Effects of freeze–thaw cycles on anaerobic microbial processes in an Arctic intertidal mud flat

Abstract

Insight into the effects of repeated freezing and thawing on microbial processes in sediments and soils is important for understanding sediment carbon cycling at high latitudes acutely affected by global warming. Microbial responses to repeated freeze-thaw conditions were studied in three complementary experiments using arctic sediment collected from an intertidal flat that is exposed to seasonal freeze-thaw conditions (Ymerbukta, Svalbard, Arctic Ocean). The sediment was subjected to oscillating freeze-thaw incubations, either gradual, from À5 to 4 1C, or abrupt, from À20 to 10 1C. Concentrations of low-molecular weight carboxylic acids (volatile fatty acids) were measured and sulfate reduction was assessed by measuring 35 S sulfate reduction rates (SRRs). Gradual freezethaw incubation decreased microbial activity in the frozen state to 0.25 % of initial levels at 4 1C, but activity resumed rapidly reaching 460 % of initial activity in the thawed state. Exposure of sediments to successive large temperature changes (À20 versus 10 1C) decreased SRR by 80% of the initial activity, suggesting that a fraction of the bacterial community recovered rapidly from extreme temperature fluctuations. This is supported by 16S rRNA gene-based denaturing gradient gel electrophoresis profiles that revealed persistence of the dominant microbial taxa under repeated freeze-thaw cycles. The fast recovery of the SRRs suggests that carbon mineralization in thawing arctic sediment can resume without delay or substantial growth of microbial populations.

Morphodynamics and lake level variations at Paiku Co, southern Tibetan Plateau, China

“…A similar phenomenon of freezethaw effects influencing the sediment structure has been previously reported . They also influence the shift of chemical components and microbiological processes (e.g., Mountfort et al, 2003;Sawicka et al, 2010).…”

Activity and community structures of sulfate-reducing microorganisms in polar, temperate and tropical marine sediments

“…Our results show that sulfate-reducing communities in these cold habitats can tolerate temperatures down to or below the freezing point of seawater, which may permit survival and recovery after temporary freezing of the sediment. Studies of Arctic sediments show that sulfate reduction decreases strongly during freezing, yet SRM may exhibit relatively high metabolic rates immediately upon thawing, even after repeated freeze-thaw cycles (Sawicka et al, 2010). Water on mineral surfaces and in liquid veins in ice can provide adequate habitats for active microbial populations (Price, 2007;Bowman et al, 2012;Ewert and Deming, 2014).…”

“…Brief descriptions of the study sites are provided in Table 1. Samples were obtained from the upper 15 cm of sediment from each site, which corresponds to the depth range where bacterial sulfate reduction peaks (Abed et al, 2006;Mazumdar et al, 2007;Kristensen et al, 2008;Niemann et al, 2009;Robador et al, 2009;Sawicka et al, 2010;Holmkvist et al, 2014;Xu et al, 2014). After sampling, sediments were kept under anoxic conditions at in situ temperatures until further processing in the laboratory, which occurred within 1 week of sampling.…”

Contrasting denitrifier communities relate to contrasting N2O emission patterns from acidic peat soils in arctic tundra

“…and Kowalchuk, 2008;Männistö et al, 2009;Sawicka et al, 2010). Increasing thaw-depth and frequencies of freeze-thaw cycles may increase the availability of organic carbon and nitrogen stored in permafrost-affected soils, finally fueling denitrification-associated N 2 O emissions (Mørkved et al, 2006;Sharma et al, 2006;Kuhry et al, 2010).…”