Study shows continued spread of 'dead zones'August 15, 2008Lack of oxygen now a key stressor on marine ecosystems A global study led by Professor Robert Diaz of the Virginia Institute of Marine Science, College of William and Mary, shows that the number of "dead zones"-areas of seafloor with too little oxygen for most marine life-has increased by a third between 1995 and 2007. Diaz and collaborator Rutger Rosenberg of the University of Gothenburg in Sweden say that dead zones are now "the key stressor on marine ecosystems" and "rank with over-fishing, habitat loss, and harmful algal blooms as global environmental problems." The study, which appears in the August 15 issue of the journal Science, tallies 405 dead zones in coastal waters worldwide, affecting an area of 95,000 square miles, about the size of New Zealand. The largest dead zone in the U.S., at the mouth of the Mississippi, covers more than 8,500 square miles, roughly the size of New Jersey. Diaz began studying dead zones in the mid-1980s after seeing their effect on bottom life in a tributary of Chesapeake Bay near Baltimore. His first review of dead zones in 1995 counted 305 worldwide. That was up from his count of 162 in the 1980s, 87 in the 1970s, and 49 in the 1960s. He first found scientific reports of dead zones in the 1910s, when there were 4. Worldwide, the number of dead zones has approximately doubled each decade since the 1960s. Diaz and Rosenberg write "There is no other variable of such ecological importance to coastal marine ecosystems that has changed so drastically over such a short time as dissolved oxygen." Dead zones occur when excess nutrients, primarily nitrogen and phosphorus, enter coastal waters and help fertilize blooms of algae. When these microscopic plants die and sink to the bottom, they provide a rich food source for bacteria, which in the act of decomposition consume dissolved oxygen from surrounding waters. Major nutrient sources include fertilizers and the burning of fossil fuels. Geologic evidence shows that dead zones were not "a naturally recurring event" in Chesapeake Bay or most other estuarine ecosystems, says Diaz. "Dead zones were once rare. Now they're commonplace. There are more of them in more places." The first dead zone in Chesapeake Bay was reported in the 1930s. Scientists refer to water with too little oxygen for fish and other active organisms as "hypoxic." Diaz says that many ecosystems experience a progression in which periodic hypoxic events become seasonal and then, if nutrient inputs continue to increase, persistent. Earth's largest dead zone, in the Baltic Sea, experiences hypoxia year-round. Chesapeake Bay experiences seasonal, summertime hypoxia through much of its main channel, occupying about 40% of its area and up to 5% of its volume. Diaz and Rosenberg note that hypoxia tends to be overlooked until it starts to affect organisms that people eat. A possible indicator of hypoxia's adverse effects on an economically important finfish species in Chesapeake Bay is the purported link between oxygen-poor bottom waters and a chronic outbreak of a bacterial disease among striped bass. Several Bay researchers, including VIMS fish pathologist Wolfgang Vogelbein, hypothesize that the prevalence of mycobacteriosis among Bay stripers (>75%) is due to the stress they encounter when development of the Bay's summertime dead zone forces them from the cooler bottom waters they prefer into warmer waters near the Bay surface. Diaz and Rosenberg's also point out a more fundamental effect of hypoxia: the loss of energy from the Bay's food chain. By precluding or stunting the growth of bottom-dwellers such as clams and worms, hypoxia robs their predators of an important source of nutrition. Diaz and VIMS colleague Linda Schaffner estimate that Chesapeake Bay now loses about 10,000 metric tons of carbon to hypoxia each year, 5% of the Bay's total production of food energy. The Baltic Sea has lost 30% of its food energy-a condition that has contributed to a significant decline in its fisheries yields. Diaz and Rosenberg say the key to reducing dead zones is "to keep fertilizers on the land and out of the sea." Diaz says that goal is shared by farmers concerned with the high cost of buying and applying nitrogen to their crops. "They certainly don't want to see their dollars flowing off their fields into the Bay," says Diaz. "Scientists and farmers need to continue working together to develop farming methods that minimize the transfer of nutrients from land to sea." Virginia Institute of Marine Science |
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| Related Dead Zone Current Events and Dead Zone News Articles Biofuel production could undercut efforts to shrink Gulf 'Dead Zone' Scientists in Pennsylvania report that boosting production of crops used to make biofuels could make a difficult task to shrink a vast, oxygen-depleted "dead zone" in the Gulf of Mexico more difficult. Earth's biogeochemical cycles, once in concert, falling out of sync What do the Gulf of Mexico's "dead zone," global climate change, and acid rain have in common? They're all a result of human impacts to Earth's biology, chemistry and geology, and the natural cycles that involve all three. New study ranks 'hotspots' of human impact on coastal areas Coastal marine ecosystems are at risk worldwide as a result of human activities, according to scientists at UC Santa Barbara who have recently published a study in the Journal of Conservation Letters. U-M researcher and colleagues predict large 2009 Gulf of Mexico 'dead zone'; Chesapeake Bay's oxygen-starved zone likely to shrink University of Michigan aquatic ecologist Donald Scavia and his colleagues say this year's Gulf of Mexico "dead zone" could be one of the largest on record, continuing a decades-long trend that threatens the health of a half-billion-dollar fishery. NOAA Forecast Predicts Large A team of NOAA-supported scientists from the Louisiana Universities Marine Consortium, Louisiana State University, and the University of Michigan is forecasting that the "dead zone" off the coast of Louisiana and Texas in the Gulf of Mexico this summer could be one of the largest on record. Nile Delta fishery grows dramatically thanks to run-off of sewage, fertilizers While many of the world's fisheries are in serious decline, the coastal Mediterranean fishery off the Nile Delta has expanded dramatically since the 1980s. Stronger coastal winds due to climate change may have far-reaching effects Future increases in wind strength along the California coast may have far-reaching effects, including more intense upwelling of cold water along the coast early in the season and increased fire danger in Southern California, according to researchers at the Climate Change and Impacts Laboratory at the University of California, Santa Cruz. Brown Scientist Finds Coastal Dead Zones May Benefit Some Species Coastal dead zones, an increasing concern to ecologists, the fishing industry and the public, may not be as devoid of life after all. A Brown scientist has found that dead zones do indeed support marine life, and that at least one commercially valuable clam actually benefits from oxygen-depleted waters. IMPACTS: On the Threshold of Abrupt Climate Changes Abrupt climate change is a potential menace that hasn't received much attention. That's about to change. Through its Climate Change Prediction Program, the U.S. Department of Energy's Office of Biological and Environmental Research (OBER) recently launched IMPACTS - Investigation of the Magnitudes and Probabilities of Abrupt Climate Transitions - a program led by William Collins of Berkeley Lab's Earth Sciences Division (ESD) that brings together six national laboratories to attack the problem of abrupt climate change, or ACC. NOAA and Louisiana scientists predict largest Gulf of Mexico 'dead zone' on record NOAA-supported scientists from the Louisiana Universities Marine Consortium and Louisiana State University are forecasting that the "dead zone" off the coast of Louisiana and Texas in the Gulf of Mexico this summer could be the largest on record. More Dead Zone Current Events and Dead Zone News Articles |
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