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<p>Lake Opinicon is a shallow, macrophyte-dominated, oligo-mesotrophic ecosystem that forms part of the Rideau Canal system linking Ottawa and Kingston (Ontario, Canada). Recent paleolimnological studies have demonstrated that, despite significant historic land-use changes over the past ~ 250&#xa0;years, limnological changes in Lake Opinicon linked to recent regional climate warming (post ~ 1990s) likely had the most pronounced influence on algal (diatom) and zooplankton (Cladocera) assemblages. The only long-term data available on changes in bottom-water conditions in Lake Opinicon were from a chironomid-based paleolimnological study conducted over two decades ago, showing only modest shifts in assemblage composition from the pre-canal construction period (pre-1830s) to the mid-1990s (when the core was taken). However, temperature and dissolved oxygen monitoring data collected between 2012 and 2015 show that Lake Opinicon was shifting from a polymictic to a dimictic mixing regime, with concurrent changes in bottom-water oxygen levels. Moreover, there is limited understanding of how benthic communities have responded within Lake Opinicon to the recent period of marked warming. Using a sediment core collected from Lake Opinicon in 2019 (~ 25&#xa0;years after the initial paleolimnological study), we assess chironomid assemblages, with a particular focus on the past ~ 30&#xa0;years, to evaluate the impacts of historic environmental stressors and regional climatic warming on benthic organisms and bottom-water oxygen concentrations. Similar to the earlier study, we show only minimal changes associated with the construction of the Rideau Canal, but with increased anoxic-tolerant taxa occurring between ca. 1910–1981, likely reflecting under-ice anoxia associated with cultural eutrophication. The most significant assemblage change occurred post ~ 1990, with a major increase in anoxic and warm-tolerant taxa. These data indicate that recent climate warming, changes in thermal stratification, and associated declines in bottom-water oxygen concentrations have had the largest impact on benthic taxa within Lake Opinicon.</p>

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Declining bottom-water oxygen concentrations recorded by subfossil chironomid assemblages follow climate-driven changes in thermal stratification

  • 期刊论文

  • 发表日期：

    2025年11月1日

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  • Dylan J. Lansing,
  • Emma L. Graves,
  • Kapillesh Balasubramaniam,
  • Neal Michelutti,
  • Andrew M. Paterson,
  • John P. Smol

摘要

Lake Opinicon is a shallow, macrophyte-dominated, oligo-mesotrophic ecosystem that forms part of the Rideau Canal system linking Ottawa and Kingston (Ontario, Canada). Recent paleolimnological studies have demonstrated that, despite significant historic land-use changes over the past ~ 250 years, limnological changes in Lake Opinicon linked to recent regional climate warming (post ~ 1990s) likely had the most pronounced influence on algal (diatom) and zooplankton (Cladocera) assemblages. The only long-term data available on changes in bottom-water conditions in Lake Opinicon were from a chironomid-based paleolimnological study conducted over two decades ago, showing only modest shifts in assemblage composition from the pre-canal construction period (pre-1830s) to the mid-1990s (when the core was taken). However, temperature and dissolved oxygen monitoring data collected between 2012 and 2015 show that Lake Opinicon was shifting from a polymictic to a dimictic mixing regime, with concurrent changes in bottom-water oxygen levels. Moreover, there is limited understanding of how benthic communities have responded within Lake Opinicon to the recent period of marked warming. Using a sediment core collected from Lake Opinicon in 2019 (~ 25 years after the initial paleolimnological study), we assess chironomid assemblages, with a particular focus on the past ~ 30 years, to evaluate the impacts of historic environmental stressors and regional climatic warming on benthic organisms and bottom-water oxygen concentrations. Similar to the earlier study, we show only minimal changes associated with the construction of the Rideau Canal, but with increased anoxic-tolerant taxa occurring between ca. 1910–1981, likely reflecting under-ice anoxia associated with cultural eutrophication. The most significant assemblage change occurred post ~ 1990, with a major increase in anoxic and warm-tolerant taxa. These data indicate that recent climate warming, changes in thermal stratification, and associated declines in bottom-water oxygen concentrations have had the largest impact on benthic taxa within Lake Opinicon.