Microbial Biomass and Utilization of Dissolved Organic Matter in the Okefenokee Swamp Ecosystem

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Abstract
The Okefenokee Swamp exhibited levels of microbial biomass and aerobic glucose uptake comparable to those of other organically rich, detritus-based aquatic ecosystems. In contrast to other peat-accumulating systems, this acidic (pH 3.7), low-nutrient environment does not show diminished water column or surface sediment microbial biomass or heterotrophic activity. The total particular ATP varied between 0.03 and 6.6 μg liter −1 (mean, 1.6 μg liter −1 ) in water and between 1 and 28 μg g (dry weight) −1 (mean, 10.0 μg g [dry weight] −1 in sediments. The turnover times for dissolved d -glucose were 1.26 to 701.25 h (mean, 110.25 h) in aerobic waters and 2.4 to 72 min (mean, 10.2 min) in aerobic surface sediments. Water column bacterial secondary production, measured as the incorporation of [ 3 H]thymidine into cold-trichloroacetic acid-insoluble material, ranged from 0.06 to 1.67 nmol liter −1 day −1 (mean, 0.45 nmol liter −1 day −1 ). The kinetics of d -glucose uptake by water column microflora are multiphasic and suggest the presence of a diverse microbial population capable of using labile substrates at nanomolar concentrations and at substantial rates. The presence of a large and active aerobic microbial community in the Okefenokee Swamp is indicative of an important role for microbes in swamp geochemistry and strongly suggests the existence of a detritus-based food web.