The Dead Zone in the Gulf of Mexico off the Louisiana coast is caused by hypoxic conditions. Hypoxia literally means lacking oxygen, and this is exactly what has happened in the Gulf of Mexico. In this case, the zone is caused by excess nutrient dumping into the Mississippi River, which eventually pours into the Gulf of Mexico. The increase in nutrients encourages an algal bloom, and they use excess oxygen when metabolizing and when they are decomposed by bacteria (5). The source of the nutrients comes from far up the Mississippi River, and even from the Ohio River(8). The Mississippi River basin drains 52% of the country’s farms and 47% of the nation’s population. It is not hard to see where all the excess nutrients come from, and why they end up in the Gulf of Mexico. This hypoxic condition is extremely important to study because it does not only occur in the Gulf of Mexico, it can happen anywhere in the world where there are excess nutrients dumped into a watershed(5).
The Gulf of Mexico hypoxic zone is created every summer after spring rainfall and melting snow flood the plains and wash the excess nutrients from fertilizers and manure into the river. These nutrients end up in the Gulf of Mexico just off the coast of Louisiana(4). The hypoxic zone can engulf as much as 7,728 square miles of water, as is what happened in 1999. The hypoxic zone in the Gulf of Mexico off Louisiana was first discovered in 1970(3). In the past, the zone had been occurring every 2 to 3 years, but in recent years, the zone has been occurring every year, possibly due to the increased use of fertilizers by farmers(2). When core samples were taken in the drainage area of the Mississippi River, an alarming trend was seen. In the last 20 years, there was a decrease in the number of skeletons of high oxygen demand organisms, and a corresponding increase in number of low oxygen tolerant organisms, such as bacteria and phytoplankton(3).
Fertilizers and manure both contain phosphorus and nitrogen. These 2 nutrients are the main contributors to algal blooms. The nitrogen input into the Gulf of Mexico has increased almost 2 to 7 times its amount a century ago(5). Nitrogen and phosphorus are not only found in fertilizers, but also in raw sewage that is sometimes directly pumped into the river systems, as in what happened in Iowa this past spring. The increase in nitrogen has a detrimental effect on sealife, because normally nitrogen is a limiting growth factor, but when it becomes readily available, algae grow exponentially(1).
During the winter, the zone is basically not there, but in recent years it has been present. The reason that the zone disappears is the decreased nutrient rich water flow into the basin, colder water, and hurricanes that break the zone up. The zone is the largest during the summer, just after spring rains bring nutrient rich water into the Gulf, and warmer temperatures that raise water temperature. Also, the increase in freshwater flow on top of the heavier saltwater slows the diffusion rate of oxygen to the deeper parts of the saltwater(7). This dependence on the spring rains allows scientists to study a natural experiment at work every spring. In the spring of 1999, there was a widespread flooding in the plains, and this produced the largest hypoxic zone yet recorded. In earlier years, a drought was present, producing less flooding, and correspondingly the hypoxic zone was much smaller, and in some areas almost negligible. This natural experiment allows scientists to test their theories on what produces this zone, and what could be done to eliminate or shrink it(4).
As I have mentioned earlier, the hypoxic zone is very depleted in oxygen. For all non-motile or slow swimmers, this zone can swallow them whole and kill them. The bloom in algae kills most invertebrates, because they are not able to avoid or tolerate the low oxygen conditions. When the invertebrates die, this causes the fish to leave the area because their food supply is gone. They also can not live in this zone because they need oxygen to live(2). The organisms that can live in this hypoxic condition are decomposing bacteria, and algae. The algal blooms are associated with excess nitrogen nutrients. Usually they are kept at normal levels, but the increase in nitrogen allows fast proliferation. These phytoplanktons produce wastes and dead bodies that drop to the sea floor, where bacteria can decompose them. The bacteria feast on the dead bodies caused by the lack of oxygen, and they hoard oxygen during the breakdown of the body. These bacteria are what really cause the hypoxic condition at the bottom of the Gulf, killing the marine organisms(6). Another potentially harmful organism that can live in this condition are the phytoplanktons that cause Red Tide. Red Tide phytoplankton produce a toxin that can be ingested by organisms that then can be eaten by humans, and these toxins can even cause death in humans(5).
