Skjervatjern, Norway, a dystrophic lake that was site of the Humex project. This project examined the role of humic substances and impacts of acid deposition; the lake was divided by a curtain (visible in photo) and half was treated with sulfuric acid and ammonium nitrate. Photo from old ASLO slide collection; taken by P. Koretlainen; scanned by K.L. Schulz.