Variable Effects of Iron (Fe (III)) Additions on Potential Methane Production in Boreal Lake Littoral Sediments

Effects of alternative electron acceptors on the activity and community structure of methane-producing and consuming microbes in the sediments of two shallow boreal lakes

“…In contrast to the potential CH 4 oxidation, the potential net CH 4 production rates (0.6-82.5 nmol g -1 DW d -1 ; 0.1-11.7 nmol cm -3 d -1 ) in the anaerobic incubations of the sediment slurries from the study lakes fell well within the range of reported CH 4 production rates in previous lake sediment studies: ~0-312 nmol g -1 DW d -1 (Schulz, Matsuyama and Conrad 1997;Marotta et al 2014;Karvinen, Lehtinen and Kankaala 2015) and ~1-23 nmol cm -3 d -1 (Sivan et al 2011;á Norði, Thamdrup and Schubert 2013). The potential net CH 4 production rates also well represent the magnitude and variation of the estimated potential gross CH 4 production rates, since anaerobic CH 4 oxidation was always a minor fraction of the potential net CH 4 production ( Table 2).…”

“…This could also suppress methanogenesis via decreasing the availability of methanogenic substrates. The recently reported Fe 3+ -induced suppression of both CH 4 and CO 2 production in boreal lake sediments and peats (Karvinen, Lehtinen and Kankaala 2015) indeed implies that this process could play an important role in reducing CH 4 emissions from freshwater systems. It is well known that MO in oxic sediment layers represents an efficient CH 4 sink in lakes (Hanson and Hanson 1996) and that increased EA availability reduces methanogenesis in freshwater sediments (Segarra et al 2013;Karvinen, Lehtinen and Kankaala 2015).…”

“…This strongly suggests that besides increasing anaerobic respiration, Fe 3+ and Mn 4+ also induced decreases in methanogenesis via increasing OM recalcitrance and protecting it from microbial degradation (Lalonde et al 2012;Karvinen, Lehtinen and Kankaala 2015;Estes et al 2017). probably depends on the sediment type, as indicated by the lack of a Fe 3+ -and Mn 4+ -induced decrease in the potential net TIC production in P 10-30 (Table 2).…”

“…The Fe 3+ reduction activity was measured as Fe 2+ production using a ferrozine-based assay (Lovley and Phillips 1986), as previously described by Karvinen, Lehtinen, and Kankaala (2015). The Mn 4+ reduction activity was measured by the accumulation of soluble Mn 2+ .…”

“…Total Fe content of the sediments was determined as in Karvinen, Lehtinen, and Kankaala (2015). Total Mn content of the sediment supernatant (pH 2) was determined as explained above for the Mn 4+ reduction analyses (Table 1).…”