CS26 Organic Carbon Dynamics
Date: Thursday, June 13, 2002
Time: 11:00:00 AM
Location: Carson C
Scully, N, M, Limnology, Uppsala University, Uppsala, Sweden, scullyn@uncwil.edu
TranvikLJ, Limnology, Uppsala University, Uppsala, Sweden, lars.tranvik@ebc.uu.se
Cooper, W, J, Dept. of Chemistry, Center for Marine Science, Wilmington, NC , USA, cooperw@uncwil.edu
Photochemical reactions greatly affect interactions between microbes and their enzymes with coloured dissolved organic matter (CDOM). We propose that direct effects of sunlight on enzyme activity in natural waters are negligible, and demonstrate a novel photochemical mechanism involving the interaction between extracellular enzymes, CDOM, Fe and ultraviolet radiation (UV-R). Both phosphatase and beta-glucosidase activities were twofold more rapidly inactivated by irradiation in an acid humic lakewater than in water obtained from a limed humic lake. This discrepancy was likely caused by a pH mediated decrease in Fe photo-reduction and Fe-enzyme binding. We also demonstrate that the photo-degradation of CDOM through microbial-photochemical interactions is dependent on the action of reactive oxygen species (ROS). ROS quenchers added to humic water during irradiation revealed that photobleaching and photomineralization to CO2 are highly dependent on the action of ROS. However, post-irradiation bacterial growth increased when ROS were quenched. The decrease in ROS activity (CO2 production) likely caused an accumulation of bioavailable DOM and enhanced microbial processes. This implies that photochemical and microbial degradation are partly competing processes.