A bigger 'dead zone' this year than usual
Heavy spring rains poured high levels of river runoff – and pollutants – into the Gulf of Mexico this year.
| NEW ORLEANS
The Gulf Coast's notorious "dead zone" – a summertime phenomenon in which coastal waters become so oxygen-deprived that marine life cannot survive there – is expected to be substantially larger than average this year, covering a patch of ocean about half the size of Maryland.
The culprit is 2006's heavy spring rains, which sent more river runoff than usual pouring into the Gulf – laced with fertilizers and other pollutants that trigger the annual reappearance of the dead zone.
For most of a decade, government-backed researchers have studied the causes and effects of this seasonal occurrence, which threatens some of the most productive commercial fisheries in America. Now they are fielding pilot projects that aim to cut the amount of nutrients flowing down the Mississippi River.
In addition, scientists are working to perfect their annual forecasts. They hope to develop tools that will help fishermen find the more-productive waters, as well as help government officials weigh the costs and benefits of different approaches to reducing nutrients in the river.
Looking at the state of the science surrounding the dead zone, "the fundamentals are sound," says Eugene Turner, a researcher with Louisiana State University's Coastal Ecology Institute in Baton Rouge. But ask whether there's much progress in reducing the nutrients flowing out of the Mississippi's vast drainage basin, he replies, simply, "No."
The outlines of the problem are well established. Nitrogen and phosphorus from farms and urban runoff deep in the continent's interior eventually feed algae in the Gulf. The algae die, fall to the bottom and decompose, consuming oxygen. If decomposers on the bottom consume oxygen faster than it can be replenished, any finny fish or crustacean that can't outswim or outscamper this "hypoxic" zone as it builds gets smothered.
One discovery of the past few years is just how knotty the problem is, Dr. Turner says. Each smaller watershed feeding into the Big Muddy has its own complex traits. Those watersheds support cities and towns with their own sets of environmental and economic concerns beyond the going price of a shrimp cocktail.
A study published last month by the University of Indiana's Todd Royer tells the tale. He tracked the amount of nitrogen and phosphorus leaving three river systems in Illinois for the past eight to 12 years. Not surprisingly, the heaviest nutrient runoff came between mid-January and June, during snowmelt and spring rain. But state standards for allowable nutrient runoff from fields were the tightest in the summer and fall, when low, lazy flowing waters and warm temperatures favor algae growth locally. State standards were less stringent during the high-flow periods in the late winter and spring, when nutrients are readily flushed downstream. Yet these are the flows that most affect the Gulf's summertime hypoxic zone.
If control strategies are designed to protect local water quality, "then this does it right," Dr. Royer says. But it shortchanges the Gulf, he adds. Thus, a fix-it strategy for the Gulf that relies on local water-quality controls may not do the job.
Potential solutions may include a shift in farmers' schedules – getting them to apply fertilizers in the spring rather than during the previous fall, he says. Or it could mean inducing them to use farming techniques that require less fertilizer.
Researchers at the University of Minnesota are looking at another approach near Madelia, Minn.: planting trees, shrubs, and perennial flowers along creeks and riverbanks as natural filters – with an eye toward plants that could be used for biofuels so that these natural filters also could augment farmers' incomes.
Indeed, adds LSU's Dr. Turner, "the overriding influence is land use." Noting that Congress will consider the next multi-year farm bill this fall, he says lawmakers might choose to cut conservation funds, or encourage farmers to grow more corn for biofuel – both of which could undercut efforts to stop Gulf Coast algae's annual feeding frenzy.
Uncertainties in how the overall river-ocean-algae system works still vex researchers, who are trying to refine their forecasting models. Currently, forecasts consider the amount of nutrients flowing down the Mississippi and Atchafalaya rivers, says David Whitall, a coastal ecologist with the National Oceanic and Atmospheric Administration. "But that's oversimplified," he says. "Our next-generation models will link river inputs with physical oceanography, but we're not there yet."