Climate Change in the Champlain Basin - The Nature Conservancy

What natural resource managers can expect and doLake levelThe level of a lake rises and falls in response to many factors,including surface inputs and outflow, evaporation,groundwater seepage, and manipulation or blockage ofoutlet channels. In the case of Lake Champlain, however,the primary climatic factors are the amount of precipitationthat falls on the watershed, the melting of snow and ice,and the permeability of the ground. Lake levels are at theirhighest in spring, as narrowoutlet morphology restrictsthe escape of excess waterfrom snowmelt and rainwaterrunning off frozen or watersoakedsoils.The 3-inch increase of annualprecipitation in the watershedduring the early 1970s wasaccompanied by a roughly1-foot increase in mean lakelevel measured at the KingStreet Dock in Burlington(Figure 3). Some of that risemight have been related tooutflow restrictions resultingfrom modification of theChambly Canal 1971–1974(M. Winslow, personal communication),but the extremelyclose correspondencebetween interannual variabilityin lake level and precipitationsuggests that climate was alsoan important factor behindthe change. If annual precipitation increases 4–6 inchesby the end of this century as most models suggest underan A2 scenario, and if the relationship between precipitationand surface levels still follows its current pattern, thenLake Champlain could stand as much as 1-2 feet higher,on average, by 2100. Future warming is also likely to movethe date of the snowmelt-driven lake level pulse earlier inthe year. Meanwhile, heat-driven evaporation and possiblesummer rainfall reductions could intensify low stands in latesummer and early autumn, producing a wider range of lakelevel fluctuations over the course of the year.However, several factors in addition to the limitations ofclimate models complicate efforts to predict Lake Champlain’shydrological future with precision. Winter warmingshould reduce the amount of snow and ice on the ground,which could decrease the volume of water that is releasedin late-season melting events and distribute runoff moreevenly through the colder months, thus allowing more ofit to escape through the outlet by springtime. This mightalso leave water tables and soil moisture contents lowerduring subsequent warmer months even if total annualprecipitation increases. In addition, summer warming islikely to increase evaporation from the lake and surroundingwatershed. Modeling byEnvironment Canada suggeststhat the surface levels of theGreat Lakes could decline by8 inches to 8 feet (0.2-2.4 m)under a doubled CO2 scenario(Mortsch and Quinn, 1996).As we seek to understand thelikely balance between waterinputs and outputs specific toLake Champlain and its tributariesin a warmer, potentiallywetter future, comprehensivehydrological modeling andmonitoring in the watershedwill become more importantthan ever.Nutrient loadingCultural eutrophication isalready a serious problem inLake Champlain due to nutrientinputs from human activityLaPlatte Natural Area © Glenn Suokkoin heavily settled and farmedportions of the watershed. Warming and possible wettingin the future are likely to aggravate the problem even if thenutrient sources themselves remain unchanged. As summerwarming increases the stability and/or duration of stratifiedconditions in the lake, nuisance blooms of nitrogen-fixingcyanobacteria that are already stimulated by phosphorus inputsmay become more frequent and abundant. And if moreabundant or intense precipitation increases the delivery ofphosphorus from soils and settlements to the lake, eutrophicationwill be enhanced even further.19