Characterizing wetland thermoregulation using multivariate water temperature patterns and site-level functional indicators

Quantifying how wetlands regulate the magnitude, variability, and responsiveness of water temperature is essential to understanding their ecological functions and informing climate-adaptive management. To investigate the mechanisms underlying wetlands’ thermal influence, we monitored groundwater, open water, channel, and outlet temperatures across seven palustrine wetlands in Oregon’s forested Cascades in summer 2024. We identified early- and late-summer thermal phases based on water temperature shifts and used principal component analysis to define site-level thermal gradients. Generalized least squares modeling and multivariate dispersion analysis further identified landscape drivers and unexplained within-site temperature variability, respectively. We compared this variability with the Oregon Rapid Wetland Assessment Protocol (ORWAP) indicators of thermoregulation. This analytical approach explores how spatial scales influence distinct aspects of thermal regimes, with broad-scale factors such as elevation and air temperature shaping overall temperature magnitude, while site-level features such as vegetation structure and hydrology regulate day-to-day variability and thermal stability. Large wetlands with ponded surface water generally stabilized outflow temperatures despite relative warming compared to smaller wetlands with relatively more permanently saturated vegetated zones, which exhibited cooler but more variable atmospherically-driven changes. Within-site sub-seasonal shifts between early and late summer were minor relative to differences across sites. While comparing rapid-assessment scores to water temperature variability resulted in low explanatory power, vegetation structure indicating shade most consistently associated with lower temperature variability. These findings highlight both merits and limitations of ORWAP, and restoration trade-offs between creating open-water habitat and sustaining cool-water conditions in headwater systems.