FEATURE
Is Coastal Eutrophication Out of Control? Although research is shedding new light on the phenomenon, it is proving difficult to manage. JANET PELLEY utrophication is a serious threat to coastal ecosystems, and, in the long term, it poses a problem of global dimensions. The nutrient enrichment of water bodies is leading to increased production of organic matter and resulting in low levels of dissolved oxygen that are killing marine life. These oxygen-poor waters, driven by increasingly excessive amounts of biologically available nitrogen, can now be found in estuaries and coastal waters throughout the world. Nonpoint source pollution, a major cause of this nutrient enrichment, is difficult to manage. "Attempts to control nonpoint sources through voluntary measures have failed across the board," said Joe Rudek, senior scientist with the Raleigh-based North Carolina Environmental Defense Fund. Nowhere has the connection between overfertilization and coastal decline been more firmly established than in the dead zone in the northern Gulf of Mexico, where each summer, oxygen concentrations in the lower part of the water column crash to nearly undetectable levels, suffocating marine animals that cannot escape to more oxygen-rich waters. The problem has also occurred in Europe's Baltic and Adriatic Seas, Chesapeake Bay, Hong Kong Harbor and Bay, and Japan's Seto Inland Sea, said Hans Paerl, Kenan professor of marine and environmental sciences at the University of North CarolinaChapel Hill. An improved understanding of the nature, scope, and impact of this phenomenon is emerging through the research findings of Paerl and other scientists who are studying coastal water eutrophication. On a global scale, Sybil Seitzinger, marine biology professor at Rutgers University in New Brunswick, N.J., found that nitrogen inputs to coastal marine ecosystems are dominated by fertilizer, air deposition, and sewage in that order. Worldwide production and application of nitrogen is projected to continue to grow rap-
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4 6 2 A • OCT. 1, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
idly, and Seitzinger predicts that by 2050, global inorganic nitrogen export by rivers could more than double from 1990 levels. Despite new knowledge, much remains to be discovered about the mechanisms of coastal eutrophication. "Nitrogen comes in different flavors," Paerl explained. "As we change the kinds of nitrogen input, we change the playing field for algae," he said. Although fertilizer dominates inputs of new nitrogen to coastal waters, scientists have recendy identified atmospheric deposition of nitrogen as the most rapidly growing source. It is now the single most important source of new nitrogen for the Western Baltic Sea, the Western Mediierranean Sea, and the North Atlantic Ocean, said Paerl. In the northeastern United States, atmospheric deposition of nitrogen exceeds all other inputs to coastal waters, according to Bob Howarth, ecology professor at Cornell University, in Ithaca N.Y., and colleague Norb Jaworski. Researchers are actively investigating how algae respond to these changes in amounts kinds and timing of nitrogen inputs "To make the most cost-effective reductions we need to know more about the sources of nitrogen how they are delivered to the coast and their effects on coastal ecosystems " said Seitzinger Although the need for more research is evident, scientists agree that there is already a sufficient knowledge base to begin reducing nitrogen inputs. "We have a reasonably good understanding to begin crafting solutions now," said Seitzinger. The nutrient control legislation passed this year by Maryland "is a big step in the right direction," said Rudek. Across Europe, nitrogen reduction goals have been applied with mixed success, said Franciscus Colijn, marine biology professor at the University of Kiel in Germany. The Dutch government in The Netherlands has responded with the most stringent nutrient control regimes in the world. 0013-936X/98/0932-462A$15.00/0 © 1998 American Chemical Society
Linkage to fertilizer use Booming productivity (eutrophication) on global ocean coasts has grabbed high-level attention. According to EPA, nutrient discharges are the major cause of impaired estuaries in the United States (i). The National Research Council (2) has described nutrient enrichment as the greatest threat to the integrity of coastal ecosystems, and a United Nations report (3) predicted that if current trends continue, discharges from a burgeoning human population will create a global problem in the next 20-30 years. Nitrogen fertilizers, hailed as the driving force behind agriculture's green revolution, are too much of a good thing when they flow into coastal rivers and estuaries, said Paerl. The coastal zone and waters beyond represent the frontier of nutrient-driven (specifically nitrogen) new production (production of organic matter by photosynthesis) and eutrophication, he explained. Whereas nitrogen-limited estuaries, coastal waters, and the continental shelf compose only 15% of the global ocean area, they account for nearly half of its primary productivity, and anthropogenic sources of new nitrogen contribute from 25% to more than 50% of this new coastal primary production. Paerl noted that within the past few decades previously pristine coastal waters in many regions of the world have been transformed to more productive conditions in some cases accompanied by harmful algal blooms These blooms have doubled worldwide between 1970 and 199f) (4)
When it comes to enriching the coast with nitrogen, fertilizer is the biggest contributor, said Scott Nixon, director of Rhode Island Sea Grant in Narrangansett (see figure at right (5)). More than 85% of nitrogen fixed (made available to living organisms) commercially goes into fertilizer, which is in great demand from a rapidly expanding human population. Changes in diet are also creating a demand for more fertilizer, he said. The global livestock population has increased 18% within the past 20 years; the number of chickens has doubled since 1970; and the pig population has increased by 57% in the Scime period (6). Per capita protein consumption and resultant nitrogen excretion increased more than 18% in the developing world during 1965-1988 Nancy Rabalais, a professor at the Louisiana Universities Marine Consortium in Chauvin, La., noted the strong link between what happens in the nation's breadbasket and offshore hypoxia (defined as a region in which there is less than two milligrams of dissolved oxygen per liter of water). Nitrogen fertilizer, applied to crops in 29 states from Montana to Ohio and south to Louisiana, is carried down the Mississippi and Atchafalaya Rivers to the coastal shelf. Since 1960, the amount of dissolved nitrogen dumped into the Gulf by the rivers has increased threefold, and phosphorus levels have doubled. These nutrients boost the production of phytoplankton, which form large blooms th
