ML070530691

Ecosystem Vulnerability and Climate Change: Aquatic Ecosystems

ML070530691
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Site:	FitzPatrick
Issue date:	01/01/2003
From:	Union of Concerned Scientists
To:	Office of Nuclear Reactor Regulation
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CHAPTER Three Ecological Vulnerability to Climate Change: Aquatic Ecosystems T

he Great Lakes region is distinguished by water temperature would be even greater using the its abundant lakes, streams, and wetlands. more recent climate scenarios on which this report is All of these aquatic ecosystems will be based, especially by 2090. Overall, changes in tem-affected in some way by the direct human perature and stratification will affect the fundamental stresses and human-driven climate changes explored physical, chemical, and biological processes in lakes in Chapters 1 and 2. (see box, p.22). Higher water temperatures, for example, result in lower oxygen levels.

Lake Ecosystems Lower oxygen and warmer temperatures also promote greater micro- F I G U R E 1 7 L

akes in the region differ widely in size, depth, bial decomposition and Impacts on Lake Ecosystems transparency, and nutrient availability, charac- subsequent release of teristics that fundamentally determine how nutrients and contami-each lake will be affected by climate change (Figure nants from bottom sedi-17). A wide variety of studies have focused on the ments. Phosphorus re-inland waters and Great Lakes, providing strong evi- lease would be enhanced49 dence of how the waters have changed and are likely and mercury release and to change in the future. uptake by biota would also be likely to increase.50 Higher Lake Temperatures Other contaminants, Warmer air temperatures are likely to lead to increas- particularly some heavy ing water temperatures and changes in summer strat- metals, would be likely ification in the Great Lakes47 and in the inland lakes to respond in a similar and streams of the region.48 Earlier model studies fashion.51 (Heavy metals project that summer surface water temperatures in such as mercury become inland lakes will increase by 2 to 12°F (1 to 7°C). more soluble in the Projections for deep water range from a 14°F warm- absence of oxygen. Oxy-ing to a counterintuitive 11°F cooling. The response gen binds with these in deep waters varies because warming air tempera- elements to form in-tures can cause a small, deep lake to stratify sooner in soluble compounds that See page 42 spring, at a cooler temperature. Projected changes in sink to the bottom.) for full-size color image of this figure C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N 21 Union of Concerned Scientists

• The Ecological Society of America

Aquatic Ecosystems Climate Change and Dead Zones in Lake Erie T

he fall of 2001 brought startling and discouraging news to residents around Lake Erie.

Testing stations in the lakes central basin reported the most rapid oxygen depletion in nearly 20 years. Its like going back to the bad old days when Lake Erie was dead, one aquatic biologist told the Toledo Blade. The bad old days were the 1960s when Lake Erie had been all but choked to death: massive phosphorus pollution had fertilized algal blooms and their decay was using up the dissolved oxygen needed to support fish and other aquatic life. Then, in 1972, implemen-tation of the Great Lakes Water Quality Agreement led to billions of dollars in new sewage treatment plants, bans on phosphate laundry detergent, new farming practices that reduced fertilizer runoff, and other measures that drastically cut phosphorus input to Lake Erie. As phosphorous loading dropped, so did the extent and duration of the summer dead zones.

FIGURE 18A Was the massive dead zone of 2001 an anomaly or a Lake Stratification and the trend, scientists and policymakers wondered? And what Development of Dead Zones had caused it this time? A committee of US congress-men traveled to the lake to investigate, and researchers in the United States and Canada launched a $2 million effort to find answers. The suspected culprits ranged from ozone depletion, which allows ultraviolet light to reach deeper into the waters, to the invading zebra mussels that now line the lake bottom down to 100 feet (30 meters). Missing from most discussions, however, was the recognition that a warming climate will mean more frequent and larger dead zones in the future.

A dead zone is an area of waterin a lake or even in a part of the ocean such as the Gulf of Mexico off the mouth of the Mississippi Riverthat contains no oxygen to support life. Dead zones form when oxygen in the water is con-See page 43 sumed by organisms, but these zones can only persist for full-size color image of this figure when the water is isolated from the atmosphere and thus from a source of new oxygen. This isolation occurs when water is stratifiedthat is, layered and separated with warmer surface waters acting as a lid on top of the cooler bottom waters, isolating them from the air (Figure 18a).

When winter ends in the Great Lakes region and surface waters become free of ice, lakes usually mix from top to bottom and the entire lake becomes saturated with oxygen. Soon after this spring mixing, however, the sun warms the surface waters and stratification sets in. Once the lake is stratified, oxygen begins to decrease (hypoxia) in bottom waters, and the race is on to see whether all the oxygen will be depleted (anoxia) and a dead zone created before the lake again mixes fully in the late fall or early winter. The more rotting biomass such as dead algae in the water, the more oxygen is consumed. In recent years, oxygen consumption has had the advantage in this race because 22 C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N Union of Concerned Scientists

• The Ecological Society of America

shorter winters have led to earlier spring stratification FIGURE 18B Lake Michigan Fish Kill in many lakes, meaning that the lake bottom runs out of oxygen even sooner in the summer. For example, winters on Lake Erie have been growing shorter since the 1960s. Also, recent increases in the near-shore water temperatures for four of the five Great Lakes indicate that their summer stratification periods have increased by one to six days per decade.25 In a warming climate, the duration of summer strati-fication will increase in all the lakes in the region.

Warming could also lead to a partial disappearance of the fall and spring periods of complete mixing that are typical of all the Great Lakes. This mixing resupplies oxygen and nutrients throughout the water column.

