Comparing surface and mid-troposphere CO2 concentration and fluxes from central U.S. grasslands

Terrestrial ecosystem dynamics influence the Earth’s climate system, which is affected by variations in atmospheric carbon dioxide (CO2). Assessments of CO2 concentration and net fluxes at regional scales are needed to diminish uncertainties related to the effects of land-use change on ecosystem processes, to identify land management practices that have the potential to mitigate CO2 emissions, and to discern sources and sinks within geopolitical boundaries for reasons of carbon accountability. Understanding how surface CO2 concentration and flux dynamics within heterogeneous landscapes scale to mid-troposphere concentrations is the focus of this study. CO2 flux data from three eddy covariance (EC) towers in northeastern Kansas are compared to mid-tropospheric data collected by the Atmospheric Infrared Sounder (AIRS). EC tower data from two watershed sites on the Konza Prairie Biological Station (KPBS) for the period 2006-2010 and one study site at the Nelson Environmental Study Area (NESA) for the period 2007-2010 are examined. KPBS site 1D is primarily C4 grasses, burned annually; KPBS site 4B is a mix of C3 forbs and C4 grasses, burned every four years; and the NESA site is a mix of C3/C4 grasses, burned approximately every five years, and experiencing woody encroachment. Results show higher concentration of CO2 in the mid-troposphere. Furthermore, mid-troposphere CO2 exhibited daily and seasonal lags and decreased amplitude in flux dynamics compared to surface CO2. Long-term, combined observations of surface and atmospheric CO2 offer the potential for a better understanding of the natural processes and anthropogenic activities related to CO2 source-sink dynamics, seasonal and interannual variability, and climate forcings, including temperature and precipitation changes.