For example, sphagnum moss growth can be compared tosponge on a plate. Beneath a thin layer of degrading plant material which is aerobic the so-called grey layer we find a zone of stabilized organic material which is virtually sterile. The sphagnum moss growth is self-limited by this growth habitat. Lakes See Figure 9.12. Littoral is where light penetrates to the bottom.
Limnetic zone is the area in open water where light penetrates.
The profundal zone is below that. Of extreme importance is the fact that water absorbs light. This leans to a selection for different photosynthetic groups as different depths. Figure 9.13 will enlighten you as to various types of algae and photosynthetic bacteria found at various depths as determined by the absorption spectra of their photosynthetic apparatus. Sediments of freshwater and saltwater represent an environment which has characteristically been considered anaerobic and within a short distance of the top of the sediment devoid of life.