Changes in concentrations of Cd, Zn, Mn, Cu and Pb in spruce (Picea abies) needle litter during decomposition

Spruce (Picea abies (L.) Karst) needle litter was placed in litterbags and incubated (greater than or equal to6 yr) at five spruce stands in southern Sweden. The litterbags were collected twice a year during year 1-2 and thereafter once a year, for total analyses (conc. HNO3) of Cd, Zn, Mn, Cu and Pb. The main objectives were to document changes in concentrations and amounts of these elements during litter decomposition and to investigate factors controlling the changes. Concentrations of Cd, Zn, Cu and Pb increased to at least 0.5, 1.5, 3 and 13 times the initial concentration. During the latter part of the incubations, concentrations became more stable or decreased. Concentrations at which the metals are considered to be toxic to micro-organisms in the mor layer were not reached during the experiment. Generally, concentrations of Mn decreased. Total amounts of Cd, Zn and Mn had decreased by at least 15, 24 and 43%, from the initial amount at the end of the experiment. The total amount of Cu increased (> 40%) before it started to decrease. The total amount of Pb increased by over 230%. Thereafter it became more constant or decreased. According to a PCA, the dynamics of total amounts of Cd, Zn and Mn in the litter were similar, as were those of Pb and Cu. Furthermore, in most cases the heavy metal amounts on any sampling occasion differed more between than within sites. The dynamics of total amounts of elements were more similar between adjacent sites than between more distant sites.