Northern Gulf of Mexico Hypoxic Zone
The northern Gulf of
Mexico hypoxic zone spans from Louisiana to Texas. Hypoxia is a condition in which dissolved
oxygen levels in the water are too low to sustain life. The hypoxic zone is
created by the excessive amounts of nitrogen and phosphorous runoff that is
dumped into the gulf from the Mississippi. The following discussion of this ecosystem will explore the general ecology of the area, anthropogenic interactions and effects on
this area, and possible courses of action regarding the future
of the ecosystem.
The northern Gulf of Mexico ecosystem is located off the coasts of Louisiana, Texas, and Florida. This area is home to
many different kinds of marine life, including at least 54 demersal fish
species. (Sulak et al, 2007) These fish are drawn to this ecosystem by coral
reefs that help tie the entire ecology of the area together. This ecosystem spans
from the open ocean or pelagic zone down to the lower abyssal layers of the sea
floor. The corals that occur in this ecosystem form large thickets and unlike many other species of corals, they are located in deep waters. (Sulak et al, 2007) Deep water corals serve in the northern
Gulf provide their ecosystem with similar functions as their counter parts in shallower waters. Most notably is that they add to the biodiversity of the ecosystem.
Fishes and other marine organisms of all sizes all benefit from the existence
of the corals. Small fish can hide in them, larger fishes are attracted by the
small fish, plankton feed off the organic particles that surround the corals,
and starfish and crabs use the corals as their habitats. The reason that these
corals exist in deep waters is due to the carbonate rock substrate. (Sulak et
al, 2007) The carbonate substrate also allows other organisms such as sponges,
anemones, and various other bottom dwelling species to take hold. Prior to the
large amounts of agricultural runoff that currently affect the area, the corals
in this ecosystem were the foundations of live. Now they are a death trap for
slow moving species. The nitrogen and phosphorous runoff from the Mississippi
river bring low levels of dissolved water and create a “Dead Zone.” (Marder, 2011)
The “Dead Zone” is likely to have appeared as early as
the beginning of this century when fertilizers with phosphorous and nitrates
began to be used by farmers. It became more severe closer to the 1950s when
fertilizer runoff from the Mississippi increased threefold. (Mississippi River Gulf of Mexico Watershed Nutrient Task Force, 2008) Waters can be
considered hypoxic when the dissolved oxygen content drops to below 2mg/l.
(Rabalais, Turner, Wiseman, Jr., 2002) This dissolved oxygen level is the
lowest possible that can sustain life. Hypoxia has its greatest effects on
animals that live closer to the ocean floor in benthic areas. Hypoxic
conditions generally occur from late February to early October, but they are
most continuous and severe during June, July, and August. (Duffy, 2008) The
fertilizer sediments bring about a phenomenon called eutrophication, which is
an overloading of nutrients. (USGS, 2011) The excessive amounts of nutrients
give rise to algal blooms. When these algal blooms die, the sink to the benthic
zone of the ocean and decompose. The decomposition of the algae robs the water
of oxygen. Animals such as fish, shrimp, and crabs that can move quickly can
escape the waters with insufficient oxygen levels. Animals that cannot move
quickly enough, such as starfish, sponges, and anemones, perish in the oxygen
deficient water.
 |
| (Wendee, 2011) |
The sources of pollution that contribute to the dead zone
are vast. The Mississippi River begins as a small outlet stream stemming from
Lake Itasca in Northern Minnesota. It then travels 2,350 miles south to the
Gulf of Mexico. The Mississippi drains the entire Mississippi River Basin,
which includes 31 states and cover 1,245,000 square miles. (Mississippi River
Gulf of Mexico Watershed Nutrient Task Force, 2008) This means that the
Mississippi carries the entire basin’s fertilizer runoff. A few states such as
Minnesota and Wisconsin are aware of this fact and have put restrictions in
place to limit the amount of nitrogen and phosphorous runoff into their rivers.
(Gannett, 2012) However, not all of the states that contribute to the nutrient
runoff are receptive to such restrictions. Farmers and political leaders in the
state of Iowa oppose nutrient runoff regulations. Corn is a regularly grown
crop in Iowa and the demand for corn is ever-increasing. A high demand for corn
leads to higher yields and therefore more fertilizer use.
The future of this ecosystem depends on multiple factors.
