Last week, I had far, far too much of several good things. Turkey, stuffing, green beans, sweet potatoes, mashed potatoes, corn, biscuits, gravy, cranberry sauce, green Jell-o salad and pie. "Uff-da," as my father-in-law says. Taken in moderation, these foods provide healthy sustenance. (OK, maybe not the sweet potatoes. Or the Jell-o salad.) Taken in excess, they meant antacids and me, bemoaning the terrible mistakes I had made.
The ecosystem in the Mississippi Delta is a lot like me at Thanksgiving, according to Nancy Rabalais, executive director of the Louisiana Universities Marine Consortium. Granted, that wasn't the exact analogy she used when I saw her speak at the 2009 Nobel Conference at Gustavus Adolphus College in St. Peter, Minn. But the comparison is apt. Rabalais studies the effects of nitrogen and phosphorus on the Delta's aquatic life.
Taken in moderation, she said, those nutrients help make fish fat and happy. Taken in excess, the fish are left in far worse shape than I was last Thursday night. Of course, unlike my holiday overeating, the fish have no control over whether their servings of nutrients are sane or gluttonous. The fish suffer, but we're responsible for the terrible mistake...
Technically, Rabalais said, nitrogen and phosphorous are good things. Without them, you don't get life. In fact, a little extra nitrogen and phosphorous actually improve fishy existence, by plumping up the plankton population. Plankton feed on nutrients, fish feed on plankton and people serve the fish up in a nice butter sauce.
Those nutrients are also food for plants. In fact, that's a big part of why we get excess nitrogen and phosphorous in the water system to begin with, because both are used as fertilizer on American farms. For example, in 2007, American corn farmers used more than 5 million tons of nitrogenous fertilizer.
But, while corn may have big appetite for plant food, but it's about as efficient at "eating" as a toddler with a bowl of spaghetti. You know the kid will wear as much food as she eats. And a corn field will often use as little as half the fertilizer it's fed. The rest just sits on the soil until it's washed away into the nearest creek by rain or irrigation. Several river systems and thousands of miles away, the Mississippi Delta vomits out water saturated with the nitrogen runoff of every corn farm in the Midwest. In the Gulf of Mexico, the nitrogen becomes a buffet for another plant--algae--which, in the sort of natural cycle that completely fails to inspire Disney song writers, first cut off light needed by underwater plants and animals and eventually die off in numbers so large that their decomposition consumes every drop of available oxygen, suffocating aquatic life for miles around. It's the Circle of Death. And it doesn't make a great musical number.
The kind of total hypoxia event that leads to a mass fish kill doesn't happen very often, Rabalais said, but the destruction doesn't have to be that vast and noticeable to still be a serious problem. Even if oxygen levels just drop a little bit, that can affect which types of fish and other marine life can live in which areas. Some will die, some will swim away...but, either way, ecosystems, human fishing businesses and food supplies suffer.
Fixing the problem is a lot harder than defining it. So many factors contribute. It's not just that the Mississippi water system happens to flow through America's agricultural heartland, or that the nitrogen load released at the Delta has tripled in the last 25 years...it's also the fact that we need to keep the big River from flooding. Historically, the River could dump some of its nitrogen load back on the land before it reached the sea. Now it's more or less firmly channeled in a way that keeps nitrogen in the water.
It's no longer a natural river," Rabalais said in her lecture. "And we've taken away natural sinks in the landscape like forests and prairies that fix nitrogen with their thick root structures. We've changed the watershed from a landscape that can absorb nutrients to a landscape that has too many nutrients put on it."
Rabalais' team has been able to document the increase in nutrients in the Gulf, but they don't have a clear way of dealing with it yet. There have been some initiatives aimed at reducing the nutrient load by reducing fertilizer runoff, she said, but most are purely voluntary and, by her account, haven't really accomplished much. This is an awkward place to leave a lecture (or a story), but Rabalais said that one of the most important things right now is making sure people are actually aware of the problem, so that they take it into account. Case in point, she said, at the same time the federal government was working with her organization to promote voluntary fertilizer-reduction initiatives, it was also pushing (via financial incentives) fertilizer-intensive corn ethanol. We may not know how to fix this problem, but we do know what doesn't work.
The image used in this story is from an actual hypoxia event, in a river in New Bern, North Carolina. Photographer BLW Photography says, "They littered the banks of the river, the steps at the park from where the water rose, and were on the surface of the river as far as you could see. Very disturbing." Used via CC.
Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.