The late-Quaternary paleoenvironmental history of the western Hudson Bay region of Subarctic Canada is poorly constrained. Here, we present a regional overview of the post-glacial history of eight lakes which span the forest-tundra biome in northern Manitoba. We show that during the penultimate drainage phase of Lake Agassiz the lake water had an estimated pH of ∼6.0, with abundant quillwort (Isöetes spp.) along the lakeshore and littoral zone and some floating green algae (Botryococcus spp. and Pediastrum sp.). Based on multiple sediment proxies, modern lake ontogeny in the region commenced at ∼7500 cal yrs BP. Pioneering diatom communities were shaped by the turbid, higher alkalinity lake waters which were influenced by base cation weathering of the surrounding till following Lake Agassiz drainage. By ∼7000 cal yrs BP, soil development and Picea spp. establish and the lakes began a slow trajectory of acidification over the remaining Holocene epoch. The natural acidification of the lakes in this region is slow, on the order of several millennia for one pH unit. Each of the study lakes exhibit relatively stable aquatic communities during the Holocene Thermal Maximum, suggesting this period is a poor analogue for modern climatic changes. During the Neoglacial, the beginning of the post-Little Ice Age period represents the most significant climatic event to impact the lakes of N. Manitoba. In the context of regional lake histories, the rate of diatom floristic change in the last 200–300 years is unprecedented, with the exception of post-glacial lake ontogeny in some of the lakes. For nearly the entire history of the lakes in this region, there is a strong linkage between landscape development and the aquatic ecosystems; however this relationship appears to become decoupled or less strong in the post-LIA period. Significant 20th century changes in the aquatic ecosystem cannot be explained wholly by changes in the terrestrial ecosystem, suggesting that future changes to the lakes of N. Manitoba will be strongly influenced by direct climatic effects to the lakes.
Bibliographical noteFunding Information:
Tom Brown at the Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory provided the radiocarbon dating of macrofossils and Dan Engstrom at St. Croix Watershed Research Station dated and provided interpretation of recent sediments using 210Pb methods. Thank you also to pilots Jon Kovac, Jason Essaunce, and Mark Leyden and the staff at The Lodge at Little Duck for assistance in the field. Undergraduates Kendra Passow, Pat Henneghan and Mark Krueger also provide much able help. This study was supported by National Science Foundation grants DEB-0743364, DEB-0904050, DEB-0092704, and DBI-0520803. Initial core processing was performed at the Limnological Research Center/LacCore (University of Minnesota).
- Holocene Thermal Maximum
- Lake ontogeny
- Little Ice Age
- Northern Manitoba