Understanding the delivery and processing of terrestrially derived organic carbon within fluvial networks is crucial in accurately defining aquatic-terrestrial-atmospheric connections. Microbial respiration and transformation of OC is a vital consideration when trying to decipher the sources of OC delivered to and processed within the aquatic system vs. those distributed to downstream ecosystems. At several sites within the Harvard Forest research area measurements of bacterial production, respiration, abundance, and community level physiological profiling were employed to gain a better understanding of these microbial transformations. Dissolved OC (DOC), DO13C and DOC lability were measured at multiple locations along a continuum from headwater streams in Harvard Forest to its final destination at the Quabbin Reservoir during both high and low flow periods. Overlaps in DO13C allochthonous and autochthonous sources impair the ability to discern in situ sources independent from additional measurements. DOC showed roughly a 2 fold difference in concentration from the headwater stream site (Bigelow Brook) to the entrance of the Quabbin reservoir. This 2 fold increase in DOC concentration was accompanied by a 10 fold increase in its bioavailability. The coupling of additional chemical, optical, and bacterial measurements will better help to elucidate the sources and sinks of OC along this continuum and its concurrent processing by the microbial community.