In the fall, the formerly warm and buoyant surface waters cool and then sink, driving mixing. This occurs only if the surface waters cool to the temperature of maximum water density (39°F or 4°C).52 Lake Ontario is particularly sensitive to this effect. Under some See page 43 climate warming scenarios,53 it would experience only for full-size color image of this figure a single, short period of complete mixing in late winter, then deep water temperatures would increase throughout the year. The deeper Great Lakes (Huron, Michigan, and Superior) would experience a similar suppression of mixing in some years, along with a significant warming of deep waters.54 No suppression of mixing will occur in shallower bodies of water such as Lake St. Clair and the western basin of Lake Erie, because there will always be sufficient wind to stir the entire water column from top to bottom.

In the end, longer stratification periods and warmer bottom temperatures will increase oxygen depletion in the deep waters of the Great Lakes55 and will lead to complete loss of oxygen during the ice-free period in many inland lakes of at least moderate depth.56 Anoxia or hypoxia in deep waters will have negative impacts on most of the organisms in the lakes. Persistent dead zones can result in massive fish kills, damage to fisheries, toxic algal blooms, and foul-smelling, musty-tasting drinking water (Figure 18b).

Reduced Ice Cover impacts. Shorter ice cover periods, for example, can Extrapolations from 80 to 150 years of records be a mixed blessing for fish. Reduced ice will lessen strongly suggest that ice cover will decline in the the severity of winter oxygen depletion in many small future. Hydrologic model simulations also predict inland lakes,56 thus significantly reducing winterkill drastic reductions in ice cover on the Great Lakes57 in many fish populations. However, small species and on inland waters in the future (Table 1). Changes uniquely adapted to live in winterkill lakes go extinct in ice cover create large ecological and economic locally when predatory fishes are able to invade and C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N 23 Union of Concerned Scientists

• The Ecological Society of America

Aquatic Ecosystems persist in lakes that previously experienced winterkill.58 used in this report (HadCM3) suggest even greater Reduced ice cover also allows greater storm distur- declines in late summer water levels because this model bance, which increases egg mortality of the commer- projects higher temperatures and lower summer rain-cially valuable lake whitefish, whose eggs incubate fall in the region than the models used in previous over winter on the bottom of Great Lakes bays.59 studies. However, the absence of long-term trends Increases in the ice-free period extend the shipping in the historic Great Lakes water levels record34 and season on the Great Lakes but reduce ice fishing, ice increases in water in some inland areas of Wisconsin35 boating, skiing, snowmobiling, and winter festivals suggest that lake water levels may not yet show the such as Wisconsins Kites on Ice (see box, p.15). decline expected from long-term climate change.

Changes in Lake Water Levels Changes in Lake Productivity Climate scenarios and lake models have consistently The growth of algae in the water and on lake bottoms predicted less runoff, more evaporation, and lower is called primary production because these planktonic water levels in both large and small lakes in the region.60 plants form the base of the food web that nourishes The most recent hydrologic models continue to pro- animals from zooplankton to fish. Primary produc-ject lower lake and groundwater levels in the future tion is controlled by a combination of temperature, (Table 2), despite a lack of clear trends in the historic light (or the portion of the ice-free year when light record. Predictions based on one of the climate models is available), and nutrients. Excessive nutrients can TABLE 1 Ice Cover Expected to Decrease in the Great Lakes Region Lake Current Situation Future Scenarios By 2030 By 2090 Lakes Superior 77 to 111 days Decrease ice cover Decrease ice cover and Erie (6 basins)a of ice cover from 1158 days from 3388 days Lake Superior No ice-free Increase ice-free winters Increase ice-free winters (3 basins)a winters from 04% from 445%

Lake Erie 2% of winters 061% of winters 496% of winters (3 basins)a are ice free are ice-free are ice-free Small inland lakesb ~90100 days Decrease ice cover by 4560 days with a doubling of ice cover of atmospheric CO2 Source: See note 61.

TABLE 2 Water Levels Likely to Decrease in the Future (as shown here for the Great Lakes, Crystal Lake, Wisconsin, and groundwater near East Lansing, Michigan)

Lake or Site 2 x CO2 2030 2090 (range of 3-4 simulations) (range of 2 simulations) (range of 2 simulations)

Lake Superior -0.23 m to -0.47 m -0.01 m to -0.22 m +0.11 m to - 0.42 m Lake Huron/Michigan -0.99 m to -2.48 m +0.05 m to -0.72 m +0.35 m to - 1.38 m Crystal Lake, -1.0 m to -1.9 m Wisconsin (2 simulations)

Groundwater near -0.6 to +0.1 m Lansing, Michigan Source: See note 62. Additional data on lake level declines can be found in the technical appendices:

http://www.ucsusa.org/greatlakes/glchallengetechbac.html 24 C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N Union of Concerned Scientists

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TABLE 3 Expected Effects of Warmer and Drier Summer Climate on Lakes and Subsequent Impacts on Algal Productivity Climate-Driven Change Impact on Production Most Sensitive Lake Type Increases in both ice-free period Increase in production Moderate in area, depth, and maximum summer water and nutrient concentration temperature Increase in duration of summer Decrease in production caused by Deep and oligotrophic stratification and loss of fall top- decrease in nutrient regeneration rates (nutrient-poor; e.g.,

to-bottom mixing period Lake Ontario)

