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Naomi Ginnever - Photobiology & Solar Radiation

University of St. Andrews, United Kingdom

Does Exposure Time and Different Wavelengths of Light Effect the Photobleaching
of Colored Dissolved Organic Matter (CDOM)?

Colored Dissolved Organic Matter (CDOM) absorbs wavelengths in the ultraviolet (UV) and visible portions of the light spectrum.  CDOM affects light availability, aquatic photochemistry, phytoplankton activity, and ocean color.  UV light ranges from below 280 nm to 400 nm while Photosynthetically Active Radiation (PAR) is 400-700 nm in range.  CDOM reduces the depth to which light penetrates attenuating the UV and blue regions of the spectrum more than green or red portions.  UV affects organisms by damaging their DNA and inhibiting photosynthesis.  UV light degrades chromophores in CDOM and hence bleaching occurs.  There have been past studies on this topic conducted by Tzortziou et al. and DelVecchio-Blough and the present study will combine timed sampling with polychromatic light and marsh derived water.  Samples were collected from a weir on the Kirkpatrick marsh, 0.2um filtered, and stored in the dark at 4 degrees Celsius.  Filtered samples were warmed to room temperature and poured into a cuvette and excited using a Xenon lamp.  Sub-samples were taken at 4 hour intervals for 40 hours.  CDOM absorbance measurements were taken using a spectrophotometer.  Conclusions were that absorbance and fluorescence of CDOM exposed to UV reduces over time.  Spectrally dependent and non-spectrally dependent photobleaching occurs during exposure and is most pronounced at the 350 nm cutoff.  Further study of the detailed analysis of CDOM photobleaching during transport through the Bay would allow for a better picture of this process in natural systems.

Funding provided by the Smithsonian Institution Women’s Committee