THE EFFECTS OF SHORT-TERM CLIMATE CHANGE ON THE THERMAL REGIME OF SHALLOW STRATIFIED LAKES

Though shallow (< 6m av. depth) dimictic lakes in temperate regions comprise significant habitat very little is understood about how climate change will affect the thermal structure of these lakes. As well, the variable internal response of these lakes to past climate change (most notably Younger Dryas cooling) is known but not well understood.  In our study we performed detailed lithostratigraphic, morphometric, and thermal analyses over a three year period on two lakes in Nova Scotia that were similar in almost all respects (volume, area, depth, chemistry etc.) but were morphometrically unique.

Lithostratigraphic records from Canoran Lake (shallow sided, high littoral:pelagic ratio) indicated a strong autochthonous response to post glacial climate change whereas Sandy Lake (steep sided, low littoral:pelagic  ratio) exhibited no discernable lithostratigraphic response.  Thermal data (2002 – Present) indicated that these two lakes react uniquely and strongly to short duration climate events. For instance, during a low-pressure influx, Sandy Lake exhibited strong metalimnic entrainment and a pronounced downwards displacement of the parent thermocline within a 24 hour period whereas Canoran Lake experienced little change.  Wind speed, duration and fetch distance were the same at both lakes. Once spring stratification had developed, hypolimnetic temperatures remained nearly constant in Canoran Lake but increased in Sandy Lake in response to each climate event.  Our results indicate that morphometry strongly influences the efficiency of storm related heat transfer.  An understanding of the variance in the thermal sensitivity of seemingly similar lakes can be used by paleolimnologists to better understand variability in paleoclimate proxies. As well, the thermal sensitivity models based on this data will allow ecologists to better understand how lakes (as habitat) will evolve and are essential to the implementation of species monitoring and conservation programs.