Drought-induced decrease Initial increase in production, Small and shallow in lake water volume followed by progressive decrease as the lake level declines Drought-induced decrease Decrease in production resulting Small and oligotrophic in annual input of nutrients from nutrient limitation (phosphorus) and dissolved organic carbon lead to eutrophication, causing increased algal growth, can also lead to lower primary production in lakes by including noxious algal blooms and degraded water preventing the mixing that brings nutrients from bot-quality. On the other hand, drops in primary produc- tom waters and sediments up into surface waters.66 tion can ultimately reduce fish production in a lake. Changes in the species composition of algae Research indicates that the longer ice-free periods and in seasonal patterns of blooms are also likely and higher surface water temperatures expected in consequences of climate change. Earlier ice-out (thaw the future will spur greater algal growth.63 Other of lake ice) and spring runoff will shift the timing of aspects of climate change, however, may offset these the spring algal bloom,67 and earlier and longer peri-productivity gains. Cloudy days can lower produc- ods of summer stratification tend to shift dominance tivity by making less light available for algal photosyn- in the algal community during the growing season thesis.64 Cloud cover has increased in the Great Lakes from diatoms to inedible blue-green algae. If climate region recently, but future trends in cloudiness are change causes inedible nuisance species to dominate not clear. Increased primary productivity could also algal productivity, or if the timing of algal production be limited or even reversed by a decline in availability is out of synch with the food demands of fish, then of nutrients, primarily nitrogen and phosphorus, all upper levels of the food chain, particularly fish, necessary for plant growth. Predicted reductions in will suffer (see box, p.22).

runoff and a general drying of watersheds during The impacts of climate change on aquatic pro-summer are likely to reduce the amounts of phosphorus ductivity will differ among lakes. Table 3 summarizes and other dissolved materials that streams carry into the likely outcomes.

lakes.65 Finally, prolonged or stronger stratification River and Stream Ecosystems T

he aspects of climate change that will have and higher rates of evaporation during a longer ice-the greatest impact on streams are warming free period. This future scenario is consistent with air temperatures and general drying of past trends toward longer ice-free periods, earlier watersheds, especially during summer and autumn. spring stream flows, and more frequent midwinter This drying will result from warmer temperatures breakups and ice jams.68 Despite a general drying, C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N 25 Union of Concerned Scientists

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Aquatic Ecosystems TABLE 4 Impacts of Climate Change on Stream Ecosystems Climate- Likely Impacts on Physical Likely Impacts on Intensifying or Driven Change and Chemical Properties Ecosystem Properties Confounding Factors Earlier ice-out Peak flows occur earlier. The timing of fish and Snowmelt occurs earlier and snow melt insect life cycles could and faster in urban areas Ephemeral streams dry be disrupted. and where coniferous forest earlier in the season. harvest has occurred.

Backwater pools experience anoxia earlier.

Lower summer More headwater streams Habitat decreases in extent. Impervious surfaces and water levels dry; more perennial streams impervious soils exacerbate Hydrologic connections become intermittent. stream drying due to reduction to the riparian zone are in infiltration and groundwater Concentrations of dissolved reduced. Groundwater recharge.

organic carbon decrease, recharge is reduced.

thereby reducing ultraviolet-Species with resting life B attenuation.

stages or rapid colonizers Groundwater recharge dominate communities.

is reduced.

More precipi- Spring floods reach Floodplain habitat for fish Precipitation occurring tation in winter greater heights. and invertebrates grows. when soils are frozen results and spring and in higher runoff and increases Surface runoff increases. Hydrologic connections increased water flood height.

with wetlands increase.

levels Nutrient and sediment retention decrease.

Groundwater recharge potential increases.

Warmer Stream and groundwater The rates of decomposition Impervious surfaces and temperatures temperatures increase. and respiration increase. both natural and human-made retention basins Insects emerge earlier. increase water temperatures.

Primary and secondary Woody riparian vegetation production per unit of can buffer stream temperatures.

biomass increases when nutrients are not limited; In areas with porous soils however, total production and active groundwater could decrease if aquatic connections, temperature habitat shrinks under extremes are smaller.

drought conditions.

More frequent Larger floods occur Fish and invertebrate Impervious surfaces increase heavy rainfall more frequently. production decreases. runoff and stream flow.

events Erosion and pollutant Fish and insect life histories Channelized streams inputs from upland and food webs are dis- increase peak flow.

sources increase. rupted by changes in the intensity, duration, Runoff increases relative and frequency of flooding.

to infiltration.

Elevated Possible changes in leaf atmospheric CO2 litter quality could impact aquatic food webs.

26 C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N Union of Concerned Scientists

• The Ecological Society of America

model predictions for the region also suggest that over invertebrates. In addition, several important fish the next 100 years precipitation will increase during species move upstream into the Great Lakes tribu-winter and spring. This could increase the magnitude taries to reproduce during spring (sturgeon, walleye, of spring floods, especially if the floods coincide with and white sucker) or fall (steelhead, Chinook salmon, snowmelt when soils are still frozen. Stream responses and brook trout), cued by either increased flow or to these climate-driven changes will vary greatly across day length. Although changes in the frequency and the region (Table 4), mainly because of differences in severity of disturbances such as floods can disrupt the relative contribution of groundwater versus surface some aquatic communities, many fish and inverte-water to their flow patterns.69 Direct human distur- brate species coevolved with seasonal flood pulses bances such as removing streamside vegetation, paving to take advantage of the FIGURE 19 or developing land, channelizing streams, depositing expanded habitat for Impacts on Stream Ecosystems nitrogen and acid from acid rain, diverting water, and spawning and nursery introducing invasive species will undoubtedly alter sites.72 In the Great Lakes the way stream ecosystems respond to climate change. region, these species in-clude bass, crappie, sun-Impacts of Changes in Hydrology fish, and catfish.73 Heavy rainfall events and flooding are increasing Apart from extreme in the Great Lakes region38 (see Figure 7, p.14), and events, summer rainfall projected increases in the frequency of these events is expected to decline in may amplify the range of conditions that make flood- the future, especially in ing more likely in the future, such as stream channel- the southern and western ing and land-use changes that increase the amount of portions of the region impervious surfaces. The likelihood of flooding will (see Figure 13, p.18).

