Testate amoebae (thecamoebian) based reconstruction of Lake Simcoe fringe wetland paleoenvironments

摘要

Lake Simcoe, Ontario, Canada, a large southern Ontarioglacial lake, has been affected by multiple environmentalstressors throughout its history. This study uses testateamoebae paleodistribution to reconstruct the environmentalconditions of Lake Simcoe's fringe wetlands before and duringthe Anthropocene.Testate amoebae are unicellular shelled protists thatinhabit almost every environment in the world from sandymarine beaches to all freshwater and terrestrial habitats.Their rapid asexual reproduction makes testate amoebaesensitive indicators of short-lived environmental change.Paleolimnological and paleoecological investigations usingtestate amoebae have been used to describe hydrology, pH,trophic status, land use, climate change, forest fires, oxygenconcentrations, metal contamination and other variables.Using compound microscopy techniques, testate amoebaeassemblages were identified and tabulated from processedsedimentary cores extracted from fringe wetlands in LakeSimcoe and Tub Lake, with the latter lake used as a referenceto assess anthropogenic impact during the Anthropocene. Onecore, taken from the outlet area of Lake Simcoe, was used toreconstruct the past variability of the paleoenvironment whileall four cores were used to reconstruct Anthropocenepaleoenvironments.Prior to European settlement three distinct testateamoebae communities inhabited the Victoria Point wetland areabased on hydrologic variability: an arctic-like, oligotrophictestate amoebae community dominated by alkaline, lacustrinespecies; a CaCo3-based community dominated by mesotrophiccalcipiles; and an "early fringe wetland community" dominatedby aquatic and soil-based species.The anthropogenic activities of the last ~200 years leadto a rapid paludification of the shoreline in all Lake Simcoewetland locations. Anthropogenic activities have also produceda constant state of disturbance along the shoreline where themean rate of change in the testate amoebae community since ~AD1300 (0.46) is greater than the rate of change in thepreceding record (0.40). Some of this change is alsoattributable to recent climate change particularly in thewinter and spring, and possibly to the introduction of theZebra mussel in the mid 1990s.While similarities in the response of testate amoebaeassemblages across wetlands do exist, this study has alsofound that local activities have affected testate amoebaeassemblage paleodistributions, species richness and diversity.