Gulf dead zone grows, perplexes scientists This summer's oxygen-starved region in the Gulf of Mexico was larger than ever before, stretching some 7728 square miles to approximately the area of New Jersey, according to the scientist who has been mapping the socalled dead zone or hypoxic region every summer since 1985. Usually, the oxygen-depleted area is found either close to shore or out in deeper waters, but this summer it was in both places, as it was during the 1993 Mississippi River flood, said Nancy Rabalais of the Louisiana Universities Marine Consortium in Chauvin. "It looks like somebody sat on [the hypoxic area] and squished it," she observed. Oddly enough, however, nutrient-laden flows from the Mississippi River basin, the main suspect behind the hypoxia problem, were not abnormally high mis spring and summer, according to Don Goolsby, chief of the U.S. Geological Survey's Midcontinent Herbicide Project. Nitrate concentrations in the lower Mississippi River, on the other hand, were a little higher than normal, Goolsby said. Nitrogen, phosphorus, and silica emptying into the Gulf through the Mississippi and Atchafalaya Rivers are thought to be the principal nutrients stimulating the excessive algal growth that reduces the biological oxygen demand and suffocates any marine life unable to swim or crawl away. As the nutrient-laden river water flows into the Gulf, it sits on top of the denser saltwater, preventing oxygen from diffusing down into the deeper part of the Rabalais explained The nutrients and warm weather enhance phvtoplankton growth Eventually the phytoplankton die and sink to the bottom where they decompose a nrocess that uses up all the oxveen in the lower water column During this summer's mapping trip, Rabalais' crew saw a large number of bottom-dwelling animals, such as portunid crabs and stingrays, swimming up near the surface, someming Rabalais specifically attributed to the lack of oxygen in the lower water col-
This summer's dead zone extended west from the Mississippi River delta all the way to the Texas border, and from very near shore along most of the Louisiana coast out to water depths of 100 feet.
umn. Other crabs and animals were found dead on the ocean bottom, along with decomposing organic matter. Just what kind of long-term effect the hypoxia is having on the marine ecosystem as a whole, however, is a subject of much scientific debate. So far, the phenomenon has not produced any visible signs of reduced fisheries productivity, something that bewilders Robert Diaz, a professor at the College of William and Mary's School of Marine Science in Gloucester Point, Va., who has studied the effects of hypoxia in other parts of the world. "The Gulf stands out as an anomaly among hypoxic systems in not showing drastic effects," Diaz said. In other cases, such as in the Baltic and Black Seas where the hypoxic area is actually larger than in the Gulf, "the economic and ecological consequences are dramatic; there's absolutely no question that these systems are altered," Diaz said. "They all start out showing signs of stress, but nothing drastic, and then all of a sudden they go critical" within a couple of years and fisheries collapse
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He suspects that, for now anyway, the fisheries species in the Gulf still have somewhere to run because the dead zone maps all show little pockets of nonhypoxic areas. Rabalais confirmed that a number of species are escaping to these areas, noting that they had observed a number of fishing trawlers and boats collected there during the mapping trip. Conversely, in the Black and Baltic Seas, "the system is so contained, they can't get out of the way," Diaz s3.id Likewise the Gulf spe* cies 3XQ all mobile and tend to grow more quickly than species found in other hypoxic regions and hence may be adapting better to the altered conditions he Research into the causes and consequences of the Gulf hypoxia has been under way for some time. Upon request from the White House Committee for the Environment and Natural Resources, EPA and the National Oceanic and Atmospheric Administration (NOAA) commissioned six reports, which were released in May for public comment, looking at various aspects of the problem. An integrated
assessment that would pull together all the findings and recommendations was expected to be available in September (see www.nos.noaa.gov), with a final report going to Congress and the president in February, said Don Pryor, a NOAA scientist coordinating the project. The work will be used to develop an action plan by August 2000, but Pryor emphasized that the plan would not necessarily result in regulatory changes. More likely are voluntary incentive programs and adjustments to existing programs ranging from reducing fertilizer application rates to agronomically recommended levels to encouraging application during the growing season as opposed to late fall,
when the fertilizer has time to leach out of the soil, Pryor said. On another front, Rabalais, along with a number of other universities across the Midwest, East Coast, and Louisiana, submitted a proposal to the National Science Foundation in July to treat the entire Mississippi basin and Gulf region as a long-term ecological research site. The project would really dig into the science behind how land use in the agricultural areas of the watershed influences nutrient export and what effect these nutrients have on various phytoplankton and the development of hvDoxia and toxic algal blooms according to John Downing a professor at Iowa State TTniversity in Ames w h i c h
DID YOU KNOW? Colloids matter: In aquatic systems, often 40% to 90% of all trace metals and organic compounds are adsorbed on marine and freshwater colloids. Source: ES,S7"1998, 32 (19), 2887-2899
is a principal collaborator. "It's rare that one sees agricultural and oceanographic institutions collaborating on a research program," Downing added. —KRIS CHRISTEN
Water shortages loom; technology, creative approaches offer solutions Global water-use efficiency will have to double over the next 25 years if the world's food supply is to keep pace with a growing population, according to a leading expert on world water issues. Many existing technologies and policies that conserve water are underused, other water experts agree. At a recent briefing that highlighted a new WorldWatch Institute book, Pillar of Sand, Sandra Postel, director of the Global Water Policy Project in Amherst, Mass., pointed out that as irrigation-based agriculture has expanded from 40 million hectares in 1900 to more than 250 million hectares today, water sources sustaining this practice have been depleted at alarming rates. As a result the roughly 40% of the global food supply that is produced from irrigated land is jeopardized Postel said Concurrent with the increasing amount of land under irrigation, groundwater has been overpumped to the point where water tables are dropping as much as 1 to 1.5 meters per year in important agricultural areas like northwest India and central and northern China, Postel said. Groundwater also is being depleted faster than nature can replenish it from the Ogallala
aquifer under the western Great Plains, which supplies water to 20% of all irrigated land in the United States, as well as in portions of Pakistan, North Africa, the Middle East, and the Arabian peninsula. "Pretty much anywhere you have sizeable irrigated areas, we're seeing groundwater depletion," Postel said, estimating that as much as 10% of the current global food supply depends on the overpumping of groundwater. Supplemental irrigation and more nonirrigated farming have reduced the groundwater overdraft problem with the Ogallala aquifer, said Herman Bouwer, chief engineer at the U.S. Department of Agriculture's Water Conservation Lab in Phoenix, Ariz. But in other regions where no
DID YOU KNOW? As much as 10% of the current global food supply depends on the overpumping of groundwater. Source: Sandra Postel, Global Water rolicy yroject Amherst, Mass.
additional water sources have been put in place, "It's really frightening to think what's going to happen," Bouwer said. The problem may be more severe than anyone realizes because "unfortunately, there's not a lot of ongoing monitoring of major aquifer systems," said Bill Alley, chief of the U.S. Geological Survey's Office of Ground Water. "It's more of a hidden problem that happens slowly over time, so it tends to get neglected." Many of the world's major rivers, another large source of water for irrigation, also are running dry during extended portions of the year. Often, as in the case of the Colorado River, river water contains dissolved salts, which, if they are not removed, accumulate wherever the water evaporates, primarily in irrigated areas. Salt buildup in the Phoenix and Tucson areas is going to be a longterm problem Bouwer said adding that desalinization facilities likely will be the only way to manage it Compounding the problem is the diversion of an increasing volume of irrigation water to supply growing cities and industries, particularly in developing countries—parts of China, southern India, the Middle East—as well as in portions of the western United
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