Impacts of Climate Change and Multiple Stressors on Water Levels and Phytoplankton in Small Temperate Lakes Within the Great Lakes Region Over Three Decades

Changes in climate influence water quantity and water quality through hydrological processes, thermal regimes, and ice phenology. This thesis investigates the impacts of climate change and additional anthropogenic stressors on water quantity and quality in two study areas with minimal anthropogenic disturbance within the Great Lakes region. Between 1984 and 2014, water levels dropped by an average of 50 cm in northern Wisconsin lakes. We found that 49% of the variation in water levels was attributed to decreased precipitation, and 30% was attributed to warmer air temperatures. Water levels are projected to rise by an average of 44 cm by the year 2070. In south-central Ontario, phytoplankton dominance shifted from diatoms to chrysophytes between 1984 and 2013. Changes in lake chemistry and lake morphometry explained 60% of the variation in phytoplankton biomass. Understanding how multiple interacting stressors affect lakes will help improve ecosystem management strategies.