Enhanced photochemical loss of organic carbon in acidic waters

Previous studies have shown that (a) a large portion of the annual total or ganic carbon (TOC) inputs to central Ontario lakes is either lost to sedime nts or degraded and lost via evasion to the atmosphere, (b) the partitionin g of organic carbon between sediments and the atmosphere appears to be a fu nction of acidity and (c) UV irradiation can account for observed long-term loss of TOC from the water column. These findings were extended by examini ng whether acidity enhances photo-oxidative losses of TOC. Stream waters (i nitial alkalinities between -97 and 233 mu eq l(-1)) were incubated in UV-t ransparent containers under incident solar radiation for periods ranging fr om 14 to 23 days. The highest photo-oxidation rates occurred when alkalinit y was negative. Additions of acid and base to stream waters increased and d ecreased photo-oxidation rates, respectively. The exceptional clarity of at mospherically acidified lakes is usually attributed to increased precipitat ion of Al-organic carbon complexes but may instead be due to higher photo-o xidation rates of allocthonous organic carbon leading to higher evasion rat es of CO2.