Sedimentary diatoms from sensitive alpine (northwest Canada) and subarctic (Iceland) lakes as indicators of environmental and climatic conditions

Postglacial climatic and limnological conditions were inferred from sedimentary diatom assemblages from an alpine lake in the northern Canadian Rocky Mountains. Throughout the Holocene, diatom assemblages were mostly dominated by small, benthic Fragilaria spp. reflecting relatively cold, shallow, alkaline and low light conditions due to turbidity or ice-cover. Compositional changes of the diatom assemblages tracked major changes in terrestrial vegetation, but the most striking changes occurred during the mid-Holocene (c. 5500 to 3500 cal. yrs BP) and the Medieval Warm Period (c. AD 800--1250) independent of inferred vegetation shifts. During these times, increased diversity and dominance of periphytic diatoms suggested higher productivity, longer growing seasons, and reduced alkalinity and turbidity at BC2 Lake with a progression to wetter climates of the late-Holocene, but still warmer-than-present temperatures.; Diatom responses to 20th century climate-related environmental changes were assessed from three high-elevation lakes in the northern Canadian Cordillera. Overall, dominance of small benthic Fragilaria diatoms reflect generally cold conditions with short growing seasons and extended periods of ice cover that have characterized these mountain lakes over at least the last ∼300 years until the period of recent warming. Limhological changes were inferred from the diatoms at all three sites with the onset of 20th century warming, however the lakes displayed individualistic responses largely attributed to differences in their physical setting (e.g., bedrock geology, elevation, catchment vegetation).; Limnological properties of 49 Icelandic lakes displayed apparent differences related to major topographic, geological and hydrological characteristics. The wide range of limnological conditions and habitat types of the lakes is reflected in the great taxonomic diversity of the diatom assemblages (329 taxa). Small benthic Fragilaria taxa were the most abundant diatoms, reflecting the generally cold lake water conditions and extended periods of ice cover characteristic of this subarctic region. Ordination analysis suggested that the distribution of diatoms was best explained by a combination of mean depth, surface water temperature, conductivity, alkalinity, total organic carbon, total nitrogen and SiO2 concentrations. Results provide a basis for ecological classification of Icelandic lakes for management purposes, as well as a framework for future diatom-based paleolimnological studies of climatic and environmental changes in Iceland.