Effect of acute exposure to hydrogen peroxide on the production of phytoplankton and bacterioplankton in a mesohumic lake

Active oxygen species such as hydrogen peroxide are produced as a result of UV radiation interaction with natural organic matter and can build up to high concentrations in many aquatic environments. Although the resulting oxidizing potential may affect biological materials and processes, the ecological effects have not yet been studied in any detail, We examined the influence of hydrogen peroxide exposure on phytoplankton and bacterioplankton production in Lac Cromwell, a small humic lake in the Laurentian Hills (Quebec, Canada). A range of hydrogen peroxide concentrations were added to natural samples that were incubated in situ; results indicate that even small amounts of added hydrogen peroxide (<50 nM) inhibited bacterial production in this lake, A 100 nM addition inhibited bacteria by as much as 40%. On the other hand, low concentrations of added hydrogen peroxide usually stimulated photosynthesis. Catalase addition to eliminate hydrogen peroxide from water usually stimulated bacterial production but had no effect on algal carbon fixation. If these results represent true changes in growth rate, they indicate very different sensitivities of phytoplankton and bacteria to oxidative stress.