Trends in major and trace elements in decomposing needle litters during a long-term experiment in Swedish forests

Abstract

The dynamics of 47 major and trace elements were examined during a long-term (up to 8 years between 1979 and 1988) litter decomposition experiment in European boreal and nemoboreal forests (Sweden). Litterbags were incubated in 11 monocultural stands at 10 different locations including seven with Norway spruce (Picea abies (L.) H. Karst.) and four with Scots pine (Pinus sylvestris L.). Principal component analysis and manual scatter plots revealed groups of elements behaving in a similar manner. One group consisted mainly of nutrients, but also of the unessential or toxic elements Rb, Sc, Sr and Tl, and had a general trend with decreasing mass-normalised (mn) concentrations during decomposition. Another group contained mostly unessential and potentially toxic elements, whose concentrations generally increased during the decay process. An exception from this increasing trend was found for Cd, Hf, Hg, Ta and Zr, for which the mn-concentrations increased initially followed by a net leaching from the litter. The influence of sea spray was identified in the early stages of the experiment (in particular for Na), and the impact of the anthropogenic component of atmospheric deposition was clearly visible (e.g. Pb, Cd, Hg). A regional northern Sb source is indicated in the pine, but not in the spruce, needles. The fact that the samples were collected at a time of higher atmospheric metal deposition than at present provides additional information and usefulness of the results.