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MADISON – Property owners’ individual projects that change the natural character of lake shores collectively harm water quality and change fish communities in their lakes, a recently published study of 17 Wisconsin lakes shows.
"People see what they do on their property as a relatively minor change – to them, it involves only a small part of the lake so it’s hard to imagine that it has an effect," says Marty Jennings, a Department of Natural Resources ecologist who was the principal investigator in the study. "But what we’re seeing is a large number of changes – vegetation clearing, paving, road construction, fertilizing lawns, installing seawalls and riprap. All of these things add up to something that can harm water quality and change fish communities in a lake."
Just since 1990, the number of people seeking permits to build seawalls, to install riprap, or to otherwise modify waterways has tripled, and the number of homes along Wisconsin’s 15,000 lakes has increased an average of 216 percent since the 1960s.
Jennings and other researchers including University of Wisconsin Stevens Point staff Michael Bozek and Gene Hatzenbeler, set out to investigate how these common modifications of individual shore lines affect the fish populations found at those specific sites. They also wanted to explore how fish communities differ among lakes with different levels of cumulative impacts from all forms of human activity.
The researchers picked 17 lakes across Wisconsin which all had some homes along their shorelines, although some had more homes than others, and the surrounding land was used for different purposes: farming, residential, forestry, etc. The researchers gathered existing data about the water quality in the lakes, and randomly selected 18 sites on each lake that featured three kinds of common shoreline treatments they wanted to investigate: seawalls, riprap and no structures. They used electroshocking surveys and netting to sample and document the kinds and numbers of fish found at each of the six sites representing the different shoreline treatments.
Their results, published in July in the North American Journal of Fisheries Management, indicate that modifying local habitat by installing a seawall or riprap led to changes in the number of fish species found in that local area. Local areas with no treatment tended to have a greater variety of species than local areas with a seawall.
The fish aren’t responding to the treatment per se, but what that treatment does to their habitat, Jennings says. Seawalls, for instance, simplify fish habitat by replacing natural shoreline that might have had rocks, logs, undercut banks, and other places for fish to hide, with a smooth surface. Riprap still allows those hiding spots at a local site, but converting a whole lake shoreline to riprap reduces overall variety of habitat found throughout the lake.
But more important than showing small site-specific changes, Jennings says, is that their research shows that contrary to popular perception, individual projects do count. Their cumulative impact spurs a broad shift in the kind of fish found in a lake. Species that can’t survive in lakes with poor water quality, i.e. low levels of dissolved oxygen, are replaced by species that can tolerate poorer water quality.
"When we looked at differences across lakes, the proportion of fish that are intolerant species like muskies and darters and smallmouth bass declined as we saw more overall development on the lake and more nonpoint source pollution," Jennings said.
The study findings suggest, he said, that conserving small habitat fragments – i.e. individual waterfronts – and having the regulatory systems that aim to do so, make sense if society wants to protect water quality and lake ecosystems.
A follow up study now underway on 35 lakes in northern Wisconsin seeks to more comprehensively examine how modifications to shore lands and land surrounding a lake affects habitat and fish communities.
Researchers will be using satellite images to determine land use around the lake, and will use aerial surveys to count the number of homes per mile of shoreline, and will look at all modifications to individual sites, not just seawalls and riprap.
"So far, our results indicate that the type of land use around a lake and the density of development affects the habitat and fish that we find in a lake," Jennings says. "Each of these small things that changes the natural character of lakes adds up."
FOR MORE INFORMATION CONTACT: Marty Jennings (715 ) 635-41606
Uploaded: 9/2/1999
Uploaded: 9/2/1999