Steeb, Philip, Linke, Peter and Treude, Tina (2014) A sediment flow-through system to study the impact of shifting fluid and methane flow regimes on the efficiency of the benthic methane filter. Limnology and Oceanography: Methods, 12 . pp. 25-45. DOI 10.4319/lom.2014.12.25.

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Abstract

The efficiency of the “benthic microbial methane filter” at marine cold seeps is controlled by diffusive sulfate
supply from the overlying seawater and advective methane flux from deep reservoirs. High fluid fluxes
reduce the penetration depth of sulfate and limit the filter to a very narrow zone close to the sediment-water
interface. Here, we introduce a new sediment-flow-through (SLOT) system, to mimic the balance between
fluid/methane flow and sulfate supply in natural sediments. SLOT enables anaerobic incubations of intact sediment
cores under natural flow regimes. In addition to traditional in- and outflow sampling, geochemical parameters
can be monitored along the sediment core using microsensors and rhizons. In a first test run, two cores
with gassy sediments from the Eckernförde Bay (Baltic Sea) were incubated and monitored for 310 days under
low (11.2 cm y–1) and high fluid flow (112.1 cm y–1) conditions. Rates of anaerobic oxidation of methane (AOM)
were one order of magnitude higher (3.07 mmol m–2 d–1) in the high flow compared to the low flow regime (0.29
mmol m–2 d–1), whereas methane efflux was twice as high (0.063 and 0.033 mmol m–2 d–1, respectively).
Sediment profiles of sulfide, sulfate, total alkalinity, pH, redox, and other parameters offered important information
on the nature and dynamics of the biogeochemical reactions in the sediment cores including methanotrophy,
sulfate reduction, carbonate precipitation, and sulfide oxidation. The SLOT system proofed to be an
effective device to study the temporal evolution of biogeochemical parameters in intact sediments subjected to
advective fluid transport.

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