Lago di Cadagno in the southern Swiss Alps (IMAGE)
Caption
Salty springs at the lake bottom prevent mixing, resulting in a stable stratification. The upper meters contain oxygen but little nutrients. The lower layer is anoxic and rich in sulfide, creating a stable intermediate layer with steep concentration gradients of oxygen and sulfide. Here, the purple sulfur bacteria use solar energy to oxidize sulfide – and fix nitrogen.
Credit
Miriam Philippi
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