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<p>Anthropogenic stressors are increasing the vulnerability of freshwater systems, causing them to alter their ecosystem functions and lose biodiversity. For this project, we combined analyses of sediment elemental composition, VRS chlorophyll <i>a,</i> and subfossil cladoceran assemblages to assess the environmental history of three eastern Canadian lakes that are currently experiencing a range of pressures in their watersheds over the past ~ 300&#xa0;years. The study lakes were sampled by the NSERC Canadian Lake Pulse Network, designed to advance the understanding of lake health in Canada. The goals of this manuscript are to 1) provide long-term trajectories for three LakePulse lakes along a modern land use gradient in Eastern Canada and 2) consider how cladocerans respond to a wide range of potential environmental drivers, including changes in lake production (VRS-chlorophyll <i>a</i>), climate change (via long term historical records) and changes in watershed and mining activities (inorganic geochemistry). In all three lake records, we observed changes in geochemical indicators to occur as early as the mid-1700s (likely related to European settlement of the area), whereas pronounced changes in sediment VRS chlorophyll<i> a</i> were observed to increase in all three lakes around 1950 CE. The key changes in cladoceran assemblages varied somewhat by lake, likely due to different anthropogenic and environmental stressors. However, with concordant rises in primary production, nutrient levels, and metal contamination (patterns that can be linked to subsequent land use changes), <i>Bosmina</i> taxa remained dominant across all three lakes, likely due to their flexible traits. <i>Chydorus brevilabris</i> increased in two lakes coincident with rising primary production, likely due to their ability to shift from a benthic to a pelagic habitat with rising nutrients and declining macrophyte coverage. A different cladoceran response was observed in the deepest lake considered (Green Lake), where we detected an initial increase of <i>C. brevilabris</i> in Green Lake around 1700 CE possibly due to land clearance and/or a lake level change, which was followed by a rise <i>Bosmina</i> taxa. Overall, the complete time series presented herein demonstrates the importance of utilizing multiple proxies and expanding research beyond top–bottom comparison to better contextualize changes observed in recent times.</p>

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Long-term changes in three eastern Canadian lake records with different land use histories: a multiproxy study

  • 期刊论文

  • 发表日期：

    2025年7月28日

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  • Madeleine E. Aucoin,
  • Zoë Rabinovitch,
  • Jennifer Pham,
  • David R. Zilkey,
  • Irene Gregory-Eaves

摘要

Anthropogenic stressors are increasing the vulnerability of freshwater systems, causing them to alter their ecosystem functions and lose biodiversity. For this project, we combined analyses of sediment elemental composition, VRS chlorophyll a, and subfossil cladoceran assemblages to assess the environmental history of three eastern Canadian lakes that are currently experiencing a range of pressures in their watersheds over the past ~ 300 years. The study lakes were sampled by the NSERC Canadian Lake Pulse Network, designed to advance the understanding of lake health in Canada. The goals of this manuscript are to 1) provide long-term trajectories for three LakePulse lakes along a modern land use gradient in Eastern Canada and 2) consider how cladocerans respond to a wide range of potential environmental drivers, including changes in lake production (VRS-chlorophyll a), climate change (via long term historical records) and changes in watershed and mining activities (inorganic geochemistry). In all three lake records, we observed changes in geochemical indicators to occur as early as the mid-1700s (likely related to European settlement of the area), whereas pronounced changes in sediment VRS chlorophyll a were observed to increase in all three lakes around 1950 CE. The key changes in cladoceran assemblages varied somewhat by lake, likely due to different anthropogenic and environmental stressors. However, with concordant rises in primary production, nutrient levels, and metal contamination (patterns that can be linked to subsequent land use changes), Bosmina taxa remained dominant across all three lakes, likely due to their flexible traits. Chydorus brevilabris increased in two lakes coincident with rising primary production, likely due to their ability to shift from a benthic to a pelagic habitat with rising nutrients and declining macrophyte coverage. A different cladoceran response was observed in the deepest lake considered (Green Lake), where we detected an initial increase of C. brevilabris in Green Lake around 1700 CE possibly due to land clearance and/or a lake level change, which was followed by a rise Bosmina taxa. Overall, the complete time series presented herein demonstrates the importance of utilizing multiple proxies and expanding research beyond top–bottom comparison to better contextualize changes observed in recent times.