WRM 2000 Decision-Making Process

Ecological value

Estimating the ecological value of your current impounded river system versus a free-flowing river system may be the hardest of all values to estimate in this module. However, it may be a very important consideration in your decision-making process. Most ecologists and indeed many other individuals believe that the natural world has an intrinsic value of its own. The waters, fish, and other biota (animals, insects, plants, and the like) in an ecosystem have some value to your community and region. The natural system has value regardless of whether humans are there to view and appreciate it (aesthetic value) or enjoy it via some type of recreation (recreational value). Another way of thinking about ecological value is to think of it as the value of habitat, a term sometimes used synonymously with ecosystem. This module will attempt to estimate the ecological value of the natural systems under the options of repair and removal of your small dam.

Biologists have long known that fish can’t get past dams to reach upstream spawning grounds. More recently, scientists have discovered that dams also have other environmental effects. For example, when a dam is built, major ecological changes may occur: the river’s natural microorganisms disappear, new aquatic plants appear, and invading fish displace native species.

Figure 16. Main picture: Fish struggling to migrate upstream at a dam. Inset: A fish ladder. (Photo courtesy of Stephanie Lindloff, River Alliance of Wisconsin.)

Because the water temperatures in free-flowing rivers tend to be cooler than in lakes impounded behind dams, the types of fisheries are generally different between dammed and free-flowing rivers. Free-flowing rivers tend to support warm, cool, and cold-water fish species, while the lakes behind dams tend to support cool and warm-water species.

Wetlands can be an integral part of a river system, free-flowing or impounded, and represent the transition between terrestrial (dry land) and aquatic environments. Because wetlands are highly productive areas, they have been historically drained for various uses, especially agriculture. In the past few decades, scientists have realized the ecological value of wetlands for plant and animal species diversity and biological productivity and for improving water quality. As such, many initiatives are underway to protect remaining wetlands, restore former wetlands, and even create new ones.

For the repair and removal scenarios, estimating how much the community values the ecology or habitat of each situation in terms of dollars is difficult because of the various problems already mentioned. Survey questions to help make this estimate might be: “If you had to pay some of your own money to ensure that wetlands remain in their current locations around the lake, how much would you be willing to give?” and “If you had to pay some of your own money to restore wetlands to their original locations next to the river, how much would you be willing to give?” The average per-person value of each wetland scenario can then be multiplied by the total population to give the total value of the wetland scenarios. An example calculation for purposes of the worksheet would look as follows:

($10 per person estimate) x (5000 people in the community) = $50,000 total value of wetlands

Similar questions can be used to assess the value of fisheries, waterfowl and animal habitat, or any other part of the ecology of each situation to your community. Your community should determine which are the most important aspects of the ecology of your community and then ask the appropriate questions.

An additional issue here may be that the value placed on fish or waterfowl by your community may be inseparable from the value they place on fishing and hunting for recreation. In using survey questions to estimate how people value fisheries and waterfowl habitat, it will be important to not “double-count” recreational values. You may want to rely on a question or set of questions that estimates values for fisheries and the recreation they support under recreation on the worksheet, and questions that ask only about other biota under the biological section of the worksheet. Again, putting dollar estimates on the ecological value of a given site is a tough task without definite answers.

Repair

Wisconsin Department of Natural Resources and the U.S. Fish and Wildlife Survey have the resources to perform rigorous surveys of the fish population currently behind the dam. Staff from these agencies will be able to make recommendations about improving the dam to aid fish migration, which may help the fishery in the impoundment and the river above the impoundment. Such improvements include fish passages and fish ladders, but it should be noted that these structures still do not allow for completely free fish migration. Wisconsin Department of Natural Resources and U.S. Fish and Wildlife Service personnel can also determine whether the dam provides a barrier to the upstream migration of unwanted invasive fish species and how to prevent their migration during and after the repair work. Also, simply talking with local anglers is likely to provide insights into the types of fish currently present and the health of the fishery in the impoundment.

Fish habitat will be disrupted during the drawdown of the impoundment for the actual repair work on the dam. Not only will the impoundment be low during the drawdown, the sediments of the impoundment bed will be exposed and easily eroded. If large amounts of sediment are eroded during the repair work, the fishery may be harmed. The overall plan for repairing the dam should include a plan for managing sediment during the drawdown.

The impoundments behind dams also support other animals including waterfowl (ducks, geese, pelicans, seagulls), amphibians (frogs, salamanders), reptiles (turtles, snakes) and mammals (otters, muskrats). Most of these animals can also find habitat in free-flowing river environments. Personnel from the Wisconsin Department of Natural Resources and U.S. Fish and Wildlife Service can assess the habitat for these types of animals.

