Enhanced photochemical loss of organic carbon in acidic waters

Previous studies have shown that (a) a large portion of the annual total organic carbon (TOC) inputs to central Ontario lakes is either lost to sediments or degraded and lost via evasion to the atmosphere, (b) the partitioning of organic carbon between sediments and the atmosphere appears to be a function of acidity and (c) UV irradiation can account for observed long-term loss of TOC from the water column. These findings were extended by examining whether acidity enhances photo-oxidative losses of TOC. Stream waters (initial alkalinities between -97 and 233 mu eq l(-1)) were incubated in UV-transparent containers under incident solar radiation for periods ranging from 14 to 23 days. The highest photo-oxidation rates occurred when alkalinity was negative. Additions of acid and base to stream waters increased and decreased photo-oxidation rates, respectively. The exceptional clarity of atmospherically acidified lakes is usually attributed to increased precipitation of Al-organic carbon complexes but may instead be due to higher photo-oxidation rates of allocthonous organic carbon leading to higher evasion rates of CO2.