Changes of Cation Pools of the Topsoil in South Swedish Beech Forests between 1979 and 1989

Repeated analyses of exchangeable K, Ca, Mg and Zn revealed that the pools have decreased significantly in the topsoil (0-5 cm) of south Swedish beech forest during the 1980s. The largest decreases of K, Ca and Mg were found in the originally least acid soils, indicating that the limit for further losses from the topsoil is being approached in the most acid soils at today's deposition climate. The decrease of Zn was, on the other hand, largest in the most acid soils. Manganese had increased in especially the least acid soils, probably due to a conversion from non-exchangeable pools as a result of the acidity change. The base saturation of the studied beech stands ranged 7.7-58.5% (mean 20.3%). The decrease rate of the exchangeable pools of K, Ca and Mg, estimated from two different time series has been relatively constant since 1949. The Zn pool has, however, decreased faster during the last decade, partly due to a lowered deposition of this element. Extrapolation of the data indicates that, as an average, only 20% of the pools of 1950 will remain in the topsoil in the year 2050.