Faculty of Sciences. Biology
Oxford :Academic Press, 2009
Encyclopedia of inland waters / Likens, Gene E. [edit.]
University of Antwerp
Silicon (Si) is the second most abundant element on planet Earth after oxygen. Under natural conditions there is no gaseous form of Si and it is not directly influenced by redox processes. Most Si is found in combination with oxygen in rocks as mineral silicates, with feldspar and quartz as the most significant silicate minerals. The chemical weathering of rocks and sediments produces a variety of end products, including dissolved silica (DSi). DSi is more formally known in chemistry as orthosilicic acid (H4SiO4) and iscalled dissolved silicate in oceanography. DSi is taken up by plants and is biologically deposited as a solid form of noncrystalline amorphous silica (ASi), also known as biogenic silica (BSi). In freshwater ecosystems there are a variety of organisms, including diatoms, silicoflagellates, chrysophytes and sponges, that take up DSi and deposit it as BSi. Although nitrogen and phosphorus are considered the most important elements that limit the rate of primary production, DSi concentrations in natural waters can also be low enough to limit the production of diatoms. As with other nutrient elements, human activities have greatly altered the natural biogeochemical Si cycle.