Fallout radiocesium and elemental redistribution in dolines in East Tennessee

Three dolines in East Tennessee were used to measure the redistribution of ¹³⁷Cs to estimate soil erosion and deposition rates in closed systems. Each doline was under a different land use system; this included cropland, grassland and forest sites.

The redistribution of ¹³⁷Cs was greatest in the cropland, followed by the grassland and then the forest. Soil erosion rates followed the same trend, with rates of 4.2 t ha^-1 yr^-1 at the cropland, 6.5 t ha^-1 yr^-1 at the grassland, and 2.2 t ha^-1 yr^-1 at the forest. These soil erosion rates were compared with those estimated using the Revised Universal Soil Loss Equation (RUSLE). The RUSLE rates showed the trend of decreasing erosion rates from cropland to grassland to forest. The erosion rate for the cropland was the same as the rate calculated using ¹³⁷Cs redistribution. This does not verify the ¹³⁷Cs equation for calculating soil erosion rates, since the cropland doline was concluded to be an open system with potential loss of ¹³⁷Cs and clay materials. The RUSLE computed grassland erosion rate of 0.6 t ha^-1 yr^-1 and the forest rate of 0.2 t ha^-1 yr^-1 were lower than the rate using ¹³⁷Cs, probably because at low erosion rates RUSLE tends to underestimate soil loss.

Paleosols were discovered in the depositional areas of the dolines, and were used to calculate the volume of sediment that had been deposited in each closed system. Radiocarbon dates from charcoal and soil samples taken from the Ab horizons provided a time frame to estimate the average rate of deposition that must have occurred to arrive at the volume of sediment accumulated above the Ab. The deposition rate at the cropland was 3.6 t ha^-1 yr^-1 (over 480 yrs.) and at the grassland, 2 t ha^-1 yr^-1 (over 980 yrs.). The forest showed a substantially higher deposition rate of 28 t ha^-1 yr^-1. This high rate was assumed to include the time when the forest was first denuded and the potential of soil movement by runoff was extremely high.