BIODEGRADATION OF ORGANIC PARTICLES BY SURFACE AND BENTHIC NEPHELOID LAYER MICROBES FROM LAKE-SUPERIOR

The biodegradation of a green alga (Chlorella vulgaris) and balsam fir wood (Abies balsamea) by microbial assemblages from the epilimnion an d deep hypolimnion of Lake Superior was determined. Algae and wood wer e radiolabeled, dried, and added to incubation bottles. Water collecte d from nearshore and offshore sites in the western arm of Lake Superio r was used to inoculate the substrates. Near surface water (5 m) or de ep hypolimnion water (1 m above the sediment)from each site was added to the bottles and incubated at 5-degrees-C or 15-degrees-C. Each bott le, including killed controls, was aerated every 48 h to recover biomi neralized (CO2)-C-14. Up to 76% of the labeled alga, but less than 40% of the labeled wood, was mineralized after 34 d Mineralization rates were up to 4.5 times faster at 15-degrees-C than at 5-degrees-C The pr esence of a benthic nepheloid layer at the nearshore site did not enha nce mineralization rates. In most cases, mineralization rates of eithe r substrate were similar at the nearshore and offshore sites. However, epilimnetic microbes from the nearshore site mineralized the wood fas ter than microbes from the offshore site. This may be explained by the higher density of bacteria in the nearshore inoculum. The type of sub strate and temperature influenced mineralization rates more than the s ite or depth in Lake Superior from which the microbial inoculum was ta ken.