Premium
Bacterial methanotrophs drive the formation of a seasonal anoxic benthic nepheloid layer in an alpine lake
Author(s) -
Blees Jan,
Niemann Helge,
Wenk Christine B.,
Zopfi Jakob,
Schubert Carsten J.,
Jenzer Joël S.,
Veronesi Mauro,
Lehmann Moritz F.
Publication year - 2014
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2014.59.4.1410
Subject(s) - hypolimnion , anoxic waters , nepheloid layer , water column , benthic zone , environmental chemistry , eutrophication , dominance (genetics) , in situ , total organic carbon , chemistry , ecology , biology , nutrient , biochemistry , organic chemistry , gene
We investigated the formation and microbial composition of a seasonal benthic nepheloid layer (BNL) in the eutrophic, monomictic southern basin of Lake Lugano. During stratification, a BNL developed at the sediment—water interface and progressively expanded 20–30 m into the water column, following the rising oxic—anoxic interface. The dominance of the fatty acids C 16:1 ω 5 , C 16:1 ω 6 , C 16:1 ω 7 , and C 16:1 ω 8 , with δ 13 C values between −62‰ ( ω 6) and −80‰ ( ω 7), suggests that the BNL was composed primarily of Type I aerobic methane oxidizing bacteria (MOB). Indeed, MOB contributed > 75% to the fatty acid carbon pool in the fully developed BNL, with cell densities up to 8.5 × 10 5 cells mL −1 . In ex situ incubation experiments, CH 4 turnover rate coefficients were up to 2.1 d −1 , which translates into potential CH 4 oxidation rates as high as 20 mmol m −3 d −1 under in situ CH 4 concentrations. CH 4 oxidation was limited by the diffusive supply of O 2 , and O 2 consumption by aerobic CH 4 oxidation (up to 13.1 mmol m −2 d −1 ) appears to be the primary driver of the seasonal growth of the BNL and expansion of the hypolimnetic anoxic zone. Methanotrophic activity at the interface between oxic and anoxic water masses can actuate the formation of a BNL, which in turn functions as an effective microbial CH 4 filter in the water column, preventing CH 4 transport to surface waters and evasion to the atmosphere. In situ biomass production by methanotrophic bacteria may represent, in addition to sediment resuspension and detritus trapping, a novel BNL formation mechanism.