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Lake Michigan Basin: Inland Aquatic Ecosystems Integrated Assessment

Digest: 
The inland aquatic habitats of the magnificent Lake Michigan basin range from slow meandering rivers, laden with silt, to cool, clear-running, high-velocity streams found in some northern watersheds, including the Menominee watershed. Along the coastline of the Lake are examples of some of the finest Great Lakes marshes and farther upland occur wet meadows, bogs and fens. However, the Lake Michigan basin has been altered by dams, dikes and drainage tiles, all of which modify the flow of water through rivers, lakes and wetlands and reduce the availability of high quality fish habitat. Being the most urbanized of the Great Lakes basins and generating a significant proportion of agricultural production, the Lake Michigan waterways and wetlands have faced considerable chemical, physical and biological changes. Learn more about Lake Michigan inland waters and the why the work of land and water managers, conservation practitioners and others is so important to the future health of the basin.

Traverse Bay Marsh, Northern Lower Peninsula, Michigan, shows the important interaction between Lake Michigan and its coastal wetlands.

Introduction to Lake Michigan's Inland Aquatic Ecosystems

The Lake Michigan basin is the land area whose all rivers and streams drain into Lake Michigan.1 Lake Michigan is the second largest Great Lake by volume and its drainage basin covers over 45,000 square miles, including parts of Michigan, Indiana, Illinois and Wisconsin. Spanning 307 miles from north to south, the Lake Michigan basin is ecologically complex and hosts a variety of inland aquatic ecosystems, including rivers and streams, varying in size, temperature and streambed characteristics; diverse wetlands, both coastal and inland, and including surface- and groundwater-fed systems; and many inland lakes and ponds, which are evidence of leftover chunks of ice from when the glaciers receded.2  There are 13 subbasins within the larger Lake Michigan watershed, each characterized by different surface and groundwater systems associated with the changing landscape across the Lake Michigan basin.

Lake Michigan inland aquatic ecosystems are home to regionally and globally rare plants and animals. There are hundreds of plant and animal species that live in or use Lake Michigan inland aquatic habitats for at least a portion of their life cycles, including several that are either endemic to the Great Lakes or have good representation in the Lake Michigan basin. For example, the Great Lakes endemic lake sturgeon (Acipenser fulvescens) lives in the nearshore waters of embayments around the basin and uses tributaries for migrating to spawning grounds (see Lake Sturgeon Fact Sheet). The Michigan monkey flower’s (Mimulus michiganensis) global distribution is restricted to just a few counties in northern Lower Peninsula and eastern Upper Peninsula of Michigan. The eastern prairie-fringed orchid (Platanthera leucophaea), a prairie and bog plant, while not endemic to the Great Lakes region, has most of its remaining occurrences in the lower Great Lakes, including portions of the Lake Michigan basin.3

This diversity of habitat and wildlife provides great value for Lake Michigan communities. More than 10,000,000 people live in the basin, primarily in the southern Lake Michigan, Chicago-Milwaukee metropolitan area.4 All of these people benefit from and depend on the health of Lake Michigan inland aquatic ecosystems. Inland lakes and wetlands are the connecting link between the water on the land and in the tributaries of Lake Michigan. These water-collecting basins also recharge groundwater aquifers that many communities, especially in the northern Lake Michigan basin depend on directly for drinking water. Furthermore, tributaries provide channels for numerous fish species to disperse, supporting recreational and commercial fisheries for salmon (multiple species), trout (multiple species), smallmouth bass (Micropterus dolomieu), northern pike (Esox lucius), walleye (Sander vitreus) and more. Lake Michigan tributaries are also navigational channels for industrial shipping of mineral ores mined from the northern basin, and in many places these rivers are dammed for hydropower production.5 Called the “fruit belt” of the region, the northeastern basin’s agriculture production requires high quality water diverted from rivers and streams for specialty crops like cherries, apples and cranberries. Lake Michigan rivers in the Fox River-Green Bay area also provide industrial processing water for the world’s highest concentration of pulp and paper mills. Finally, the lakes, rivers and wetlands offer tremendous recreational opportunities and a desire to live in the Lake Michigan basin for its aesthetic value.

