Nancy Rabalais isn’t just executive director of the Louisiana Universities Marine Consortium. She’s also a recent Heinz Award winner for her work on aquatic environments, specifically the Gulf “dead zone.”
Below are excerpts from our recent interview.
How did aquatic environments become the lifelong focus of your work?
I knew since eighth grade that I wanted to be a biologist. I followed that through high school, taking more biology than most students. Maybe I was afraid of physics. There were a lot of marine-oriented courses at my college, and I spent a lot of time at the beach. Training in marine biology merged with exploring beaches and learning to scuba dive. It went from there.
Your research centers on the Gulf Coast. What attracted you to that region?
My background has always been in Texas. I studied the Texas coast for my Master’s and PhD. Then I took a job in Louisiana. I’ve been here for 27 years now. This is my home now. I care about all shorelines and coast lines but the Gulf of Mexico receives a large part of my attention. Among the issues on the Gulf Coast, perhaps more there than other places, are climate change, storm hazards and multiple other stressors. You can restore the coastline, but you have to look at the long-term landscape and not just short-term fixes.
What is a “dead zone” and how does it form?
It’s a low oxygen area in the Gulf, primarily west of the Mississippi River Delta. The Mississippi River brings in fresh water. That water is more dense than salt water, so it creates a layered system. With the sun heating the surface water in the summer, warm water is less dense than cold water. It creates a layered system where there is a density difference between the upper and lower layers. That prevents oxygen from surface waters moving to the bottom. It’s been that way for a long time.
The other part of the formula to create low oxygen water is the nutrients that come down the Mississippi. Nitrogen and phosphorous have been going up over time. We’re getting 200 to 300 times more of these nutrients than we had historically. The materials sink to the bottom. In the bottom water and sediments, there are bacteria that consume carbon and use up oxygen. There’s so much organic debris at the bottom that the response from the bacterial community is high. There’s uptake of oxygen by those bacteria at a much faster rate than they can come from the surface.
You have the physics set up by the freshwater and warming. You have the biology stimulated by nitrogen and phosphorous. There’s a situation now that did not occur historically.
How large is the Gulf dead zone?
The dead zone is on an annual cycle. In the winter, the water column gets mixed up a lot. That layered system is broken down. Beginning in the spring, along with increased freshwater from the river, those cold fronts start to become less frequent. The water settles down and starts to develop those layers. I’ve seen it as early as February. It’s widespread by June and July. We’ve recorded it as late as October. It’s a spring-summer situation.
It’s not across the whole Gulf all the time. In the summertime, we map the whole area from our research vessel. The largest area was 22,000 square kilometers. The average is 18,000 to 19,000 square kilometers. The task force addressing the issue has a goal of 5,000 square kilometers by 2015.
Is that goal within reach?
That goal was accessible when it was first developed. The low oxygen area at the time was much smaller than it is now. There continues to be an overloading of nitrogen and phosphorus. As we progress, it is becoming more difficult to manage the nutrients to reach that goal. Initially, we predicted about a 30 percent reduction in nitrogen. The last EPA science advisory board recommended a 45 percent reduction in nitrogen and a 45 percent reduction in phosphorous.
How has oxygen depletion in the Gulf changed since the 1950s?
The first data collected that showed low oxygen on the bottom in the Gulf was in the 1970s. With time, those instances increased. The number of people studying the Gulf also increased over time. The physics makes the system prone to low oxygen. But because we don’t have water column measurements, we’ve done what a lot of other people do: take sediments from the bottom and date them. You know how old the sediments are. Then, you look for proxies for environmental change. We’ve done a lot of that work.
What impact did the 2010 oil spill have on the Gulf dead zone?
We’ve had two back-to-back whammies in the Gulf. The first was the oil spill in 2010. This year, we had record flooding in the Mississippi River. The oil spill was in deeper water. We did get oil in the area where low oxygen forms in the summer. In the low oxygen areas that got oil, the oxygen at the surface was high. That’s a result of the river discharge in 2010, which was above average. The bottom was not different than you’d expect. My thoughts — without having done all the analyses — are that the oil spill did not affect the Continental shelf low oxygen.
What’s next for you and your research?
My research future depends a lot on the U.S. economy. We’ve had success in competitive research funding through NOAA. We’re in our third year of a five-year award period. We’ve changed some of our activities offshore, so we’re looking at rates. We’re trying to maintain the basics and continue to do the process work, but we’re not as well-funded on that. We never run out of research ideas.