Paleolimnology and cyanobacterial blooms

As freshwater cyanobacterial blooms increase in frequency, duration, and toxicity, scientists and managers face mounting pressure to assess risk and develop effective interventions. Yet these efforts are constrained by the limited temporal span of monitoring records which often fail to capture the full range of bloom variability or the conditions that trigger blooms. Paleolimnology, the study of lake sediment archives, offers a powerful means to overcome this constraint by reconstructing long-term records of cyanobacterial characteristics in lakes. In this review, we evaluate how recent advances in harnessing data from sedimentary records—including proxies that characterize cyanobacteria (e.g., relative abundance, species), cyanotoxins, and the environmental triggers of cyanobacterial bloom formation—can inform cyanobacterial bloom risk assessments. We synthesize the strengths and limitations of each proxy type, outline the specific questions to address, and offer guidance for combining proxies in ways tailored to distinct research and management objectives. Building on this synthesis, we propose a framework for using paleolimnological records to establish baselines, detect early warning of rises in cyanobacteria, and attribute triggers of cyanobacterial bloom propagation—knowledge crucial for informing effective cyanobacterial bloom management. We emphasize the value of these records not only for hindcasting bloom dynamics but also for enhancing predictive models that can inform risk management. By reimagining sediments as archives of risk, this review positions paleolimnology as an important, but still underutilized, tool in the global response to freshwater cyanobacterial blooms.