Benthic Bacterial Biomass and Production in Two Blackwater Rivers

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Abstract
Bacterial biomass and production in sediments of two blackwater rivers were measured via epifluorescent direct counts and rate of thymidine incorporation into DNA. Biomass ranged from 3 to 1500 mg C∙m−2 and production ranged from 0.01 to 22.0 mg C∙m−2∙h−1. Both biomass and production were correlated with organic content of the sediment. Neither biomass nor production was related to temperature. Allochthonous detritus apparently serves as a growth substrate for sediment bacteria. Despite differences in water chemistry and flow between the two rivers, comparison of similar sites between rivers showed similar bacterial standing stock and production. During most of the year these fourth- and sixth-order rivers are highly heterotrophic, yet at low water autochthonous carbon may serve as growth substrate for bacteria.