U.S. Department of the Interior
U.S. Geological Survey

For release: July 11, 2008

Spring Nutrient Delivery to the Gulf Estimated Among Highest in Three Decades

Spring nutrient delivery from the Mississippi-Atchafalaya River Basin to
the northern Gulf of Mexico is estimated to be among the highest in the
last three decades.

Nutrient delivery, particularly during the months of April through June,
has been identified as one of the primary factors controlling the size
of the hypoxic zone that forms during the summer in the northern Gulf of
Mexico. The Gulf hypoxic zone is an area where oxygen levels drop too
low to support most life in bottom and near-bottom waters. Estimated
nutrient contributions from October 2007 through June 2008 are available
at http://toxics.usgs.gov/hypoxia/mississippi/oct_jun/index.html.

The large nutrient contributions are primarily due to near
record-breaking streamflows this spring (April through June) in the
Mississippi River Basin. Streamflows were about 50 percent higher this
year compared to the long-term spring average flows since about 1980.
Nutrient contributions for a given spring vary depending on the amount
of flow in the Mississippi-Atchafalaya River Basin, as well as average
stream water nutrient concentrations.

Contributions of phosphorus to the Gulf of Mexico are estimated to be
the highest for the USGS record since the 1980s. Total phosphorus
(83,000 tons) and dissolved orthophosphate (26,000 tons) are about 60
and 85 percent higher than the long-term spring average for the nearly
30-year period.

Similarly, nitrogen contributions to the Gulf of Mexico from April
through June are estimated to be about 35 to 40 percent higher than the
long-term spring average since the early 1980s. Contributions for total
nitrogen and dissolved nitrate during the three months are estimated to
be about 817,000 and 578,000 tons, respectively.

USGS releases preliminary estimates of monthly nutrient fluxes from the
Mississippi and Atchafalaya Rivers to the Gulf of Mexico in early July
each year for the previous nine months (October through June). These
estimates are used by the National Oceanic and Atmospheric
Administration, Louisiana Universities Marine Consortium, U.S.
Environmental Protection Agency, and other researchers for modeling the
areal extent of the hypoxic zone.

Final USGS nutrient fluxes are based on streamflows and nutrient
information for the full water year (through September 2008), and will
be available in 2009 after data are finalized. Nutrient fluxes for
previous years are available at

http://toxics.usgs.gov/hypoxia/mississippi/nutrient_flux_yield_est.html

USGS has monitored streamflow and water quality in the Mississippi River
Basin for decades. More information on the monitoring network used to
estimate total delivery of flow and nutrients to the Gulf; dataset
preparation steps; and nutrient flux estimation methods are available in
an online report at http://toxics.usgs.gov/pubs/of-2007-1080/index.html.


For more than 125 years, the USGS has monitored flow and (or) quality in
selected streams and rivers across the U.S. Access data from more than
7,400 streamgages, many of which provide real-time data in 15 minute
increments at http://water.usgs.gov/waterwatch/

For an even larger variety of USGS data, such as for ground water and water quality, access
the National Water Information System Web Interface (NWISWeb), which
contains over 1.5 million sites, and averages over 25 million hits per
month (at http://waterdata.usgs.gov/nwis/ ).

In addition, USGS uses innovative geo-spatial modeling (referred to as
SPARROW) to help understand relations among sources of nutrients,
watershed characteristics, and resulting transport of nitrogen and
phosphorus throughout the Mississippi-Atchafalaya River Basin.
http://water.usgs.gov/nawqa/sparrow/gulf_findings/

USGS provides science for a changing world. For more information, visit

http://www.usgs.gov\

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Jennifer LaVista
Public Affairs Specialist
U.S. Geological Survey, Office of Communications
703-648-4432
Email: jlavista@usgs.gov
Science sounds like this: usgs.gov/podcasts

Contact: Brent Aulenbach, 770-903-9148, btaulenb@usgs.gov

Jennifer LaVista, 703-648-4432, jlavista@usgs.gov