Resolving the environmental factors that determine pond thermal refuge quality

Cold thermal refuges may mitigate detrimental effects of future climate warming; yet, pond ecosystems have been largely omitted from thermal refuge research despite being globally numerous and providing critical ecosystem services. We create a formal definition for pond thermal refuge quality, then operationalize this definition by measuring the thermal characteristics and environmental attributes of ponds near Mount St. Helens (Washington, USA) to determine the environmental features that promote or hinder pond thermal refuges. Our results reveal substantial variation in thermal refuge quality between ponds and indicate that within-pond thermal refuges are a distinct metric from pond surface temperature. Denser floating surface vegetation promoted thermal refuges during summer conditions, while floating surface vegetation, water clarity, and canopy cover were associated with reduced mean pond temperatures during summer and heatwave conditions. These findings help identify ponds with high conservation value and suggest actionable steps for heightening the quality of pond thermal refuges.