Introduction
Throughout the world, large areas of our coastal waters are becoming so polluted
that they lack sufficient oxygen, one of the basic building blocks of life. This condition is
called “Hypoxia” Although sometimes this is sometimes a natural condition, the increased
area of water affected, extended length of each episode and higher frequency in recent
decades are due to human activities. Over-enrichment of estuaries and coastal waters with
nutrients, especially nitrogen, stimulates outbreaks or “blooms” of algae that consume
vital oxygen from the water when they decompose. The effects of hypoxia include fish kills
and shellfish bed losses. These losses can have significant detrimental effects on the
ecological and economic health and stability of coastal regions. —Ecological Society of
America Fact Sheet
The passage quoted above presents a general over view of an environmental hazard that
today has risen to potentially catastrophic proportions—Hypoxia. It may not have the media
attention other environmental issues like global warming and air pollution has, but it is a real
problem that needs to be dealt with by law makers and policy makers. It should also be an issue to
be thought about by scientists, educators, and anyone that is concerned about their environment. It
is therefore appropriate and relevant for this or any course that seeks to educate someone on
environmental issues and the dilemmas that man has created by recklessly exploiting and
“trashing” the planet.
The purpose of this paper is to fully explain what a Hypoxic zone is and how it is formed,
to report its ever increasing prevalence around the world in recent decades, and its commercial and
environmental impact. The purpose is also to examine who is responsible for its occurrence, and
what steps are being taken to remedy all conditions of Hypoxia and to prevent further episodes.
The controversy over the issue of hypoxia results in a measure of unwillingness and resistance to
accept responsibility on the part of some, but that is outside the scope of this article.
Hypoxia is the name
Hypoxia is the name given to a condition that
exists when the levels of available oxygen in a body of
water such that marine life inhabiting the area is stressed.
This stress might take the form of forced migration or
mass mortality. The affected areas become incapable of
supporting marine life. The condition in most cases is not
continuous or permanent, but rather seasonal. Most
hypoxic conditions seem to occur during the start of the
summer months when it starts to get warm.
Under normal conditions (normal in this case
referring to the absence of any human activity), the
levels of dissolved oxygen (DO) can fluctuate
periodically with temperature changes (Table 1), but the
Table 1- Maximum dissolved oxygen levels
Temperature
(° C)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
DO
(mg/l)
14.60
14.19
13.81
13.44
13.09
12.75
12.43
12.12
11.83
11.55
11.27
11.01
10.76
10.52
10.29
10.07
9.85
9.65
9.45
9.26
9.07
8.90
8.72
Temperature DO
(° C)
(mg/l
23
8.56
24
8.40
25
8.24
26
8.09
27
7.95
28
7.81
29
7.67
30
7.54
31
7.41
32
7.28
33
7.16
34
7.16
35
6.93
36
6.82
37
6.71
38
6.61
39
6.51
40
6.41
41
6.41
42
6.22
43
6.13
44
6.04
45
5.95
Source: Environmental Protection Agency
levels tend to remain constant over time. Factors that
affect DO levels include temperature, altitude, and whether the body of water moves vigorously or
remains still. The colder the water temperature, the higher the DO levels will be. Higher altitudes
also mean lower DO levels.
At higher altitudes, there is less oxygen to mix with water. The action of the body of water
also determines the level of oxygen it is likely to contain. Churning, fast moving waters tend to
mix oxygen from the air better than waters that are calm or still (such as lakes or ponds). Besides
the oxygen from the air that mixes with the water, another supply of DO comes from the
photosynthesis of aquatic plants. Other factors include wind and rain.
The conditions that lead to the creation of a Hypoxic zone usually varies significantly from
normal conditions and these conditions tend to get very complex as it involves the acceleration of
biological activity, which consumes the DO at a rate that exceeds the ability of the aquatic
ecosystem to replenish the oxygen that is used. Under hypoxic (insufficient oxygen), or anoxic (no
oxygen) conditions, “oxygen depletion results from the combination of several physical and
biological processes.” (Rabalais, 1998)
Hypoxic conditions begin miles away from the scene of coastal waters, where nitrogen and
other types of nutrients (i.e. phosphorus) from fertilizer used by farmers to grow their crops and
other organic waste pollutants from factories and other sources end up in the ground water and get
transported downstream where they eventually find their way down to the coastal waters. “As a
general rule, the nutrients delivered to the estuaries and coastal systems support biological
productivity. Excessive levels of nutrients however, can cause intense biological productivity that
depletes oxygen.” (Rabalais, 1998)
The nature and scope of the hypoxia problem since its discovery in the 1950’s continue to
alarm scientists, environmentalists, government agencies, educational institutions and the public.
