Photoreduction of iron in the epilimnion of acidic lakes

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Abstract
Two acid soft‐water lakes in the east of Belgium contain appreciable amounts of soluble ferrous iron in the epilimnetic zone which change diurnally and annually. A considerable drop in redox potential in the same zone confirms the existence of an active reduction of ferric iron, with a concomitant solubilization of particulate iron and of deposited iron supplied from the sediments in contact with epilimnetic water when the latter is well oxygenated. The reduction process is essentially photochemical, promoted by optimal pH conditions and by the presence of organic matter (humic acids).