See page 44 also increase with changes in land use. Streams in the Drier conditions will trans- for full-size color image of this figure agricultural areas on fine-textured soils and flat topo- late into lower summer graphy at the eastern end of Lake Erie, for instance, stream flow and less stream habitat.74 Headwater rise quickly in response to rain and are likely to be streams, which often make up more than 75 percent especially vulnerable to intense summer storms. of the river miles in a watershed, are probably the Floods exert their greatest physical influence by most vulnerable of all aquatic ecosystems under reshaping river channels, inundating floodplains, and warmer and drier conditions (Figure 19).75 Drought moving large woody debris and sediments. Flooding effects can lead to warmer water temperatures, de-can degrade water quality when untreated human, pleted oxygen, higher concentrations of contaminants commercial, or agricultural wastes overflow from as water volume declines,76 reduced transport of nu-treatment facilities or when soils are eroded from trients and organic matter,77 and disruption of food agricultural fields treated with pesticides and ferti- webs.78 Regions with intensive agricultural produc-lizers.70 High water flow also diminishes the capacity tion on fine soils and flat topography, such as those of a stream to recycle nutrients and sequester sus- found at the eastern end of Lake Erie,69 will be most pended or dissolved organic matter.71 Channelized vulnerable to extreme events and reduced summer urban and agricultural streams have little capacity to rainfall, since their hydrology is controlled largely retain water, and the anticipated increases in spring by surface water. In small streams where flow comes runoff by the end of the century will result in increased primarily from surface runoff, one study predicts that height of spring floods and lower nutrient and 50 percent of the streams will stop flowing if annual sediment retention in these streams. runoff decreases by 10 percent.79 Not all impacts of flooding are negative, of One consequence of periodic droughts is that course. Aquifer recharge is one benefit. Floods also sulfates and acidity are mobilized during post-drought transport fine sediments downstream, increasing the rains and can deliver a strong acid pulse to streams quality and quantity of habitat for some fish and and lakes in the watershed. Because of this phenom-C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N 27 Union of Concerned Scientists

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Aquatic Ecosystems enon, climate warming may slow or even halt the forests and other vegetation and by water storage recovery of many acid-stressed aquatic ecosystems.80 in wetlands.81 Locally, cool groundwater seeps will Streams most susceptible to acid rain include those provide some buffering for streams against warming on the Canadian shield of Ontario, along the higher- air temperatures. Warmer water will affect stream gradient reaches of New York, and in northern organisms from plankton to insects and fish (fish are Michigan, Minnesota, and Wisconsin. discussed below). In response to warmer waters, some insect species increase growth rates, emerge earlier, Impacts of Higher Water Temperature are smaller at maturity, alter their sex ratios, or reduce Across the watershed, stream temperatures will close- fecundity.82 Plankton productivity tends to increase ly mirror increasing air temperatures, although the with warmer temperatures and longer growing warming may be modified by shade from riparian seasons,83 but reductions in water volume, coupled TABLE 5 Impacts of Climate Change on Wetland Ecosystems Climate- Likely Impacts on Intensifying or Driven Change Physical Properties Likely Impacts on Ecosystems Confounding Variables Earlier ice-out Wet periods are shorter, Fast-developing insect and amphibian Snowmelt occurs and snow melt especially in ephemeral species are favored, as are species with earlier and faster in wetlands. resting stages. urban areas and where coniferous forest The timing of amphibian and insect life harvest has occurred.

cycles could be disrupted.

Lower summer Isolation and Habitat and migration corridors are Agricultural and water levels fragmentation within reduced, as are hydrologic connections to urban development wetland complexes riparian zones and groundwater recharge. exacerbate frag-increase. mentation effects.

Emergent vegetation and shrubs Fens store less carbon. dominate plant communities.

Reductions in dissolved Amphibian and fish reproduction organic carbon result fails more often in dry years.

in less attenuation of Organisms with poor dispersal ultraviolet-B radiation.

abilities become extinct.

Warmer Evaporative losses The rates of decomposition Impervious surfaces temperatures increase. and respiration increase. increase water temperature.

Fens and bogs Insects emerge earlier.

store less carbon. More competition from Primary and secondary production invasive species may per unit of biomass increase when accelerate extinctions.

nutrients are not limited.

Species at the southern extent of the range become extinct.

More frequent Wetlands Habitat area increases. Wetland losses from heavy rainfall increase in extent. development reduce Ground-nesting birds may events flood storage capacity.

be lost during floods.

Elevated Possible changes in leaf litter quality atmospheric CO2 could impact aquatic food webs.

28 C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N Union of Concerned Scientists

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with possibly intermittent flow in smaller streams, survive better than other organisms during reduced should lead to reductions in overall aquatic production. water flows.87 Fish species presumed to be at higher The effects of increasing water temperature would risk of extinction are those that have small geographic be compounded by forest harvest (especially of coni- ranges, require steady water flows or slack water fers), which opens up the canopy and promotes ear- habitats, reproduce at an older age, or require specific lier snowmelt.84 Northern Michigan, Minnesota, Wis- foods. Of 146 fish species in Wisconsin, 43 percent consin, and western Ontario will be most vulnerable have two or more of the F I G U R E 2 0 to this phenomenon. Urban areas also experience above traits, indicating Impacts on Wetland Ecosystems earlier and faster snowmelt than do rural areas. potential sensitivity to Warmer temperatures should enhance decom- global warming. Darters position and nutrient cycling in streams, allowing and sea lampreys are microbes to break down human and agricultural among the species that wastes into nutrients that fuel greater primary produc- are especially sensitive.86 tivity. However, other impacts of climate change, such Another potential as prolonged low flows combined with higher temp- impact on stream food eratures, may lead to oxygen depletion, which will webs and the biodiversity slow decomposition and waste-processing functions.85 they support comes directly from increasing Impacts on Biodiversity and Food Webs atmospheric CO2 levels.

