Biofuels may stifle global warming, but scientists warn that agricultural runoff causes new problems
Each year in April and May as farmers in the central US fertilize their crops, nearly 450 thousand metric tons of nitrates and phosphates pour down the Mississippi River. When these chemicals reach the Gulf of Mexico, they cause a feeding frenzy as photosynthetic algae absorb the nutrients. It’s a boom-and-bust cycle of epic proportions: The algae populations grow explosively, then die and decompose. This process depletes the water of oxygen on a vast scale, creating a suffocating “dead zone” the size of Massachusetts where few, if any, animals can survive.
The EPA has been working to reduce the size of the dead zone, with a goal of shrinking it to about 5,000 square kilometers—a quarter of its current size—by 2015. But a new study in Environmental Science & Technology shows that other efforts to preserve the environment may be exacerbating the dead zone. Kristopher Hite, a graduate student in biochemistry at Colorado State University, explains the implications of the study on his blog, Tom Paine’s Ghost.
The study examined the implications of a 2007 law that requires the US to annually produce 36 billion gallons of biofuels by 2022. Barring major biofuel production breakthroughs from sources like algae or microbes, most of this fuel will come from crops grown in the central US; the fertilizers and other agricultural waste they produce will flow straight down the Mississippi and feed the dead zone. Hite says the study, led by Christine Costello, found that meeting this goal will make it impossible for the EPA to reach its target reduction in the size of the dead zone. Even if fertilizer-intensive corn is replaced with more eco-friendly crops like switchgrass, the vast increase in agricultural production will cause the dead zone to grow unless preventive measures are taken.
So what can be done about it? The Society for Conservation Biology suggests that increasing the size of wetlands or other buffer zones around the source of the pollution—the farms themselves—could help.
Unfortunately, artificial wetlands have their own negative ecological side effects. As this post at Conservation Maven shows, some created wetlands are dominated by invasive species. Apparently, the heavy equipment used to build the sites also compacts the soil in a way that makes it more difficult for native species to flourish.
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