Terrestrial Carbon Dioxide Dominates Headwater Stream Emissions: Lessons Learned from One Year of SIPCO2 Sensor Deployment

Recent studies show river networks are important sources of carbon dioxide (CO₂) to the atmosphere. Improved measurement of aquatic CO₂ is thus critical for a better understanding of the factors controlling carbon delivery to and processing within river networks and will expand our ability to predict how changing climatic patterns and land use will alter rates of aquatic CO₂ emissions. The emergence of cheaper and reliable ways of measuring CO₂ in situ are allowing for more robust investigations for high frequency and affordable data collection. We constructed and deployed SIPCO2 sensors in four headwater streams to examine CO₂ dynamics using this novel technology. SIPCO2 sensors are simple, inexpensive surface water pCO₂ sensors in which a non-dispersive infrared (NDIR) detector is paired with an air pump in an enclosed housing to produce air-water equilibration. Once issues associated with deploying these sensors in flowing freshwaters was addressed (e.g., biofouling, power supply, changing stage), we were able to effectively monitor stream CO₂ in concert with monitoring of stage, temperature, and dissolved oxygen. Emissions of CO₂ increase during storm event flows as the aeration rate increases and terrestrially derived CO₂ is transported to the stream. Estimates of stream metabolism suggest a majority of CO₂ in all four streams is terrestrially derived. Further analysis will investigate the photosynthetic quotient of these streams. In improving the application of SIPCO2 sensors in stream ecosystems, we have developed a more robust means of using these affordable sensors which could economically allow for a proliferation of CO₂ measurements in stream and river systems.