Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2002
Publication Date: 2/1/2003
Citation: Emmerich, W.E. 2003. Carbon dioxide fluxes in a semiarid environment with high carbonate soils. J. Ag. and For. Meterol. 116:91-102.
Interpretive Summary: Human activities are releasing more carbon dioxide to the atmosphere than can be accounted for in the world's carbon budget. Soils contain the second and third largest pool of carbon in the world in the form of organic and inorganic carbon, and perhaps also functions as a sink removing carbon from the atmosphere. By taking measurements above rangeland soils with high amounts of inorganic carbon in them, it was determined that the soils are slowly releasing this inorganic carbon to the atmosphere under the present climatic conditions. This is an important scientific finding in the process of understanding how human activities are affecting carbon dioxide in the atmosphere and the potential for climate change.
Technical Abstract: Carbon dioxide is increasing in the atmosphere, presumably from human activities. Over long time periods semiarid soils have sequestered inorganic carbon to accumulate the third largest global carbon pool. The hypothesis is that these soils are maintaining this carbon pool under present climatic conditions and are a sink for some of the increasing atmospheric carbon. Bowen ratio systems were used to measure CO2 fluxes from a brush and a grass community with different soil types over four years in southeastern Arizona. Spring and fall aboveground biomass and soil samples were analyzed to determine seasonal changes in carbon content. Contradictory to the hypothesis, the two sites were found to be losing carbon annually. The brush site with higher inorganic carbon in the soil, had an average annual loss of 144 g C m-2 and the grass site 126 g C m-2. Average annual daytime CO2 flux from the brush site was a loss of 26 g C m-2, while the grass site had a gain of 86 g C m-2. Based on measured aboveground biomass data and estimates of belowground biomass, the brush site sequestered 80 g C / m2 and the grass site 135 g C / m2 of organic carbon during the growing season. Combined site inorganic soil carbon analysis showed a significant seasonal difference with more in the fall season. The average annual fall season soil inorganic carbon was 2.24% and the spring season was 1.96% to a depth of 30 cm. This significant seasonal difference indicated some of the measured CO2 fluxes were into and out of the inorganic carbon pool. The source of carbon for the measured annual losses from these sites was concluded to be from the large inorganic carbon pool with carbon cycling through both the organic and inorganic pools at the sites.