A warmer climate will combine with land-use change Some studies indicate See page 44 for full-size color image of this figure and the introduction of invasive species to pose great that plant leaves grown threats to aquatic biodiversity in the coming century. under elevated CO2 have lower food value.88 If these Native plant and animal species will differ widely in changes in leaf chemistry turn out to be significant, their responses to changing stream temperature and they could slow microbial decomposition of plant hydrology. Some will respond by adapting to warmer material that falls into streamsa major source of temperatures, or expanding their ranges northward, energy and nutrients in many aquatic ecosystems or seeking refuge in areas where temperatures and and also reduce growth and survival in some stream flow patterns remain suitable. Others will decline to insects that feed on the leaves.89 Any such impacts extinction.86 Insects and plants that have resistant or would be magnified up the food chain.

mobile life history stages (larvae, cysts, seeds) will Wetland Ecosystems B

ecause of low topography or the presence of Wetlands near the Great Lakes occur as three impervious soils, the Great Lakes region his- distinct types: fringing coastal marshes that are direct-torically harbored extensive expanses of wet- ly impacted by lake levels and wave action, riverine lands, particularly in the prairie regions of Minnesota wetlands that are partially influenced by both lake and Illinois, the boreal regions of northern Minnesota and river, and protected lagoons or barrier beach and Ontario, and the low-lying fringes of Lake Michi- systems that are hydrologically connected to the lake gan (Figure 20) and Lake Erie, including the Great only via groundwater.91 Where they have not disap-Black Swamp in western Ohio. For more than a cen- peared, coastal marshes in the southern part of the tury, however, these wetlands have been extensively basin, particularly on Lake Erie and southern Lake modified or drained for urban development and Ontario, have been extensively diked to protect them agricultural production, resulting in 40 to 90 percent from water level fluctuations. Coastal wetlands such losses in wetland area in the Great Lakes states and as those in Saginaw Bay and large estuaries such as Ontario.90 These losses are especially apparent in the Green Bay are hot spots of primary productivity be-southern portion of the region. cause nutrients and sediments from throughout the C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N 29 Union of Concerned Scientists

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Aquatic Ecosystems Climate and Bird Diversity on Michigans Upper Peninsula O

ne of the most popular bird-watching destinations in the Midwest is Michigans Upper Peninsula, a densely forested neck of land that stretches 384 miles east from the northern Wisconsin border into the heart of the Great Lakes. Although parts of the peninsula lie farther north than Montreal, the climate is moderated by Lakes Superior, Michigan, and Huron, which create a continuous 1,700-mile shoreline around the Upper Peninsula. This shoreline and the peninsulas 16,500 square miles of largely unfragmented forest contain a rich diversity of terrestrial and aquatic habitats that provide refuge for more than 300 bird species. About 25 to 30 percent are year-round residents; the rest are migratory species that arrive in the Upper Peninsula each spring to breed or each fall to winter. A warming climate will drive complex changes in habitat, quality, FIGURE 21A and timing of food resources, and other factors that Songbird Declines Expected are likely to diminish bird diversity on the Upper Peninsula in the future. Hardest hit will be the migratory and wintering species.

Habitat changes, particularly the expected north-ward shift of boreal forest species such as spruce and fir, will have profound impacts on bird communities.

Spruce, fir, and hemlock are vital to a number of species such as crossbills, siskins, grosbeaks, and breeding warblers (Figure 21a). The nature of a See page 45 peninsula will also make it more difficult for plant for full-size color image of this figure communities to respond quickly to changes since the land is isolated from sources of new colonists. Human land-use changes such as second-home development and logging will interact with climate to exacerbate habitat loss or degradation.

A number of resident bird species might, however, benefit from warming, including mockingbirds, chickadees, woodpeckers, titmice, and northern cardinals. For example, northern cardinals, chicka-dees, and titmice might be able to start breeding earlier and raise more broods within a season than they do now.92 More important, reduced winter-related mortality might increase populations of these year-round residents. It may also enable some cold-intolerant species such as the Carolina wren and sharp-shinned hawks to expand their range northward.93 The prospects are less rosy for songbirds that migrate to the Upper Peninsula from the tropical forests of Central and South America to breed. Food may be scarce along the route if trees leaf out and insects hatch earlier than normal in response to warming. More vital in the Upper Peninsula may be any change in the spring emergence of aquatic insects along the shoreline and in the wetlands, since this flush of insects serves as the primary food supply for arriving migrants.

Another concern arises from the fact that different parts of North America are warming and will probably continue to warm at different rates. Spring temperatures immediately to the south of the 30 C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N Union of Concerned Scientists

• The Ecological Society of America

Great Lakes region are warming less than spring temperatures observed in the region itself. If these areas to the south continue to be cooler relative to areas further north, migratory birds may face a dilemma: They need to arrive earlier on their northern breeding grounds, but may be unable to migrate because food resources such as caterpillars are not yet adequate to allow them to fatten up for the flight from their more southern staging areas. Already some warblers such as the yellow-rumped warbler seem to be arriving earlier on their FIGURE 21B Climate Change Impacts breeding grounds, as expected if they are respond-on Waterfowl ing to earlier springs, whereas other species such as the chipping sparrow are arriving later, perhaps in response to colder springs immediately to the south of the region.94 If some year-round resident birds do thrive and expand in a warming climate, their success may further reduce the food available to populations of migratory songbirds breeding in the region, espe-cially if the pulse of midsummer insects is also See page 45 reduced. Forest bird diversity in the Great Lakes is for full-size color image of this figure highest in northern areas such as the Upper Penin-sula largely because of the increased diversity of migratory species. Warming therefore may reduce forest bird diversity if fewer resources are available to migratory songbirds. One study projects that the Great Lakes region could lose more than half its tropical migrants, although new bird species colonizing from outside the region could cut the net loss in bird diversity to 29 percent. Waterfowl are also expected to decline. Studies based on earlier and milder warming forecasts than those used in this report project 19 to 39 percent declines in duck numbers by the 2030s in response to lost breeding and migratory habitats as well as declines in the aquatic plants on which ducks feed.95 Loss of bird diversity will have economic as well as ecological consequences. Wildlife watching principally bird watchingis a $3.5 billion (US) a year industry in northern Michigan, Minnesota, and Wisconsin. In addition, huntingincluding waterfowl huntingis a $3.8 billion (US) industry in these three states (Figure 21b). Besides these potential economic losses, a decline in birds will mean a loss in ecological services such as seed dispersal and insect control.

