Application of 137Cs for measuring soil erosion/deposition rates in Romania
Ionita, I.; Margineanu, R.M.
Acta Geologica Hispanica 35(3-4): 311-319
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 downward 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 discontinuous 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.