Dead zones off the Oregon Coast cause alarm
The National Marine Fisheries Service has been examining Oregon coastal dead zones for years to determine why huge populations of crab have disappeared.
Tuesday, October 19, 2010 - 12:05
Oregon's coastline has long been considered one of the most abundant and productive fishing waters along the West Coast of the United States, falling in line with the Washington state coastline for fish populations. Scientists have been studying the dwindling marine life for several decades in an attempt to zero in on the cause of dead zones.
These dead zones are not able to support marine life as a result of oxygen-poor subsurface waters. Some are quick to blame global warming, while others who spend considerable time studying the phenomenon hypothesize that overuse of nitrogen-laden agriculture fertilizers may be the culprit. Still other scientists say waters from polar regions are having a serious impact on aquatic life at the subsurface level.
Global waters are affected
Worldwide hypoxic waters are making it harder for marine life to survive. Low oxygenated water kills fish because they need oxygen to migrate, breed and grow. Increases of phosphorus and nitrogen cause eutrophication, which creates deoxygenation at various depths of the oceans. The National Marine Fisheries Service (NMFS) has been examining Oregon coastal dead zones for years to understand why huge populations of crab have disappeared.
NMFS has been managing studies of tributary waters that empty into the ocean at various points. This requires volunteers to kayak throughout parts of rivers taking water samples and temperatures and describing the general conditions. Scientists say these efforts may help explain why coastal dead zones exist and how the zones devastate marine wildlife. (This correspondent has been involved in such record keeping along the southern Oregon Coast.)
Hypoxic levels at depth
Francis Chen, a biogeochemist with Oregon State University, was tapped eight years ago by the U.S. government to find the cause of hypoxic waters. His findings are troubling, to say the least. In his studies, Chan has found hypoxic waters at water depths of 150 feet, a place where many fish usually thrive. The numbers bear out his findings. At 150 feet, the oxygen levels were measured at 1.43 milliliters per liter. In normal conditions that oxygen level should be between 5-8 milliliters of oxygen per liter of water.
This phenomenon is global, according to eco-system scientists. With currents bringing hypoxic flows to all areas of regular current patterns, these dead zones appear to be increasing in size and depth, causing massive oxygen starvation. Changes in winds may also contribute to this exasperating challenge faced by marine life, because upwelling of waters from deeper areas typically brings new life to other ocean levels. The upwelling brings marine life to shallower waters to breed and feed. In addition, nutrients rise to subsurface levels. Researchers are finding the upward currents are oxygen-poor and are further devastating fisheries. Normally, upwelling contributes to big populations of fish and crab with nutrient-rich waters. Now, with low oxygenated water, marine wildlife is dying in unprecedented numbers.
Oxygen minimum zones
Since the 1970s, scientists have suspected that the decreasing population of fish from the coast to the continental shelf was a result of increasing ocean temperature, which is caused by overfertilizing crops. As nitrogen and phosphorus increase, oxygen decreases. Algae and other microorganisms such as phytoplankton, which grow in nitrogen-rich water, then die, using more oxygen to decompose. These organisms require great amounts of oxygen to survive, thereby depleting the oxygen from the water.
Now these areas of oxygen-starved waters are expanding well beyond the continental shelf. These areas are dubbed oxygen minimum zones (OMZ). These increases are alarming, in that figures show substantial hypoxia in coastal waters — and not just along the Oregon Coast. The areas affected are global. According to the National Marine Fisheries Service, about 8 percent of global waters are losing oxygen. This will have a serious impact on worldwide fisheries.
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