Evaluation of Matrix Effects in Aquatic Dissolved Organic Matter Photochemistry

Leanne Powers and Michael Gonsior, University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, Solomons, MD, United States
It has been well established that photochemical reactions are involved in aquatic biogeochemical and redox cycles. However, given the complexity of natural systems, quantifying the importance of photoreactions in the environment is still a challenge. Dissolved organic matter (DOM) is generally considered the dominant absorber of solar ultraviolet radiation and the primary driver of both direct and indirect photochemical processes. Thus many studies have focused only differences in DOM composition when trying to understand the differences in sample photoreactivity from freshwater to marine systems. Here we attempt to understand the role of sample matrix on DOM photoreactivity using DOM isolated by solid phase extraction and reconstituted in various buffers (borate, carbonate, phosphate) and halide mixtures (Br, Cl, I). Sample absorbance and fluorescence were monitored semi-continuously while circulating through a custom-built irradiation system that allows for pH and temperature control and prevents oxygen starvation. Results highlight the importance of sample matrix alone on DOM photodegradation rates and suggest that sample matrix should be selected carefully when attempting to replicate photoreactions in the environment.