Lead in Soils of the Selenga River Delta

Distribution of total and acid-soluble lead in five major soil types and soil-forming rocks have been studied in the Selenga River delta, the largest affluent of Lake Baikal. A low content of this element in soil-forming rocks (6.0 mg/kg on the average) along with the local soil-geochemical conditions is responsible for its small amount in soils. The bulk lead content in the topsoil (0-20 cm) layer varies from 3 to 17 mg/kg (the mean is 10 mg/kg), which is lower than the maximum permissible concentration and the natural abundance (clarke) of lead in soils of the world. The lead content in swampy and soddy alluvial soils is two times higher than in meadow alluvial and gray forest soils and in sands under pine forests. Differences in the lead content in soils on the left and right banks of the Selenga River delta have been revealed. The content of acid-soluble lead varies within 24-68% of the total lead content in alluvial swampy and alluvial meadow soils, within 15-43% in alluvial soddy soils, and within 11-26% in gray forest soils and sands under pine forest. The distribution pattern of lead in the vertical soil profile is eluvial-illuvial in alluvial swampy and alluvial meadow soils and sands under pine forest and accumulative-eluvial-illuvial in soddy alluvial and gray forest soils. Lead accumulation in the organic and gley horizons of alluvial swampy and alluvial meadow soils is revealed. In alluvial soddy and gray forest soils with relatively uniform particle-size and mineralogical composition, lead is evenly distributed in the soil profile with a particular accumulation in the top sod layer. The dependence on soil properties is slight for the total lead content and is somewhat stronger for acid-soluble lead. The data obtained may be used for biogeochemical monitoring in the Baikal region.