Cladocera responses to ~200-year history of environmental stressors on Rideau Canal (Ontario, Canada) lakes

This is the authors' abstract. We don't add key points for this paper.

Five lakes within the Rideau Canal system (Ontario, Canada) were studied ~25 years ago using lake sediment cores for diatom analysis. More recently, new sediment cores were collected to assess limnological changes linked to more contemporary stressors, such as accelerated regional climate warming. However, long-term changes in the cladoceran assemblages remained unstudied in the earlier collections. Here, we reconstruct cladoceran assemblage dynamics over the past ~200 years to assess how this key intermediate trophic level has responded to multiple catchment disturbances and recent environmental change. The Rideau Canal was constructed in the early-1830s as a way to connect Ottawa to Kingston for military transport, but is now primarily used for recreational purposes. The construction of the canal resulted in many land-use changes including flooding, deforestation, and settlement, that likely impacted lakes within the system. Recently, environmental changes, including accelerated climate warming, zebra mussel invasions, and cyanobacterial blooms, are affecting these waterbodies. Despite relatively major changes recorded in diatom assemblages, only moderate shifts were observed in cladoceran assemblages during the period of canal construction. In contrast, the past ~25 years were characterized by increased dominance of Bosmina spp., a pattern widely associated with climate warming, along with declines in the relative abundance of most littoral cladoceran taxa. Overall, biological turnover in cladoceran assemblages was consistently lower than that observed for diatom assemblages across all lakes. These recent compositional changes are consistent with accelerated regional warming and associated limnological shifts, as well as reduced total phosphorus concentrations and altered food resources.