The hypoxic condition has harmed many marine industries on the Louisiana coast. The fishing industry is harmed because the fish either leave or die. They move to deeper water that is further off the coast. This means that the fisherman have to spend more money to even get to the fish, and that means less profit. Some of the smaller operations can not even afford to venture that far off land. The shellfish fishermen are also hurt from this condition because either their catch is killed by the large hypoxic zone, or they are contaminated with Red Tide toxins or other potentially deadly toxins(5). Either way they are losing catch. The tourist industry is also hurt, because a lot of money is made in the chartering business and when there are no fish to catch people do not come. The fishing industries annual catch is worth $26 billion(4). This is a lot of money for the local, state and national governments. This problem is of great concern to the fisherman because if this problem continues many of them will not be able to sustain a living by fishing(5).
Marine organizations along the Gulf, and even the government, agree that their needs to be something done. Most scientists believe that the cause of the hypoxic zone is the increased use of fertilizers, and the recent massive decrease in wetland areas all along the Mississippi. These wetlands act to “soak” up excess nutrients, not allowing some of them to enter the Gulf of Mexico at the mouth of the Mississippi River. Taking away these wetlands forces the nutrients that would have been soaked up to continue down the river and in to the Gulf of Mexico. A bill called Action Plan would allow $322 million to be spent researching and fixing the hypoxic condition. A task force created out of the bill would decide what needs to be done, and where problems needed to be fixed. This bill wants to create 2 million miles of nitrogen-trapping buffer zones around farms. These would effectively decrease nutrient loss off farms and into the river systems. This loss of nutrients is what can be the largest contributor to the large quantities of nitrogen and phosphorus in the rivers. These plans would help the problem significantly(8).
The way to fix the problem is to decrease use of fertilizers, and increase wetland areas along the river basin. The only problem with this is that it costs a lot of money, and it hurts crop and livestock production for the farmers. Since it will cost the farmers so much, many of them are not likely to decrease their fertilizer use. Also, since the scientists do not know exactly what causes the hypoxic condition and what will happen with a decreased nutrient load, many farmers will not do anything to help unless it is conclusively proven. Many of the farmers in Louisiana do not even know that a hypoxic condition exists off the coast. It is hard to tell a farmer to cut production capacity to save a problem that he can not even see or know about(5). Another problem is that the condition mainly affects the fishing industry in Louisiana, but the problem is created in many of the states that drain water into the basin. The governmental question is how to regulate all these states because of a problem in one? The government is working on bills that could limit the amount of fertilizer used and bill that would increase wetland areas, but none have made it very far because of the farmer and state to state conflict. As with everything, it is hard to get everybody to agree on one point. The problem is that they do not realize that this hypoxic problem could affect everybody, whether they want it or not(8).
From the looks of things, the hypoxic zone is not likely to go away anytime soon, and this means less catch for the fisherman, and less tax income for the local, state, and national governments. The lower the profit gets, the more serious people get about a problem. If this is what it takes, then it will happen because of the smaller fish catch each year. This condition needs to be seriously addressed in the very near future. Farmers need to realize that this problem could indirectly hurt them. They could lose money from all of this. Also, it is possible that if they do not voluntarily decrease their fertilizer use, they may be forced to by the national government. The problem is occurring all over the United States and the world, and unless the problem can be solved soon, there may be nothing to save.
(1) Beardsley, T. (1997) “Death in the Deep.” Scientific American, Nov. 17-20.
(2) Malakoff, D. (1998) “Death by Suffocation in the Gulf of Mexico.” Science 281, 190-192.
(3) Sen Gupta, B., Turner, R., Rabalais, N. (1996) “Seasonal oxygen depletion in continental-shelf waters of Louisiana: Historical record of benthic foraminifers.” Geology 24, 227-230.
(4) http://www.fishingnj.org/artedzn.htm “A ‘Dead Zone’ grows in the Gulf of Mexico”
(5) http://www.tulane.edu/~bfleury/envirobio/enviroweb/DeadZone.htm “The gulf of Mexico Dead Zone and Red Tides”
(6) http://www.cop.noaa.gov/deadzone.html “Gulf of Mexico ‘Dead Zone’”
(8) http://www.epa.gov/msbasin/actionplan.htm “Action Plan”
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