Appendix 2

This appendix presents a synthetic summary of current scientific understanding of the structure and dynamics of the actors, linkages, and ecosystems in Wisconsin's Northern Highlands Lake District (NHLD). This synthesis was conducted for the purpose of understanding the use and production of aquatic ecosystem services. It was used to develop the scenarios presented in the main text by 1) refining the key variables that were considered, 2) defining the key uncertainties that the scenarios would explore, and 3) qualitatively supporting the development of the scenarios.

The 2000 census estimated that about 43,000 people reside in the NHLD (U.S. Bureau of the Census 2001). As seen in Fig. 2 of the main text, the population is centered around a few small towns. The residents of the NHLD are different from those of Wisconsin as a whole. They tend to be older, are more likely to be Native American, and usually have lower incomes than the general population. Currently, Native Americans make up about 9% of Vilas County, which is where the Chippewa Lac du Flambeau reservation is located (U.S. Bureau of the Census 2001). In 1990, the average per capita income of Native Americans was 40% of that of the overall population of the NHLD (U.S. Bureau of the Census 1992). The population of this region has been changing due to the emigration of young people and the much larger immigration of older people.

Tourism is very important to life in the NHLD. It is closely linked to lakes and the northern landscape. Major recreational activities include fishing and boating in summer, and hunting, snowmobiling, and ice fishing during the colder months. Many visitors also participate in hiking, bicycling, and bird-watching. In Oneida and Vilas counties, approximately $340 x 10⁶ dollars or $6500/resident are spent per year on tourism activities (Wisconsin Deptartment of Tourism, unpublished data). There are many tourism-related facilities in the NHLD. There is an extensive network of trails, many public boat landings, campgrounds, and large amounts of public land. Private ventures that cater to outdoor recreational enthusiasts include numerous resorts, golf courses, fishing and hunting guides, and other recreation-related industries.

Fishing, one of the primary human uses of the northern lakes, occurs year round (Staggs et al. 1990). Peak fishing effort in this region occurs during the summer months, although the highest catch rates are in spring and early winter (Fayram 2000). Fishing pressure is unevenly distributed across the region (Staggs et al. 1990; T. D. Beard Jr. et al., unpublished manuscript). Fish densities can be good predictors of angling effort on particular lakes in this region, and anglers are attracted to the lakes that appear to offer them greater harvest opportunities (T. D. Beard Jr. et al., unpublished manuscript). Management policy also influences lake choice, with more effort directed at lakes with less stringent regulations (T. D. Beard Jr. et al., unpublished manuscript). The open-access fisheries of this region have led to lakes that have generally similar catch rates, fish densities, and fish catchability (Hansen et al. 2000).

Boating is a highly valued recreational activity in Wisconsin. Most boats are used for fishing, but other kinds of boats are becoming more common. The impacts of motorboats on lake ecology include reductions in water clarity and quality, increased shoreline erosion, damage to aquatic macrophytes, and interference with wildlife (Asplund 2000). Most studies of boating impacts have been short term. The physical effects of waves and turbulence appear to be more serious than pollution from motorboats. The most striking impacts have been found in shallow and near-shore waters, where increases in nutrients, turbidity, and shoreline erosion and decreases in aquatic plant biomass are associated with boat traffic (Asplund 2000). Reed-Anderson et al. (2000) found that the distribution of boats on lakes was related to lake area, distance from major roads and population centers, measures of public facilities on lakes (i.e., lots of boat ramps and campgrounds), and the perception of good fishing. In general, isolated lakes high in the landscape and lacking public facilities have fewer boats. Currently in Wisconsin, personal watercraft are required to operate at no-wake speeds within 200 m of shore, and other motorboats are required to operate at no-wake speeds within 100 m of the shore (Asplund 2000).

Many people visit the NHLD as tourists for part of the year. Some of these people stay in motels, cabins, or campgrounds, whereas others have second homes. Most of the houses in the NHLD are in Vilas and Oneida counties. Summer homes make up almost 60% of the housing units in Vilas County. Most of the ecological impacts of settlement are probably produced by nonresidents (Fig. A.1). For example, many people appear to manage their land for aesthetic rather than commercial values. An economic analysis of forest management decisions in northern Wisconsin estimated that people found the nontimber value of trees to be more than twice the potential timber revenue and that this value increased from the 1960s to the mid-1980s (Scarpa et al. 2000).

