Agricultural runoff fuels large phytoplankton blooms in vulnerable areas of the ocean

Field events: blooming oceans Runoff of nutrients from agricultural regions and cities are a growing threat to the world's oceans, as highlighted in the Pew Oceans Commission report ( www.pewoceans.org ) and in the UN Environment Programme's Global Environment Outlook Year Book 2004, which identifies 150 oxygen-starved marine ‘dead zones’. A five-year study of the Gulf of California highlights just how vulnerable nitrogen-deficient areas of the oceans are to nitrogen pollution. Here, within days of fertilizer application to fields, the runoff fuels large phytoplankton blooms. These algae are at the base of the marine food web and can influence ocean ecosystems across large distances. The use of nitrogen fertilizers is increasing in developing countries, and because many of these are in the tropics and subtropics, where oceans are characteristically depleted in nitrogen, the implications for marine life are likely to be serious.