Print PageUnderstanding carbon (C) cycling in rivers is essential to predict responses to climate and anthropogenic alterations of the world’s rivers. A major flux component of C cycling is dissolved organic carbon (DOC) and quantifying sources and fluxes of DOC is needed to accurately describe riverine C-cycling. Regulation of rivers by dams has altered C dynamics by reducing particulate organic C and sediment from upstream and dampening seasonal hydrology. Because dams cutoff rivers from the upper watershed, regulated rivers are an opportune ecosystem to study how rivers process DOC. Our study site is the Colorado River below Glen Canyon Dam, which forms Lake Powell. We quantified the sources and fates of DOC via short-term organic C budgets, 13C stable isotope analysis, DOC quality experiments, and modeling.
Results/Conclusions
DOC originates from Lake Powell, autochthonous DOC from primary production, and allochthonous DOC from tributaries and leaching of buried organic matter. Autochthonous sources of DOC in the upper reaches of the Colorado River below Glen Canyon Dam contribute 2% of the daily DOC flux. This flux equates to a contribution of 0.3 – 0.7 g C m-2 day-1. Although this flux is small relative to the Lake Powell DOC pool, bioavailability experiments indicate that this autochthonous source of DOC is labile and potentially subsidizes microbial communities downstream. While direct DOC input from tributaries is minimal, modeling results indicate that leaching of buried organic matter contributes to the DOC pool in the lower reaches of the Colorado River, Grand Canyon. Our results indicate that terrestrial C leached from buried organic matter is a significant flux of the C budget, which indicates that terrestrial organic matter can be stored and later processed in rivers.