As a consequence of high intensity resource use in the basin, the Lake Michigan inland waters and semi-aquatic wetlands have been significantly degraded.  The rich soils and flat topography of southern Lake Michigan watersheds, perfectly suited for farming and development, have led to coastal and inland wetlands being replaced by extensive farms and cities. Today, development trends in the basin reveal an increased desire to live in low density developments near the coast, putting more pressure on the remaining wetlands.6 Thousands of dams and poorly constructed road-stream crossings in the Lake Michigan tributaries and streams block migratory fish from reaching spawning grounds and create erosion, nutrient flow, and habitat disruptions downstream of impoundments. Home to the largest proportion of steel manufacturing in the nation along the southern lakeshore, nearby inland aquatic habitats have endured tons of pollution emitted to streams and the atmosphere.7 Plant, fish, and pathogen invasions introduced via ballast water and artificial channels between the lakes and the Atlantic Ocean have caused severe ecological changes in almost all Lake Michigan inland aquatic ecosystems.

In order to find the appropriate and sustainable balance between resource use and ecological change, where people can continue to benefit from the basin’s inland fisheries, wetlands, water supplies and beauty without losing the functions of these ecosystems, we need to understand more about how Lake Michigan inland aquatic ecosystems have been altered over time, what their current status is and in some cases how future changes may impact their ecological functionality (see Essential Ecological Attributes of Ecosystems). Building on this knowledge, natural resource professionals can make better informed decisions about targeting conservation work where it will have the greatest socioeconomic and ecological value (see Assess & Adapt).

Map of Lake Michigan inland aquatic geography

Ecological Condition of Lake Michigan's Inland Aquatic Ecosystems

Rivers and Streams

Lake Michigan streams and rivers are liquid expressions of the basin’s diverse landscape. The streams in the north can be high gradient, are often groundwater-fed and run through areas of exposed bedrock and coarse glacial till. Rivers and streams in the southern basin are often wider, warmer, and flow over deep clay sediments. The largest rivers are the Fox and Menominee in northeastern Wisconsin, and the St. Joseph, Kalamazoo and Grand Rivers in southwestern Michigan.8

Some of the rivers are near pristine, including the Pere Marquette in west-central Michigan and the Wolf River watershed inland of Green Bay, Wisconsin, both of which are designated National Wild and Scenic Rivers. However, many Lake Michigan rivers and streams have been altered by channelization, dredging, damming, sedimentation, loss of bankside vegetation, eutrophication, increased spring flooding, and toxic contamination.9  The Grand River, for example, the longest river in the Lake Michigan basin spanning 262 miles, runs through Michigan’s agricultural and orchard region and is impacted by sediment and non-point source pollution loading, urban runoff and the structural and ecological effects of several dams along its length. Connectivity between the tributaries and the lake is a particularly large concern for many Lake Michigan rivers.
 
Historically, many native and economically important Lake Michigan fish species, including lake sturgeon, lake trout (Salvelinus namaycush), walleye , yellow perch (Perca flavascens), whitefish (Coregonus clupeaformis), and northern pike have relied on connectivity between nearshore habitat and tributaries and wetlands upstream for spawning and juvenile fish development (see Data Catalog or Lake Michigan Migratory Fish). In fact, most Great Lakes fishes use tributaries for at least a portion of their lifecycles.10 Freshwater mussels also rely on this connectivity to reach upstream habitat via host fish that carry the mussels upstream. River connectivity is also important for material, nutrient and sediment transport.

Yet, only 18 percent of Lake Michigan tributaries are currently accessible to Lake Michigan fishes due to blockage from dams. And an unknown number of those are inaccessible due to other barriers such as poorly installed road-stream crossings (see Data Catalog for data on Lake Michigan dams and barriers).  Barriers, in addition to other factors like habitat degradation and historic overfishing have led to the loss or decline in many migratory fish populations throughout the Lake Michigan basin.11

One poignant example of how the loss of connectivity in Lake Michigan’s tributaries has affected aquatic life and people that rely on aquatic resources in the region is the steep decline of lake sturgeon related to blocked migration routes.  Dams, in addition to overfishing and pollution, have decreased the Lake Michigan basin sturgeon population significantly since its peak, from an estimated two million fish to about 3,000 sturgeons today.12 Lake sturgeon is now considered a rare species in Lake Michigan, as are several other native migratory fish, many of which have experienced population declines greater than 50 percent.13

This map shows Lake Michigan accessible streams and healthy remnant sturgeon locations, emphasizing the importance of maintaining well-connected streams to support migratory fish.