The wetlands adjacent to an impoundment probably exist because of the hydrologic changes the dam has made to the river system. As long as the dam is kept in place, these wetlands will remain and continue to play their important ecological roles. During the drawdown of the impoundment for repair work on the dam, these wetlands may receive less water and even temporarily dry up. Once the impoundment is refilled, the wetlands should return shortly thereafter.

Examples: Repair

Lemonweir Dam, Lemonweir River, Wisconsin

Maintain warm water fishery and large area of wetlands that are prime waterfowl habitat

Onieda Dam, Iron River, Wisconsin

Prevent invasive sea lampreys from migrating upstream from Lake Superior without installation of an additional fish barrier

Removal

Whether and how the character of a fishery may change with the removal of a dam will be site-specific. Changes in the fishery are likely to result from the change in the speed of flow, the water temperature, and the free migration of fish throughout the length river. Rivers may support warm-water and cold-water species of fish through the seasonal migration of fish. The removal of a dam may provide the opportunity to restore cold-water fishery habitat, which is important because cold-water habitat is much less common because it is the result of spring fed river systems. (See Dam and River Ecosystem Basics module.) Consequently, cold-water fisheries cannot be created, but only restored by removing dams. Dams as a barrier to the upstream migration of desirable fish seems to be a negative impact; however, a barrier to migration is desirable in dealing with unwanted invasive species. The Environmental Assessment that the Wisconsin Department of Natural Resources performs will provide insight as to the possible changes in the character of the fishery. The Environmental Assessment will also have information about the effects of dam removal on other types of species, such as plants, waterfowl, mammals, reptiles and amphibians. Free-flowing river environments provide habitat for all of these types of species.

Sediment management during and after the dam removal is critical to protecting the fish and other species in the river. Just as sediment is an issue with dam repair, it is even more critical with dam removal, as the drawdown will be permanent. The dam-removal plan should include a sediment-management plan, either removing the sediment or stabilizing it with vegetation or other means.

Figure 17. Coarse stream gravels provide necessary habitat for fish and other aquatic organisms.

Because the wetlands adjacent to the impoundment are the result of the impoundment changing the hydrology of the area, if the dam is removed, the wetlands adjacent to the impoundment may well dry up (or at least change significantly). However, wetlands are likely to form in the floodplain of the newly free-flowing river. These “new” wetlands may not exactly be new; they may likely occupy areas that were wetlands before the dam was built and the resulting impoundment flooded them. At any dam site, the change in the type and extent of wetlands caused by dam removal will be different. These changes can be difficult to predict and are highly dependent on the topography, soils, and hydrogeology of the area. Many times there is very little change in type and areal extent of wetlands present, but only a change in their location. An Environmental Assessment performed by the Wisconsin Department of Natural Resources will provide information as to what types of wetland changes to expect. The full establishment of these new wetlands in terms of plant and animal species diversity will take some time, perhaps even years or decades.

Examples: Removal

Oak Street Dam, Baraboo, Wisconsin

Little new wetlands or elimination of old wetlands
Expect carp to migrate away (downstream); smallmouth bass to come back
Also hope that paddlefish and sturgeon return
No threatened or endangered species present
Free migration of fish and other species

Deerskin Dam, Deerskin River, Wisconsin

Wisconsin Department of Natural Resources predicts no net change in amount, but changes in locations and types of wetlands
Expect trout to migrate into free-flowing area
Warm-water fish will migrate downstream to next dammed lake
Ducks will find new habitat, either at site or elsewhere
Free migration of fish

Orienta Dam, Iron River, Wisconsin

Installation of a sea lamprey barrier designed by Wisconsin Department of Natural Resources and the U.S. Fish and Wildlife Service after dam removal

Ward Paper Mill Dam, Prairie River, Wisconsin

Expected net gain in area and diversity of wetland types present (four different wetland habitats)
Expect trout to be able to tolerate free-flowing stretch
Some warm water fish will migrate downstream to Merrill Hydro Dam on Wisconsin River
Ducks will find new habitat at restored site or elsewhere
Provide better habitat for wood turtles and no change for bald eagles (both threatened species)
Free migration of fish from mouth at Merrill (confluence with Wisconsin River) to headwaters of Prairie River (approximately 221 miles)

Edwards Dam, Kennebec River, Maine

Officials responded to concerns that the dam removal would adversely impact local wetlands. It was said that there would still be wetlands after removal, but that some local wetlands might now be drier during part of each year. In short, dam removal would likely result in different kinds of wetlands than before removal of the dam. Source: Central Maine Morning Sentinel, 9/29/98.

Next section: Appendix

URL: http://www.ies.wisc.edu/research/wrm00/econeco.htm