BACTERIAL BIOMASS AND CELL-SIZE DISTRIBUTIONS IN LAKES - MORE AND LARGER CELLS IN ANOXIC WATERS

We measured bacterial abundance, cell size distribution, and related m icrobiological and geochemical parameters in 20 stratified lakes from three regions in the U.S. Both largest cell size and greatest bacteria l abundance occurred in anoxic waters. Bacterial size distributions fr om the hypolimnia of lakes that were oxic were identical to those in s urface waters. Bacteria from anoxic hypolimnia were 2-10 times larger than those from oxic water and cell size was independent of temperatur e under either oxic or anoxic conditions. For all lakes and strata, ba cterial abundance was strongly related to the concentration of total p hosphorus (TP). Cell size was not related to TP or to bacterial abunda nce, suggesting that abundance and size may be regulated by different processes. Bacterial biomass (calculated from the product of mean cell size and bacterial abundance) was typically 4 times greater in anoxic than in oxic waters of lakes.