Figure A.1. Housing occupancy in northern Wisconsin vs. Wisconsin as a whole in 1990 (U.S. Bureau of the Census 1992).

Because the population of northern Wisconsin is sparse, the state government plays a substantial role there. The use of natural resources is regulated primarily by the Wisconsin Department of Natural Resources (DNR). The state also owns the 14% of the NHLD that is inside the Northern Highland-American Legion State Forest.

Local government influences local land-use decisions and zoning. However, federal and state regulations provide a regulatory framework for issues such as land conversion, pollutant emission, the protection of endangered species, and fish and game management.

Another influence on ecological management in the NHLD was the reconfirmation of Ojibwe treaty rights in 1983. Following federal occupation of northern Wisconsin, various groups of Native Americans signed treaties with the U.S. government, surrendering their sovereignty in exchange for the right to hunt, gather, and fish on the lands ceded to the federal government (Loew 2001). As the result of a series of court decisions, fisheries in northern Wisconsin are now regulated by the Wisconsin DNR. The Great Lakes Indian Fish and Wildlife Commission is responsible for monitoring the off-reservation extraction of natural resources by tribal members. Spearfishing is a separate fishing activity that is conducted only by Native Americans. The resumption of Native American spearfishing was originally protested by non-native sportfishers and sportfishing business interests, and the issue is still a source of tension between Native Americans and other people in the NHLD.

The management of individual lakes is also influenced by lake associations. Lake associations are groups of people who own lakeshore property and work in partnership with the state government and the DNR to achieve mutually agreed upon goals for the lake. Lake associations are local organizations that can operate dams, maintain lake access, remove aquatic plants, purchase wetlands, improve fish habitat, and stock fish.

The institutional regulation of fishing, lake development, and other extraction activities is a necessary condition for the sustainability of these activities. However, the success of particular institutions depends on both human behavior and ecological dynamics. In the following sections we describe the ecological processes that influence fish populations and water quality.

The fish communities of the larger lakes in the region are dominated by walleye (Stizostedion vitreum), the primary piscivore (Becker 1983). These larger lakes are a focus of human use and fish management (Beard Jr. et al. 1997, Fayram 2000, Nate et al. 2000). In smaller lakes, fish communities are usually dominated by either mudminnow, Umbra limi, or bass (Tonn and Magnuson 1982). Mudminnow lakes commonly contain shiners and dace and generally lack specialized piscivores. These lakes are usually small and shallow. Bass lakes commonly contain bluegills (Lepomis macrochirus) and yellow perch (Perca flavescens). Bass lakes also tend to be small, but these lakes are deep and isolated with high oxygen levels in the winter. Panfish such as bluegill are the most popular fish in Wisconsin. Consequently, the small bluegill-dominated lakes are valuable for fish, whereas mudminnow lakes are not.

Walleye are the main sport fish and the subject of treaties with Native Americans. Consequently, walleye management has been contested and has become the focus of considerable management and research activity. Over the past several decades, walleye population densities have been stable (Fayram 2000), although there has been substantial year-to-year variation within individual lakes (Hansen et al. 1998). There is little information about the dynamics of other species, except in a few lakes used for long-term ecological research (see http://limnosun.limnology.wisc.edu/).

People have substantially influenced the fish communities of the NHLD. Within the fish communities of individual lakes, community structure is typically controlled by age- and size-dependent competition and predation (Colby et al. 1987, Kerfoot and Sih 1987). Fishing, fish management, the introduction of species, and habitat modification have all transformed the fish communities across the NHLD. Fishing and fish stocking can strongly influence fish populations (Carpenter et al. 1994). Fishing changes the age and size structure of fished species, and fish stocking changes the genetic mix of fish populations. Both these changes can in turn influence nonfished species that are also present in lakes. Case studies have shown that the response of a particular fish community is dependent on specific circumstances (Colby et al. 1987).

Indirectly, people have substantially altered aquatic ecosystems by introducing new species. In some lakes, rainbow smelt have driven the native planktivore cisco, Coregonus artedii, extinct and reduced the abundance of yellow perch (Hrabik et al. 1998). Hrabik and Magnuson (1999) modeled the spread of smelt based on current rates and predicted that lakes with less human access would provide important refuges for native fish communities. The invasion of the rusty crayfish has negatively affected macrophyte communities, fish, and other crayfish. Although invasions are difficult to predict (Lodge et al. 1985), further introductions of non-native species into the NHLD seem highly likely.

