MBGC – Biogeochemical Model of Microbial Mats
(The First Photosynthetic Ecosystems) |
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MBGC – Microbial BioGeochemistry ecosystem simulation model is a mathematical representation of a
hypersaline microbial mat from Exportadora del Sal, Guerrero Negro, Baja California Sur, Mexico. |
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Microbial mats are
interesting because they represent some of the most ancient ecosystems on earth. Fossil remains of
microbial mats called ‘stromatolites’ have been dated to 4 billion years in age. |
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The microbial mat from Guerrero Negro was modeled because it
contains within it an entire complex food web that represents the full biogeochemical cycle of carbon from
initial fixation through decomposition. |
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MBGC builds on the work of deWit et al. (1995) and simulates the
carbon, oxygen, and sulfur cycles of several guilds of bacteria (Cyanobacteria (CYA); Colorless Sulfur
Bacteria (CSB), Purple Sulfur Bacteria (PSB), Sulfate reducing bacteria (SRB), and Methanogens (MET). |
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Model components include: environmental inputs of photosynthetically active radiation (PAR), near
infrared radiation (NIR), and temperature. Attenuation of PAR with each layer is modeled, and NIR
attenuation depends on the abundance of bacteriochlorophyll a. Growth of each bacterial guild depends
on their specific metabolic relationship of each physicochemical state factor combined with the size
of the biomass pool and factors which account for 1) movement through the mat and 2) conversion
efficiency. Growth of cyanobacteria occurs by either oxygenic or anoxygenic photosynthesis, depending
on the available substrate (O2 or H2S). Purple sulfur bacteria growth occurs by
anoxygenic photosynthesis using NIR and H2S or by chemosynthesis chemosynthesis, using O2
and H2S. Growth of colorless sulfur bacteria occurs via chemosynthesis, also using
O2 and H2S. Sulfate reducing bacterial growth occurs via anaerobic chemosyntheis
utilizing SO42- and creating H2S in the process. A Methanogen
metabolism model is currently under construction as an addition to the MBGC model. |
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The model consists of multiple layers, and gas diffusion occurs between successive layers. The model
was constructed in a Stellatm environment. |
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Slice of a hypersaline microbial mat, superimposed with a simple diagrammatic overlay describing the
features simulated in the current and future MBGC model versions. Shown are those features in the
current version of MBGC (Cyanobacteria (CYA), sulfate-reducing bacteria (SRB), purple sulfur bacteria
(PSB); colorless sulfur bacteria (CSB) are circled and are in the current version of MBGC.)
(Methanogens (MET), green non-sulfur bacteria (GNS), and organotrophs (ORG) will be completed in
future.) The model simulates dissolved inorganic carbon (DIC), sulfide, and O2 cycling through a
mat that experiences daily light fluctuations (PAR:photosynthetically active radiation, and NIR:near
infra-red radiation). |
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Authors: Kelly Decker & Christopher Potter |
