Farming practices can ease impact of climate change on wetlands

Adopting such practices as strategic use of biomass crops and conversion of row crops to managed grass near wetlands could compensate for a Celsius degree or two of warming, South Dakota State University wetland ecologist W. Carter Johnson said.

Johnson, a distinguished professor in SDSU's Department of Horticulture, Forestry, Landscape and Parks, said that's one of the more hopeful aspects in studies that he and his colleagues have done in recent years. Johnson has worked with other scientists to develop models that can project how climate change could affect wetlands in the Prairie Pothole Region, an area of about 750,000 square kilometers, or nearly 300,000 square miles, that is home to millions of glacially formed wetlands. The Prairie Pothole Region includes some of western Iowa and Minnesota, the central and eastern Dakotas, and parts of Manitoba, Saskatchewan, and Alberta.

Study: Waterfowl may face "ecological trap"

Johnson and his colleagues published their latest study in February 2010 in the journal BioScience, building on earlier research they published in 2005. The study uses an updated model that includes data for more types of wetlands, including seasonal wetlands that are critically important in drier parts of the region.

"The broad conclusion from the study is that we see even heightened vulnerability in the newer study compared to what we concluded five years ago," Johnson said. "One of the concerns we have is what ecologists call an 'ecological trap.' We expect to have reasonably good water conditions at the start of the growing season, even in a warmer climate. So ducks may find good places in the spring and begin to nest. But the rate of evaporation is going to increase a lot if the summer temperatures are warmer. So these ducks are going to be left high and dry and won't be able to finish their reproduction, their young won't be able to complete their life cycle, and the adults may not even be able to complete their molting cycle with a shortened summer water season."

Johnson notes that he and his colleagues don't make their own climate projections. Their wetland model -- based partly on their own careful monitoring of the water cycle in selected prairie wetlands -- also relies in part on climate projections of the Intergovernmental Panel on Climate Change, or IPCC.

"We're basing our projections of what's going to happen to wetlands on their projections of what's going to happen to the climate," Johnson said.

Regional differences

The model Johnson and his colleagues use allows them to build in different scenarios -- what happens if the temperature rises by 2 degrees Celsius or 4 degrees Celsius, for example (3.6 or 7.2 degrees Fahrenheit). The latter scenario could be devastating if the region doesn't experience accompanying increases in precipitation. Johnson said that especially in the Missouri Coteau, a plateau rich in wetlands that lies east of the Missouri River but west of the James River Valley, warmer temperatures without an increase in rainfall would mean far fewer years when conditions favor waterfowl.

"We almost lose the western part of the pothole region to duck production under a 4-degree Celsius warmer climate," Johnson said.

On the other hand, parts of the eastern Prairie Pothole Region could actually be better for waterfowl under some climate change scenarios.

"In some cases the drier climate projected for the future is a benefit to wetland dynamics and productivity in western Minnesota. That's because the current condition is that wetlands are really a little bit too wet and they don't dry up enough to cycle nutrients and to be in their most productive condition."

Johnson adds that even if conditions get better in the east, the problem for that part of the region is that landowners have drained most of the wetlands. Even though the few that remain might be quite good for reproduction, there aren't enough of them to make up for the losses in the west.

Restoring wetlands in corn and soybean country would mean acquiring expensive cropland or costly easements and seeding areas to grass that are now in cropland, in addition to the cost of restoring basins that were drained.

"The cost to get enough wetlands back to compensate for lost wetlands in the west would be considerable. That isn't to say that it shouldn't be attempted or it shouldn't be looked at more carefully," Johnson said. "In the west we've got the basins and the grass, but we may not have the water. In the east, you may have the water, but you don't have the basins and the grass. This poses a conservation dilemma."

Farming could lessen the impact of climate change

One possible item of good news is that producers who manage their resources wisely could help lessen the effects of climate change on their wetlands.

"Dr. Rick Voldseth, one of my former graduate students, found that one can influence the water budget of a wetland by how that land in the watershed is farmed or managed," Johnson said. "We found that almost the worst condition, the condition that dries up wetlands, is having a heavily grassed watershed that is not utilized -- grass that is produced, but left. Even though that's good for nesting cover, it's not very good from the water budget standpoint. So if that grass were managed -- hayed or grazed responsibly -- then those water levels would improve and could actually make up for some of the water losses we expect to happen in the future under a warmer climate."

Johnson noted that many field studies, such as those being conducted at EcoSun Prairie Farms near Colman, S.D., are showing that utilizing grassland by proper grazing and haying is actually good for the grassland by stimulating root and shoot growth and speeding up the nutrient cycle.

"You could also improve the water budget of a wetland by converting row crops to managed grassland. That would reduce sedimentation rates as well. If we managed our wetlands differently, we could probably compensate for at least a degree or two of warming by improving the water budgets," Johnson said.

Growing plants such as native grasses as biomass feedstocks to make cellulosic ethanol could be another strategy to help buffer wetlands, Johnson said.

"If we grew grass and that grass were managed -- and it would be, of course, if it were targeted for harvest for biofuels -- then that would be a positive situation. The farmer would still get a good benefit from the sale of that biomass as feedstock, and the wetland would be better off for it. We'd be able to offset some of the negatives of climate change."