Isotope Constraints on the Sources of Particulate Organic Carbon in a Subtropical Deep Reservoir

Abstract

AbstractReservoirs are active sites in the terrestrial environment in terms of carbon transformation and storage. Continuous reservoir construction reinforces the importance of such artificial storage; however, knowledge pertaining to the sources, cycling, and preservation of autochthonous/allochthonous particulate organic carbon (POC) in reservoirs remains incomplete. We monitored the flux and carbon isotope composition of sinking particles in a subtropical deep reservoir, and the results were compared with the isotopic signatures of potential POC sources (soil) and the sedimentary sink. We found that the typhoon‐induced POC flux was transported laterally at intermediate water depths within the reservoir and that it contributed more than 70% of the annual deposition. An isotope ternary mixing model showed that over 87% of the POC preserved in sediments was allochthonous. Although the autochthonous POC from primary production was preferentially degraded, the preserved autochthonous POC (42 ± 14 gC m−2 yr−1) was comparable to the observed carbon dioxide uptake (35 gC m−2 yr−1) by the reservoir, suggesting a high efficiency of carbon preservation in subtropical deep reservoirs.