Tuesday, April 26, 2016
Confluence Ballroom Foyer (The Westin Denver Downtown)
Brock Norwood
,
Department of Geology, University of Kansas, Lawrence, KS
G.L. Macpherson, Ph D.
,
Department of Geology, University of Kansas, Lawrence, KS
Randy Stotler, Ph D.
,
Department of Geology, University of Kansas, Lawrence, KS
Michael Rawitch
,
Department of Geology, University of Kansas, Lawrence, KS
Scientists still debate the sources and sinks of carbon on the earth’s surface. Headwater streams, a carbon source often overlooked in the carbon balance equation, cover more than 50% of the total stream length in the conterminous U.S. Shallow groundwater discharge is the main contributor to the baseflow and CO
2 concentrations in headwater streams. Groundwater datasets at the Konza Prairie Long-Term Ecological Research Site (Konza) demonstrate an increase in groundwater
pCO
2 by approximately 29% from 1990 to 2009. This continuous increase suggests that headwater streams, recharged by shallow groundwater, could be a significant carbon source.
We used a floating chamber to measure CO2 degassing rates in a headwater stream reach at Konza. Temperature contrasts, seen with an infrared camera, between discharging groundwater and the stream, located groundwater seeps. We found that groundwater discharge occurs primarily along the stream bank or in fractured bedrock on the stream bottom. At each seep, we collected water samples for major-ion chemistry, δ13C of CO2, and δ13C of dissolved inorganic carbon (DIC). Because the limestone aquifers crop out in the stream, we also collected groundwater samples from nearby wells completed in those limestones.
We compare stream water and groundwater to assess the changes that occur during groundwater discharge to a headwater stream. Preliminary results show stream water degassing at rates between 1.82 and 58.4 g C m2-day1-. The CO2 fluxes and pCO2 decreased with distance from the seeps (~2 meters). Decreases in fluxes and pCO2 were accompanied by heavier carbon isotopic ratios, with δ13C—CO2 increasing downstream of groundwater seeps. Furthermore, groundwater and stream water chemistry were similar for major anions, major cations, and alkalinity. This study provides additional understanding of groundwater and surface water interactions and evidence of a significant contribution to atmospheric carbon from headwater streams in the region.
Brock Norwood, Department of Geology, University of Kansas, Lawrence, KS
I am a master's candidate in the Department of Geology at the University of Kansas. My research and professional interests are groundwater, climate change, and geochemistry. I plan to graduate spring 2015 and pursue a career in environmental consulting.
G.L. Macpherson, Ph D., Department of Geology, University of Kansas, Lawrence, KS
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Randy Stotler, Ph D., Department of Geology, University of Kansas, Lawrence, KS
Randy Stotler is an Associate Professor in the Department of Geology at the University of Kansas. He received his Ph.D. from the University of Waterloo in 2008.
Michael Rawitch, Department of Geology, University of Kansas, Lawrence, KS
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