Submitted to: Interagency Conference on Research in the Watersheds
Publication Type: Proceedings
Publication Acceptance Date: 8/20/2003
Publication Date: 10/27/2003
Citation: Emmerich, W.E. 2003. Carbon dioxide fluxes on walnut gulch experimental watershed. Proc. 1st Interagency Conf. on Research in the Watersheds, K.G. Renard, S. McElroy, W. Gburek, E. Canfield, and R.L. Scott (eds.), Oct. 27-30, Benson, AZ, pp. 554-559.
Interpretive Summary: Human activities are releasing more carbon dioxide to the atmosphere than can be accounted for in the worlds carbon budget. Soils contain the second and third largest pools of carbon in the world in the form of organic and inorganic carbon and perhaps are removing some of this additional carbon from the atmosphere. Carbon dioxide flux measurements were made on Walnut Gulch Experimental Watershed rangeland soils containing large amounts of inorganic carbon. 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 and natural process 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. Many soils on Walnut Gulch Experimental Watershed (WGEW) in southeaster Arizona contain carbonates that have accumulated over long periods of time. 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 on WGEW. 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 127 g C m-2. Based on measured aboveground biomass data and estimates of belowground biomass, the brush site took up 80 g C / m2 and the grass site 135 g C / m2 of organic carbon during the growing season. Inorganic soil carbon analysis showed a significant seasonal difference with more in the fall season. The average 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