watershed are deposited there, and these systems Impacts of Changes in Hydrology support rich plant, bird, and fish communities.96 All wetland types are sensitive to alterations in Inland wetlands are even more diverse and range hydrology that are likely to accompany climate from entirely rain-driven systems such as bogs to change (summarized in Table 5, p.28).97 A warmer riparian wetlands fed by contributions from both and drier climate will threaten both inland and surface and ground water. Bogs and fens cover coastal wetlands, although higher precipitation extensive areas in the northern Great Lakes region during winter and spring and intense storm events and contain a wide variety of acid-loving plants, may at times offset the generally decreased water including the widely known pitcher plant. levels.98 The largest impact should be on rainfall-C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N 31 Union of Concerned Scientists

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Aquatic Ecosystems dependent wetlands, since systems that are largely bacteria in wetland soils. Increased oxygen concentra-recharged by ground water are more resistant to tions in exposed soils, especially when accompanied climate-driven changes. Projected declines in sum-99 by acid precipitation, may release other metals such mer rainfall in the southern and western portions of as cadmium, copper, lead, and zinc,51 and wetlands the region (Figure 12, p.18) will also cause drying of downstream of industrial effluents could face in-prairie potholes and similar depressional wetlands. creased risk of heavy metal contamination during Some impacts will be positive. Although dropping periods of low water.

water levels will cause wetlands to shrink, new vegeta- Carbon stored in wetland soils may also be lost to tion may colonize formerly open-water habitats on some the atmosphere in a warmer climate. Northern peat-exposed shorelines, creating new types of habitat.100 lands such as those found in Minnesota and Ontario In wetlands fringing the Great Lakes, shoreline form when cold temperatures and waterlogged soils damage and erosion are likely limit the rate of decomposition to decrease as water levels of carbon-rich plant organic drop.101 Climate change will exacerbate matter.105 Warmer tempera-The impacts of climate human disturbances such as tures are likely to increase the change will often exacerbate rate of organic matter decom-continuing direct human dis- dredging and filling, water position and accelerate carbon turbances such as dredging and diversion, and pollution. release to the atmosphere in filling, water diversion, and the form of CO2. Carbon pollution.102 As demands for release from wetlands in the public drinking water supplies and irrigation water form of methane, which is 25 times more potent increase, for example, groundwater pumping may pose than CO2 as a greenhouse gas, will be enhanced by the greatest threat to ephemeral wetlands. Also, the warmer temperatures and higher water levels.106 spread of invasive species such as phragmites, purple Reduced stream flow in summer will also decrease loosestrife, and Eurasian water milfoil poses an added the amount of dissolved organic carbon washed from threat to many wetland communities, especially when land into surface waters. Less dissolved organic car-habitat or ecological processes are disrupted. 103 bon results in clearer water, which allows higher doses of ultraviolet-B radiation to penetrate further through Ecosystem Functioning the water column.107 Organisms such as frogs living Wetlands serve as the main interface for moving in shallow waters will be at greatest risk because UVB nutrients, pollutants, and sediments from land to penetration is generally restricted to the top two to water. Decreased runoff from the land, particularly in eight inches of the surface water.108 In deeper waters, summer, will decrease the deposition of material from organisms can find refuge from the harmful uplands into wetlands. The material that does enter radiation.109 wetlands will be retained longer, however, before high-water pulses flush it downstream into lakes and rivers. Impacts on Biodiversity Although decomposition rates will increase with Wetland plant and animal communities are contin-warmer temperatures, fluctuating water levels combined ually adapting to changing water levels, although with warmer temperatures are likely to reduce the extreme events such as drought or flooding can result capacity of wetlands to assimilate nutrients and in persistent disturbance to community structure and human and agricultural wastes. functions such as decomposition rates and produc-Fluctuations in water levels and soil moisture also tivity.110 Climate warming is likely to cause some influence the release of nutrients and heavy metals.104 wetland species to shift their ranges to accommodate Lower water levels expose more organic wetland soils their heat tolerances. Because of differences in breed-to oxygen, which may reduce exports of mercury (mer- ing habits, age to maturity, or dispersal rates, some cury binds with oxygen and is immobilized), but also species are more vulnerable than others to disturbance may reduce the breakdown of nitrate by denitrifying and change.111 Earlier spring or summer drying of 32 C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N Union of Concerned Scientists

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ephemeral wetlands, for example, will threaten repro- upon seasonal flood pulses and gradual drops in ductive success of certain species such as wood frogs water levels. Changes in the timing and severity of and many salamanders in the Great Lakes region the flood pulse will affect the availability of safe breed-(Figure 22).112 ing sites for birds and F I G U R E 2 2 In times of drought, when individual wetlands are amphibians. Midsummer Leopard Frog in Wisconsin Wetland isolated from one another, deep wetlands serve as a spike floods, for ex-safe haven or refugia for plants and animals until ample, can flood bird water levels are restored in dried-out wetlands. Loss nests in small wetlands of these refugia during longer or more severe droughts and attract predators will threaten populations of amphibians and other such as raccoons to areas less-mobile species. Landscape fragmentation exacer- where birds and amphi-bates this situation, leaving refugia scarcer and more bians breed. Changes in isolated.113 the timing of the spring Wetland loss and degradation also threaten to melt also greatly alter drive the yellow-headed blackbird locally extinct in migratory pathways and See page 44 the Great Lakes region. This songbirds habitat is timing. Canada geese, for full-size color image of this figure restricted to a small subset of marshes that have suit- which formerly wintered able vegetation in any given year as a result of fluctu- in flocks of hundreds of thousands in southern ations in water level. Land-use changes have greatly Illinois, now mainly winter in Wisconsin and further reduced the amount of suitable habitat, and further north in Illinois. The availability of seasonal mud-changes in water levels caused by increases in spring flats for migratory shorebirds and endangered, rain or summer drying could render remaining beach-nesting species such as the piping plover marshes unusable (see box, p.30). will be affected by the drying or loss of wetlands.

