Biodegradation is an important process controlling the removal and transformation of organic matter in both pristine and polluted environments. The chemical quality of dissolved organic matter (DOM), as the substrate for these processes, will determine how quickly biodegradation will occur, if it occurs at all. This thesis is concerned with the biodegradability of DOM from atmospheric deposition in an alpine catchment and from wastewater treated by anaerobic processes in an anaerobic baffled reactor. Although it comes from completely different environments, the microbial utilization of DOM from both sources has the potential to influence processes that can have important implications for human and ecosystem health. Therefore, biodegradability of samples from both environments was estimated using two different approaches: (1) microbial bioassays and (2) biodegradability incubation experiments in which dissolved organic carbon concentrations and fluorescence were measured. Overall, most of the DOM in atmospheric deposition was found to be labile. Microbial metabolic activity increase ranged from 0.02 d-1 to 0.22 d-1. This research for the first time identified two pools of DOM, one that decayed rapidly with degradation rates ranging from 0.013 d-1 to 0.413 d-1, and one that decayed more slowly with degradation rates ranging from 0.000 d-1 to 0.009 d-1. Phosphorous addition to deposition samples increased degradation rates in only two out of four samples. Fluorescence analyses of biodegradability incubations showed that, although initial samples had low fluorescence intensities, more fluorescent DOM, particularly centered at excitation/emission wavelength of 400 nm excitation/450 nm emission, was produced over time, suggesting that microbial transformation of atmospherically-deposited DOM results in production of more double-bonded and aromatic organic carbon. For wastewater, diluted samples showed little biodegradation in terms of DOC concentration measurements and fluorescence analyses. However, excitation emission matrices (EEMs) of raw wastewater samples collected from treatment train showed a definite decrease in fluorescent material over time that was not observed in the biodegradability experiments using diluted wastewater. Microbial assays also showed greater biodegradability in undiluted wastewater samples with formazan formation rates ranging from 0.22d-1 to 0.29d-1. Taken together, these results suggest that dilution of highly concentrated samples may result in inaccurate estimates of biodegradability.