Introduction
Scientific investigations in the Gulf of Mexico have documented a large area of
the Louisiana continental shelf with seasonally-depleted oxygen levels (< 2mg/l). Most
aquatic species cannot survive at such low oxygen levels. The oxygen depletion, referred
to as hypoxia, begins in late spring, reaches a maximum in midsummer, and disappears in
the fall. After the Mississippi River flood of 1993, the spatial extent of this zone more
than doubled in size, to over 18,000 km2, and has remained about that size each year
through midsummer 1997. The hypoxic zone forms in the middle of the most important
commercial and recreational fisheries in the coterminous United States and could threaten
the economy of this region of the Gulf.
Nutrient over-enrichment from anthropogenic sources is one of the major stresses
impacting coastal ecosystems. Generally, excess nutrients lead to increased algal
production and increased availability of organic carbon within an ecosystem, a process
known as eutrophication. There are multiple sources of excessive nutrients in watersheds,
both point and non-point, and the transport and delivery of these nutrients is a complex
process which is controlled by a range of factors. These include not only the chemistry,
but also the ecology, hydrology, and geomorphology of the various portions of a watershed
and that of the receiving system. Both the near-coastal hydrodynamics that generate water
column stratification and the nutrients that fuel primary productivity contribute to the
formation of hypoxic zones. Human activities on land can add excess nutrients to coastal
areas or compromise the ability of ecosystems to remove nutrients either from the
landscape or from the waterways themselves.
The Assessment Process
As part of a process of considering options for response to hypoxia, the EPA
formed the Mississippi
River/Gulf of Mexico Watershed Nutrient Task Force during the Fall of 1997. The Task
Force asked the White House Office of Science and Technology Policy to conduct a
scientific assessment of the causes and consequences of Gulf hypoxia through its Committee
on Environment and Natural Resources (CENR). A plan to develop the assessment was
completed in March of 1998 and presented to a Task Force convened by the EPA which
includes federal, state and tribal government representatives. More recently, the charge
to submit an assessment of hypoxia in the Gulf of Mexico was written into law at the end
of the 105th Congress (Section
604a of P.L. 105-383).
While the National Oceanic and Atmospheric Administration (NOAA) has been asked
to lead the CENR assessment, oversight is spread amongst several federal agencies and the
assessment itself is being conducted by teams that include academic, federal, and state
scientists from within and outside the Mississippi River watershed The assessment of the
causes and consequences of Gulf hypoxia is intended to provide scientific information that
can be used to evaluate management strategies, and to identify gaps in our understanding
of this problem. While the focus of the assessment is on hypoxia in the Gulf of Mexico,
the effects of changes in nutrient concentrations and loads and nutrient ratios on water
quality conditions within the Mississippi-Atchafalaya riverine systems is also addressed.
Under the leadership of CENR, a Hypoxia Work Group was formed to conduct the
hypoxia science assessment. The Work Group is composed of representatives from the
Department of Agriculture, the Department of Commerce, the Department of Defense through
both the Army Corps of Engineers and the Office of Naval Research, the Department of
Health and Human Services through the National Institute of Environmental Health Services,
the Department of Interior through the Minerals Management Service and the U.S. Geological
Survey, the Environmental Protection Agency, the National Science Foundation, and the
Smithsonian Institution.
The goals of the hypoxia science assessment are to document the state of
knowledge of the extent, characteristics, causes, and effects (both ecological and
economic) of hypoxia in the northern Gulf of Mexico. The assessment will compile existing
information on nutrient sources, identify alternatives for reducing nutrient inputs, and
examine the costs and benefits associated with reducing the nutrient loads to surface
waters.
Hypoxia Assessment Reports
As a foundation for the assessment, six interrelated reports which examine
various aspects of the hypoxia issue were developed by six teams with experts from within
and outside of government. The research teams were not established to conduct new
research, but rather to analyze existing data and applied existing models of the
watershed-gulf system. However, they were encouraged to specifically identify additional
research or data needed to fill knowledge gaps.
Each of the reports underwent extensive peer review by independent experts. To
facilitate a comprehensive review process of the reports, an editorial board was selected
by the Work Group based on nominations from the Task Force and other organizations.
Editorial Board members were Dr. Donald Boesch from the University of Maryland, Dr. Jerry
Hatfield from the US Department of Agriculture, Dr. George Hallberg from the Cadmus Group,
Dr. Fred Bryan from Louisiana State University, Dr. Sandra Batie from Michigan State
University, and Dr. Rodney Foil from Mississippi State University. The Editorial Board
worked with the Hypoxia Work Group to select reviewers for the six reports, and served as
brokers between the lead authors and the reviewers to ensure that significant comments
were addressed.
These six now completed reports are to provide the foundation for the final
integrated assessment that will be used by the Task Force to evaluate alternative
solutions and management strategies. To download and view the reports using Adobe Acrobat,
please click on the titles.
TOPIC 1. Characterization of hypoxia.