Lakes and Ponds

Inland lakes and ponds drain into rivers, collect groundwater seepage, and fill depressions in the ground moraines across the Lake Michigan watershed. Both Michigan and Wisconsin have thousands of lakes ranging from shallow spring ponds, just a few feet deep, to large lakes and impoundments over several hundred feet deep. Wisconsin has over 15,000 documented inland lakes,14 while Michigan has over 11,000.15 Wisconsin’s largest lake, Lake Winnebago, which has a surface area of 55,728 hectares, is also the largest lake in the Lake Michigan basin.16  Michigan’s largest inland lake is Houghton Lake in Roscommon County, which is 8,106 hectares. Houghton Lake lies at the very eastern edge of the Lake Michigan watershed in the Muskegon subbasin.

Lake Michigan inland lakes vary in size, depth and water chemistry according to changes in landscape features and water input/output dynamics. Where limestone geology dominates in combination with thick glacial deposits in Michigan’s Lower Peninsula and eastern Upper Peninsula, lakes are mineral and have a high buffering capacity.17  Most of Wisconsin’s Lake Michigan watershed area is also dominated by thick glacial till and limestone based geology.18 By contrast, parts of the northern Lake Michigan basin in northeastern Wisconsin and the western Upper Peninsula are underlain by igneous bedrock and sandstone geology.19 There are a greater percentage of soft-water (low mineral content) lakes in this region of the basin.20

 

Although inland lakes and ponds, whether natural or artificial, continue to provide important resources for Lake Michigan recreationists, industries, land owners and wildlife, there are fewer lakes today than in the past.21 While numerous inland lakes have been created by dams for hydropower and recreational use, many lakes in the region have also been drained for development. Furthermore, many lakes have been affected by shoreline development, where habitat has been reduced or degraded by infrastructure and polluted runoff. No regional assessments of inland lake conditions exist, however a national lake assessment was completed in 2007, which highlighted problem areas of inland lakes across the United States. According to Michigan’s survey, which was designed to be representative of thousands of lakes in the basin, loss of lakeshore habitat and physical lakeshore complexity are the greatest concerns for biodiversity.22 In fact, Michigan inland lakes were worse off than other regional states in this regard.  The loss of lake habitat puts pressure on important Lake Michigan fish species, including lake sturgeon, yellow perch, smallmouth bass, northern pike and walleye.

Northern pike, a regionally important game fish, prefers shallow weedy areas of inland lakes along the Lake Michigan shoreline.

Wetlands

Once covering vast acreages, Lake Michigan’s wetlands have largely been drained, filled and converted to agriculture and urban land use. Prior to European settlement, the southern Lower Peninsula had extensive marshes, fens and swamps. From Muskegon, Michigan to northwestern Indiana, wetland-dune complexes lined the lakeshore. In the northern basin, great conifer swamps dominated much of the Door Peninsula up through Michigan’s Upper Peninsula to the Mackinac Bridge.23 However, millions of inland and coastal wetlands have been lost to agriculture, urban development and industry over the last century—a disproportionately large amount compared to the rest of the nation (approximately 70 percent compared to 50 percent loss on average for the nation).

Moving southward  on both sides of the basin, forests and wetlands rapidly gave way to cities and farms with the most extreme urban intensification occurring in the very southern portion of the basin in northern Illinois and Indiana, where nearly 50 percent of the basin area is classified as urban.24

Though highly modified and in many cases entirely transformed, Lake Michigan's wetlands still have remarkable socioeconomic and ecological value. For example, approximately 20 percent of the remaining Great Lakes coastal wetlands occur within the boundaries of the Lake Michigan watershed.25 Across the Lake Michigan basin, there are 61 wetlands that are over 100 hectares, 13 of which are over 1,000 hectares.  Along the western shore of Green Bay and the eastern Door Peninsula are some of the best examples of extant Great Lakes marshes. Even in the highly urbanized area of Cook County, Illinois and Lake County, Indiana, remnants of the Calumet region wetlands remain. Though surrounded by a highly urban landscape, more than 700 plant species, 200 birds, 14 mammals, 21 reptiles and amphibians, 22 fish, 29 macroinvertebrates, and 15 butterflies, many rare and endangered, have been recorded in the Greater Calumet Wetlands recently.  The Allegan marshes of inland Michigan are recognized as the least disturbed remaining complex of globally imperiled Inland Coastal Plain Marsh community in North America.26 These remarkable facts highlight the importance of continued conservation efforts towards protecting the remaining Lake Michigan wetlands.

