¹³⁷Cs and ²¹⁰Pb profiles in North Morrocan soils: Inventories and erosion rate estimates

¹ CEREGE, BP. 80, 13545 Aix-en-Provence, France
² Department of Earth Sciences, Faculty Sciences and Technology, Natural Resources and Risks Observatory (ORRNA), BP. 416, Tangier, Morocco

Abstract

Various studies have been conducted during the fast decade onto atmospheric deposited ²¹⁰Pb and caesium isotopes in soils in order to quantify soil erosion rates. In North Morocco (Tangier area), erosion is a real problem leading to silting up of artificial lakes. Soil profiles were collected in cultivated areas from the catchment basin of one of this lake in order to quantify the erosion. ¹³⁷Cs and ²¹⁰Pb concentrations and inventories were measured and their spatial distribution was studied in relation with other parameters : granulometry, pH, organic matter content. Mean ¹³⁷Cs inventory in stable soils was found to be 2582 Bq.m^-2 in 1999, in agreement with literature data for Spanish and Portuguese soils. Depth profiles were usual, showing an exponential decrease with depth for ²¹⁰Pb and a subsurface peak for ¹³⁷Cs in reference soils where it was found until 30 cm depth. No clear relations appeared with organic matter content or pH and the distribution of the inventories is probably linked to erosion process. Estimated erosion rates varied from 5 to 66 t.ha^-1y^-1, but the use of different models for such estimation led to important differences.