Irena Creed

Rewired Watersheds and Toxic Blooms in Northern Lakes

Wednesday, May 27

Accelerating environmental change is reshaping the “wiring” between northern landscapes and their lakes. Shifts in hydrologic connectivity - driven by warming, altered precipitation, and intensifying extremes - change the timing, magnitude, and chemistry of material transfers from land to water. At the same time, unconventional, toxin-producing cyanobacterial blooms are emerging in northern lakes historically considered low risk, raising a central question: how do changing land-water connections create new bloom pathways? Three lines of evidence link connectivity change to bloom emergence. First, nutrient regimes are becoming more pulsed in timing and magnitude, reshaping competition and selecting for persistence and toxicity traits. Second, altered flowpaths modify terrestrial organic carbon export, accelerating browning and reshaping lake light and thermal structure in ways that can suppress or promote cyanobacteria. Third, freshening and salinization shift ionic constraints, sometimes triggering threshold-like community turnover that favors toxin-producing taxa. Together, these changes connect watershed reorganization to shifts in bloom biomass, composition, and toxicity in unexpected northern settings.

Speaker Bio

Irena Frances Creed is an ecosystem scientist internationally recognized for advancing understanding of how climate change and other large-scale pressures are reshaping connections between northern landscapes and their lakes. Her research examines the movement and transformation of water, carbon, and nutrients across coupled atmospheric-terrestrial-aquatic systems, from headwater catchments to wetlands, streams, and lakes. She has shown how watershed processes regulate the timing, magnitude, and chemistry of material export from land to water, and how shifting landscape hydrology—interacting with multiple stressors—can favor or constrain harmful, toxin-producing cyanobacterial blooms. She leads interdisciplinary collaborations on climate-driven risks to freshwater ecosystems and nature-based solutions, integrating long-term observations, experiments, GIS and remote sensing, quantitative modelling, and policy partnerships. A full biography, publication list, and contact information are posted on Creed’s faculty page. https://discover.research.utoronto.ca/32110-irena-creed