Effects of recent climate and environmental changes on the ecology of a boreal forest lake in Manitoba, Canada

Application of paleoenvironmental approaches provides insight into the magnitude and timing of responses to climate warming in aquatic-ecosystems of northern Canada. We examined subfossil biological (Diptera:Chironomidae) and geochemical indicators (organic carbon and elemental nitrogen and stable isotope composition) in a sediment core from Buckland Lake, northern Manitoba, to assess the influence of recent warming (1981–2011) in the central subarctic region of Canada. The earlier part of the paleolimnological record (1830–1980) was characterized by relatively low chironomid diversity (N2 ~ 6), consisting primarily of profundal taxa (Orthocladius consobrinus and Chironomus), low organic matter content of sediments (< 12%), low C:N ratios (< 9), and high δN values (> 3‰), indicative of a cold-water environment with low nitrogen demand. Between 1910 and 1980, there was a decline in profundal taxa, with small gradual increases in littoral taxa, such as Cladotanytarsus mancus-group. Post-1980 sediment core intervals had distinct geochemistry, with declines in δC from − 27.5‰ to almost − 29‰, consistent with warming, increased terrestrial influence, and increased snowfall and runoff. We found substantial inferred warming (+ 1–2 °C), with several chironomid-inferred temperatures nearly 3 °C warmer than typical pre-1980 inferences. Concurrently, several warm-water-adapted littoral chironomid taxa (Cladopelma, Cryptochironomus, Polypedilum) recorded increases. The post-1990 records reflected continued increases in warm-water taxa, changes in the benthic:pelagic trophic structure, and reversal of previous trends in the δC, %Organic Carbon, and δN profiles, suggestive of increased aquatic productivity. The meteorological station at Gillam, Manitoba, also recorded warming (1.5 °C) and a reduction in snowfall during that time period. A reduction in spring recharge may have increased littoral habitat associated with lake-level drawdown. The climate-driven shift observed ~ 1980 is in generally good agreement with other regional analyses, which show regime shifts occurred ~ 1995. The earlier lake response (~ 1980), however, demonstrates the role of increased catchment-mediated influences on northern boreal lake productivity that may only appear in records with sufficiently high resolution and multiple paleolimnological indicators.