Corn has been and will continue to be a major crop in the United States,
therefore the need for nitrogen and phosphorous fertilizers are going to
persist. This is an ugly truth for the people that depend upon the health of
the northern Gulf. Shrimp fishermen that maintain their livelihood are
suffering the consequences of high use of fertilizers. There are many people
that contribute to the pollution of the Mississippi River, and none of them are
affected by how much they pollute the water. When shrimp fishermen want to go
out and harvest shrimp and the areas that are normally full of shrimp are now
hypoxic, then they will not be able to catch shrimp and lose substantial
amounts of money. The human population will continue to grow for some time,
meaning the demand for corn will continue to grow as well. For Midwestern corn
farmers, this means higher yields during growing seasons are necessary, so
fertilizer inputs need to be increased. For the northern Gulf ecosystem and the
shrimp farmers, this could result in awful consequences. The hypoxic zone
varies in size each summer for a combination of reasons including fertilizer
runoff as well as precipitation rates. (WSA, 2006) In years that precipitation
is low, the fertilizer runoff decreases and that leads to a smaller hypoxic
zone. (Slivka, 2012) Since rainfall cannot be controlled, other techniques
to lessen the hypoxic zone need to be utilized.
Reducing the amount of nitrogen and phosphorous runoff
that enters the northern Gulf of Mexico is a challenging task, but it is not
impossible. The keys to achieving this goal are the distribution of information
and cooperation amongst polluters of the Mississippi River. In order to bring
attention to any sort of issue, the proper information must be presented to the
proper audience. In this case, people and industries that pollute the
Mississippi River need to be made aware of the consequences of their actions.
Some polluters may already know how they are impacting others that depend on
the health of the northern Gulf yet output must be continued otherwise they
will lose profits and begin to struggle. The best option is to put in place a
system of pollution credits, not unlike the carbon trading system that is going
to be implemented in California. A cap needs to placed on the total amount of
nitrogen and phosphorous runoff that can enter the Mississippi. This cap can be
determined by the main polluters of the states in the Mississippi Basin and the
lawmakers of those states in conjunction with northern Gulf fisherman, research
organizations such as the Louisiana Universities Marine Consortium (LUMCON),
and the lawmakers of the affected states. Another option is to push for a shift
in farming practices. Farmers in the Mississippi Basin have many choices in
advanced farming technology and methods that can reduce dependency on
fertilizers and the cut down on runoff. Drip irrigation, organic farming, and properly
timed fertilizer applications are all methods that are effective.
Prior to the overloading of nutrients in the northern gulf ecosystem, hypoxia was not a problem. Without the occurrence of hypoxia, marine organisms did not have to flee for their lives from the suffocating waters or perish because they could not escape. The northern Gulf of Mexico ecosystem feels the pressure
of anthropogenic pollution daily; the runoff from the Mississippi River will
never cease. The hypoxic zone that exists there is in no way a damning sentence
that humans have placed on the ecosystem. The effects of the dead zone can be
diminished if the area is properly managed. This coastal ecosystem can thrive
and continue to be a home to many marine creatures as well as serve the coastal
communities that depend on it.
Works Cited
Duffy, J. Emmett. “Gulf of Mexico Large
Marine Ecosystem.” Encyclopedia of Earth
Online.
Encyclopedia of Earth, 28 Dec. 2010. Online.
Gannett, Perry Beeman. “What is Hypoxia?”
The News Star, 24 Nov. 2012. Online.
Marder, Jenny. “Farm Runoff in
Mississippi River Floodwater Fuels Dead Zone in Gulf.”
Public
Broadcasting Service, 18 May 2011. Online.
Mississippi River Gulf of Mexico
Watershed Nutrient Task Force. “The Mississippi-
Atchafalaya
River Basin (MARB).” Environmental Protection Agency, 2008.
Online.
Nicole, Wendee. "Dead Zone." Adventures in Climate Change, The Wendee Nicole Report,
7 July 2011. Online.
Rabalais, Nancy N., Turner, R. Eugene., and Wiseman Jr., William J. Gulf of Mexico
Hypoxia, a.k.a “The Dead Zone.” Annual Review of Ecology and Systematics 33
(2002): 235-63. Online.
Slivka, Kelly. “Big Drought Makes for a
Small Dead Zone.” New York Times, Green
Blog. 2 August 2012. Online.
Sulak, Kenneth J., et al. Demersal Fishes Associated with Lophelia Pertusa Coral and
Associated Biotopes on the Continental Slope, Northern Gulf of Mexico. Bulletin
of Marine Science 81.1 (2007): 61-92. Online.
United States Geological Survey.
“Eutrophication.” Toxic Substances Hydrology
Program], 27 Dec. 2011. Online. <
http://toxics.usgs.gov/definitions/eutrophication.html>
Wadeable Streams Assessment. “Nitrogen
and Phosphorous Pollution in the
Mississippi
River Basin: Findings of the Wadeable Streams Assessment.”
Environmental Protection Agency,
2006. Online.
