• Downward Movement of Soil Organic Matter and Its Influence on Trace-Element Transport (210Pb, 137Cs) in the Soil

      Dörr, Helmut; Münnich, K. O. (Department of Geosciences, The University of Arizona, 1989-01-01)
      Data on depth distribution and 14C content of soil organic carbon, and on soil CO2 production in forest ecosystems are presented and discussed. Downward movement and turnover of soil organic matter is estimated from a box chain model. The downward transfer velocity of soil organic material depends on the litter material composition and on the annual rate of microbial decomposition. Depth distribution of 210Pb and 137Cs was measured. The identical transfer velocity of 210Pb and soil organic material suggests that lead transport is due to movement of the organic material itself. Lead in organic-rich soils obviously is bound rather tightly to the organic carrier by ion exchange or organic complexing. 137Cs migration depends on the turnover and downward movement of soil organic material. Results suggest that cesium is not transported only by the downward movement of solid organic matter, but, due to chemical exchange between the organic and hydrous phases, travels faster than organic matter.
    • Fast 14C Sample Preparation of Organic Material

      Dörr, Helmut; Kromer, Bernd; Münnich, Karl Otto (Department of Geosciences, The University of Arizona, 1989-01-01)
      A fast 14C sample preparation technique for organic material in conventional 14C counting is described. The basic difference from conventional preparation is oxidation of the organic substances in a closed system under an oxygen pressure of ca 10 bars. After the explosion-like combustion, the reaction products SO2 and NO2 are oxidized immediately to SO4^-2 and NO3^- and precipitated on the wall of the reaction vessel. The residual gis mixture is passed first through a cold trap at -78 degrees C to remove water vapor and then through an activated charcoal column at 0 degrees C for purification. CO2 is removed from the remaining O2-CO2 gas mixture in a LN2 trap at a pressure approximately equal to 100mbar. With this method sample preparation time is reduced from ca 10 hr to ca 1 hr. The efficiency and reproducibility of the procedure is shown with 14C and 13C measurements of a sugar-carbon standard. The results obtained by the new technique agree well with conventionally prepared wood and bone samples.