Working on an isolated, undeveloped suite of lakes in Michigan's Upper Peninsula, the Wisconsin scientists were able to manipulate the flow of carbon between an entire, intact ecosystem and the atmosphere by placing either minnows or bass at the apex of the lake food web.
Bass, by preying on the minnows that consume algae-grazing zooplankton, effectively increased the flow of carbon to the atmosphere by freeing zooplankton from their predators. The booming zooplankton populations grazed the algae to the point where they were no longer a force to use the lake's excess carbon. The lakes, in effect, became pumps, expelling unused carbon to the atmosphere.
In lakes dominated by minnows, whose menus include algae-eating zooplankton, burgeoning algae populations and their photosynthetic requirements resulted in a carbon deficit, and the lakes become carbon sinks, drawing carbon directly from the atmosphere.
"This effect of fishes on gas exchange results from the changes in aquatic food webs that are regulated by the species of fish present in a particular lake," said Schindler.
The changes in lakes, Schindler emphasized, will not have implications for global climate. However, the new understanding of the processes that alter the exchange of carbon dioxide between lakes and the atmosphere can be generalized to other ecosystems such as oceans.
"Although the consequences ... are much less known for marine systems than for lakes, we should expect that the ecological responses to exploitation are similar in many ways," Schindler said.
The work done by the Wisconsin scientists was funded by the National Science Foundation and conducted under the auspices of the UW-Madison Center for Limnology.
CONTACT:
'"/>
Contact: Stephen Carpenter
srclake@macc.wisc.edu
608-262-8690
University of Wisconsin-Madison
10-Jun-1997