Status: this preprint was under review for the journal BG but the revision was not accepted.
CO2 and CH4 fluxes are decoupled from organic carbon loss in drying reservoir sediments
Tricia Light,Núria Catalán,Santiago Giralt,and Rafael Marcé
Abstract. Reservoirs are a prominent feature of the current global hydrological landscape, and their sediments are the site of extensive organic carbon burial. Meanwhile, reservoirs frequently go dry due to drought and/or water management decisions. Nonetheless, the fate of organic carbon buried in reservoir sediments upon drying is largely unknown. Here, we conducted a 45-day-long laboratory incubation of sediment cores collected from a western Mediterranean reservoir to investigate carbon dynamics in drying sediment. Drying sediment cores emitted more CO2 over the course of the incubation than sediment cores incubated with overlaying water (206.7 ± 47.9 vs. 69.2 ± 18.1 mmol CO2 m−2 day−1, mean ± SE). Organic carbon content at the end of the incubation was lower in drying cores, which suggests that this higher CO2 efflux was due to organic carbon mineralization. However, the apparent rate of organic C reduction in the drying sediments (568.6 ± 247.2 mmol CO2 m−2 day−1, mean ± SE) was higher than C emission. Meanwhile, sediment cores collected from a reservoir area that had already been exposed for 2+ years displayed net CO2 influx from the atmosphere to the sediment (−136.0 ± 27.5 mmol CO2 m−2 day−1, mean ± SE) during the incubation period. Sediment mineralogy suggests that this CO2 influx was caused by a relative increase in calcium carbonate chemical weathering. Thus, we found that while organic carbon decomposition in newly dry reservoir sediment causes measurable organic carbon loss and carbon gas emissions to the atmosphere, other processes can offset these emissions on short time frames and compromise the use of carbon emissions as a proxy for organic carbon mineralization in drying sediments.
How to cite. Light, T., Catalán, N., Giralt, S., and Marcé, R.: CO2 and CH4 fluxes are decoupled from organic carbon loss in drying reservoir sediments, Biogeosciences Discuss. [preprint], https://doi.org/10.5194/bg-2019-128, 2019.
Received: 09 Apr 2019 – Discussion started: 14 May 2019
Water reservoir sediments can store large amounts of organic. However, it is unclear what happens to this organic carbon when water reservoirs go dry due to drought, water diversion, etc. Here, we conducted laboratory incubations of reservoir sediment to determine the effect of drying on this stored organic carbon. We found that while some of the organic carbon in water reservoir sediments is released to the atmosphere as reservoirs go dry, other sediment processes can offset these emissions.
Water reservoir sediments can store large amounts of organic. However, it is unclear what...