CO2 FLUX FROM GRASSLAND HEADWATER STREAMS

Groundwater concentrations of CO₂ are typically 10 to 100 times the atmospheric concentration, and a significant gradient exists where aquifers interact with the atmosphere in low-order headwater streams such as those at the Konza Prairie Long-Term Ecological Research Site and Biological Station (Konza). Previous investigations at Konza have shown a steady increase in the concentration of CO₂ in groundwater over the last several decades, so stream CO₂is likely also increasing, and the degassing rate may have ramifications to carbon budget evaluations.

Headwater streams occupy a significant portion of surface area in the conterminous United States, varying between 0.2 to 1.5% of watershed area, with 20% of the total stream surface area considered headwater streams. Streams and rivers are demonstrated net sources of CO₂ to the atmosphere and, although estimates have been made, there has been little effort to directly measure CO₂gas evasion in headwater streams. The flux of carbon dioxide in streams could be an important aspect of water and atmospheric chemistry, and directly measuring flux is crucial to determining the full impact of this phenomena.

The floating chamber method has proven a logistically simple method of measuring CO₂efflux from lentic and ocean systems. However; controversy remains about its accuracy under certain conditions, and no testing has been conducted on its effectiveness in a shallow turbulent environment. We have tested the effectiveness of the floating chamber method under headwater stream flow conditions in the laboratory and in the field.

The project comprises a series of experiments that develop and test a method of quantifying the natural flux of CO₂ from headwater streams that have variation in CO₂ evasion rates because of stream morphology, non-uniform groundwater discharge points, and turbulent water flow. The experiments evaluate chamber-induced turbulence and the influence of stream velocity on chamber-induced turbulence in the University of Kansas Water Resources Laboratory, and the influence of groundwater discharge points at the Konza.