Finally, most aquatic birds in the region depend Fish Responses to Climate Change T

he body temperature of a fish is essentially red temperature by 3.5 to 9°F (2 to 5°C, depending equal to the temperature of the water in on the species) and seek out refuges provided by sources which it lives, and each species has a charac- of cooler water such as groundwater or seepage areas teristic preferred temperature. Rates of food consump- and headwater streams.114 Physical constraints such tion, metabolism, and growth rise slowly as the prefer- as drainage patterns, wa-red temperature is approached from below, and drop terfalls, and land-locked F I G U R E 2 3 Temperature Groupings rapidly after it is exceeded until reaching zero at the areas play a large role in of Common Great Lakes Fish lethal temperature. Common species of fish can be determining the boun-grouped according to their preferred temperatures daries of a species range into guilds (Figure 23). Fish will respond strongly and the rate at which it to changes in water volume, water flow, and water may respond to changing temperatures, either by shifts in distribution or in conditions. For example, overall productivity. temperature constraints prevented white perch Changes in Fish Distribution from the Atlantic coast Individual fish actively select and rapidly change from invading Lake On-living areas based on suitable temperatures, oxygen tario until the 1930s.

concentrations, and food availability. Cold-water fish Then, a series of warm See page 46 actively avoid temperatures that exceed their prefer- winters over a 20-year for full-size color image of this figure C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N 53 Union of Concerned Scientists

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Aquatic Ecosystems period permitted this species to spread through the nows and negative impacts on native top predators, Hudson River and Erie barge canal and into Lake Ontario particularly lake trout, in newly invaded lakes.118 by 1950.115 Table 6 summarizes the potential impacts These findings clearly demonstrate the ecological of climate warming on the distribution of fish species disruptions that will occur throughout the region as in the Great Lakes region. cold-water species disappear and warm- and cool-water Populations living near the edge of the species range species vie to take their place in a warmer world.

often exhibit greater year-to-year variation in abun- These disruptions are likely to be compounded by dance than populations living near the center of the invasions of nonnative organisms, many of which are range.116 Thus, when a southern boundary retracts north- capable of totally restructuring existing food chains ward, populations with historically stable abundances and causing significant consequences for native fish may become more variable. Populations living at the communities.119 The zebra mussel and European carp northern edge of the range tend to exhibit lower growth invasions in the Great Lakes region are perhaps the rates and greater sensitivity to exploitation. Thus, when best examples of such major disruptive events. Climate a northern boundary extends northward, populations warming is likely to permit zebra mussels and com-near the old boundary may become less sensitive to mon carp to expand their existing ranges northward exploitation and exhibit more stable abundance. in the Great Lakes region.

Many studies have forecast a potential northward As noted earlier, higher summer surface water expansion of the distribution of smallmouth bass, a temperatures and increased summer anoxia in deeper typical warm-water species that is native to the south- waters may lead to greater release of mercury from ern part of the Great Lakes basin.117 Recent work sediments.120 That would lead to higher mercury levels indicates that the consequences of that expansion in fish, which would harm not only fish populations could include local extirpation of many native min- but human consumers as well.50 TABLE 6 Changes Observed, Predicted, and Possible in the Ranges of Fish Species in the Lakes and Rivers of the Great Lakes Basin Distributional Changes Impacts on Species Extension at Perch, smallmouth bass: Predicted 300-mile extension of existing boundary northern limit across Canada with 7°F increase in mean annual air temperaturea Smallmouth bass, carp: Predicted 300-mile extension of existing boundary in Ontario with 9°F increase in mean annual air temperatureb Minnows (8 species), sunfishes (7 species), suckers (3 species), topminnows (3 species): Predicted extension into Great Lakes basin possible with warmingc Retraction at Whitefish, northern pike, walleye: Predicted retraction because of northward southern limit shift in sustainable yields expected to result from climate changed Lake trout and other cold-water species: Retraction predicted in small shield lakes at southern limit because lower O2 levels will shrink deep-water refuges from predation in summere Brook trout: Retraction predicted for streams at lower elevations throughout the southern edge of the range because of expected increases in groundwater temperaturesf Barrier release and White perch: Observed invasion and spread through Great Lakes basin when 1940s range expansion warming of Hudson River and Erie barge canal waters effectively removed thermal barrier and permitted accessg Striped bass: Predictions indicate that warming may permit this species to invade the Great Lakes basin and thus expand its range eastwardh Sources: See note 121.

