V. Heuer, M. Krüger, M. Elvert
2010
Citations
7
Influential Citations
59
Citations
Journal
Organic Geochemistry
Abstract
Abstract Acetate is an important intermediate in the anaerobic degradation of organic matter and highly relevant for the cycling of carbon in nature. The water soluble C 2 compound is produced by fermentation of organic matter as well as by reduction of CO 2 with H 2 via the acetyl-CoA pathway (acetogenesis) and serves as an important substrate for a variety of microorganisms including sulfate reducing bacteria and methanogenic archaea. The relative importance of the different metabolic processes in acetate production and consumption is thought to be reflected in the stable carbon isotopic composition of pore water acetate. δ 13 C values of acetate have been shown to be highly variable in marine sediments, ranging from –85‰ to –3‰, and distinct isotopic fractionations have previously been reported to be associated with fermentation, acetogenesis and acetoclastic methanogenesis in pure microbial cultures. Aiming to better understand the stable carbon isotope biogeochemistry of sedimentary acetate, this study investigates if process related carbon isotopic signals of acetate are also expressed in the pore water pool of complex freshwater environments. We report findings from incubation experiments with lake sediments, in which we manipulated the relative importance of single processes by addition of specific substrates and inhibitors. In particular, we found: (a) δ 13 C values of acetate closely resembled δ 13 C values of total organic carbon in the sediment’s solid phase (TOC) where fermentation was the dominant process; (b) a distinct 13 C enrichment of the acetate pool relative to δ 13 C TOC where acetate was consumed by acetoclastic methanogenesis; and (c) a distinct 13 C depletion of acetate relative to both δ 13 C TOC and δ 13 C values of dissolved inorganic carbon (DIC) where high levels of H 2 stimulated acetogenesis. Our study provides further evidence for the diagnostic value of the stable carbon isotope chemistry of acetate for the detection of biogeochemical processes in natural systems.