|Herrick, Jeffrey - Jeff|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/28/2005
Publication Date: 5/1/2006
Citation: Serna-Perez, A., Monger, H.C., Herrick, J.E., Murray, L. 2006. Carbon dioxide emissions from exhumed petrocalcic horizons. Soil Science Society of America Journal. 70:795-805. Interpretive Summary: Global climate change is associated with increases in atmospheric carbon dioxide (CO2). A number of systems have been proposed for reducing the rate of increase in atmospheric CO2. One possibility is to increase soil carbon content. Soil carbon exists in two primary forms: as soil organic matter generated by plants and as soil carbonates, of which calcium carbonate (CaC03) is the most common. In addition to limestone, many arid soils have developed calcium-carbonate-rich layers. If these layers (soil horizons) increase in mass, carbon is removed from the atmosphere. However, it is also possible that when these horizons are exposed at the soil surface (e.g., by erosion), carbon might be lost to the atmosphere, effectively increasing atmospheric CO2. By measuring CO2 loss rates from three different types of soils in the Chihuahuan Desert, we were able to test the hypothesis that soil CaCO3 exposed at the land surface might be a source, in addition to a sink, of atmospheric CO2. We found that CO2 loss rates were similar from soils with and without carbonate-rich horizons and on from soils where the carbonate-rich was both buried and exposed at the surface. We concluded that petrocalcic horizons can be considered a recalcitrant reservoir within the decadal timeframes pertinent to carbon sequestration policies.
Technical Abstract: The second largest pool of terrestrial carbon is pedogenic CaCO3. In addition to being an important sink of atmospheric CO2, pedogenic carbonate has the potential to be an important source of atmospheric CO2. The cemented form of pedogenic carbonate (the petrocalcic horizon) develops in geomorphically stable soil in arid, semiarid, and various subhumid climates. In many of these dryland areas, such as the Chihuahuan Desert of North America, erosion has stripped away overlying soil and exhumed the petrocalcic horizon, thereby lifting it into a weathering zone above the calcification zone where it normally forms. This research tested the hypothesis that Aridisols with exhumed petrocalcic horizons will emit more CO2 than neighboring noneroded Aridisols with petrocalcic horizons or neighboring Entisols. We tested this hypothesis by comparing the amount of CO2 and the delta 13C of CO2 released from the three soil types. Using a randomized complete block design, CO2 emissions were measured using NaOH and soda lime traps from June 2002 to October 2003. Neither NaOH traps nor soda lime traps detected any statistical difference in cumulative CO2 emissions from the three soil types at the P = 0.05 level. Moreover, the isotopic analysis of CO2 did not match the isotopic values of pedogenic carbonate nor were there any statistical differences (p = 0.05) in delta 13C of CO2 among the three soil types. We conclude, therefore, that exhumed petrocalcic horizons are not actively emitting CO2 at a rate significantly greater than adjacent soils; and thus, carbon stored in petrocalcic horizons can be considered a recalcitrant reservoir within the decadal timeframe pertinent to carbon sequestration policies.