Baptiste Lake, Alberta ? A late Holocene history of changes in a lake and its catchment in the southern Boreal forest

Abstract

Palaeoenvioonmental investigations based upon sediment cores retrieved from Baptiste Lake, Alberta (longitude 114° 34′ W; latitude 54° 45′ N) show that the sedimentary record spans approximately 4600 years. The pollen record reflects the dynamic nature of the southern boreal forest. These dynamic changes are reflected in the lake record itself. Climate and vegetation do not appear to have changed significantly; however, the lake does appear to have responded to climate change, particularly during the last 1000 to 700 years when temperatures decreased to modern values. It is at this time that there is a marked change from laminated to unlaminated sediments suggesting a change from meromixis to one where complete circulation takes place. As a result monolimnetic nutrients are released into the epilimnion. Catchment perturbations have occurred with fire appearing most important. Sedimentation rates are high on average and irregular, due in part to the many inflowing streams, catchment topography and fire. Lake production has always been high. Carbonate bands occur in the core at irregular intervals and appear to originate biogenically. Peaks in the number of pyrite spherules suggest that deoxygenation of the water column occurs irregularly, and the intensity of anaerobic conditions again varies. The diatom record indicates a eutrophic lake with Stephanodiscus hantzschii the dominant species. The lake appears to have steadily become more eutrophic with time and a succession of species has occurred with Asterionella formosa being succeeded in turn by Stephanodiscus niagare, Cyclotella comta and finally, Melosira granulata. The appearance of Melosira granulata corresponds to the change from laminated to unlaminated sediments, and to then both autochthonous and allochthonous nutrient input.