Fig. 3.2
A typical modern microbial mat with characteristic layering. (a) Steep gradients in physicochemical parameters (O
2 and H
2 S concentration gradients
and light penetration) that govern the distribution of microorganisms. (b) Photograph of the layered structure of microbial sediments. (c) Schematic
representation of a typical microbial mat dominated by cyanobacteria. The layer of green sulfur (anoxygenic) bacteria is not always present and marks the
maximum penetration of the far-red light wavelengths. Microbes in (c) not drawn to scale
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J. Pan