(Text and tables available for downloading in .pdf format, Topic 1 (9 Mb). For
easier download, the topic is available in three files, Topic 1a (3,291
kb), Topic 1b
(3,729 kb), Topic 1c
(2230 kb); Appendices
available for downloading in pdf format, 653 kb) This report describes the seasonal,
interannual, and long-term variation of hypoxia in the northern Gulf of Mexico, and its
relationship to nutrient loadings. It also documents the relative roles of natural and
human-induced factors in determining the size and duration of the hypoxic zone. Lead:
Nancy Rabalais, Louisiana Universities Marine Consortium.
TOPIC 2. Ecological and economic
consequences of hypoxia. (Text and tables
available for download in pdf format, 371 kb, Figures are a
separate file in pdf format, 238 kb) This report presents an evaluation of the ecological
and economic consequences of nutrient loading, including impacts on Gulf of Mexico
fisheries and the regional and national economy. Ecological co-lead: Robert Diaz, Virginia
Institute of Marine Science. Economics co-lead: Andrew Solow, Woods Hole Oceanographic
Institution, Center for Marine Policy.
TOPIC 3. Flux and sources of nutrients in
the Mississippi-Atchafalaya River Basin. (Text available for
download in pdf format, 357kb. Tables available
as a separate download document, pdf format, 122 kb. Figures available as two separate
download documents, Figures for Chapters
1-4 (1,963 kb), and Figures for Chapters
5 and 6 (1,327 kb)) This report identifies the sources of nutrients within the
Mississippi/Atchafalaya system and within the Gulf of Mexico with two distinct components.
The first is to identify where, within the basin, the most significant nutrient additions
to the surface water system occur. The second, more difficult component, is to estimate
the relative importance of specific human activities in contributing to these loads. Lead:
Donald Goolsby, U.S. Geological Survey. For more on the USGS role in the hypoxia issue,
including additional on-line information and reports on nitrogen sources and transport in
the Mississippi River Basin, please go to the USGS Hypoxia in the Gulf of
Mexico Web page.
TOPIC 4. Effects of reducing nutrient
loads to surface waters within the Mississippi River basin and Gulf of Mexico. (Text available for
download in pdf format, 280kb. Tables and figures
available as a separate download document, pdf format, 2,527 kb).) This report estimates
the effects of nutrient source reductions in the Mississippi-Atchafalaya Basin on water
quality in these waters and on primary productivity and hypoxia in the Gulf of Mexico.
Modeling analyses was conducted to aid in identifying magnitudes of load reductions needed
to effect a significant change in the extent and severity of the hypoxia. Upper watershed
co-lead: Patrick Brezonik, University of Minnesota. Gulf of Mexico co-lead: Victor
Bierman, Limno-Tech.
[NOTICE: Please take notice that between May 4 th and the morning of May 11 th
, the internet posted version of the CENR Report on Topic 4, Effects of reducing nutrient
loads to surface waters within the Mississippi River Basin and the Gulf of Mexico,
contained a series of formatting errors which resulted from faulty translation of the
authors original text into PDF format. These included pagination and editorial errors, but
significantly the errors included the conversion of µg unit measurement to g unit
measurements in several sections of the report, such that microgram units were mistakenly
viewed as gram units. These error specifically occurred in Sections 3.2.3 and 5.1, and
have since been corrected; please either download a more recent version of the report or
note the correction in any existing version.]
TOPIC 5. Reducing nutrient loads,
especially nitrate-nitrogen, to surface water, groundwater, and the Gulf of Mexico. (Text available for
download in pdf format, 272kb. Tables
(pdf
format, 131 kb) and Figures
(pdf
format, 2,094 kb) are separate files, ) The focus of this report was to identify and
evaluate methods to reduce nutrient loads to surface water, ground water, and the Gulf of
Mexico. The analysis was not restricted to reduction of sources alone, but included means
to reduce loads by allowing the system to better accommodate those sources through, for
example, modified hydraulic transport and internal cycling routes. Lead: William
Mitsch,
Ohio State University.
TOPIC 6. Evaluation of economic costs and
benefits of methods for reducing nutrient loads to the Gulf of Mexico. (report available
for download in PDF format, 1200K.) In addition to evaluating the social and economic
costs and benefits of the methods identified in topic 5 for reducing nutrient loads, this
analysis included an assessment of various incentive programs and any anticipated fiscal
benefits generated for those attempting to reduce sources. Lead: Otto
Doering, Purdue
University.
As published in the Federal Register on May 4,
1999, the public has been invited to comment on these report for the purposes of providing
input to the Integrated Assessment and, subsequently, the Action Plan. (Download a copy of
the Federal
Register Announcement, pdf format, 21kb). Upon completion of the draft integrated
assessment, this too will be posted on this website and otherwise made available for
public comment. For more information on how to provide comments to these reports, please
consult the federal register notice. Please note that comments themselves must be mailed
to the address listed in the federal register notice.
This page will be updated regularly to reflect the latest developments in the
assessment process. Email specific questions about the project to: hypoxiawg@cop.noaa.gov.
The National Ocean Service's
MapFinder - The National Ocean Service's (NOS) MapFinder Web service provides
direct Internet access to NOS imagery and data holdings for coastal photography, nautical
charts, historical maps, coastal survey maps, environmental sensitivity index maps,
hydrographic survey outlines, water level stations, estuarine bathymetry, and geodetic
control points...
Revised by NOS Web Team
on June 23, 1999 .
URL: http://www.nos.noaa.gov/
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