The Potential Hidden Age of Dissolved Organic Carbon Exported by Peatland Streams

Abstract

Abstract Radiocarbon ( 14 C) is a key tracer for detecting the mobilization of previously stored terrestrial organic carbon (C) into aquatic systems. Old C (>1,000 years BP) may be “masked” by postbomb C (fixed from the atmosphere post‐1950 CE), potentially rendering bulk aquatic dissolved organic C (DOC) 14 C measurements insensitive to old C. We collected DOC with a modern 14 C signature from a temperate Scottish peatland stream and decomposed it to produce CO 2 under simulated natural conditions over 140 days. We measured the 14 C of both DOC and CO 2 at seven time points and found that while DOC remained close to modern in age, the resultant CO 2 progressively increased in age up to 2,356 ± 767 years BP. The results of this experiment demonstrate that the bulk DO 14 C pool can hide the presence of old C within peatland stream DOC export, demonstrating that bulk DO 14 C measurements can be an insensitive indicator of peatland disturbance. Our experiment also demonstrates that this old C component is biologically and photochemically available for conversion to the greenhouse gas CO 2 , and as such, bulk DO 14 C measurements do not reflect the 14 C signature of the labile organic C pool exported by inland water systems more broadly. Moreover, our experiment suggests that old C may be an important component of CO 2 emissions to the atmosphere from peatland aquatic systems, with implications for tracing and modeling interactions between the hydrological and terrestrial C cycles.