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Study: Man-made reservoirs more likely to spread invasive species

Anita Weier  —  10/15/2008 4:38 pm

Man-made reservoirs are contributing to the spread of non-native species in Wisconsin lakes, a study has found.

In a comparison of natural lakes and reservoirs created by damming rivers, the reservoirs were up to 300 times more likely than lakes to harbor invasive aquatic species, according to the study published in September in the journal Frontiers in Ecology and the Environment.

Moreover, the reservoirs were providing "stepping stones" for the invasive species to move into the lakes, the study found.

Jake Vander Zanden of the University of Wisconsin-Madison, Pieter Johnson of the University of Colorado-Boulder and Julian Olden of the University of Washington looked at five common aquatic invasive species -- Eurasian watermilfoil, spiny water flea, zebra mussel, rusty crayfish and rainbow smelt -- in 1,281 lakes and reservoirs in Wisconsin and Michigan's Upper Peninsula.

The reservoirs had greater risk of invasion by each of the five species, ranging from a modest two-fold risk increase of harboring watermilfoil or rusty crayfish to 300 times the risk of containing spiny water flea. Reservoirs were also more likely than natural lakes to host multiple invasive species.

Reasons likely included physical and biological differences between lakes and reservoirs.

The reservoirs were generally lower in water clarity, higher in number of boat landings, and larger in surface and watershed area. They were also more likely than natural lakes to be accessible by humans and more likely to have upstream lake or river connections.

But even in accounting for such differences, the man-made lakes were more likely to have invasive species, Vander Zanden said, a professor at the UW-Madison Center for Limnology,which is the study of inland waters.

"We looked at where they overlap -- where they are the same. If situations such as water quality and lake size are equal, there is still more likelihood that the reservoirs have invasives," he explained.

"The cause may be something we were unable to measure, such as more people using them or water level fluctuations. But we do know that if we change the way water flows on the landscape, we increase the spread of invasive species."

Another possible reason why man-made reservoirs might tend to have invasive species is that they typically contain young, less established ecological communities that might allow invasive species to gain a foothold, said Johnson, a former UW-Madison researcher/graduate student who is now an ecologist at UC-Boulder.

The reservoirs also appear to increase the invasion risk of natural lakes by providing an entry point where they can spread to nearby lakes. For example, the spiny water flea was first discovered in inland Wisconsin in the Gile Flowage, a reservoir situated halfway between Lake Superior and the Northern Highlands Lake District. It has since spread to at least one natural lake in the region -- Stormy Lake in Vilas County.

Invasive species can have profound ecological and economic impacts, including changing water quality, fouling boats and industrial equipment, and competing with or preying on native species.

"Invasions are one of the major drivers of global change, one of the major ways we are changing the surface of this planet," said Vander Zanden.

Much of the data used for the study came from resource management agencies, including the Wisconsin Department of Natural Resources and the Great Lakes Indian Fish and Wildlife Commission. The researchers hope the study will help guide and prioritize management and eradication efforts.

"Targeted prevention and control efforts can give more bang for the buck," Johnson says. "Impoundments may be a good target for those efforts."

Anita Weier  —  10/15/2008 4:38 pm