AME 12:233-238 (1997)  -  doi:10.3354/ame012233

Dissolved humic substances from 5 different aquatic habitats in the Okefenokee Swamp, USA, ecosystem were tested for their ability to support growth of natural bacterial communities in batch bioassay experiments. The in situ dissolved organic carbon (DOC) concentration in samples from all sites was high, ranging from 46 to 58 mg C l^-1; 63 to 78% of the DOC was humic substances. Humic substances were isolated by adsorption onto Amberlite XAD-8 resin and provided to natural bacterial communities either from the same site or one of the other sites as the only carbon source. Humic substances from all sites supported bacterial growth; generally there were no significant differences among the bacterial communities in the rates or extent of utilization of humic substances. The average specific growth rates of bacteria, determined as changes in biovolume, were 0.026 to 0.044 h^-1 for all experiments and were comparable to rates measured in situ. The cumulative bacterial carbon production ranged from 58 to 176 μg C l^-1. Based on measures of bacterial carbon production and oxygen consumption, bacterial growth efficiency on humic substances was estimated at 22%, and the percentage of the humic substances pool utilized during the 1 wk bioassay was 0.8 to 1.8%.

Humic substances · Bacterial growth · Okefenokee Swamp · Freshwater marsh