Modeling the distribution of acetate in anoxic estuarine sediments

Abstract

Concentrations and rates of production and oxidation of acetate were studied in anoxic, estuarine sediments of Flax Pond, New York. Molecular weight separations by Sephadex gel indicated that in some, but not all, casts pore-water acetate consisted of multiple "pools." We developed a onedimensional kinetic model that uses measured oxidation rates (14C-labeled acetate conversion to 14C0,) and production rates (MoO,~-inhibition experiments) as model parameters. Appropriate diffusion coefficients were calculated with a free-solution value (1.3 +0.3 x 1 Op5 cm2 s-l) measured in this study. In general, oxidation rate constants estimated from modeled profiles agree well with those from [ 14C]acetate incubation experiments. Results imply that differences in acetate oxidation rates inferred from the two methods (MoO,~-inhibition, [14C]acetate oxidation) can be caused by diffusion of acetate along sharp concentration gradients in sediments.[14C]acetate uptake experiments account for such diffusion by using measured steady state acetate concentrations to infer oxidation rates, whereas MoO,~-inhibition experiments do not account for in situ acetate diffusion.

Fatty acid oxidation in anoxic marine sediments: the importance of hydrogen sensitive reactions

“…All cores were maintained at in situ temperatures in the dark until processed, and all sediment sectioning and sample preparation was done in a nitrogen-flushed glove bag. For all the experiments reported in this paper, the 4-8 cm interval of the sediment column was used, as this depth range is characterized by rapid sulfate reduction and rapid turnover of organics (Novelli 1987;Novelli et al 1988;Michelson et al 1989;Swider & Ma&in 1989). Previous experiments have shown that sulfate reduction rates (Swider & Mackin 1989) and acetate oxidation rates (Michelson et al 1989) for Flax Pond are comparable, although no direct measurements were made of sulfate reduction during our study.…”

“…If production doesn't change when uptake is inhibited, the rate of accumulation of fatty acids in pore waters of sediments treated with molybdate (a specific inhibitor of sulfate reduction) should reflect the rate of oxidation of fatty acids in undisturbed in situ sediments (Smith & Klug 1981;Sorensen et al 1981;Banat & Nedwell 1983;Christensen 1984;Michelson et al 1989). However, because sulfate reducers maintain low hydrogen levels in sediments and thus also play an indirect role in fatty acid oxidation by affecting the extent to which hydrogen sensitive fatty Table 1.…”

Sulfate reduction, acetate turnover and carbon metabolism in sediments of the Ao Nam Bor mangrove, Phuket, Thailand

“…cornrn.). Furthermethods for estimating rates and collecting pore water more, the monsoon periods preceding the 1992 study is required, molybdate inhibition perhaps offers the may have caused a deposition of low reactive detritus least problematic approach, subject to constraints disin the Ao Nam Bor mangrove system, which has previcussed by Michelson et al (1989). Previous estimates of ously been dregded from deep layers in the seabed by acetate uptake based on radiotracer analysis have nearby offshore tin mining plants (Chansang et …”

“…Acetate is the most important carbon source for sulfate reducers in these sediments and its production Michelson et al 1989, Shaw & McIntosh 1990, King 1991. Problems with 'biologically unavailable, but chemically measured' acetate pools should be minimal in this study, since acetate concentrations were assayed using tensen et al (1991) at the same site in January 1990. an enzymatic method that presumably detects only Their flux rates were 2 to 3 times higher and sulfate those pools available to bacteria.…”

Decomposition of organic matter in aggregated seston from the Elbe estuary:redox dependency and production of low molecular weight DOC compounds

“…Therefore, algal production of glyoxylate is found at high oxygen and low CO2 concentrations and is favoured by an increase in radiation and temperature (Stewart & Codd 1981). The observed production of glyoxylate in the Elbe must be explained by the formation of acetate, under low oxygen concentrations, as an end product of fermentation (Michelson et al 1989) and the subsequent production of glyoxylate by bacteria living on acetate as the organic substrate (Schlegel 1992). A significant input of glyoxylate apart from that produced by phytoplankton activities in the water column of the New York Bight (USA) apex was also assumed by Edenborn & Litchfield (1987).…”