Methane cycling in lake sediments and its influence on chironomid larval delta13C.
Stable carbon isotope analysis of chironomid larvae gave rise to the hypothesis that methane-oxidizing bacteria can provide an important food source for higher trophic levels in lakes. To investigate the importance of the methane cycle for the larval stable carbon signatures, isotope analysis and microbiological and biogeochemical investigations were combined. The study was based on comparison of a dimictic lake (Holzsee) and a polymictic, shallow lake (Grosser Binnensee), both located in northern Germany. Both lakes are inhabited by Chironomus plumosus larvae, which exhibited a stronger (13)C-depletion in Holzsee than in Grosser Binnensee, indicating a greater contribution of methane-carbon in the former. Indeed, the processes involved in the microbial methane cycle were found to be more active in Holzsee, showing higher potential methane production and methane oxidation rates. Consistently, cell numbers of methane-oxidizing bacteria were with 0.5 - 1.7 x 10(6) cells g(dw)(-1) about one order of magnitude higher in Holzsee than in Grosser Binnensee. Molecular analysis of the microbial community structure revealed no differences in the methanotrophic community between the two lakes, with a clear dominance of type I methanotrophs. The methanogenic population seemed to be adapted to the prevailing substrate in the respective lake (H(2)/CO(2) in Holzsee and acetate in Grosser Binnensee), even though differences were minor. In conclusion, the stronger larval (13)C-depletion in Holzsee was not reflected in differences in the microbial community structure, but in the activity and size of the methanogenic and methanotrophic populations in the lake sediment.
Eller
Gundula
G
Max Planck Institute for Limnology, August-Thienemann-Strasse 2, 24306 Plön, Germany. eller@mpil-ploen.mpg.de
Deines
Peter
P
Grey
Jonathan
J
Richnow
Hans-Hermann
HH
Krüger
Martin
M
D000704:Analysis of Variance; D000818:Animals; D002247:Carbon Isotopes / Q000378:metabolism*; D002683:Chironomidae / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D015169:Colony Count, Microbial; D020387:Food Chain; D005618:Fresh Water; D019015:Geologic Sediments / Q000032:analysis / Q000382:microbiology*; D005858:Germany; D017404:In Situ Hybridization, Fluorescence; D007814:Larva / Q000378:metabolism; D008697:Methane / Q000378:metabolism*; D008772:Methylococcaceae / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA
D002247:Carbon Isotopes; D012336:RNA, Ribosomal, 16S; D008697:Methane