Examining the Impact of Stream Permanence on Headwater Stream Carbon Emissions

Quantifying headwater stream carbon emissions is important for our understanding of the global carbon cycle because these emissions (an estimated 0.93-1.15 Pg C year) can be substantial compared to the terrestrial flux. Headwater stream networks can have high emissions due to their coupling with the terrestrial environment and high turbulence with some estimates predicting headwater stream networks can contribute 70% of the global riverine stream emissions. These carbon emissions are challenging to predict, especially with regards to headwater stream network spatiotemporal heterogeneity. The majority of headwater streams exhibit changes in stream network area on a seasonal basis, and these locations and extents are not often well documented because they are based on topographic maps with limited spatial accuracy. Research suggests 50-80% of river networks are comprised of non-perennial stream segments.  Physically based models are a potential solution to both mapping streamflow permanence and carbon dioxide emissions by accounting for the spatiotemporal heterogeneity that can occur in stream networks.

In this study, we modeled stream permanence at three streams across the United States in different ecosystems using the Watershed Erosion Prediction Project (WEPP) hydrological model to simulate changes in stream network area over the year. We then used these results to inform a process-based stream network model to predict carbon emission from these networks throughout the year. We calibrated these network model with longitudinal data collected at the three sites during both low and high flow. Our results show the importance of considering stream permanence when predicting stream network carbon emissions, and how some ecosystems may emerge as hotspots for these emissions during high flow periods.