Climate Change in the Champlain Basin - The Nature Conservancy

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Climate Change in the Champlain BasinLake-connected wetlands and shorelinesLake Champlain has 587 miles of shoreline encompassingbeaches, rocky bluffs, talus slopes, and developed shorefrontproperty as well as extensive wetlands (LCBP, 2004).There are 166 wetlands larger than 50 acres with a directhydrologic connection to the lake, including marshes, silvermaple/ash swamps, shrub swamps and floodplain foreststhat provide critical habitat for a rich diversity of wildlife(Munno et al., 2005).Wetland plants and animalscan be sensitive to changes intemperature or water supply.A rise in temperature may allowsome kinds of invasive plantsto colonize new locations oroutcompete native species(see “Invasive species andclimate change,” page 32), anda change in the seasonality ofprecipitation can affect plantsor animals whose life cyclesrequire certain levels of water atspecific times of year (EnvironmentCanada, 2009). However,the likely impacts of climaterelatedchanges on wetlandorganisms in the ChamplainBasin during this century haveyet to determined.Least bittern © Benoît Jobin, Canadian Wildlife ServiceThe relationship between the seasonality of lake levels andthe shoreline ecology of Lake Champlain is another areain need of further study. Long-term warming in winter mayreduce snowpack and the magnitudes of lake level maximain spring, which might change the amount of seasonallyflooded shoreline habitat available to some organisms. Increasedevaporation and/or a possible reduction of rainfallduring summer might drop lake levels more than usual duringthe warmer months and thereby alter the distribution ofshoreline habitats as well.Lakeshore wetlands may either gain or lose acreage ifmean or seasonal lake levels change during this century,depending upon availability of unoccupied ground upslope.Wetlands can accommodate rising lake levels onlyto the extent that their inland migration is not limited bytopography, seawalls or other development. Some marginalwetlands may be at risk of being pinned against immovablebarriers if the lake rises substantially in the future.Reductions in the extent and duration of ice cover duringthis century are likely to expose Lake Champlain’s shorelinesto wave action for longer periods of the year, therebypotentially increasing annual erosion rates even withoutconcurrent changes in lake levels or wind activity. However,vegetated buffer zones can help to resist wave erosion whileenhancing shoreline habitat and absorbing stormwaterand pollutants. Such buffers also contribute plant detritusto littoral habitats, which can provide shelter, food and/orcolonization sites for aquatic invertebrates and fish as wellas reptiles, amphibians, birds andmammals (Connin, 2003).Artificial shoreline “hardening”by retaining walls and otherstructures resists wave erosion,too, but it restricts the naturalmovements of water, substrates,vegetation and wildlife (Connin,2003). As a result, fishdiversity and abundance tendsto decline along deforestedand walled shorefronts (Trial etal., 2001). Shoreline hardeningmay increase or creep inland iflake levels and the frequencyof strong storms rise, but atpresent, guidelines and oversightare inconsistent from onetown and state to the next, andconservation is not always a required design consideration.For instance, code-enforcement officials from the heavilydeveloped lakeshore communities of Colchester, VT, andWillsboro, NY, report an increase in shoreline hardeningduring the past decade, but mandatory building setbacksdiffer between locales (100 feet from 95.5-foot normalwater level in Colchester, and 50, 75 or 150 feet from 99.8-foot mean spring high water level in Willsboro).Littoral zoneThe littoral zone is the relatively shallow, biologically richnear-shore portion of the lake, where sunlight easilyreaches the bottom. It encompasses slightly more thanhalf of Lake Champlain’s surface area, and includes bedsof submergent vegetation, rocky or soft bottoms, and riverdeltas. Although compromised by invasive zebra mussels,the littoral zone still supports the lake’s most biologicallyproductive and diverse communities of plankton, plants,vertebrates and macroinvertebrates.22
What natural resource managers can expect and doMajor Ecological Impacts to Watch ForTributary systems• Earlier spring high flows, ice jams and flooding• Decrease in snowpack and ice, resulting in moremeltwater flow in winter but possibly less severeconditions in spring• Lower, warmer and less oxygenated tributaries insummer• Less habitat for cold-water species• Increased likelihood of nuisance cyanobacterialblooms• Lower oxygen content at depth• Changes in the timing of plankton growth andcommunity structure• Decreased water quality from enhanced nutrientand sediment inputs• Changes in the timing ofspawning• Increased nutrient inputs frompotentially enhanced precipitationand increased intensities ofrainstorms• More erosion and siltation• Physical disruption of streambedhabitat for fish eggs and invertebratesWetlands and shorelines• Possible changes in average lake levels• Changes in the acreage of lakeshore and riparianwetlands• More extensive artificial hardening of lakeshoresin response to water level changes, resulting inblockage or degradation of breeding and spawninghabitatFragile papershell © Darby Creek AssociationFish assemblages• Plankton-based food webchanges in fish communities• New invasive species• Temperature-driven shifts in thelocations and extent of habitats• Competitive advantages towarm-water over cold-waterspecies• Potential dominance of alewives over smelt withnegative effects on the health of predators such aslake trout and Atlantic salmon• Impaired habitat quality from increased nutrientinputs, sedimentation and prolonged thermalstratification• Spawning affected by changes in the timing, temperatureand/or volume of seasonal stream flow• Increased methlymercury in food webs• Sensitivity of wetland plants and animals towarming and changes in hydrology• Possible larger array of invasive wetland plantsNearshore and offshore lake habitats• Decreased ice cover• Warmer surface temperatures• Longer and more extreme summer thermalstratificationNative mussels• Sensitivity to changes in temperature, oxygen content,toxins, sedimentation and hydrologic regimes• Altered host-fish availability• Increased damage from pollutants that interferewith calcium assimilation• Possible competition with new invasive mollusks23
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Climate Change in the Champlain Basin - The Nature Conservancy

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