"It's encouraging that this wetland acted as an effective sink, even when runoff from fertilized fields was especially high," Mitsch said. "Of course, that could change as time goes on, however."
Most of the water entering the wetland came as runoff from farm fields, and nitrate and phosphorus levels all peaked after fertilizer application in the spring. Still, the wetland was able to retain a significant portion of these nutrients.
Algae thrive on phosphorus and nitrogen. While phosphorus is more of a concern in freshwater areas, as freshwater algae thrive on this nutrient, nitrogen is a considerable problem in the Gulf of Mexico.
Each spring, the rush of chemicals that runs into lakes and streams in the Mississippi watershed ?an area encompassing about 40 percent of the United States ?ultimately turn more than 7,000 square miles of the Gulf of Mexico into a "dead zone," a condition known as hypoxia.
Hypoxia happens when excess nutrients, such as nitrates and phosphorus, accumulate in a body of water and cause excessive growth of algae and algal blooms. These blooms thrive on the nutrients and deplete the water of nearly all of its oxygen.
Wetlands experts estimate that the American Midwest has lost about 80 percent of its wetlands in the last two centuries, compared to a 50 percent loss overall in the lower 48 states.
About 577,000 acres of wetlands have already been created or restored under current conservation programs, Mitsch said. But about 10 to 25 times that many are needed in the Mississippi watershed region in order to see a significant reduction of nitrogen levels in the Gulf.