Two living cells of the genus Epithemia. The golden brown in the cells are chloroplasts. Photo by Lee Stanish.

Diatoms are single-celled algae found in nearly every aquatic habitat, and are an important component of phytoplankton providing both oxygen and food for higher organisms. Diatoms are particular in their tolerances of various environmental conditions with different species surviving in different ranges of pH, salinity, nutrient and suspended sediment concentrations, flow regimes and the like. This makes them good indicators of both current and past water quality and potential proxies for environmental variables such as flow. 

Additionally, diatoms have cell walls made of silica (like window glass).  Also known as frustules, the cell walls are resistant to decay.  Diatom frustules that have accumulated in lake or marine sediments over time can provide important information about past environmental conditions.  As a result, diatoms are an important component of environmental assessment, for example, in programs such as the USGS’s National Water Quality Assessment (NAWQA) Program and the U.S. Environmental Protection Agency’s monitoring programs.

CWEST Participants: Diane McKnight (lead investigator), Sarah Spaulding


A 5-year, one million dollar agreement between National Water Quality Assessment (NAWQA) and CWEST was implemented early in 2015. Diane McKnight (PI) is collaborating with Sarah Spaulding of USGS. The cooperative agreement will support (1) analysis of algal samples for the National Water Quality Assessment Program, (2) develop habitat and distribution coverage of diatom across the country and (3) further taxonomic consistency for federal programs using algae.

We now have a full time diatom taxonomist (Ian Bishop), MS student (Meredith Tyree, ENVS) and 2 undergraduate students working on diatoms of rivers of the southeast US across an agricultural and urban gradient.

An important outcome of the collaboration is development of the Diatoms of the United States, an online flora. Diatoms of the US is an online tool for analysts and includes over 120 genus pages, nearly 700 completed species pages and autecological data accessible to users.The website is a broadly collaborative effort and represents an initial investment, of actual and in-kind dollars, totaling nearly $2 million. It has supported over 1.8 million views, from over 150,000 unique users, since its inception in 2010. Over 60 contributors have participated in the project.

Collaborative research: Diatoms Past and Present

Luticola murrayi

Luticola murrayi can be found in Antarctica’s Green Lake, at the foot of Mt. Erebus, Earth’s southernmost active volcano. Photo by Katerina Kopalova

One challenge in the use of diatoms as indicators of environmental conditions is the lack of taxonomic data. To facilitate accurate identification, USGS and INSTAAR researchers are collaborating with scientists from other institutions to develop two publically accessible databases that are continually updated as new taxonomic and distributional data are obtained:

Contact: Dr. Sarah Spaulding, Lab Director, Sarah.Spaulding@colorado.edu

Diatoms of the U.S
Antarctic Freshwater Diatoms