Original paper

Increased sediment-water interface bacterial [3H]-L-serine uptake and biomass production in a eutrophic reservoir during summer stratification

Christian, Bradley W.; Lind, Owen T.


Bacterial consortia at sediment-water interfaces (SWIs) conduct metabolic processes that affect lake and reservoir organic matter cycling and nutrient composition. Seasonal reservoir dynamics such as stratification and overturn influence SWI bacterial activity and bacterial biomass production. We measured SWI bacterial uptake rates of tritium-labeled L-serine (Ser) to assess SWI bacterial activity and production in a monomictic, eutrophic reservoir. Total microbial Ser uptake (Sertot) and uptake in the protein fraction (Serpro) were measured seasonally. Serpro was approximately 40 percent of Sertot which demonstrated that Ser was incorporated into cellular material other than protein. Highest bacterial Sertot and Serpro occurred during the onset of summer stratification (Jun 2005) followed by late-season stratification (Oct 2005). Lower Sertot and Serpro were observed after the onset of autumnal overturn (Oct 2004) and during winter mixing (Feb 2005). Higher SWI temperature, lower dissolved oxygen, and decreasing redox potential, which are a function of summer stratification, were associated with higher Sertot and Serpro. Estimates of SWI bacterial production and growth rates indicated that highest production and fastest community generation times also occurred at onset of summer stratification and during late-season stratification. These data suggest summer stratification, and not autumnal overturn and winter mixing, is responsible for higher SWI bacterial metabolism, even under anoxic conditions during which bacteria utilize less energetically favored electron acceptors. We conclude that stratification is an important event that increases SWI bacterial metabolism, which results in increased carbon mineralization and nutrient cycling from sediments to the water column that affects water quality and reservoir trophic status.


sediment-water interfacebacterial dynamicsreservoir stratificationl-serineradiolabeled substrates