The accumulation of ~137Cs in the biological compartment of forest soils

摘要

Soil samples were collected in various forest stands, located about 40 km north-west from Uppsala. The various stands were: (1) Clear cut area made in 1987, (2) Normal forest with 50-100 old Norway spruce and Scots pine and with a thick humic layer of about 10 cm; (3) Raised bog with 50-year-old Scots pine and Sphagnum moss layer over peat soil. (4) Rocky area with old Scots pine, growing on a shallow soil, mainly of organic origin. (5) Normal forest with nearly 100-year-old spruce and pine, growing a shallow humic layer over sandy soil. Soil blocks of about 20 × 20 cm and down to a depth of 10-15 cm were collected on each site. The soil samples were mechanically separated into various fractions: bulk, rhizosphere and soil-root interface. The results showed that ~137Cs was unevenly distributed between the three soil fractions. The highest activity concentrations — 3-4 times higher than in the other two fractions — as well as the highest organic content ? usually more than 95/100 — were found in the soil-root interface fraction. Of the total ~137Cs activity in the soil, 18/100 as a mean value was found in the soil-root interface fraction. The results thus show that a substantial fraction of the ~137Cs in the soils in some way associated with the biological part of the soil, probably with the fungal component.