EFFECTS OF PRECIPITATIONS OF IRON HYDROXIDES ON LEPTOPHLEBIA-MARGINATA (L) (INSECTA, EPHEMEROPTERA) IN THE FIELD

For 3 months, nymphs of L. marginata (Ephemeroptera) were exposed in a clearwater stream (Wispe) with permanent Fe2O3 precipitations on the streambed and in a brownwater stream (Mullra-stream) with Fe-x(OH)(y)- humus precipitations. The body burden of Fe of mayflies exposed in the Wispe were significantly higher than those in the Mullra-stream. Fe-p recipitations on the body surface of the mayflies accounted for 80 % o f the Fe-body loads in the Wispe, whereas only 40 % of the body loads in Mullra-stream were adsorbed on the body surface of the mayflies. Ho wever, survival of the mayflies was not affected by the different kind s of Fe-precipitations on the mayflies' body and gills. The internal u ptake of Fe by the mayflies was higher in Mullra-stream than in Wispe. Frequent molting did not allow for an incrustation of more than 50 % of the body. Incrustation occurred randomly as no body part was prefer red. The chemical composition of the precipitations on the mayflies di ffered. Fe3+ was found in the precipitates on mayflies in the Wispe, w hile Fe3+ and Fe2+ were found on the nymphs in Mullra-stream. Within t he body, Fe2+ was found in eye- and cuticle-pigments and in the eggs o f the last instar.