Dam tailwaters compound the effects of reservoirs on the longitudinal transport of organic carbon in an arid river

[摘要] Reservoirs on rivers can disrupt organic carbon (OC) transport andtransformation, but less is known how river reaches directly below damscontribute to OC processing. We compared how reservoirs and their associatedtailwaters affected OC quantity and quality by calculating particulateOC (POC) and dissolved OC (DOC) fluxes, and measuring composition andbioavailability of DOC. We sampled the Yampa River near Maybell, Colorado,USA, and the Green River above and below Fontenelle and Flaming Gorgereservoirs as well as their respective tailwaters from early snowmelt to base flowhydrological conditions. In unregulated reaches (Yampa River, Green Riverabove Fontenelle reservoir), DOC and POC concentrations increased withsnowmelt discharge. POC and DOC concentrations also increased with streamdischarge below Fontenelle reservoir, but there was no relationship betweenDOC and stream flow below Flaming Gorge reservoir. The annual load of POCwas 3-fold lower below Fontenelle Reservoir and nearly 7-fold lower belowFlaming Gorge reservoir, compared to their respective upstream samplingsites. DOC exported to downstream reaches from both reservoirs was lessbioavailable, as measured with bioassays, than DOC upriver of thereservoirs. Lastly, tailwater reaches below the reservoirs generated OC,exporting potentially 1.6–2.2 g C m⁻² d⁻¹ of OC to downstreamecosystems. Therefore, the effect of impounding rivers on C fluxes isgreater than the impact of the reservoirs alone given the additive effect oftailwater reaches below dams, which may produce and export comparableamounts of likely autochthonous carbon to downstream reaches.

[学科分类] 地球化学与岩石