Premium
Photosynthetic performance of benthic microbial mats in Lake Hoare, Antarctica
Author(s) -
Vopel Kay,
Hawes Ian
Publication year - 2006
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.2006.51.4.1801
Subject(s) - microbial mat , benthic zone , irradiance , photosynthetically active radiation , photosynthesis , downwelling , water column , atmospheric sciences , environmental science , environmental chemistry , oceanography , chemistry , cyanobacteria , geology , botany , biology , optics , physics , paleontology , upwelling , bacteria
We measured in situ photosynthesis of benthic microbial mats at various depths in Lake Hoare, a permanently ice‐covered lake of the McMurdo Dry Valleys, Antarctica, using oxygen (O 2 ) microelectrodes. We further investigated the vertical distribution and activity of pigments in the microbial mats using an imaging pulseamplitude‐ modulated fluorometer. Microbial mats to at least 16.6‐m water depth are net producers of O 2 during the summer period. Net O 2 production ranges from 100‐500 µmol m −2 h −1 at incident downwelling irradiances of photosynthetically active radiation (PAR) of 1.0‐4.6 µmol quanta m −2 s −1 . Photosynthesis of mat‐forming cyanobacteria and diatoms occurs at all lake depths at or close to maximum efficiency. We measured absorption by the pigment arrays at a single water depth and, by assuming that absorption is water‐depth invariant, we estimated an area‐specific maximum community quantum yield of 0.073 mol carbon per mol photons. A community compensation irradiance of 0.1 µmol quanta m −2 s −1 was estimated, reflecting extreme shade acclimation. These results confirm estimates previously derived from laboratory gas‐exchange measurements and imply that even minor changes in the intensity of the incident downwelling irradiance of PAR caused by, for example, changes in the transparency of the ice cover or the optical properties of the water column can significantly alter rates of benthic carbon fixation. In situ measurements were confined to mats with flat surfaces. Laboratory measurements at the surface of mats with pinnacled surfaces revealed a complex small‐scale chemical structure at the mat‐water interface.