Development of cosmogenic nuclear methods for the study of soil erosion and formation rates

Two quantitative nuclear methods for the study of soil formation rates using the cosmogenic radionuclide 10Be for determination of soil erosion rates using the cosmogenic radionuclide 10Be are discussed. The radionuclide 10Be(half-life=1.5 m.y.) produced by cosmic rays in the earth's atmosphere, and in situ cosmogenic 14C (half-life=5730 yr) have both been detected in soils/rocks using accelerator mass spectrometry. 10Be concentrations have been studied in several soil samples: they have yielded useful but qualitative ideas about soil dynamics. For determining soil formation rates, studying the specific activities of 10Be in soil minerals with respect to its stable element 9Be is proposed. In the model, backed by some laboratory tests and analyses of samples analysed earlier for 10Be, it is expected that the 10Be/9Be ratios in soil minerals formed at different depths would constitute a fairly quantitative measure of the soil formation rate. For measuring soil erosion rates, study of the in situ produced 14C activity in quartz in surface soil samples is proposed. The in situ radiocarbon method is ideal for study of erosion rates of 10-3 to 5x10-2cm yr-1. Soil renewal rates and 'low' soil erosion rates fall in the bracket 5x10-3 to 2.5x10-2cm yr-1 as pointed out by Revelle. Appreciable aeolian contributions of quartz may occur in certain soils, but this does not constitute any problem since the aeolian quartz can be separated from the in situ generated quartz by grain-size separation. (author). 24 refs., 3 figs., 1 tab