• The Use of Natural and Anthropogenic 14C to Investigate the Dynamics of Soil Organic Carbon

      O'Brien, Bernard John (American Journal of Science, 1986-01-01)
      Radiocarbon has been measured in two soil profiles, one of which has been covered by a building since 1956. A comparison of the Delta-14C values in horizons of each profile gives an estimate of the total input of atom bomb 14C into the soil profile. From the Delta-14C and carbon density profile data, the carbon input rates, respiration rates, and diffusivity are calculated. The lack of vegetation on one soil affects the mobility and the respiration rate of the soil carbon in that soil. The data from this soil profile are also used to check the assumption, used in previous analyses, that there is a uniform distribution of "old" carbon down the soil profile. The input rate, turnover time, and diffusivity parameters determined from the Delta-14C profiles in these soils are compared with other published data on pasture and forest soils.
    • Thin Layer delta-13C and Delta-14C Monitoring of "Lessive" Soil Profiles

      Becker-Heidmann, Peter; Scharpenseel, Hans-Wilhelm (American Journal of Science, 1986-01-01)
      The natural 14C and 13C content of soil organic matter and their dependence on depth for two Alfisols are presented. This soil type which covers a large area of the earth's surface is characterized by clay migration processes ("Lessivé"). The samples were taken as successive horizontal layers of 2cm depth from an area of ca 1 m2 size as deep as the C content allows 14C analysis. The minima of the D14C distribution decrease with depth, while the maxima increase in the upper, leached horizon (A1) due to bomb 14C and decrease in the lower, clay illuviated (Bt). delta-13C indicates proceeding decomposition in Al and protection of carbon, probably due to the formation of clay humus complexes in Bt. delta-13C values were also used for age correction of the 14C data due to isotopic fractionation. The D14C and delta-3C depth distributions are characterized by sharp peaks at the boundaries of the horizons, probably caused by the influence of textural changes on the transport of C with percolating water.