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Cool markings of a diatom of the genus Placoneis

Diatoms are single-celled algae found in nearly every aquatic habitat that are often used as environmental indicators. As University of Colorado graduate student - and diatom expert to be - Tyler Kohler explains, preparing diatoms for examination under one of the Diatom Lab’s three research microscopes is a multistep process. First the diatom samples are digested for a couple of days with acid. This dissolves the organic material inside the diatoms’ glass cell walls so that the cool markings characteristic of diatoms are visible under the microscope, enabling the diatoms to be identified.


Diatom Lab Tyler Kohler

University of Colorado graduate student, Tyler Kohler, checks out diatoms in a sample from Antarctica. Photo by Karen Cozzetto.

The samples are next centrifuged, decanted, and diluted with water several times to remove the acid. Each diatom sample is then allowed to dry on a microscope cover slip and mounted on a microscope slide. The samples are mounted with a special mounting medium to fix the cover slip to the slide. Because the microscope slides are glass and the diatom cell walls are amorphous silica (essentially glass), a high refractive index mounting medium allows the diatom features to “pop out.” The task of identifying the diatoms under the microscope can then begin, aided by the ability to take photos and view the images on the computer screen adjacent to the scope.

Diatom identification involves training and access to taxonomic resources and is not readily automated.  Instead it takes place by visual examination.  If the diatoms aren’t immediately recognizable, this may involve the aid of internet databases and/or reference to the lab’s Diatom Library.  This library contains several thousand archived diatom microslides primarily from Arctic, Antarctic, and alpine streams and lakes.  If all else fails - or even if it doesn’t - it can always be nice to get the opinion of INSTAAR’s ace diatom analysis team.

Contact: Dr. Sarah Spaulding, Lab Director
Link: INSTAAR’s Diatom Lab webpage

Diatom Lab Team

INSTAAR's Ace Diatom Analysis Team - from left to right - Tyler Kohler, Ian Bishop, Dr. Elena Jovanovska, and in front, Dr. Sarah Spaulding.