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