QUANTIFYING CO2 FLUX AND δ13C FRACTIONATION USING A SUSPENDED CHAMBER IN THE SOUTH FORK OF KINGS CREEK, KONZA LTER, NORTHEAST KANSAS

Headwater streams account for approximately 53% of the total stream length in the U.S., and recent studies found high rates of CO₂ flux in headwater environments. Despite their significant influence in the carbon cycle, these stream reaches are often overlooked when investigating carbon cycling and contributions to the atmosphere. Long-term datasets at the Konza Long Term Ecological Research Site (Konza LTER) show pCO₂ concentrations in groundwater increased 20% from 1991 to 2005 while atmospheric concentrations only increased 7%. The discrepancy between groundwater and atmospheric concentrations indicates that groundwater containing carbon in the form of DIC is a possible carbon sink.

We used a suspended chamber to measure CO₂ flux rates along the South Fork of Kings Creek at the Konza LTER. Point-source measurements of carbon flux, such as the suspended chamber method, better characterize the small scale heterogeneities found in headwater streams when compared to tracer tests or hydrogeomorphic equations. 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 and δ¹³C of CO₂. Preliminary results show carbon flux rates between 1.82 and 58.4 g C m^2-day^1- near bedrock fractures and stream seeps. The CO₂ flux rates and pCO₂ decreased with distance from these locations (~2 meters). Decreases in flux rates and pCO₂ also correlated to heavier isotopic signatures with δ¹³C—CO₂ increasing downstream of groundwater seeps.

In order to better characterize carbon flux from the South Fork of Kings Creek, we collected water and gas samples along the entire reach at locations with varying lithology, stream substrate, channel type, and discharge. This data provides additional understanding of groundwater and surface water interactions and evidence of a significant contribution of atmospheric carbon from headwater streams in the region.