Though hypoxia conditions have been observed world-wide, it is the result of hypoxic conditions
right here in our own coastal waters that has raised our own awareness and concern for the
progressively worsening state of the marine environment and its impact on marine life.
In 1970, the most important hypoxic zone —the Hypoxia in the Northern Gulf of Mexico,
began to alarm scientists at Louisiana State University, in particular Dr. Nancy Rabalais, who to
this day continues to study it:
Midsummer coastal hypoxia in the Northern Gulf of Mexico was first recorded in
the early 1970’s. In recent years (1993-1999), the extent of bottom-water hypoxia
(16000 to 20000 km2) has been much greater than the surface area of Chesapeake
Bay, rivaling extensive hypoxic/anoxic regions of the Baltic and Black Seas. Prior
to 1993, the hypoxic zone averaged 8000 to 9000 km2 (1985-1992 Rabalais et al,
1998, and 1990). The hypoxic area covered 12,400 km2 in 1998, about the size of
Connecticut.
Conditions necessary for Hypoxia
Anthropogenic activity (activity caused or produced by humans) is a pre-condition
of hypoxia. The most common means of creating a hypoxic event is by excessive use of
fertilizers that contain nitrogen and phosphorus in the growing of crops. When the soil
contains very high levels of nutrients, irrigation and groundwater carry the nutrients down
stream until they reach the coast.
The river discharges into coastal waters carrying the nutrients that fall to the
bottom. Next, the biological and physical processes described earlier (Rabalais) will bring
about ecosystem changes that lead to formation of hypoxic zone, such as the hypoxic zone
in the Gulf of Mexico.
While the oxygen is being consumed by the decomposition of the algae bloom,
external factors that contribute to the replenishing of oxygen and allow it to mix well with
the water are not present. Consequently, the DO does not get replaced to the levels suitable
to sustain marine life. These conditions are present during the hypoxic event. Now let’s see
how a Hypoxic Zone is formed.
Death in a nutshell: One picture is worth a thousand words.
Source Louisiana University Marine Consortium (LUMCON)
http://www.gulfhypoxia.net/research/
Hypoxia around the world
Though the world’s attention is on the Northern Gulf of Mexico hypoxic event and on the
work of Dr. Nancy Rabalais and other LUNCOM scientists, it is not the only hypoxic event.
Hundreds have in fact been reported since the 1970’s and while an accurate inventory of hypoxic
events have been taken, a great difference in the actual number reported by different sources exist.
For example, Janet Larsen of the Earth Policy Institute assesses the number at 146:
Worldwide, there are some 146 dead zones—areas of water that are too low in
dissolved oxygen to sustain life. Since the 1960s, the number of dead zones has
doubled each decade. Many are seasonal, but some of the low-oxygen areas persist
year-round. (Larsen, 2004)
By contrast, this report of the United Nations Environmental Programme indicated a much higher
figure:
A review of global hypoxic and anoxic zones (estimated at 375) could be undertaken to
determine a subset of those with major nitrogen mediated impacts, out of which a short list
of between 10 and 15 would be selected for further assessment and possible pilot activities
(UNEP-GPA, 2007).
The environmental impact of Hypoxia
Large numbers of studies have been made on Hypoxia. The studies made of the Northern
Gulf of Mexico Hypoxia by Dr. Rabalais are probably the most thorough and according to her
leave “little doubt that human population growth and its associated activities have altered the
landscape” (Luncom, 2008).
Excess nutrients are finding their way to the coastal ocean in increasing amounts
especially during the last half of the 20th century. There are thresholds of nutrient loading
above which the nutrient inputs no longer stimulate entirely positive responses from the
ecosystem such as increased fisheries production. Instead, land-based sources of nutrients
are causing problems, for example, poor water quality, noxious algal blooms, oxygen
depletion and in some cases, loss of fisheries production. Over the last four decades it
has become increasingly apparent that the effects of excess nutrients that lead to
eutrophication are not minor and localized, but have large-scale implications and are
spreading rapidly (Luncom, 2008).
What’s being done?
In 2000, the Environmental Protection Agency (EPA), under the mandate of Public Law
105-383, the Harmful Algal Bloom and Hypoxia Research and Control Act of 1998, gave a public
notice of availability and request for public comment on a Draft Action Plan. The plan was
authored by the Mississippi River/Gulf of Mexico Watershed National Task Force.
