The distribution of organic carbon compounds varies spatially in stream networks and temporally at individual sites. To understand the fate of carbon within watersheds, and its delivery to coastal ecosystems we must understand the controls on its transport and transformation. We examined temporal and spatial variation of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in the South Fork Eel River, a pristine forested watershed in northern California. We measured DOC and DON bioavailability in six streams at seven locations in the watershed at the beginning of the summer dry season in June and later in July. We determined the decomposition rates of DOC and DON using long-term incubations of filtered stream water with common microbial communities.

Results/Conclusions

June stream DOC and DON concentrations increased with the size of the drainage basin of the stream from 114 µg C L^-1 to 815 µg C L^-1 as DOC (R²=0.88, p=0.001) and 4.9 µg N L^-1 to 53.2 µg N L^-1 as DON (R²=0.69, p=0.025). Decomposition rates of DOC in June were not significantly different among sites in the watershed (mean=0.019 day^-1, p=0.996). However, in July DOC decomposition rates decreased by 70% in smaller streams with more canopy cover, but remained steady in larger, more open stream sites (p=0.019). Large mats of decaying algae in the open canopied stream sites probably provided large concentrations of readily degradable DOC to those sites. These results suggest that terrestrial and algal DOM vary greatly in their bioavailability.