(2-6 weeks; this technique also works in wells)

The red precipitates of iron made by Gallionella ferruginea also coat wellheads such as this one at Muddy Creek, Md.


Two microscope slides, magic marker or diamond scribe, wire, fishing line or rubber bands, pencils or bamboo skewers, something to put slides in (slide box, centrifuge tube, slide mailer), flagging for trees.

Microscope slides left in red flocs (bottom) and near black-coated rocks (top) become colonized by the iron- and manganese-precipitating bacteria.


1. Take two microscope slides to make a slide set; mark date or place code on both of them (or else write collecting date and place code in your field notebook).

2. Put the two microscope slides back-to-back with dates on the inside surfaces.

3. Tie wire or string around them as if you were wrapping a package.

4. Find a place in a creek where rocks are coated black. The black is usually manganese. (The best place to look is in the shallow part of the stream where the water flows swiftly; these areas are called riffles.)

5. Tie loose end of wire around tree roots (best), pencils, or bamboo skewers (skewers are less likely to be noticed and disturbed), and leave the slides there in the creek.

6. Tie flagging to a nearby tree so you can find your samples again (tie loosely so as not to hurt the tree).

7. Come back 2-6 weeks later and retrieve your slides. (Remember to take the flagging away when you are done.) In wells, make sure you leave the slides in the zone of oxidation.

Rocks in riffles coated with black manganese oxide, Cosca Regional Park, Md. The bacteria precipitating the manganese are Leptothrix discophora.

Collecting Hint


"Viewing Techniques through a Microscope"

Contact: Norrie Robbins
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