The hydrology and water chemistry of prairie pothole wetlands vary spatially and temporally, on annual and decadal timescales. Pesticide contamination of wetlands arising from agricultural activities is a foremost concern. Photochemical reactions are important in the natural attenuation of pesticides and may be important in limiting ecological and human exposure. Little is known, however, about the variable influence of wetland water chemistry on indirect photochemistry. In this study, seasonal water samples were collected from seven sites throughout the prairie pothole region over three years to understand the spatiotemporal dynamics of reactive intermediate photoproduction. Samples were classified by the season in which they were collected (spring, summer, or fall) and the typical hydroperiod of the wetland surface water (temporary or semi-permanent). Under photostable conditions, steady-state concentrations and apparent quantum yields or quantum yield coefficients were measured for triplet excited states of dissolved organic matter, singlet oxygen, hydroxyl radical, and carbonate radical under simulated sunlight. Steady-state concentrations and quantum yields increased on average by 15% and 40% from spring to fall, respectively. Temporary wetlands had 40% higher steady-state concentrations of reactive intermediates than semi-permanent wetlands, but 50% lower quantum yields. Computed quantum yields for reactive intermediate formation were used to predict the indirect photochemical half-lives of seven pesticides in average temporary and semi-permanent prairie pothole wetlands. As a first approximation, the predictions agree to within two orders of magnitude of previously reported half-lives.
Bibliographical noteFunding Information:
The authors thank David Mushet, Matthew Solensky, David Richardson, Jessica Dowler, Megan Zopfi, Trina Brennan, and two others who wish to remain anonymous for help coordinating sampling trips and collecting samples. The authors also thank Jennifer Strehlau for help with dissolved iron measurements. Funding for this work was provided by the United States Geological Survey-National Institutes for Water Resources ( G12AP20153 ) and by the Moos Fellowship from the College of Biological Sciences, University of Minnesota (awarded to A.M.). Ancillary support was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR).
© 2016 Elsevier Ltd.
- Apparent quantum yield
- Dissolved organic matter
- Photochemically-produced reactive intermediates
- Prairie pothole wetlands