While swarms of flying insects may have little appeal for most people, USGS biologist Thomas Edsall says the clouds of burrowing mayflies emerging from western Lake Erie this summer are a welcome sign of an ecosystem in recovery.
"They're telling us that the water's clean out there," Edsall says.
Burrowing mayflies are large aquatic insects that spend most of their lives -- about two years -- in their larval form, living in shallow bottom sediments of lakes. On the bottom of western Lake Erie, larval mayflies -- known as nymphs -- once numbered in the hundreds per square meter. But populations decreased dramatically in the 1950s due to deteriorating water quality, and throughout most of the next three decades burrowing mayflies were virtually absent from their former Great Lakes habitat.
For the last five years, however, a remarkable recovery has been under way. Edsall and his colleagues at the USGS Great Lakes Science Center report that nymphs in western Lake Erie have increased from near zero to numbers approaching those of the early twentieth century.
Edsall says the mayfly recovery is a strong sign that improvements in water quality, which have been taking place since the 1970s, have resulted in a healthier, more normally functioning ecosystem. "This is a real tribute to the EPA's enforcement of water pollution control laws, such as the Clean Water Act and U.S. and Canadian cooperation through the Great Lakes Quality Agreement," he says.
USGS and Canadian biologists have used several different methods to determine
the past distribution and abundance of burrowing mayflies in Lake Erie and to
understand how the insects have responded to different forms of water and
sediment of contamination. Sediment core samples, dating back to about 1740,
contain jaw parts and other preserved remains that provide a continuous record
of burrowing mayfly densities in different regions of the lake. Other
information comes from pe
Contact: John Gannon
United States Geological Survey