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Changes in Fish Productivity lakes in the region because of summerkill, a lethal Within a lake, the productivity of a fish population combination of high surface water temperatures and is related to the amount of suitable living space, that decreased oxygen in bottom waters. This forecast is is, the volume of thermally suitable water. Studies of consistent with earlier work that predicted cold-water walleye, lake trout, and whitefish have demonstrated fish living in large, cold F I G U R E 2 4 that the abundance and productivity of fish increase lakes will be the most Water Temperature with increased time spent at the optimal temperature.122 secure against the nega- and Fish Distribution Changes There is also a trade-off between the positive effect of tive impacts of climate warmer temperatures on fish production and the nega- change.124 tive effect of lower lake levels due to drying. For In contrast, other stu-example, given a scenario where annual air tempera- dies predict less winterkill ture rises 5°F (3°C) and lake depth drops 3 feet, data of warm- and cool-water from North American lakes suggest that fish produc- fish living in shallow tion will decrease in lakes with a mean depth of 10 inland lakes because feet or less and increase in lakes with a mean depth shorter periods of ice greater than 10 feet.123 cover would eliminate Production of several species of sport fish (lake winter oxygen deficits.56 trout, walleye, and pike) and commercially harvested Most northern lakes are See page 46 fish (whitefish) in the region currently varies with the likely to develop more for full-size color image of this figure amount of thermally suitable habitat122 (Figure 24). suitable temperatures for Predictions are that climate warming will greatly walleye, a typical cool-water species in Ontario.

reduce the amount of thermally suitable habitat for However, a few southern lakes are likely to become lake trout in many inland lakes.56 This would effec- less suitable, with summer temperatures reaching tively eliminate lake trout from almost all shallow levels too warm for optimal growth.26 Economic Consequences of Climate and Ecological Change in Aquatic Systems Water Levels, Shipping, environmental costs. The direct costs of dredging and Hydropower Generation could exceed $100 million (US) annually.125 But D

ecreases in water levels have broad implica- dredging often stirs up buried pollutants, which may tions for both ecological and human systems impose additional costs on society. The estimated in and around the large lakes. Ship clear- costs for a four- to eight-foot drop in water level ance in channels and harbors is reduced, requiring range from $138 million to $312 million (US), and ships to carry less weight in order to ride higher in the price for extending water supply pipes, docks, the water. The Great Lakes Carriers Association esti- and stormwater out-falls to the new waterline would mates that with a one-inch drop in lake level, a 1,000- add another $132 million to $228 million (US).125 foot ship loses 270 tons of cargo capacity.125 An earlier Decreased water levels could reduce hydropower assessment based on milder projections of warming generation by as much as 15 percent by 2050, an es-found that shipping costs could increase by 5 to 40 timate that is likely to be conservative because it was percent as a result of lower lake levels.126 A potential based on older climate models.126 Hydropower accounts counter to this negative impact is that reduced ice cover for almost 25 percent of the electricity generated in will lengthen the shipping season on the Great Lakes. Ontario,16 while in the United States, significant Stepped-up dredging of channels and harbors hydropower is generated at the Moses Niagara Plant is often used to increase ship clearance in times of in New York State (Figure 25). Demand for more low water, incurring both direct economic costs and hydropower will be created in the future by the need C O N F RO N T I N G C L I M AT E C H A N G E I N T H E G R E AT L A K E S R E G I O N 55 Union of Concerned Scientists

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Aquatic Ecosystems TABLE 7 Climate Change Impacts on Fish Ecology and Consequences for Fisheries Climate Change Impacts on Fish Ecology Consequences for Fisheries Change in overall fish production in a particular Change in sustainable harvests for all fish populations aquatic ecosystem in the ecosystem Change in relative productivity of individual fish Change in the relative levels of exploitation that can populations in a particular aquatic ecosystem be sustainably directed against the fish populations of the ecosystem Large-scale shifts in geographic distribution Change in mixture of species that can be sustainably of species harvested within a specific geographic area Change in location of profitable fishing grounds Small-scale shifts in the spatial distribution Change in sustainable harvest for the population of members of a specific population Change in efficiency of fishing gear, leading to change in sustainable levels of fishing effort to reduce CO2 emissions from fossil fuel-fired power specific population in a specific location may increase plants. As hydropower opportunities decline in the substantially or fall to zero, depending on how new Great Lakes region, pressure may increase to build climate conditions and species-specific temperature such projects elsewhere, such as in the James Bay needs interact.

region. The commercial fishing sector in the region is rela-Water withdrawals from the Great Lakes are tively small. Landed catches in the late 1990s were FIGURE 25 already subject to conten- valued at about $47 million (US), including $33 mil-Water Changes Affect Hydropower tious debate, and political lion taken by Canadian fishers and $14 million taken leaders in the region have by US fishers. Most of the commercial catch in Canada opposed further withdraw- comes from Lake Erie and that in the United States als, especially for water to from Lake Michigan.

be shipped out of the basin. In contrast, the recreational fishing sector is quite Given projections for drier large in both countries. In the 1990s, 7.7 million summers in the region, recreational anglers spent $7.6 billion (US) on fishing pressure to increase water in US waters13 and 2 million anglers spent $3 billion extraction for irrigation, (Cdn) on fishing in Canadian waters.128 These anglers drinking, and other uses spent about 9 million fishing days on the Great Lakes See page 47 will grow even within the alone, not counting fishing on inland lakes, rivers, for full-size color image of this figure basin. One study found that and streams. Large changes in the distribution and the synergistic effects of predicted decreases in runoff productivity of fish species in the region will signifi-and increases in irrigation could be devastating to cantly impact the nearly 10 million anglers that the regions streams.127 actively fish these waters.

These dollar figures do not reflect the full value of Fisheries ceremonial and artisanal fisheries practiced by Native Climate-driven changes in fish populations and com- Americans and First Nations in many settlements scat-munities will produce a variety of impacts on existing tered throughout the Great Lakes basin. Fishing plays fisheries (Table 7). Most of these impacts will stem an important role in the traditional social structures from two mechanisms: (1) the sustainable harvest of these communities, a role that defies easy quanti-of fish will rise and fall with shifts in overall aquatic fication and will not be reflected in cost accountings productivity, and (2) sustainable harvests from a of impacts that are based purely on market measures.

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