Roach, J., B. Griffith, D. Verbyla, and J. Jones. 2011. Mechanisms influencing changes in lake area in the Alaska boreal forest. Global Change Biology 17:2567-2583. doi: 10.1111/j.1365-2486.2011.02446.x
Abstract
During the past 50 years, the number and area of lakes have declined in several regions in boreal forests. However, there
has 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 lake
area. Eight lake characteristics (d18O, electrical conductivity, surface : volume index, bank slope, floating mat width, peat
depth, thaw depth at shoreline, and thaw depth at the forest boundary) were compared for 15 lake pairs in Alaskan boreal
forest where one lake had decreased in area since 1950, and the other had not. Mean differences in characteristics
between paired lakes were used to identify the most likely of nine mechanistic scenarios that combined three potential
mechanisms for decreasing lake area (talik drainage, surface water evaporation, and terrestrialization) with three potential
mechanisms 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 paired
lakes were generated for each scenario. Decreasing lakes had significantly greater electrical conductivity, greater
surface : volume indices, shallower bank slopes, wider floating mats, greater peat depths, and shallower thaw depths at
the forest boundary. These results indicated that the most likely scenario was terrestrialization as the mechanism for lake
area reduction combined with thermokarst as the mechanism for nondecreasing lake area. Terrestrialization and
thermokarst may have been enhanced by recent warming which has both accelerated permafrost thawing and lengthened
the growing season, thereby increasing plant growth, floatingmat encroachment, transpiration rates, and the accumulation
of organic matter in lake basins. The transition to peatlands associated with terrestrialization may provide a transient
increase in carbon storage enhancing the role of northern ecosystems as major stores of global carbon.