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

Abstract

In the former copper shale mining district of Mansfeld, central Germany, weathering of slag heaps and dumps resulted in 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% (H9) or 0.36% (H4) of total detrital mass, corresponding to 6 and 2%, respectively, of maxima reported from nonpolluted 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 (H9) or 4 (H4) wk over unconditioned leaves.