This Map shows the current extent of Lake Michigan coastal wetlands.

Water Quality

Like other areas around the Great Lakes, there are many sources of pollution that disrupt and degrade aquatic and semi-aquatic ecosystems in the Lake Michigan basin, and multiple pathways by which chemical pollution is introduced into these ecosystems. Although more stringent laws and policies have been put in place over the decades to prevent ecological and public health consequences of introduced chemicals, from the Clean Water Act (CWA) and Clean Air Act (CAA) to the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as Superfund, new streams and legacy sources of pollution continue to alter the Lake Michigan inland aquatic habitats. Large scale industrial processing facilities in the southern basin and extensive mineral mining operations in the northern basin are ongoing sources of polluted runoff into lakes and streams. Additionally, the Lake Michigan drainage basin is the most agricultural intensive lake basin out of all the Great Lakes, and farms contribute significantly to nutrient loading into streams, lakes and wetlands.27

Some of the greatest water quality concerns are linked to toxic pollutants, including heavy metals (lead, mercury, zinc, copper, chromium, etc.), volatile organic compounds released via combustion of fossil fuels and municipal waste materials, as well as persistent toxic compounds found in common agricultural pesticides, such as dieldren, aldrin and toxaphene. Many of these pollutants were introduced to Lake Michigan lakes and streams decades ago and are now banned from use, but are still present in the sediments along riverbeds and especially at the mouths of rivers in highly urbanized areas. Most of the 11 Areas of Concern (AOCs) identified in the Lake Michigan basin, out of 42 in the entire Great Lakes region, are impacted by legacy sources of pollution related to past emissions from mining, pulp and paper and other industries (see Data Catalog).28 The most degraded rivermouths, including the Kalamazoo, Grand Calumet and Fox River/Southern Green Bay have collected large quantities of contaminated sediments, which can be recycled into aquatic and terrestrial biota through food chains and/or volatilized back into the atmosphere from the surface waters and exposed sediments. 

Current emissions also affect Lake Michigan's inland aquatic ecosystems, especially in the southern basin. Though pollutants can travel long distances before being deposited into lakes and streams, the proximity to sources of pollution still matters. Gaseous and particulate concentrations of persistent toxics, including PCBs, dichlorodiphenyltrichloroethane (DDT), dieldrin, chlordane, and several trace metals (manganese, zinc, chromium, and lead) were found to be 10 to 40 times higher in the Chicago-Gary industrial area than in other remote sites in the southern Lake Michigan basin.29 A series of studies of Wisconsin lakes indicate that air is a major contributor of mercury to these lakes, and that modest increases in local air deposition of mercury could lead directly to higher levels of mercury in fish.30 Likewise, agricultural and sewage overflow can cause algal blooms and reduced dissolved oxygen levels in adjacent waterbodies; however, there is a lack of comprehensive data on nutrient loading into Lake Michigan inland aquatic ecosystems to provide an accurrate status of this impact.

Lake Michigan Areas of Concern (AOCs)

Carbon Storage

As with all Great Lakes inland aquatic ecosystems, Lake Michigan streams, lakes and wetlands are characterized by ecological processes that keep these ecosystems functioning and that ultimately benefit people. Lake Michigan streams and rivers cycle and transport nutrients and other materials, like organic carbon to downstream aquatic habitats. The wetlands lining the coasts and farther inland also cycle nutrients, remove pollutants from running waters and store significant quantities of carbon that otherwise would end up in the upper atmosphere and contribute to global climate change.31

