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Low sediment‐water gas exchange in a small boreal lake
Author(s) -
Kokic Jovana,
Sahlée Erik,
Brand Andreas,
Sobek Sebastian
Publication year - 2016
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2016jg003372
Subject(s) - sediment , flux (metallurgy) , water column , eddy covariance , environmental science , boreal , hydrology (agriculture) , environmental chemistry , mixing (physics) , oceanography , atmospheric sciences , chemistry , geology , ecology , ecosystem , geomorphology , biology , physics , geotechnical engineering , organic chemistry , quantum mechanics
Boreal lake sediments are carbon sources by producing CO 2 . CO 2 flux from sediments is partly controlled by turbulence in the water column, which is not given the same attention as CO 2 production rates in current estimates of CO 2 fluxes from sediments. We quantified the in situ CO 2 flux across the sediment‐water interface in a small (0.07 km 2 ) lake in Sweden by measuring the in situ O 2 flux with the Eddy Correlation (EC) method and using the apparent respiratory quotient (CO 2 production:O 2 consumption) derived from sediment incubations. We demonstrate that median CO 2 flux estimated by EC was ~70% smaller than estimated by sediment incubations with artificial water mixing (1.0 × 10 −2 and 3.6 × 10 −2 µmol C m −2 s −1 , respectively). Additionally, we show that inducing artificial mixing of supernatant water in the incubation experiment has a positive effect on observed fluxes, enhancing CO 2 flux by ~30% compared to not mixing supernatant water. We suggest that the difference between the methods is due to the strong artificial water mixing in sediment incubations compared to the turbulent mixing in this small lake. Additionally, low O 2 supply to sediment aerobic heterotrophic microbes during extended periods of low water currents can inhibit respiration and thus CO 2 production. These findings suggest that the sediment contribution to total lake CO 2 emission might currently be overestimated for small boreal lakes. Care should be taken when upscaling sediment CO 2 flux derived from incubation experiments to entire basins of small lakes, as incubation experiments are unlikely to accurately mimic in situ bottom water currents and gas exchange.