Superoxide dynamics in aquatic systems have been of interest for many years because superoxide participates in a suite of redox reactions critical in many biogeochemical cycles. Because superoxide can act as both an oxidant (producing hydrogen peroxide) and a reductant (returning to the dissolved oxygen pool), our understanding of its complex reactivity and fate in natural waters remains incomplete. The photoproduction of superoxide from chromophoric dissolved organic matter (CDOM) has been well studied, but most photoproduction estimates rely on measurements of superoxide steady-state concentrations and dark-decay decay rates. However, in sunlit waters, regardless of superoxide source (i.e., photochemistry or biology), superoxide may be impacted by reactions with short-lived photoproduced transients that are missed by solely examining superoxide decay in the dark. In this work, we investigated superoxide kinetics ‘in the light’ by monitoring the decay of nanomolar superoxide additions during irradiation experiments. Superoxide decayed more rapidly during irradiation when compared to superoxide decay in the dark, suggesting the presence of a light-dependent sink. A wavelength dependence of the light-dependent sink was also demonstrated, whereby superoxide decay rates decreased with increasing wavelength cut-off filter. Thus, understanding light-dependent sinks for superoxide should have significant impacts on the modeling of superoxide cycling in natural waters, especially those with significant penetration of solar radiation.  

Primary Presenter: Leanne Powers, State University of New York College of Environmental Science and Forestry (lcpowers@esf.edu)

Authors:

Danielle Le Roux, University of Maryland  (dleroux@terpmail.umd.edu)

Leanne Powers, State University of New York College of Environmental Science and Forestry  (lcpowers@esf.edu)

Neil Blough, University of Maryland  (neilb@umd.edu)