RAPID BREAKDOWN OF ALLOCHTHONOUS AND AUTOCHTHONOUS PLANT-MATERIAL IN A EUTROPHIC RIVER

Carbon/nitrogen ratios and breakdown of leaves of Populus tremuloides (allochthonous) and the aquatic macrophytes, Ceratophyllum demersum an d Potamogeton pectinatus (autochthonous), were investigated in a eutro phic river. The allochthonous material had a C/N ratio 5-6 x greater a nd decayed slower than either of the macrophytes. The decay rates meas ured for these species were greater in this eutrophic system than has been reported for the same species in more oligotrophic systems. The r apid breakdown of the plant material and the eutrophic condition of th e river suggest the microbial decomposer community may have been limit ed, at least in part, by the availability of detrital organic carbon, rather than dissolved nutrients only.