Many lake organisms require the habitat structure provided by coarse woody debris (CWD) and macrophyte beds for growth and survival. Physical structures protect young fish and macroinvertebrates from predators and provide food for young fish (Crowder and Cooper 1982). Some fish appear to grow more slowly when the amount of CWD is limited (Schindler et al. 2000). The distribution and abundance of CWD is influenced by climate, soils, stream flow rates, and topography as well as forest age, density, and composition. Humans have decreased the production of new CWD by removing trees from the edges of lakes and have even removed CWD from within the lakes themselves. Both the density and basal area of CWD have been observed to decline as the density of shoreline cabins increases (Christensen et al. 1996). Consequently, unless people stop removing CWD and riparian trees, the increasing settlement of lake shorelines will homogenize and simplify lake habitat.

Most lakes in the district receive the majority of their water from direct precipitation; many are seepage lakes with no surface-water inputs or outputs and are connected only by groundwater flow. Consequently, they are highly sensitive to changes in the precipitation regime. Short-term dry and wet periods related to the El Niño Southern Oscillation have caused lake level fluctuations of up to a meter (Webster et al. 1996). Land use in catchments affects the delivery of water to catchments and lakes through its effects on infiltration and evapotranspiration rates (Stednick 1996).

From an anthropocentric perspective, the quality of water depends on how it looks, i.e., whether people find it aesthetically pleasing; whether it is healthy, which depends on the presence of toxins and disease-causing organisms; and its ability to maintain healthy fish populations. The interrelated factors that determine water quality are water color, trophic status, the presence of toxins, and the presence of disease-causing organisms.

Northern highlands lakes show a wide range of water color, mainly because of variations in dissolved organic carbon (DOC) concentrations (Fig. A.2). Lakes with high concentrations of DOC appear brown or "stained," and lakes with low DOC concentrations appear blue or "clear." Most DOC is derived from the soils or wetlands in the surrounding catchment (Hope et al. 1996, Gergel et al. 1999). The amount of DOC entering a lake from the catchment may be altered by drought, fire, or long-term weather patterns (Schindler et al. 1992, Schindler et al. 1997b). Inputs of DOC to lakes could also change with residential development as wetlands are drained or filled in.

Figure A.2. Lake attributes in northern Wisconsin. Most lakes are relatively clear and somewhat basic. a) Lake acidity, b) lake color (platinum units), c) lake algal biomass (Chl-a).

DOC influences many properties of lake ecosystems (Jackson and Hecky 1980, Jones 1992, Williamson et al. 1999). High DOC levels reduce the penetration of solar radiation, which can in turn reduce primary production, decrease mixing depth, and change vertical distributions of organisms. DOC also alters the availability of nutrients and the toxicity of contaminants in complex ways and provides a substrate for microbial metabolism.

Phosphorus, nitrogen, and other nutrients are supplied to lakes from the surrounding catchment, from precipitation, and, in the case of nitrogen, by the process of nitrogen fixation. Inputs of P have received the most attention, because P limits the growth of algae and thus is a primary controller of eutrophication (Schindler 1977). P concentrations in a lake are a function of direct P inputs, lake depth, flushing rate, and rate of sedimentation. Accumulation of P in lake sediments can lead to high rates of recycling of P from lake sediments back into the water column, exacerbating problems of eutrophication (Carpenter et al. 1999). Sources of P inputs from the watershed include weathering of geologic materials and nonpoint (diffuse) pollution (Bennett et al. 1999).

Residential development has been associated with increased lake P concentrations (Dillon and Rigler 1975, Dillon et al. 1994). Inputs from fertilizers or septic systems can increase nutrient loading. In 1990, there were more than 50,595 septic tanks in the Northern Lakes region, most of which (72%) were in Vilas and Oneida counties (U.S. Bureau of the Census 1992).

Algal growth is affected not only by nutrient availability but also by predation and the presence of macrophytes and grazers. In shallow lakes, macrophytes also influence overall algal biomass and water clarity by competing for light and nutrients with phytoplankton (Scheffer et al. 1993). Large-bodied daphnids are the most effective predators of algae. They are able to significantly reduce algal biomass and thus improve water quality. The size structure of the zooplankton community is, in turn, a function of cascading effects generated by changes in fish communities (Carpenter and Kitchell 1993). Feeding by planktivorous fish can cause a shift from large- to small-bodied daphnid assemblages with no changes in the total biomass of zooplankton (Carpenter et al. 1985). Piscivorous fish can suppress populations of planktivorous fish (Carpenter and Kitchell 1993, Schindler et al. 1997a). As shown in Fig. A.3, because of the vastly different generation times of the components of pelagic food webs, responses in the plankton to changes in the balance between piscivores and planktivores are rapid (Carpenter and Kitchell 1993).

