USING KEELING PLOTS TO MEASURE RESPIRATION FLUX AND CARBON ISOTOPES IN THE VALLES CALDERA

In the Valles Caldera outside of Los Alamos, New Mexico, the carbon cycle has interesting qualities that should be studied in depth. Recently, carbon flux has been monitored in great detail in areas of the caldera, mainly through eddy covariance and chamber flux systems. For this study, carbon isotopes were measured both in vegetation and air samples during the growing season (June through August). Two locations were monitored; an exposed grassland, composed of C3 and C4 grasses, and a location at the mouth of the caldera where both grass and evergreen trees exist. We used the isotopes of CO2 in air to create Keeling plots. Keeling plots deal with calculating the respiration, or &delta13CR contributions to a system. Over the course of a day, this value can increase and decrease according to weather and time of day. The flux in the carbon isotopes reveals valuable information about the ecosystem, primarily where the CO2 is originating. These graphs are being used more and more to best display research conducted on the carbon cycle. We hypothesize that Keeling plots accurately describe the source of CO2 in this mixed vegetation system. Through the experiment, both the validity of the Keeling plots was tested and the variation of these plots due to vegetation type was researched. Constraints of Keeling plots are a concern for a system like this, but it is believed that the plots can help extrapolate data over entire regions. This is important to global carbon cycle models that use results from Keeling plots to determine the source terms for terrestrial CO2 respiration.