The influence of riparian vegetation and season on stream metabolism of Valley Creek, Minnesota

Climate change will undoubtedly influence stream ecosystems by affecting water temperature, discharge, and riparian vegetation phenology. It has been suggested that increasing the extent of riparian buffers may help to mitigate these impacts and contribute to ecosystem resilience. Measures of stream metabolism are one way to examine the changes in ecosystem function as they respond to climate change and management strategies used to respond to these impacts. In this study we examine the influence of riparian vegetation (open vs. forest) and season on ecosystem metabolism in a small stream in MN, USA. The stream was heterotrophic regardless of the type of riparian vegetation but the presence of a forested buffer depressed gross primary production (GPP) and also resulted in lower (less negative) ecosystem respiration (ER) and net ecosystem production (NEP). We also found significant daily and seasonal variation in GPP, ER, and NEP. Stream metabolism was more variable in the fall than in the summer. The study design was complicated by the fact that there were differences in groundwater dynamics between the two locations; the forested location was a losing stream while the open location was a gaining stream. Despite the fact that groundwater input likely influenced the oxygen dynamics of the open location, the impact of the forest buffer outweighed the impact of groundwater. The presence of a forested riparian corridor resulted in decreased GPP likely through the attenuation of light. The low O-2 groundwater input at the open location likely biased measures of ER and NEP. Modifying stream corridors with increased forest vegetation to offset the impacts of climate change will likely result in less in-stream primary production and a shift to a more heterotrophic system. This shift will undoubtedly influence many ecosystem functions in-stream systems.