The Action Plan contains a list of long and short term goals considered to be necessary to
reduce the size of the Hypoxic Zone. The long term goals offer three alternative actions and results
which are to be decided upon completion of a comment period. There are also short range goals
that focus on assisting farmers and land owners with programs to help (i.e. Clean Water Grants)
with reducing the amount of Nitrogen run-off to the Gulf of Mexico.
The report highlights the results of scientific investigation previously conducted and
describes a Hypoxic area in the Northern Gulf of Mexico occurring during the summer months.
The size of this zone is reported to be 4000 square miles. It goes on to describe the causes of the
Hypoxic zone as being predominantly due to nitrogen and phosphorus “run-off” from excessive
fertilizer use by agriculture.
What’s ahead?
There is a measure of controversy and debate over the issue of Hypoxia with scientists (e.g.
LUMCON), government agencies (e.g. NOAA, EPA) and environmentalists (e.g. The Ecological
Society of America) on the one hand and farmers on the other. Mainstream scientific studies of the
Gulf of Mexico Hypoxic Zone brought out irrefutable conclusions on the role of nitrogen
fertilizers applied excessively to the soil during the growing of crops. I believe that farmers were
amenable to the problem and seemed to concur with President Clinton’s Hypoxia Action Plan (as
it’s sometimes called). It has called for nitrogen load reduction of 30% and also for a 30%
reduction in the size of the hypoxic area in the Gulf of Mexico. The status of the plan is unclear,
but a new Hypoxic Action Plan was published in November of 2007 with the intent of reviewing
and restructuring the goals of the 2001 Plan.
The response of the “The Voice of Agriculture” AKA the American Farm Bureau (AFB) to
the 2001 Action Plan was highly unfavorable. It was decried for its alleged scientific inaccuracy,
for its imposition upon agriculture to change its practices regarding the use of fertilizers, and it was
also deemed unfair and unjust of the EPA to put the blame on agriculture for creating the Hypoxic
conditions. This was the gist of two letters that the AFB submitted to the authors of the plan, the
EPA Watershed Task Force. These letters reflected the indignation of the AFB over the technical
concerns they had over the wording of the plan, mindless of the fact that the plan contained only
suggestions to solicit feedback from the various interested parties and the public as to a final
strategy.
The letter from AFB Executive Director Richard Newpher lists seven “concerns” over the
wording of the plan:
1. the adequacy of scientific analysis
2. the effect of a 20 to 40 percent nitrogen reduction in agriculture
3. the use of water-quality standards and TDMLs to protect the Gulf
4. the impact of river flow management on the hypoxic zone and other resources
5. the lack of any economic and social analysis, as required by law.
6. the composition of any task force that may continue to exist after the Action Plan has
been finalized and
7. the lack of substantive involvement of state governors in the action plan
If those two letters are any indication, there will not soon be a “common cause” to guide
and persuade all those involved in agriculture in order to put aside their interests and “make peace
with the land”. When you are put on the “spot” it’s difficult to “act in the best interest of the earth”
(to borrow a phrase from juvenile law). Who shall be the “voice of the earth?”
References
Larsen, Janet. “Dead Zones Increasing in World's Coastal Waters” 2004.
The Earth Policy Institute- http://www.earth-policy.org/Updates/Update41.htm.
Newpher, Richard. “Comments of the American Farm Bureau Federation on the Draft Plan of
Action for Reducing, Mitigating, and Controlling Hypoxia in the Northern Gulf of Mexico”
http://www.epa.gov/msbasin/taskforce/pdf/afbf.pdf
Rabalais Nancy N. PhD. “Hypoxia in the Gulf of Mexico”National Oceanic and Atmospheric
Administration http://www.csc.noaa.gov/products/gulfmex/html/rabalais.htm(1998).
Anonymous. “Mississippi River Basin and Gulf of Mexico Hypoxia Draft Action Plan”
Environmental Protection Agency (2000) http://www.epa.gov/mbasin/taskforce/draft.htm
Anonymous. “Policies and part held during the 4th International Nitrogen Initiative Conference, 2 October
2007, United Nations Environment Programme(UNEP)
http://www.gpa.unep/documents/ini_workshop_final_report_english.pdf
Anonymous. “What_is_Eutrophication?” Louisiana Universities Marine Consortium (Lumcon),
2008. http://www.gulfhypoxia.net/research/#What_is_Eutrophication