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Impacts of Tributaries on Optical Properties and Singlet Oxygen Concentrations in the Great Lakes
Citation:
Zepp, R., G. Whelan, M. Molina, Mike Cyterski, K. Wong, B. Acrey, AND A. Commodore. Impacts of Tributaries on Optical Properties and Singlet Oxygen Concentrations in the Great Lakes. 251st American Chemical Society National Meeting & Exposition, San Diego, CA, March 13 - 17, 2016.
Impact/Purpose:
To be presented at the 251st American Chemical Society National Meeting & Exposition
Description:
The Great Lakes have over 100 tributaries that contribute natural organic matter and othernatural photosensitizers to nearshore sites on the lakes. Absorption of sunlight by thesesensitizers results in indirect (sensitized) photoreactions of the widespread chemical andbiological contaminants that occur in these locations. Singlet molecular oxygen is onereactive transient that plays a dominant role in indirect photoreactions. For example,singlet oxygen reactions inactivate bacteriophages that are being evaluated as indicators ofviral pathogens in recreational waters. We emphasized indirect photoreactions involvingchromophoric dissolved organic matter (CDOM) in these studies. In addition to itsimportant role as a photosensitizer, CDOM also modulates photoreactions as one of themost important UV-protective substances in Great Lakes waters. Here, we present actionspectra (wavelength studies), UV-visible spectral data, and other data and relationships forevaluating photoproduction and steady state concentrations of singlet molecular oxygen inselected tributaries and nearshore areas in Lake Michigan and Lake Erie. The results showthat steady-state concentrations of singlet oxygen, and thus near-surface indirectphotoreaction rates mediated by this reactive oxygen species, are approximatelyproportional to CDOM concentrations in the water. Based on analysis of these results weconclude that indirect photoreactions of contaminants are strongly linked to the delivery ofterrestrially-derived CDOM by tributaries but the net effect on depth-integrated rates issurprisingly invariant from one near-shore area to another. This lack of variability islargely attributable to compensating effects of acceleration by photosensitization andretardation caused by UV light screening. Implications of this interesting "buffering" oftransformation rates involving CDOM will be discussed during the presentation.
