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The $ sp3$H thymidine incorporation (TTI) method has been frequently used to estimate benthic bacterial production rates in well oxygenated marine and river sediments, but not in the frequently more reduced lake sediments. In chapter 1, I evaluate the published sediment production literature and examine useful predictors of in situ bacterial production in mostly marine and riverine sediments. In chapters 2 and 3, I estimated and compared benthic production rates by TTI, frequency of dividing cells (FDC), the dilution method (DIL) and sediment respiration (SR) in 13 Quebec lakes to assess the reliability of the TTI based production rates. The TTI method was first calibrated, but despite keeping incubation times short and at in situ temperature, using optimal sediment volumes to saturate $ sp3$H thymidine (TdR) uptake rates, and correcting production rates for $ sp3$H-DNA recovery efficiencies, only a maximum of 10% of $ sp3$H TdR was incorporated into DNA and only extracellular isotope dilution could be accounted for (chapter 2). Most problematic, however, is the increasing presence of active bacteria unable to take up and incorporate TdR as lake sediments become more reduced (chapter 3). TTI based results are also not nearly as well correlated to environmental factors as those obtained from SR. (Abstract shortened by UMI.)

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