In the natural order of things, the waters at the mouths of major river
deltas are filled with abundant life (molluscs included!!), nourished by
nutrients resulting from erosion. However, when our species becomes
involved, the nutrient ratios are skewed by the massive amounts of
fertilizer used in agriculture: much more "bio-available" nitrogen and
phosphorus are added to the river's waters, resulting in massive algal
blooms when they reach the sea - result: anoxic benthic conditions over
large areas, due to mounds of rotting algae: AKA "Dead Zones". There are
many of these around the world, but the one at the mouth of the
Mississippi is one of the largest, and getting bigger all the time. This
is a good article about the situation:


  http://www.sciencedaily.com/releases/2008/07/080715114149.htm


  NOAA Predicts Largest Gulf Of Mexico 'Dead Zone' On Record


ScienceDaily (July 16, 2008) — 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.

The researchers are predicting the area could measure a record 8,800
square miles, or roughly the size of New Jersey. In 2007, the dead zone
was 7,903 square miles. The largest dead zone on record was in 2002,
when it measured 8,481 square miles. The official measurement of this
year's dead zone is slated to be released in late July. Researchers
began taking regular measurements of the dead zone in 1985.

"The prediction of a large dead zone this summer is due to a combination
of large influx of nitrogen and exceptionally high flows from the
Mississippi and Atchafalaya rivers," said LSU scientist R. Eugene Turner.

The dead zone is an area in the Gulf of Mexico where seasonal oxygen
levels drop too low to support most life in bottom and near-bottom
waters. This low oxygen, or hypoxic, area is primarily caused by high
nutrient levels, which stimulates an overgrowth of algae that sinks and
decomposes. The decomposition process in turn depletes dissolved oxygen
in the water. The dead zone is of particular concern because it
threatens valuable commercial and recreational Gulf fisheries.

Research indicates that the nearly tripling of nitrogen levels into the
Gulf over the past 50 years from human activities has led to a dramatic
increase in the size of the dead zone. Various models are useful in
evaluating the influence of nitrogen loads and other factors on the size
of the dead zone. The LSU model has a strong track record of accurately
predicting the dead zone's size.

"The strong link between nutrients and the dead zone indicates that
excess nutrients from the Mississippi River watershed during the spring
are the primary human-influenced factor behind the expansion of the dead
zone," said Rob Magnien, director of the NOAA Center for Sponsored
Coastal Ocean Research. "This analysis will greatly inform the
development of federal, state and local efforts to reduce the dead
zone's size."

The forecast is based on a mathematical model developed by LSU through
NOAA's long-term research investment by CSCOR's Gulf of Mexico
Ecosystems and Hypoxia Assessment. The model incorporates U.S.
Geological Survey data on the amount of nitrogen reaching the Gulf of
Mexico in May. NOAA has been funding investigations into the dead zone
since 1990.

------------------------------------------------------------------------
/Adapted from materials provided by National Oceanic and Atmospheric
Administration <http://www.noaa.gov>/.

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