68 Chapter 2 Sulfide toxicity hinders methane removal by ANME Based on the highest ngCOV of ANME-2 MAG 011, we selected sediments from Site 5 at the depth interval of 8-28 cm to experimentally test the hypothesis that sulfide inhibits AOM activity in these sediments (Figure 6 and Supplementary Table 2). We pre-incubated sediments with 13C-methane until AOM activity was detected. Then, we added 0, 0.5, 1, 2, or 4 mM of sulfide to triplicate incubations and monitored AOM rates as well as final sulfide concentrations. Additionally, we included one control to which we added 2 mM of sulfide at the beginning of the pre-incubation. Average AOM rates were highest when no sulfide was added (31.3 nmol of methane g dry sediment-1 day-1), decreasing with increasing sulfide concentrations: 23.2, 16.9, 14.5, and 12.1 nmol of oxidized methane g dry sediment-1 day-1 when, respectively, 0.5, 1, 2, and 4 mM of sulfide were added to incubations (Figure 6, Supplementary Table 2). The average AOM rate in the control incubation that received 2 mM of sulfide at the beginning of the pre-incubation was 10.5 nmol of oxidized methane g dry sediment-1 day-1. This resulted in an average of 3.62 mM sulfide at the end of the experiment, and inhibition of 67% of AOM activity relative to incubations that received no sulfide, which had an average of 0.55 mM of sulfide at the end of the experiment. In pre-incubated bottles with no added sulfide, additions of 0.5, 1, 2, and 4 mM of sulfide resulted, respectively, in average final sulfide concentrations of 0.8, 1.12, 1.88 and 3.41 mM, and inhibition of 26, 46, 54 and 61% of AOM activity respectively (Figure 6 and Supplementary Table 2).
RkJQdWJsaXNoZXIy MTk4NDMw