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As development increases along coastlines worldwide, water quality-and everything that depends on it-degrades.
The world's coastal ecosystems are under stress. The numbers tell the story: Over 50 percent of the global population resides within 100 kilometers of a coastline, a thin ribbon of land that includes three-fourths of the megacities with more than 10 million residents. Farms and factories needed to sustain all those people release fertilizers and toxic chemicals into our rivers, streams, and estuaries. Degraded water quality is the most obvious result, but the onslaught of nutrients has a more insidious effect. Fertilizer runoff causes coastal algae to proliferate; the algae take most of the oxygen in the water, causing fish to die and disrupting the food chain for humans and other organisms. As coastal populations keep increasing, the stresses are increasing with them.
The production of reactive nitrogen- from sources such as synthetic nitrogen fertilizers, legume and rice cultivation, and fossil fuel combustion-began in earnest during the Industrial Revolution and has increased sharply in recent decades; by 2005, global production reached 187 million metric tons of nitrogen. Since the 1970s, all that production has dramatically altered the flux of nutrients-not just nitrogen but also phosphorus from fertilizers, sewage, and detergents-from the landscape to receiving waters. The over-enrichment of such nutrients, commonly defined as eutrophication, has emerged as one of the leading causes of water quality impairments in coastal marine ecosystems.
Coastal ecosystems cover approximately 20 percent of the Earth's surface and are extremely diverse. More than 415 of these areas worldwide are experiencing symptoms of eutrophication, according to a 2008 World Resources Institute study, and that number is growing. These areas represent half of the value of global economic services, such as tourism, recreation, coastal fisheries, and aquaculture.
Coastline waterways are important to everyone in some way: They harbor fisheries and other resources, prevent erosion, protect people from floods and storm surges, maintain ocean biodiversity, support recreation and tourism, and are culturally important to local heritages. Often the centers of activity for beachside recreation, these areas are also resources for minerals and geological products. Without these ecosystems, people would not be able to eat seafood, because 90 percent of global fishery activity occurs in coastal waters.
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