Monday, October 4, 2010

Climate change is threatening the prairie wetlands

By John Kubal
The Brookings Register

SDSU ecologist W. Carter Johnson
surveys the rolling hills of South Dakota’s
Prairie Pothole Region
For the past 15 to 20 years W. Carter Johnson, Distinguished Professor of Ecology at South Dakota State University, has been studying "climate change and how it might affect our prairie wetlands."

In terms of space and time, his subject is enormous, as is its importance to South Dakota and the nation. And Johnson, an acknowledged expert on all things wetlands, can explain his subject in terms understood by both the scientific and lay communities.

For the scientific community, Johnson and fellow scientists, some of them SDSU colleagues, had published in the February 2010 issue of BioScience an article titled "Prairie Wetland Complexes as Landscape Functional Units in a Changing Climate."

For The Brookings Register, Johnson kept it simple. In layman’s language, he explained that "wetlands" are "depressions or lower spots in the topography that hold surface water or water long enough so that the soil is changed and the vegetation is changed compared to what's present on higher ground." Think of cattails and bulrushes with a pond of water in the middle; but wetlands are not wet all the time, but wet long enough to change the soil.

And think big: A Department of the Interior U.S. Geological Survey fact sheet ("Prairie Wetlands and Climate Change – Droughts and Ducks on the Prairies") provided by Johnson notes that the "Prairie Pothole Region (PPR) contains 5-8 million small wetlands and is one of the most ecologically valuable fresh resources of the Nation."

On a map of the United States and Canada, the PPR covers 300,000 square miles across five states and three Canadian provinces. The area provides what Johnson calls "ecosystems goods and services."

Biodiversity and ducks
Under goods, Johnson cited a product such as lumber; as services, he noted hunting and purification of water.

"Those are two things that our ecosystems, the national ones, do for us," he said. "It doesn't cost us anything. They do it without charge, and they've been doing it and they're still doing it."

A PPR laundry list would note that it caters to ducks and those who hunt them; serves as winter habitat for pheasants; provides water holes for cattle in the summers; promotes biodiversity in the form of beneficial insects and mammals; holds muskrats for trapping; recharges zones to the aquifer; helps with flood water retention, with more wetlands in the landscape and fewer flooding problems in our rivers.

Contrast some of the above with the draining of wetlands and tiling of fields, which leads to water going into small streams and creeks. Johnson noted that people living along the Missouri River saw floods in the 1990s "made worse by the fact that we drained wetlands."

And the hunting? Johnson pointed out that the PPR is the "duck factory." Some estimates are that the PPR produces more than 50 percent of the ducks in North America.

With that said, Johnson moved on to what climate change could do to the PPR and what the Minnesota Conservation Volunteer magazine calls the PPR's "duck-producing powerhouses."

Climate change drives 'weather cycles'
Johnson is well-versed on climate change and the global warming debate; his BioScience article zeroes in on the PPR and its future, based on "climate-warming simulations" using computer modeling.

He called global warming "very complex," noting that a "trend line" is trending upward, or if not that, leveling off and then again climbing. "From that measure the earth's temperature is getting warmer. So that's global warming. There's no known cycle that matches this one."

As to humankind's contribution to global warming via the burning of fossil fuels, he added, "It's always difficult to tease out a single factor." But carbon dioxide (CO2) must be factored into the equation.

Again turning to wetlands, Johnson explained how "weather cycles" are considered. He said "a wetland has to dry up at some point to maintain its productivity." Wetlands standing wet all the time turn into "biological deserts."

He used the analogy of the three bears' porridge, and the need to have a weather cycle that is "just right." A just-right 10-year cycle would have one or two dry years, one or two wet years, with the six or seven years in-between being the most productive.

He explained that a weather cycle is shorter than a climate change, but climate change will drive a weather cycle change.

Johnson explained, "If the climate changes, that weather cycle's probably going to change. If we go to a warmer and drier climate, we're probably going to see in that weather cycle an increase in the frequency of dry years."

Three or four years of drier weather out of 10 years could change the wetlands and make them less productive. And looking at weather cycles, some forecasters are seeing extreme events in both directions

"We might have even longer droughts," Johnson said. "And then we might have some even longer deluge periods, which we've been having lately."

The average, however, is "going to be probably more toward the dry end of things. You'll have fewer of the deluge years or strings of years; you'll have more of the drought strings of years. So the average will turn out to be drier."

'Big deal, little deal, no deal at all?'
Johnson explained that computer modeling was used to look at the past conditions in the PPR and its role as duck factory.

"The models show highly-favorable conditions in the 20th century for duck production," he said. "We know eastern South Dakota was a really important part of the duck factory, as was eastern North Dakota."

The modelers then changed the climate by raising the temperature 2 degrees Celsius but not changing the precipitation patterns; following that was a 4-degree rise in temperature; and then came a 4-degree rise "with a little more precip and see what that combination does."

Johnson added, "When we first thought about doing this, we had no idea how sensitive the system was. Is it going to really matter if you raise the temperature 1 or 2 degrees Celsius, which is about 2 to 4 degrees Fahrenheit?"

The scientists checked and double-checked the models. Raising temperatures a "couple degrees" makes a big difference; the Pothole Region "dries out much more quickly."

And that "just right" could get out of balance. "You get stuck in one end or the other. Either it's too wet, and it stays as a pond," Johnson explained.

He said that western Minnesota and Iowa "have wetlands that are too wet to be the most productive." Farther west in South Dakota conditions are "a little drier."

The bottom line in the BioScience article was that the modeling "portrays the future Prairie Pothole Region as a much less resilient ecosystem. The western PPR will be too dry, and the eastern PPR will have too few functional wetlands and nesting habitat to support historic levels of waterfowl and other wetland-dependent species."

It notes that the conservation community faces a major challenge if the ecosystem goods and services are to be maintained "at current levels in a warmer climate."

Johnson sees the wildlife community facing a dilemma struggling with the forecasts if they're right. He added, "There's always uncertainty. There's uncertainty with the global models; we use the global projections and the local ones. We're not climatologists."

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