Appalachian hardwood forests may be getting a respite from acid rain but data from a long-term ecological study of stream chemistry suggests that the drop in acid rain may be changing biological activity in the ecosystem and hiking dissolved carbon dioxide in forest streams.
"These are unexpected results," says David DeWalle, professor of forest hydrology at Penn State. "Rising amounts of carbon dioxide in streams and soil could have implications for the forest ecosystem, and the carbon balance in general."
DeWalle and his colleagues have been monitoring stream water chemistry in the Appalachians since 1990. They are studying the effect of reduced sulfur emissions required under the Clean Air Act on the water quality of five streams in Pennsylvania.
"These streams are as pristine as you can get, and we have been sampling them nearly every month over the past 15 years," he says.
Some expected changes in stream chemistry are already showing. Water quality in the streams is gradually improving from the reduced sulfur emissions, and researchers are also seeing less nitrogen from the atmosphere and in the streams.
"This reduction in nitrogen deposition is yet to be seen in many parts of New England," DeWalle says. "We are probably seeing it earlier than others because we are pretty close to the sources of these emissions."
There have also been some unexpected changes. DeWalle and his Penn State colleagues Bryan Swistock, extension specialist, and Anthony Buda and Sarah MacDougall, graduate students, say they are recording rising amounts of dissolved carbon dioxide in all five streams.
DeWalle, whose work is funded by the U.S. Environmental Protection Agency, thinks that by reducing pollutants emitted to the atmosphere, we are creating a different set of conditions for organisms in the soil. The rising dissolved carbon dioxide in the streams, he suggests, might be traced to increased respiration by these organisms.