Dams increase risk of alien aquatic invaders

ACS Publications, via Environmental Science & Technology: In the unfolding global biodiversity crisis, freshwater ecosystems are losing even more species than terrestrial or marine environments are. Evidence points to dam construction and biological invasions as major culprits in these losses. In the U.S. alone, more than 80,000 major dams and 2.5 million smaller impoundments (such as reservoirs) have altered natural hydrology, and nearly 1000 introduced species now disrupt native aquatic systems. A new study published in the September issue of Frontiers in Ecology and the Environment (2008, 6, 357-363) concludes that dam construction and biological invasions are closely linked.

Pieter Johnson of the University of Colorado Boulder and colleagues analyzed conditions in 4200 natural lakes and 1081 impoundments in Wisconsin and Michigan. The team looked at levels of boating activity; water characteristics favorable to colonization by invaders; and geographical distribution for five widespread nuisance species: the plant Eurasian water milfoil (Myriophyllum spicatum), zebra mussel (Dreissena polymorpha), spiny water flea (Bythotrephes longimanus), rainbow smelt (Osmerus mordax), and rusty crayfish (Orconectes rusticus). They found that these species were 2.4–7.8 times more likely to occur in the dammed water bodies than in the natural lakes. Furthermore, the impoundments were significantly more prone to hosting multiple non-native species.

Boating and fishing activities were implicated in the introduction and spread of the aliens, Johnson says. “Zebra mussels attach to boat bottoms, milfoil clings to boat trailers, and smelt and crayfish were previously used as bait, although they’re now illegal,” he adds…..

The Glen Canyon Dam on the Colorado River, USGS, Wikimedia Commons