By Lynn Betts
There was a time when farmers considered natural wetlands to be wasted land, since they couldn't be farmed. That's not the case anymore, with all the emphasis on nutrient reduction in water that leaves the farm.
In fact, as farmers, conservationists, and concerned groups continue to look for ways to make water cleaner before it leaves the farm, they're actually creating wetlands where they fit the landscape.
"Restored or constructed wetlands -- properly placed -- would be my number one choice of all the edge-of-field practices available to reduce the amount of nitrates in water that leaves the farm," says Dr. Maria Lemke, an aquatic ecologist with The Nature Conservancy in the Mackinaw River Watershed in Illinois. "The other practices have their niches, too, and there are places wetlands won't work. But where they fit, they have so many advantages."
Lemke and the TNC have worked a number of years with researchers and farmers alike to find and establish practices in the Mackinaw River Watershed that will cut the amount of nitrates in water. She's been part of a team that's helped encourage and assist farmers in speeding adoption of soil-saving practices like grassed waterways, stream buffers, and strip till in an effort to improve water in two water supply reservoirs that serve 80,000 people in the city of Bloomington.
"We got more practices on the land, but what we found was, after seven years of monitoring, we had no significant changes in nitrate-nitrogen in the water," Lemke says. "We knew then we had to focus on practices that specifically reduce nitrates coming from tile water."
Why a wetland should be considered first
Lemke offers half a dozen reasons to consider wetlands as a high priority practice for nitrate removal if they fit your land.
1. High rate of nitrate removal. "We've found a wetland that's 5% to 6% of the area being drained by tiles removes about 50% of the nitrates from tile water," says researcher Dr. David Kovacic of the University of Illinois. "Wetlands with that ratio give you the most bang for the buck -- larger wetlands have diminishing returns."
"Research at the Franklin Family Research and Demonstration Farm in McLean County shows us these wetlands work," says Lemke. "We think we've got the answer to the question of how large wetlands need to be to effectively reduce nutrients from tile water. Now we have to figure out how to expand their use to a watershed scale."
2. Capture both underground and surface waters. Our focus is tile drained water, since that's the missing piece for nitrate removal after good soil conservation and runoff measures are taken. Since nitrates are soluble in water, both underground and surface waters need to be treated before leaving the farm. While a bioreactor may remove as much nitrate as a wetland, it will only treat tile water. Soil saving practices that keep soil in place do a good job for phosphorus reduction in streams, but don't capture the nitrates in tile waters. Restored or constructed wetlands, on the other hand, can remove nitrates from both surface runoff water and tile water that is directed into the wetland.
3. Low maintenance, last a long time. Properly designed wetlands will function for many years with very little maintenance. Bioreactors and restored oxbows have a shorter lifespan.
4. Offer top shelf wildlife habitat. Some wildlife experts say no single practice offers more wildlife habitat than a wetland. Habitat isn't limited to amphibian and migratory waterfowl -- pheasants, deer, raccoons, and many bird species frequent wetlands as well. Of course, an underground bioreactor has grass as a surface but is very limited in habitat.
5. Diversify the landscape. Since wetlands offer shallow water, plants that thrive in that environment are encouraged to grow there. Those plants and water also attract a diversity of animal life.
6. Incentive payments available. While most water quality practices qualify for some kind of incentive payments, USDA has a number of programs that may pay most of the costs of restoring or constructing wetlands. One USDA program, the Conservation Reserve Program, pays half the cost of building the wetland, offers a $100 per acre signing incentive, and offers annual rental payments for up to 15 years as well.Betts writes from Johnston, Iowa.