Methanogenesis pathways in a stratified eutrophic alpine lake (Lake Bled, Slovenia)

Abstract

The production pathway and carbon source of CH4 in the surface sediment of a eutrophic alpine lake (Lake Bled, northwest Slovenia), in which the hypolimnion is anoxic for most of the year, were determined from molecular and biogeochemical studies. The average δ13CCH4 value of ‐69.5‰ ± 1.2‰, associated with low acetate concentrations, suggested that CH4 should be formed, predominantly, hydrogenotrophically. The proportion of “fresh” autochthonous lipids in total extractable lipids in sediment decreased from 62% at the surface to 41% at a depth of 20 cm. The contribution of lipids of bacterial origin was more pronounced at the surface, comprising 13%. Terminal restriction fragment length polymorphism (T‐RFLP) analysis of 16S ribosomal ribonucleic acid (rRNA) sequences of bacterial and archaeal community members suggested that larger sediment‐depth‐dependent changes occurred in the latter. The majority of archaeal sequences belonged to Euryarchaeota. The methanogenic population accounted for 73% and 38% of the archaeal community at depths of 0‐2 cm and 10‐12 cm, respectively. In the upper 2 cm, hydrogenotrophs, mostly Methanomicrobiaceae, were dominant. In the deeper sediment, archaeal sequences were mostly those of unknown affiliation with Euryarchaeota, Thermoplasmatales, and related linkages, and only 21% of the hydrogenotrophic methanogenic archaea were detected. Somewhat lower percentages (< 18%) of sequences representing acetotrophic archaea (Methanosaetaceae) were present in the two layers. The biogeochemical processes and structure of the archaeal community support the hypothesis that hydrogenotrophic methanogenesis is the dominant pathway in the sediment of alpine Lake Bled, despite low temperature and the prevalence of “fresh” autochthonous‐derived organic matter.

Distribution of sediment bacterial and archaeal communities in plateau freshwater lakes

“…Liu et al (2009) found that most of archaeal sequences retrieved from sediments of Lake Taihu were affiliated with Euryarchaeota, while a small proportion with Crenarchaeota. In sediments of Lake Kivu, Lake Bled, Lake Wivenhoe, and LakeTaihu, the archaeal communities were also mainly composed of Euryarchaeota (Bhattarai et al 2012;Green et al 2011;Mandic-Mulec et al 2012;Ye et al 2009), while all archaeal sequences from sediments of Lake Geneva were affiliated with Euryarchaeota (Haller et al 2011). In contrast, Crenarchaea organisms were the predominant archaea and only one phylotype affiliated with Euryarchaea was detected in Lake Hovsgol sediment (Nam et al 2008).…”

“…Rodrigues et al (2014) suggested the seasonal effects on archaeal community diversity in lake sediment of the Brazilian Savanna. Lake sediment archaeal community structure could be influenced by pollution (Haller et al 2011), sediment depth (Borrel et al 2012;Mandic-Mulec et al 2012), and salinity (Jiang et al 2007). To date, investigation on the archaeal communities in sediments from a number of lakes has not been addressed.…”

An inter-regional assessment of concentrations and δ13C values of methane and dissolved inorganic carbon in small European lakes

“…However, d 13 C values remarkably more negative than -65 % have recently been reported for lacustrine CH 4 , leading to the conclusion that hydrogenotrophic methanogenesis might also be a significant pathway in lake ecosystems (e.g. Murase and Sugimoto 2001;Kankaala et al 2007;Mandic-Mulec et al 2012). In all our 32 lakes, the d 13 C value of CH 4 measured in the sediments is more negative than -61 % and in 30 lakes more negative than -65 % (Fig.…”

Sources of Lipids in Anoxic Lacustrine Sediments Using Stable Carbon Isotopes

“…At the surface sediment, the odd-numbered alcohols, especially those between C 22 and C 30 , that are considered to be of terrigenous origin (Albro 1976;Weete 1976), were more abundant than the even-numbered ones (Mandi c-Mulec et al 2012). Their 13 C isotopic composition, ranging mostly between À41.4 and À26.6%, reflects their prevalently mixed terrigenous and microalgal inputs.…”

“…Our previous investigation, based on Archaeal community analyses, indicated that hydrogenotrophic methanogenesis is the dominant pathway of CH 4 production in the sediment of the alpine Lake Bled, despite its low temperature and the prevalence of autochthonous, and therefore more labile, organic carbon (Mandi c-Mulec et al, 2012).…”