Causes and Consequences of Nutrient Overenrichment of Coastal Waters

While developed societies made significant progress in reducing the discharge of many wastes— including industrial wastes, organic matter in sewage, sludge, contaminated sediments and other material dumped at sea, toxic compounds, and oil— into coastal waters, nutrient over-enrichment intensified and spread widely among the planet’s coastal environments during the last half of the 20 century. This has often had devastating effects on the fisheries, biodiversity and services provided by these ecosystems. Eutrophication, as used here, is the enrichment of aquatic environments by nutrients, especially compounds of nitrogen and/or phosphorus, causing an accelerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of organisms present in the water and to the quality of water concerned. These nutrients come not only from treated waste streams, but also from land runoff, particularly from agriculture, and the atmospheric deposition of byproducts of fossil fuel combustion. These so-called nonpoint sources grew dramatically and are particularly hard to control. Its pervasive extent, consequences, trends, and challenges qualify the eutrophication of coastal waters as a planetary emergency of the early 21 century. This report provides an overview of the causes and consequences of coastal eutrophication, its global patterns and trends, sources of nutrients and efforts to control them, and efforts to restore degraded ecosystems.