Storms Disproportionately Contribute to Carbon Dioxide Efflux from Streams and Rivers on Annual Timescales

Abstract:

Streams and rivers contribute to the global carbon cycle by emitting significant amounts of carbon dioxide (CO₂). One major uncertainty in this process is the effect of stormflows on CO₂ efflux. Storm events generally increase the gas transfer velocity within streams and may enhance the transport of soil CO₂ to the stream; however, the cumulative role of storm CO₂ emissions from streams remains uncertain and patterns of pCO₂ during storms are not well-constrained across land use, seasons, or storm sizes. With the proliferation of high frequency pCO₂ sensors, we can now monitor aquatic environments at timescales necessary to characterize patterns in CO₂ efflux during storms. We combined measurements of pCO₂ and discharge to examine how storms contribute to CO₂ efflux from ten headwater streams and two small rivers in New Hampshire and Massachusetts. Our study streams include forested and developed catchments. Preliminary results suggest that storm flows contribute disproportionately to total CO₂ emissions. While storms represented about 10% of flows, approximately 15-40% of CO₂ was emitted during this time. This elevated contribution to emissions appears to be due to both increased gas transfer velocities associated with higher flows as well as increased CO₂ transport to the stream from the terrestrial landscape. By further quantifying the relationship between pCO₂ and discharge, we can improve our understanding of CO₂ transport pathways and active source areas. Furthermore, examining the relative differences in storm CO₂ responses across our sites and over time will help elucidate factors that influence stream CO₂ dynamics. Together, our results suggest that pCO₂ monitoring during high flow events is necessary to accurately represent streams and rivers in the global carbon cycle.