Diatoms are single-celled algae, in the family Bacillariophyceae, with a cell wall composed of opaline silica. The silica wall is referred to as a frustule, and has two parts that fit together much like a jewelry box and lid. Diatoms are identifiable to species or even subspecies level, based on variations in size, shape and the ornamentation of the cell wall. These algae occur worldwide and in virtually every aquatic environment with enough light for photosynthesis, including oceans, lakes, streams, rivers, wetlands, and springs. Diatom communities exist
in a wide variety of micro-habitats, free floating in open waters (planktonic) or attached to various objects in the lake.Many are unattached and mobile (benthonic). Diatoms are an important food for other marine organisms. The image at left is a scanning electron micrograph of Diploneis puella, a diatom about 20 microns in length.
One micron is 1 millionth of a meter, so these plants are pretty small.
The silicate cell wall helps preserve these plants as fossils in lake and ocean sediments. They are abundant both while alive (as plankton) and as fossils. Because individual species are often characterized by narrow ecological tolerances, diatoms have become one of the most useful fossils for studying environmental change. In fact, it is often possible to quantitatively infer past hydrologic conditions, such as nutrient levels, lake levels, salinity, pH, temperature and others. Different species of diatoms thrive in different water temperatures, pH and mineral concentrations, water clarity, nutrient concentrations and at varying water depths. A thick layer of warm-water types that live at shallow depths may indicate a long period of swamp-like conditions in a lake caused either by flooding of lowlands or shrinking of the lake to a shallow pond.
The diatoms' fossil record goes back to the Cretaceous (about 65 million years ago). Some rocks are made up almost entirely of fossil diatoms, formed when ancient diatoms died and settled to the bottom of lakes and oceans. As rocks they look white and chalky. This rock is known as diatomite or diatomaceous earth. These diatom-rich rocks are mined commercially and sold as abrasives and filters common in cleansers and paints. Many toothpastes contain bits of fossil diatoms - the silica in the fossils helps scrape bacteria and food off of your teeth. Check out the diatom results from the Bear Lake Project.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://esp.cr.usgs.gov/info/lacs/diatom.htm
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Page Last Modified: Fri 28-Jun-2002 19:56:44 MDT