296 Recent Advances in Hydrogeology (Posters)

Wednesday, 4 November 2015
9:00 AM - 6:30 PM
Exhibit Hall

QUANTIFYING CO2 DEGASSING AND δ13C USING A FLOATING CHAMBER IN A GAINING HEADWATER STREAM

Paper number: 296-8
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Headwater streams comprise more than half of the total stream length in the conterminous U.S.A., and despite their high rates of CO2 degassing, these stream reaches are often overlooked when accounting for carbon contributions to the atmosphere. Shallow groundwater is the main contributor to the baseflow in headwater streams and the source of the CO2. At the Konza Tallgrass Prairie Long-Term Ecological Research Site (Konza), CO2 in shallow groundwater has been increasing continuously over the past 25 years of observation, suggesting that the contribution of headwater-stream CO2 may also be increasing.

We used a floating chamber to measure CO2 flux in a headwater stream located on the Kings Creek watershed divide at Konza during the summer of 2015. We identified exact locations of groundwater seeps using an infrared camera, because of temperature difference between the discharging groundwater and stream water. We collected stream water samples and groundwater samples from nearby wells completed in the same merokarst limestones that crop out in the streambed, and determined major-ion chemistry as well as δ13C of the CO2 and of dissolved inorganic carbon (DIC). Preliminary data show that three different groundwater seeps, located along the stream bank or in fractures in the bedrock on the stream bottom, were degassing with CO2 concentrations between 5500 and 500 ppm. Locations downstream from the seeps had slower CO2 degassing rates and lower CO2 concentrations. We compare the CO2 concentrations, degassing rates, and water elemental and isotope chemistry of the stream water with groundwater in order to assess the changes that occur during groundwater discharge to a headwater stream and the potential contribution of headwater streams in the region to atmospheric CO2.