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Diving Deeper: Episode 12 (July 1, 2009) —
What is a Dead Zone?

HOST: Welcome to Diving Deeper where we interview National Ocean Service scientists on the ocean topics and information that are important to you! I’m your host Kate Nielsen.

Today’s question is….What is a Dead Zone?

Dead zone is a more common term for hypoxia. Hypoxia, in this context, refers to a reduced level of oxygen in the water. Less oxygen dissolved in the water can cause problems for fish and other aquatic organisms.

To help us dive a little deeper into this question, we will talk with Dr. Rob Magnien on dead zones – what they are, where they are located, and why they matter to us. Rob is the director of the Center for Sponsored Coastal Ocean Research. Hi Rob, welcome to our show.

ROB MAGNIEN: Thanks Kate, it’s great to be here and talk about a topic that I’ve been researching and helping to manage for almost 30 years.

HOST: Rob, can you expand a little bit more on hypoxia from our initial definition?

ROB MAGNIEN: Sure Kate. Hypoxia is just as you described it – areas of our estuaries, coasts, or oceans with low levels or no oxygen dissolved in the water. These areas are often referred to as “dead zones” since most marine life either dies, or, if they are mobile such as fish, leave the area. Thus, habitats that would normally be teaming with life become, essentially, biological deserts.

HOST: What causes a dead zone or hypoxia to occur?

ROB MAGNIEN: Hypoxic zones can occur naturally, but the ones we are most concerned about are those created or enhanced by human activity. There are many physical, chemical, and biological factors that conspire to create dead zones, but nutrient pollution is the primary cause of those created by humans. Excess nutrients that run off land or are piped as wastewater into our rivers and coasts can stimulate an overgrowth of algae, which then sinks and decomposes in the water. The decomposition process consumes oxygen and depletes the supply available to healthy marine life.

HOST: Where do dead zones occur in the U.S.?

ROB MAGNIEN: Kate, dead zones occur in many areas of the country, particularly along the East Coast, the Gulf of Mexico, and the Great Lakes, but there is no part of the country, or the world for that matter, that is immune. The second largest dead zone in the world is located right here in the U.S. in the northern Gulf of Mexico and the ones in the Chesapeake Bay and Lake Erie are not far behind in size.

HOST: Rob, how large is the Gulf of Mexico dead zone that you just mentioned?

ROB MAGNIEN: Well, the size of the Gulf of Mexico dead zone actually varies from year to year, but the average size is about the size of the state of New Jersey or the states of Rhode Island and Connecticut combined, and that’s an average from the years of 1993 to 2001.

HOST: How long do dead zone events last and also what is their frequency, are they seen several times per year?

ROB MAGNIEN: Well, the frequency and length of dead zones varies from place to place and year to year. Most dead zones start to form in the spring, most are severe in the summer, and then they break up in the fall. If spring rainfall is high, more nutrients can be washed into coastal waters and that leads to larger dead zones in that particular year. On the other hand, in an area like the Gulf of Mexico, hurricanes can stir up the water sufficiently to re-oxygenate the bottom water, even in summer, but even then the dead zone usually reforms in about a week or two.

HOST: Rob, can we visually see dead zones?

ROB MAGNIEN: Not really. Unless you dive into an area experiencing hypoxia, lower a remote camera, dead zones and the devastation that they create are not normally visible. Sometimes we can observe the factors leading to the formation of a dead zone such as a large surface algal bloom or the consequences such as a fish kill.

HOST: Since it doesn’t sound like there’s much of a visual or aesthetic disruption from dead zones, what are some of the economic impacts?

ROB MAGNIEN: Kate, although we know that there are clear impacts to important habitat for fish and shellfish, there actually have been very few studies that quantify those economic impacts. One of the keys to calculating an economic impact, as you might imagine, is the ability to precisely measure or predict the impacts in a large regional fishery that is subject to many pressures and includes various life stages of the fish and migratory patterns that can bring them in and out of a dead zone.

