Application of 137 Cs for measuring soil erosion/deposition rates in Romania

Abstract

Two methods of monitoring soil redistribution along agroterraces were explored in Tarina basin of the Moldavian Plateau: the classical method of annual or periodic field measurements and the 137C technique. Results obtained by both methods indicate that the aggradation rate of the agroterrace edge averages 5.0-6.0 cm/yr, but the 137C technique is more efficient because it requires only one field visit. Much of the dow n ward movement of soil in these agroterraces can be related to contour ploughing, although some erosion/deposition undoubtedly occurs. The future of using 137C as a tracer of erosion and sedimentation within discontinuous gullies is promising. Some results obtained in the Moldavian Plateau near Barlad support this assumption. A field study, based on a depth - incremental sampling method, was undertaken in two small basins, Roscani and Timbru. Depth distribution of 137Cs from recent sediments deposited along the floor of dis-continuous gullies allowed the establishment of a mean sedimentation rate of 4.4 cm/yr over the period 1963-1996, and 2.5 cm/yr after 1986 for short gullies. In the case of long gullies, after the Chernobyl nuclear accident this value is to 4.9 cm/year. Furthermore, it was possible to estimate: the age of the gullies (23-48 years), the mean gully head advance (0.9 m/yr), the mean total mass of sediment deposited/ eroded within the gully system (up to 124 t/yr) and the main sediment source (the active gully head and banks). Conservation practices and tillage were first implemented during 1982-1983 in the upper Racatau basin of 3,912 hectares. Significant changes in land management practices resulted from the application of the Landed Property Law no.18/1991. The marked shifting from contour to up and down hill farming created a doubling in the amount of soil erosion and deposition. Depth distribution of 137Cs in recent sediments of the Bibiresti reservoir indicates a mean sedimentation rate of 5.0 cm/yr over the period 1986-1992 and 10.0 cm/yr for the period 1993-1996.