As cleanup efforts in the Gulf of Mexico continue and scientists work to understand the long-term impact of the BP oil spill on marine and coastal ecosystems, it’s becoming more clear that the world’s oceans are under enormous pressure from human activity. Now that so much attention and activity is focused on cleaning up the Gulf, it’s worth looking at another major pollution-related problem in the area: agricultural runoff and the expanding hypoxic “dead zone” along much of the Gulf coast.
Each year since 1972, a hypoxic, or low oxygen zone, appears near the mouth of the Mississippi. Low oxygen in water can be very bad: plankton, fish, shellfish, and other marine life need oxygen to breathe and live. If they cannot breathe, they die, and we see tremendous and devastating fish die-offs that affect ecology, regional livelihoods, the food industry supply and thus commodity and consumer prices, and much more.
This article will profile hypoxia and present simple solutions that can be found in keener agriculture practices, in US environmental policymaking, and in public awareness and enthusiasm to amend the problem.
The annual hypoxic event in the Gulf extends westward to the Texas coast, covering thousands of square miles. Each year there is a general trend upward in the size of this hypoxic zone. Beginning in summer, and extending often late into the fall, this area of ocean becomes inhospitable to most animal life. In a region where given the climate and geology we might otherwise expect to see healthy waters supporting diverse marine communities, we instead have an ecological disaster.
While the Gulf experiences one of the larger hypoxic zones in the world, it is by no means unique to this region. Around the globe, hundreds of coastal areas are suffering the same problem.
In the Gulf, the reasons for this yearly event are generally well understood. However, understanding the long-term ecological and economic consequences and developing a way to reverse this trend is far more difficult.
Why is there a dead zone in the Gulf of Mexico?
In the Gulf, the problem largely stems from agricultural runoff from the Mississippi River.
The Mississippi River forms a vast watershed that drains much of the central United States. Nitrogen from fertilizer and manure on farms throughout the region is the main culprit fueling nutrient enrichment (also known as eutrophication) in the Gulf, and also of course fueling the subsequent hypoxia.
Many people are familiar with algal bloom events, like red tide, because of the economic impact and the threat to human health. The underlying cause – excess nutrients fueling an explosion in the growth of algae – is not unusual, and is often a natural process in the ocean. However, pollution from human activities is creating many of these hypoxic zones globally in recent decades.
The process of hypoxia is as follows: as excess fertilizer enters the watershed and flows into the Mississippi River, the nutrient-rich freshwater is carried out to sea, where stratification, or layering, occurs. Heat rises, and the hyper-fertilized freshwater sits on top of the colder, denser saltwater of the Gulf. This layering keeps oxygen-rich water near the surface, while oxygen-poor water is stuck below. The nutrients and sunlight in the upper surface waters create ideal conditions for algae to grow. They proliferate. Eventually the algae die off, sink, and decompose, which consumes nearly all of the remaining oxygen in the deeper water. When this happens, some mobile species may survive by migrating to less affected areas. But when fish, shellfish, and other organisms aren’t able to escape, we see die-offs and massive fish kills. It isn’t until autumn – when changing factors like cooler temperatures and more frequent storms churn the waters – that animals can survive there again.
As a result of all this, we are left with several big questions, which environmental experts are still trying to answer:
1. How much worse will these hypoxic zones get?
2. Could they become permanent dead zones?
3. What are the economic impacts?
4. What, if anything, can be done to reverse this trend?
In addition to industrial agriculture, other sources of contributing pollution include:
–residential and commercial use of fertilizers
–the burning of fossil fuels
–wastewater treatment facilities
What can be done to mitigate dead zone damage in the Gulf?
In general, experts agree on a few steps towards easing the damage from over-fertilized waters and resulting hypoxic zones.
The solution must include concerted efforts to:
1. reduce unnecessary use of these negative influencers
2. restore natural habitats so marine life isn’t stressed to begin with
3. restore natural ecosystems, which evolved over millions of years to develop the perfect filtering/replenishing systems
4. improve consumer awareness of the problem
Change often comes through inciting consumer outcry. There is a tipping point when enough people raise a voice against something: lawmakers and other stakeholders suddenly have to listen or risk losing elections, reputation, or even market share. Clearly, updates to Wetland and Water Allocation Policy are in order. Luckily, these appear to be a priority for current EPA water initiatives. Whether the public will jump on board to get these initiatives going in a reasonable timeframe is yet to be seen.
One example of an agricultural best practice that would detract nothing and would mitigate pollution, according to the USDA Economic Research Service, is also one of the most cost-effective solutions to hypoxia. The solution is to lean or rationalise the use of nitrogen-containing fertilizer. If agriculture decreased the amount of nitrogen that escapes into waterways by 1.2 million metric tons (which is only 26% of the nitrogen that works its way into the Mississippi Basin), there would likely be no significant decrease in crop yields as a result.
Improving wetland habitats throughout the Mississippi basin would improve the situation still further, by capturing a portion of the flushed-fertilizer nutrients before they reach open water.
Everything from warming oceans and acidification to over-fishing is taking a toll on both the natural world and our ability to use the ocean as a sustainable resource. The problem of hypoxic zones around the globe is not likely to improve in the foreseeable future, given population growth, the real or perceived need for fertilizers, and the fact that there are so many non-point sources of pollution involved. Like so many other environmental challenges, part of the solution must be greater public awareness and expressions of public concern for the problem, along with improved use, management, and conservation of resources.
Chris Watts currently serves as an Environmental Regulation Expert at Actio Corporation in Portsmouth, NH. He is pursuing advanced studies in Environmental Science at Johns Hopkins University, Baltimore, MD.