Pollutants such as metals and hydrocarbons also affect the water quality of lakes. Mercury, a neurotoxin, is the pollutant of greatest concern in the NHLD. Fish with mercury levels high enough to warrant health warnings (> 0.5 ppm) have been found in one-third of the lakes tested in Wisconsin (Wisconsin Environmental Decade Institute 2000), and many of these are in the NHLD. The combustion of fossil fuels is the primary source of above-background atmospheric mercury. From the atmosphere, mercury enters lake water in precipitation and is methylated by microbial processes. The methylation process is enhanced by low pH, high levels of organic matter, and anoxic conditions (Driscoll et al. 1994, Rudd 1995). Fish absorb mercury directly, through their gills, and from prey; it accumulates over time in their body tissues, and consequently the highest mercury levels are found in fish that are older, larger, and piscivorous. The concentration of methylmercury in piscivorous fish can be 1–10 x 10⁶ times higher than in the surrounding water (Wisconsin Department of Natural Resources 1996). Mercury is also likely to affect wildlife, particularly species such as loons that feed intensively on fish (Meyer et al. 1998).

The Wisconsin DNR generally assumes that most lakes in Wisconsin are contaminated with mercury. Therefore, it advises people not to eat many fish from inland waters. It recommends that children under 15 and women who could become pregnant should not eat more than one meal of panfish a week and one meal of gamefish a month. People who cannot become pregnant are advised to eat no more than one meal of gamefish per week.

Motorized watercraft are another source of pollution in the NHLD. Two-stroke engines such as those used by jet skis are particularly inefficient, emitting about 25% of their fuel unburned directly into the environment (see http://www.earthisland.org). Wisconsin now requires four-stroke boat engines.

In general, studies have shown minimal short-term effects of boat pollution on aquatic organisms, although, in some cases, polyaromatic hydrocarbons and fuel additives have been detected that could be a concern for drinking water supplies (Asplund 2000). The long-term effects of these fuel emissions on human health have not been studied.

Whereas lake water quality is threatened by development and toxins, most drinking water comes from groundwater in the NHLD. In 1990, only 20% of houses were connected to public water systems. Although groundwater can be affected by contamination in surface water, filtering through soil generally removes many contaminants. A more direct threat to groundwater quality is abandoned wells. If not filled with impermeable material, wells can channel contaminated surface or soil water directly into the groundwater.

Over the past century, Wisconsin's climate has remained largely unchanged. It is expected that during the 21st century the average temperature will increase by several degrees Celsius, especially during fall, winter, and spring. Precipitation is expected to increase 15–20% in summer, fall, and winter (Environmental Protection Agency 1999). These changes would have a variety of effects on the functioning of the ecosystems in the NHLD, but their cumulative consequences are uncertain. Expected impacts of climate change on aquatic systems include declines in cool-water fish such as trout and increases in warm-water species such as rainbow smelt and yellow perch (King et al. 1999), an overall decrease in fish habitat (Magnuson et al. 1997, Meyer et al. 1999), declines in the stability of invertebrate food webs (Beisner et al. 1997), the elimination of winterkill events (Fang and Stefan 2000), altered mixing regimes, and changes in the magnitude and seasonality of runoff patterns (Meyer et al. 1999). Although change is to be expected, the magnitude and type of ecological change produced by climate change is highly uncertain.

Invasive species

During the past several centuries, more than 100 species of plants, animals, and invertebrates have been introduced into the Great Lakes region, and a number of them have also become established in the NHLD. Some of these introductions were intentional and include managed populations of species such as brown trout (Salmo trutta) and carp (Cyprinus carpio). Other invasive species were introduced unintentionally as passengers in or on boats, in bait buckets that were indiscriminately emptied, or as escaped aquarium species (Rahel 2000). Among the more detrimental introductions for aquatic systems in the NHLD are Eurasian watermilfoil (Myriophyllum spicatum), purple loosestrife (Lythrum salicaria), rainbow smelt (Osmerus mordax), and rusty crayfish (Orconectes rusticus). These species have changed both the composition and functioning of many aquatic ecosystems.