The four most important components in the sediments of modern north temperate lakes are detrital clastic material, biogenic silica, carbonate minerals, and organic matter. Detrital clastic material is derived from those materials that are available in the drainage basin. Biogenic silica occurs mostly in the form of diatom frustules that are common and almost ubiquitous components in lake sediments and can make up the bulk of the sediment when conditions [that] prevent dilution by elastics and(or) carbonate minerals.
The dominant carbonate mineral in lacustrine sediments is low-Mg calcite, but some high-Mg calcite, dolomite, and(or) aragonite may be present, largely depending on the Mg: Ca ratio in the water.
Assimilation of CO2 by photosynthesis is the most important mechanism of CaCO3 precipitation in hard-water lakes. In some lakes, the rate of precipitation of CaCO3 from waters that are supersaturated with respect to CaCO3 is directly proportional to rates of assimilation of CO2 by phytoplankton.
The rate of CaCO3 accumulation is greater in the littoral zone than in the profundal zone, mainly because the littoral zone has more production and accumulation of calcareous plant and animal debris (charophytes, ostracodes, mollusks) and has a large component of CaCO3 precipitated by both algal and macrophyte photosynthesis.
Organic matter is a mixture of both herbaceous allochthonous material (pollen grains, leaves, needles, seeds, woody material and other organic detritus, etc.) from the drainage basin and lipid-rich autochthonous material (largely debris from planktonic algae and aquatic macrophytes). If a significant proportion of the organic matter is preserved in the sediments, these sediments may be potential sources of both oil and natural gas. Studies of sedimentary plant pigments in Holocene lake sediments indicate that most of the organic matter in moderately to highly productive lakes is derived from autochthonous algae. Sediments in these lakes usually are olive gray and contain more than 20% dry weight organic matter (10% organic carbon).
In most marl lakes there is a direct relationship between organic productivity and production of CaCO3. However, most (usually more than 90%) of organic matter produced is destroyed by respiration and decay in the water column and in the sediments, as much of the CaCO3 generated in the epilimnion is dissolved in the undersaturated hypo- limnion. Because CaCO3 and organic matter are destroyed at different rates, often there is not a clear relationship between organic productivity of the lake and the contents of either organic matter or CaCO3 in the sediments.