Unfortunately, there is a lack of data showing comprehensively how much carbon is stored in Lake Michigan wetlands or the degree to which rivers and streams throughout the basin are able to cycle nutrients, sediments and other materials compared to historical conditions. However, it is clear that the extent of habitat degradation from land use change and water infrastructure has altered patterns of nutrient and carbon cycling. Sheer losses of wetlands from draining and infill amounting to approximately 60 percent of all coastal wetlands have dramatically reduced the nutrient and carbon cycling potential of Lake Michigan ecosystems.32 Where wetlands are still intact, they often are degraded by chemical pollution, which can also limit material cycling. For example, northern coastal marshlands found in the protected embayments along the eastern Upper Peninsula, the western shore of Green Bay and the eastern length of the Door Peninsula are among the remaining coastal marshes in the Lake Michigan basin that have not been affected by nutrient enrichment from agricultural fertilizers and sewage effluents.33 These few healthy marshes are rich with submergent plants and adjacent wet meadows with deep organic soil capable of storing large amounts of carbon. In general, widespread draining, filling and converting wetlands to residential and commercial and industrial development, as well as the creation of industrial and recreational marinas, has dramatically reduced the extent and integrity of these wetlands, and hence the ability of the marshes to capture carbon and recycle nutrients.

Wetlands  in the Lake Michigan basin not only provide habitat for wildlife, like this Great Blue Heron wading along the Au Sable River in Michigan, but they also can store massive quantities of carbon in plant material and soils.

Hydrologic Issues

Lake Michigan inland aquatic resources are inherently defined by interactions between land and water. Patterns in hydrology and geomorphology across Lake Michigan aquatic habitats and wetlands create and sustain these ecosystems and are important natural disturbance regimes that enhance biological diversity. For example, all Lake Michigan wetlands are influenced by naturally occurring lake level fluctuations.34 Short term variations in lake levels caused by storm sieches (waves) can destroy wetland habitat, but also are important for maintaining the diversity of plants in coastal marshes that are adapted to periodic changes in water levels. These and longer term seasonal and interannual lake level changes, which vary by as much as 3.5 to 6.5 meters, are habitat defining factors for marshlands along the lake. Lake Michigan’s rivers and streams are also naturally connected to the lake and adjacent floodplain habitat. Fishes and aquatic plants and invertebrates require natural flow patterns to trigger migration events and emergence during spring and fall. Similarly, neighboring wetlands and riparian vegetation interact with rivers and streams in important ways by mediating sediment and nutrient loads from the terrestrial environment. Finally, below the land’s surface, groundwater flows replenish and sustain water to the majority of streams that ultimately flow into Lake Michigan.35

Compared to the other Great Lakes, especially, Lakes Ontario and Superior, which are regulated directly to maintain navigation, maximize hydropower generation, and protect shoreline development from wave damage and flooding, Lake Michigan and Lake Huron lake levels rise and fall according to historic patterns.36 Still, evening out natural lake level fluctuations under future regulation may cause concern for Lake Michigan landowners and conservationists. Whether the lake is regulated to keep water levels higher for hydropower and navigation, or if water levels are controlled to protect shoreline property, changing the periodic high and low water levels may have impacts on ecosystems, businesses and homeowners alike.

More alarming for many Lake Michigan communities than the threat of reduced lake level variation, is the recent trend of decreasing lake levels in general. Previous projections of lake supplies and lake levels have suggested that a changing climate may reduce lake levels by increasing evapotranspiration related to higher air temperatures.37 The projected lower lake levels could disrupt functioning harbors, actually increase erosion by exposing sediments and degrade wetlands that normally experience upland flooding.38 And trends do show recent declining lake levels correlated with warmer temperatures. In 2001, Lake Michigan levels were the lowest since 1966, at 61 centimeters below the long-term average and more than 102 centimeters below the record high in 1997. However, new findings suggest that prior projections were based on a weak assumption that temperature is a good proxy for potential evapotranspiration, whereas in reality net radiative energy transfers need to be incorporated into the analysis to properly adjust evapotranspiration losses under climate change scenarios.39 This research suggests that under a properly adjusted model, Lake Michigan and the other Great Lakes could have reduced declines in lake levels or may even have increased lake levels concurrent with climate change.

