A Thesis of Warming and Drought Effects on Mountain Pond Communities

Global climate change predictions indicate small freshwater systems being among the most impacted ecosystems. A meta-analysis and review of the literature on climate related stressors on freshwater, highlighted drought and warming as ecologically important stressors affecting these systems, specifically in northern climates. The objective of my thesis is to identify the effects of warming and drought on freshwater algae communities, which are the foundation of the larger community. This will be done through a survey of algal species in 30 mountain lakes at different elevations followed by two cross-factor experiments to quantify local species responses. In 2016, 12 1000 L mesocosms were populated with algae and zooplankton from alpine ponds. The mesocosms were either kept at their source elevation or relocated lower to simulate warming of approximately 7.96◦ C. In August 2019, I induced a 1.5-year complete drought treatment on mesocosms at both elevations. In the spring of 2021 the drought treated mesocosms will be refilled to simulate spring melt and the populations will be sampled bi-monthly. In addition to a field experiment, I will be conducting an in-vitro experiment using alpine pond sediments in pond microcosms to see how the encysted algae respond to combinations of warming and drought. The community compositions, functional traits, and water chemistry from both experiments will be analyzed to identify trends and understand how local mountain pond communities will respond to these climate stressors. This research in progress is key to understanding how vulnerable or resilient these important freshwater communities are in the face of climate change.