Osburn, C. L.. Earth & Environmental Sciences, Lehigh University, clo2@lehigh.edu
Morris, D. L.. Earth & Environmental Sciences, Lehigh University, dpm2@lehigh.edu
Hargreaves, B. R.. Earth & Environmental Sciences, Lehigh University, brh0@lehigh.edu

 
MODELLING THE SPECTRAL DEPENDENCE OF PHOTOOXIDATION OF DISSOLVED ORGANIC MATTER USING ABSORBANCE AND FLUORESCENCE
 
The spectral dependence of photooxidation of dissolved organic matter by solar UV radiation remains largely unknown. We present initial results of our attempt to model this process in lakes using absorbance and fluorescence. Our experimental design involved the use of long pass cutoff filters to exclude portions of the UV spectrum using solar radiation as a light source. We exposed four different types of water (groundwater from a sphaghnum bog, water from two lakes, and water from an algal culture) in the surface waters of an optically-clear lake for seven days during the summer of 1998. We found that incremental addition of UV wavelengths in treatments resulted in an increasing loss of absorbance compared to dark controls: 298 nm treatment lost 39 to 60%; 317 nm, 36-50%; 340 nm, 29-39%; 385 nm, 9-21%. Similar results were obtained for fluorescence measurements. For all water samples, increasing the relative amount of UV-b (280-320 nm) did not significantly increase the loss of absorbance nor fluorescence. Moreover, our results suggest that most photooxidation occurs from UV wavelengths below 340 nm. These results will be used to model changes in lake transparency due to increases in the amount of solar UV radiation that might occur from stratospheric ozone depletion.
 
Day: Wednesday, Feb. 3
Time: Poster
Location: Sweeney Center
 
Code: CS65WE0477S