You probably know this brown-reddish layers floating on top of pools and streams. Nope it’s not oil but FeOH ( iron hydroxide). A one week dry spell in the Alptal resulted in low flow condition of the system -> water levels in the streams where unusual low. In this low flow condition macrospores became visible see pic 1. by their reddish color, transporting small amounts of water with FeOH. The low discharge in the stream itself resulted in almost no turbulence. This calm flow made it possible for the FeOH to precipitate see pic. 2 and form a layer on the bottom waiting to be transported in the next high flow.
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| pic 1. macropore with FeOH |
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| pic 2. precipitated FeOH on the stream bottom |
