nitrogen entering the earth’s biogeochemical system has increased by about 150% compared to pre-industrial times. A 2009 Nature Report1, “A Safe Operating Space for Humanity”, determined that excess nitrogen in the environment was one of 3 of the 9 ‘planetary boundaries’ that had already been exceeded. In effect, mankind is ‘mining’ the atmosphere for nitrogen; with a practically limitless supply, this process could proceed for hundreds if not thousands of years leading to continually worsening conditions for coastal areas and groundwater.

North Atlantic Ocean

North Pacific Ocean

Fertilizer use, 2005

Kilograms per hectar of arable land

Less than 10

10 to 50 50 to 100 100 to 160 More than 160 Dead zones

South Pacific Ocean

Note: Low-oxygen zones appear as a consequence of nutrient input to the oceans. Low levels of oxygen make it difficult for marine creatures to survive.

14

South Atlantic Ocean

Indian Ocean

Source: World Bank, World Development Indicators database, accessed in October 2011; NASA Earth Observatory, data acquired in 2008.