Coastal Eutrophication and Agriculture: Contributions and Solutions
Biological Resource Management Connecting Science and Policy
Many coastal waters of developed nations have experienced widespread and rapid eutrophication (the increase in supply of organic matter) during the last half of the 20 th century. This has resulted in increased phytoplankton production, decreased water clarity, often-severe depletion of dissolved oxygen in bottom waters, loss of seagrasses and, in some cases, declines or changes in the quality of fisheries production. Large-scale changes resulting from eutrophication have been documented for
... n documented for continental shelf waters in the Gulf of Mexico, Mediterranean, Black and North Seas, relatively confined seas such as the Baltic and Seto Inland Sea, large bays such as the Chesapeake Bay and Long Island Sound and numerous smaller estuaries and lagoons. These trends are closely tied to the increased use of chemical fertilizers in agriculture, human population growth, and increasing atmospheric deposition of nitrogen resulting from fossil fuel combustion. Although atmospheric and human waste sources are significant in some heavily populated areas, agricultural inputs of phosphorus and nitrogen are the largest source of nutrients driving the increased production of organic matter in most extensively affected areas, including coastal waters receiving drainage from large river basins with extensive agriculture (e.g. Mississippi, Po and Danube Rivers). Agricultural inputs of nutrients are driven not only by applications of chemical fertilizers, but also by animal wastes, irrigation, drainage, and the conversion of wetlands and riparian zones (important sinks for nutrients) for agricultural land uses. More efficient agronomic practices, use of crop rotation and cover crops, and avoiding the overapplication of manure can result in reductions in nutrient losses by 20 to 30%. Reconfiguration of agricultural landscapes through reconstruction of strategically placed wetlands, riparian forests and flood plains can trap a similar fraction of the remaining nutrient losses, such that total reductions of 50% may be feasible without devastating economic impacts and with numerous local benefits to environmental quality. Efforts to restore large coastal ecosystems such as the Baltic Sea, northern Gulf of Mexico and Chesapeake Bay through commitments to reduce nutrient loading have been underway or are beginning. They represent substantial challenges in working across political jurisdictions and across scientific disciplines and internalizing the external environmental costs of food production.