Photolytic processes also release inorganic carbon from chromophoric organic substances as mentioned above. In iron-rich, acidic lakes, the photo-Fenton pathway of CO2 and CO release prevails over the release of short-chained organic compounds. This efficient shunting of bioavail-able organic photoproducts to dissolved inorganic carbon is most expressed in postmining lakes, which are strongly acidified from pyrite (FeS2) weathering. In these lakes, for instance in Lusatia, Germany, with pH-values between 2.0 and 3.0 and high iron contents, organic carbon compounds are oxidized (eventually to carbon dioxide, CO2) via the photo-Fenton reduction of Fe(ni). Due to the very low pH, CO2 escapes from the water column, leading to limitation of inorganic carbon for primary production. The processes are summarized in Figure 7. Primary producers have developed interesting strategies to overcome this limitation (see Acidification).
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