Decomposition of alder leaves in two heavy metal-polluted streams in central Germany

In the former copper shale mining district of Mansfeld, central Germany, weathering of slag heaps and dumps resulted m groundwater, lakes and streams with extremely high heavy metal and metalloid concentrations (Zn up to 2.6 g l^-1; Cu, Pb, Cs, Cd, As up to 13 mg l^-1). We followed decomposition of Alnus glutinosa leaves in 2 streams, one with a high (H4) and one with a moderate (H9) load of these metals. In H9, mass loss closely followed an exponential decay curve (k = 0.055 d^-1); in H4, leaf mass remained constant after a very rapid initial decay (k = 0.12) during the first 4 wk. Fungal biomass, estimated by ergosterol measurements reached values of up to 1.1% (Hg) or 0.36 % (H4) of total detrital mass, corresponding to 6 and 2 %, respectively, of maxima reported from non-polluted streams. Conidium production by aquatic hyphomycetes was reduced to 10% (H9) and 0.01% (H4) of highest literature values. After 4 wk of stream exposure, leaves had greatly increased levels of As, Cu, Fe, Mn [both streams), Pb and Zn (H4). Gammarus fossarum preferred leaves that had been conditioned in the stream for 2 (Hg) or 4 (H4) wk over unconditioned leaves.