Wildfire smoke reduces water temperature and metabolic rates in lakes and ponds across a small headwater watershed

Abstract Pervasive smoke from wildfires can alter fundamental aspects of lake ecosystems, such as water temperature and rates of gross primary production and ecosystem respiration (ecosystem metabolism). However, understanding the effects of smoke on lake temperature and metabolism remains challenging, due to spatiotemporal variability in smoke cover and density, and variability in lake‐specific factors that mediate responses. To control for variability in smoke exposure and lake trophic state, we examined thermal and metabolic responses to smoke in six oligotrophic lakes and ponds in one small headwater watershed from 2020 to 2022. Lakes and ponds were exposed to 37 days of high‐ and medium‐density smoke on average. Smoke cover reduced water temperature and metabolic rates. The magnitude of responses varied by waterbody size and smoke density. Smoke reduced rates of primary production by 3–49% and rates of respiration by 12–60%, highlighting the potential for smoke cover to influence local and global carbon cycling.