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Diatoms: Then and Now

Submitted By: Joy Ramstack (St. Croix Watershed Research Station)
Age Range: 4-6, 7-8, 9-12
Time Needed: Minimum 30-40 minutes

Materials Needed: Microscope with 100x oil immersion lens (a connected camera or video monitor is helpful but not needed), pre-made diatom slides from at least two lakes or two core levels that show different diatom assemblages (for example, an oligotrophic or mesotrophic assemblage on one slide and a eutrophic assemblage on another slide), and printed worksheets (download here).

Main Learning Objectives:(1)

Description of Activity:The activity started with a whole group discussion of what kinds of things get into lakes as “pollution” and the discussion is guided toward lawn fertilizer, soaps, etc. that can affect the growth of plants and algae in lakes. The same group of students had previously completed an exercise in coring and understood the idea of time sequences and changes over time represented by core levels – those ideas were briefly reviewed. Students were then divided into groups of 3-4, each working together at one microscope. They were asked to draw and name 5-10 diatoms from each slide, using the provided worksheet as a reference. They were then asked to compare and contrast the two slides, and as a whole group we discussed differences in the size, shape and abundance of the different slides.

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Diatom Activity