Though resource professionals are unclear as to impacts of future lake level regulation and climate-related changes on Lake Michigan wetlands, the streams and subsurface groundwater flows in the basin are clearly affected by human-induced changes in hydrology.  There are more dams on Great Lakes streams and rivers in Michigan than any other Great Lakes state (see Data Catalog for data on Lake Michigan dams).40 Many Michigan and Wisconsin tributaries are dammed, blocking migratory fish and accumulating sediment loads behind impoundments.41 Consequently, populations of native migratory fish, including yellow perch and lake trout are unable to reproduce naturally to support viable populations. In addition to hydrogeomorphic modifications by dams and misplaced or poorly constructed road-stream crossings, urban areas throughout the Lake Michigan basin are increasing in impervious surfaces (roads and rooftops). More impervious surface in the region is contributing to the degradation of streams by increasing water temperature and runoff volume.

Groundwater flows are also facing increasing pressure hydrogeomorphic modifications, specifically groundwater pumping for consumptive use and drainage for agriculture.  Groundwater is especially important for Lake Michigan streams because of the high number of tributaries that are sustained by groundwater due to the basin’s abundance of sand and gravel aquifers near the Lake.  It is estimated that 80 percent of the Lake Michigan tributaries originate as groundwater, more than in any other Great Lakes basin.42  Pumping is so extensive in the southern basin that in some confined aquifers, the groundwater divides, which determines the direction and quantity of subsurface flows, have been displaced by as much as several kilometers.

This figure shows average groundwater and surface-runoff components of selected watersheds in the U.S. portion of the Great Lakes Basin ; of the five Great Lakes, Lake Michigan receives the largest proportion of stream flow from groundwater sources (from Holtschlag, D.J., and Nicholas, J.R., 1998, Indirect ground-water discharge to the Great Lakes: U.S. Geological Survey, Open-File Report 98-579, 25 p.)

Invasive Species

Beyond the direct habitat alterations through blocking the flow of rivers, filling wetlands and inputting pollutants, many Lake Michigan inland aquatic ecosystems have been transformed by introductions of non-native and invasive species.  Lake Michigan’s waters now harbor 182 non-native species, though only a portion of these are considered invasive.43  Some of the main invaders include the sea lamprey (Petromyson marinus), which is parasitic to large predator fish like lake trout;44 Asian carps (Hypophthalmichthys nobilis and Hypophthalmichthys molitrix), which have not yet invaded the Great Lakes system, threaten to invade via the Illinois waterway connecting to the Mississippi River; and invasive freshwater mussels, including the zebra mussel (Dreissena polymorpha) and quagga mussel (Dreissena rostriformis bugensis), a relatively new invasive species that now accounts for approximately 98 percent of the mussels in Lake Michigan.45 The sea lamprey, which had fully decimated the lake trout and burbot (Lota lota) by the 1940’s, led to the invasion of alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax).  These preyfish flourished as the native predator fishes declined, and are thought to have contributed to the extirpation of endemic sculpin and deepwater cisco species and the decline of water quality in the lake (see Data Catalog for data on Lake Michigan sea lamprey collection locations).46 Other aquatic invasives in the Lake Michigan basin include Eurasian watermilfoil (Myriophyllum spicatum) (an aquatic plant), rusty crayfish (Orconectes rusticus), round goby (Neogobius melanostomus), Eurasion ruffe (Gymnocephalus cernuus) and a viral pathogen called viral hemorrhagic septicemia (VHS).  These species not only degrade the Lake Michigan nearshore/offshore waters, but also reduce habitat and outcompete native species in streams and lakes inland of the lake. The Eurasian watermilfoil and VHS, for example, are known to have invaded many Lake Michigan inland lakes.47

Alternatively, Lake Michigan wetlands are heavily impacted by invasive emergent plants, especially purple loosestrife (Lythrum salicaria) and common reed/phragmites (Phragmites australis).  Both species are highly invasive and retain huge biomass below the surface, making eradication very difficult. Purple loosestrife is found in all counties of southern Lower Peninsula, in various locations of the northern Lower Peninsula and in scattered areas across the Upper Peninsula.48  It has also been identified in 70 of 72 counties in Wisconsin, though mostly in low density.  The largest invasions of purple loosestrife are in the extreme southeastern portion of Wisconsin and along the Wolf and Fox River watersheds.49 Phragmites occurs in disturbed areas with altered hydrology and sedimentation and is now found in coastal and interior wetlands, especially in the northern marshes of Green Bay, Wisconsin,50 and throughout coastal wetlands in the eastern basin.  Phragmites has been identified by the Michigan Departments of Natural Resources and Environmental Quality as a priority invasive species in Michigan given the extent of invasion and its associated ecological impacts.51

