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Mechanisms influencing changes in lake area in Alaskan boreal forest

TitleMechanisms influencing changes in lake area in Alaskan boreal forest
Publication TypeJournal Article
Year of Publication2011
AuthorsRoach, J, Griffith, B, Verbyla, D, Jones, J
JournalGlobal Change Biology

During the past 50 years, the number and area of lakes have declined in several regions in boreal forests. However, therehas been substantial finer-scale heterogeneity; some lakes decreased in area, some showed no trend, and others increased.The objective of this study was to identify the primary mechanisms underlying heterogeneous trends in closed-basin lakearea. Eight lake characteristics (d18O, electrical conductivity, surface : volume index, bank slope, floating mat width, peatdepth, thaw depth at shoreline, and thaw depth at the forest boundary) were compared for 15 lake pairs in Alaskan borealforest where one lake had decreased in area since 1950, and the other had not. Mean differences in characteristicsbetween paired lakes were used to identify the most likely of nine mechanistic scenarios that combined three potentialmechanisms for decreasing lake area (talik drainage, surface water evaporation, and terrestrialization) with three potentialmechanisms for nondecreasing lake area (subpermafrost groundwater recharge through an open talik, stable permafrost,and thermokarst). A priori expectations of the direction of mean differences between decreasing and nondecreasing pairedlakes were generated for each scenario. Decreasing lakes had significantly greater electrical conductivity, greatersurface : volume indices, shallower bank slopes, wider floating mats, greater peat depths, and shallower thaw depths atthe forest boundary. These results indicated that the most likely scenario was terrestrialization as the mechanism for lakearea reduction combined with thermokarst as the mechanism for nondecreasing lake area. Terrestrialization andthermokarst may have been enhanced by recent warming which has both accelerated permafrost thawing and lengthenedthe growing season, thereby increasing plant growth, floatingmat encroachment, transpiration rates, and the accumulationof organic matter in lake basins. The transition to peatlands associated with terrestrialization may provide a transientincrease in carbon storage enhancing the role of northern ecosystems as major stores of global carbon.

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