Anoxygenic phototrophic bacteria and aerobic phototrophs in Normans Lagoon, a ‘billabong’ adjacent to the Murray River, south-eastern Australia

摘要

The development and demise of substantial populations of bacteriochlorophyll (BChl) a and d containing phototrophs are documented within the bottom waters of a billabong (oxbow lake) in south-eastern Australia. The observation of such populations within a freshwater body is unusual, illustrating an unexpected source of organic carbon within the floodplain ecosystem of one of Australia's principal rivers. Values of up to 1086µgL−1 BChl a and 490µgL−1 BChl d were recorded during an 11 month study of physico-chemical parameters, algae and bacteria. An unusual density stratification was observed within the billabong, fostered by an increase in bivalent ions at depth, and leading to persistent anoxia below 0.75m depth over summer. A marked vertical distribution was observed for both algae and bacteria, that for the bacteria being lost with a mixing event in late March. The presence of up to 74µgL−1 BChl a at the surface of the billabong during the summer months is ascribed to entrainment of bacteria within bubble plumes rising from the sediments.