The effects of inland aquatic and wetland invasions are expected to be made worse by the influence of climate change throughout the Lake Michigan basin. With climate models predicting that by the end of the century, temperature in the region will warm by 5 to 12°F (3 to 7°C) in winter, and by 5 to 20°F (3 to 11°C) in summer, these concerns are growing.52

Aside from the damaging effect of climate change, including lower lake levels; lower stream flows during dry periods and more intense flows during the wet season; and the myriad potential effects of warmer temperatures on lake, stream and wetland water quality, such as eutrophication,53 the trend of warmer and drier conditions in the Lake Michigan basin may benefit invasive species.  For example, the alewife is a warm water fish and has increased in abundance as the Great Lakes have warmed over geologic time.54  Similarly, the round goby, which spawns multiple times, has a shortened interval between spawning periods when water temperatures exceed 20 degrees Celsius.

There may also be interactions between the different effects of climate change on native and invasive species that might facilitate invasions.  For example, a study of 13,000 lakes in Wisconsin showed that warmer lake temperatures positively affect the invasive rainbow smelt, while negatively affecting the native cold water ciscos, which the smelt outcompete.55 Wetlands are similarly at a greater risk to invasion with the added impact of climate change. As Lake Michigan and inland lake levels recede, invasive plants like purple loosestrife and phragmites are expected to invade more aggressively because the newly exposed wet sediments are the ideal conditions for seed germination.56

A comparison of zebra and quagga mussels, two very invasive mollusks in the Lake Michigan basin and througout the Great Lakes region (from USGS, Nonindigenous Aquatic Species website > http://nas.er.usgs.gov/queries/factsheet.aspx?speciesid=95).

Conservation Outlook

From altered flow regimes to barriers to fish passage; from dredged and filled wetlands to declining lake levels; from increased pollutant loads to widespread plant and animal invasions, the Lake Michigan drainage basin has undergone dramatic changes that have diminished the socioeconomic and ecological value of these habitats. Yet, the inland waters and wetland habitats remain a vital resource. Although many native species of fish, amphibians, reptiles, birds and plants have declined with habitat loss and degradation, regionally important communities and populations remain. For example, remnant stocks of lake sturgeon occur in eight tributaries of Lake Michigan, and a restocking program is currently underway.57 Even the most heavily altered wetlands around the basin are being protected and restored for improved recreational, commercial, and ecological value, like the protected areas of the Calumet Wetlands.

In fact, Great Lakes landowners, businesses and natural resource professionals around Lake Michigan are coordinating many inland aquatic restoration activities. Through the AOC program, for example, the U.S. Environmental Protection Agency (EPA) has completed remedial action plans (RAPs) for five of the ten AOC designated waterways tributary to Lake Michigan, and the Waukegan Harbor is now on the road to delisting because the PCB contaminated sediments have been removed.58 Various barrier removal projects are underway in the Lake Michigan basin through the Great Lakes Restoration Initiative (GLRI), including the dam removal and road-stream crossing improvement project on the Manistee River’s North Branch, or the Lancaster Brook Culvert Replacement northeastern Wisconsin.  Another recent GLRI funded project established streamside lake sturgeon rearing facilities on the Manistee, Whitefish, Cedar, Kalamazoo, Kewaunee and Milwaukee rivers.59 These are just a few examples of many efforts to restore and increase the value of Lake Michigan inland waters and aquatic habitat. With greater understanding of the status and trends of ecological conditions, the impacts of human activities and the effectiveness of conservation strategies, more successful conservation work can be achieved in the Lake Michigan watershed (see Assess and Adapt and Decision Tools).
 

This image shows tractors moving dirt at the Lancaster Brook Culvert Replacement project, Oneida, Wisconsin. The newly constructed culvert will promote better fish passage in the stream.