That said, there is obvious cause for concern in an area such as the Gulf of Mexico where fisheries generate about $2.8 billion annually for the economy. This is one of the major outstanding questions that we are pursuing with our research portfolio on hypoxia. As is typical of my Center’s research, it requires a large-scale multidisciplinary approach with state-of-the-art computer modeling to fully understand and quantify the various factors at work.

HOST: I understand that this may vary and be different in each area that experiences a dead zone, but in general, are dead zones increasing or decreasing in their size and frequency in the U.S.?

ROB MAGNIEN: Well, the number of dead zones has actually greatly increased worldwide since the 1960s, according to a new research study funded, in part, by my Center here at NOAA. Four hundred systems, including 166 in the U.S. waters, now have documented dead zones.

HOST: What is the role of the National Ocean Service in dead zone research?

ROB MAGNIEN: Kate, there are a number of laboratories in NOAA, across the federal government, and in academic institutions working on dead zone research projects. My office, the Center for Sponsored Coastal Ocean Research in the National Ocean Service administers the only national-level hypoxia programs and provides competitive funding for the brightest minds to attack the most urgent gaps in knowledge required to manage this problem. Hypoxia is really emblematic of some of our most difficult coastal problems that require large-scale sustained research to achieve the understanding needed to drive management actions. For example, over approximately 15 years, my office has invested over $27 million for research into the Gulf of Mexico dead zone. Fortunately, that investment has paid off by providing the fundamental science underpinning for a management action plan first issued in 2001 and then revised in 2008.

HOST: Thanks Rob. It’s great to hear that such a program exists to help managers protect coastal communities and economies. How are you able to predict a dead zone event before it happens?

ROB MAGNIEN: Kate, to be able to predict something like a dead zone, one must first construct and validate a mathematical model that simulates the key processes of the ecosystem. These vary in complexity and must be tailored to each system based on its physics, chemistry, and biology. These models also require large amounts of monitoring data for development and validation.

Currently, we are working with researchers to issue seasonal predictions of the dead zones in the Gulf of Mexico and Chesapeake Bay. These are some of the same models that are guiding long-term management by quantifying the amounts of nutrient pollution that must be reduced to shrink dead zones in a number of areas.

HOST: Hypoxia and dead zones sound like rather complicated topics from our discussions today. We touched a little bit on this so far, but what is NOAA doing to address this problem?

ROB MAGNIEN: Kate, essentially what we’re trying to do is support the research required to understand a complex phenomena such as hypoxia, and then work to synthesize this information, typically in a computer-based mathematical model of great complexity these days and requiring a lot of computer power, which then, in turn provides straightforward and reliable advice for managers on alternative courses of action that can be taken. And it also, I believe, helps the public understand this issue, so everyone involved, including those who must support often very difficult decisions, have the best information to make those decisions.

HOST: And to add to that question, is there anything our listeners can do?

ROB MAGNIEN: Absolutely. Since, as we discussed earlier, the primary human influence that makes dead zones worse is nutrient pollution. Anything that one can do to prevent nutrient runoff will help. This can include minimizing fertilizer use right at home on your lawn or supporting local governments in their efforts to upgrade wastewater treatment plants which can at times be costly, but are necessary to protect our waterways.

HOST: Thanks Rob. I think you gave us a few great examples of things we can do in our everyday lives to help with this problem. Do you have any final closing words for our listeners today?

ROB MAGNIEN: Perhaps one Kate and that would be that in studying these problems and learning more about their origin and their consequences, I think it teaches us that these difficult coastal problems are often connected to things far away, up in the watersheds; and therefore the actions of farmers – maybe a hundred, two hundred, or three hundred miles away – or homeowners and how they treat their land has consequences downstream. And this is very important to understanding how we can reverse some of the degradation we’ve seen and in turn protect these valuable resources along the coast for the enjoyment of us and our children and also for protection of the coastal economies that are just so important for this country.

HOST: Thank you Rob for joining us on today’s episode of Diving Deeper and talking more about dead zones and the impacts they can have on us. To learn more about dead zones, please visit

That’s all for this week’s show. Please tune in on July 15th for our next episode on hydrography.