Biological invasions increasing due to freshwater impoundments, says CU-Bou...(servoir construction and the conversion ...)

The team looked at data from 4,200 lakes and more than 1,000 impoundments across Wisconsin and the Upper Peninsula of Michigan. The study showed non-indigenous species are up to 300 times more likely to occur in impoundments than in natural lakes, increasing the invasion risks for natural lakes.

"Collectively, these results suggest the benefits of building more reservoirs should be carefully balanced against the potential negative consequences, including increased biological invasions," Johnson said.

The study was funded in part by the National Science Foundation.

The study showed impoundments significantly reduced the average distance between "uninvaded" lakes and lakes inhabited by zebra mussels, increasing the number of natural lakes considered vulnerable to zebra mussel invasion by 50 percent.

The zebra mussel, first introduced into the Great Lakes in 1987 and which affects plankton abundance, nutrients and water clarity, also has caused declines in native mollusks and fouled industrial pipes. Another invader, the Eurasian watermilfoil, was introduced in the United States in 1944 through the aquarium plant trade and is now in 44 of the 48 contiguous states, causing changes in both vertebrate and invertebrate communities, said the team.

Other invaders posing threats include the Eurasian spiny water flea -- which colonized the Great Lakes region in the 1980s and which affects lake diversity and fouls commercial equipment -- and rusty crayfish, native to the Ohio river drainage and which has been shown to upset the balance of natural ecosystems, Johnson said.

A fifth, the rainbow smelt -- indigenous to marine environments -- has spread through the Great Lakes region and into the Mississippi and Hudson Bay watersheds, impacting local fish popu
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