Hydrogen peroxide and other reactive oxygen species (ROS) influence the redox chemistry and cycling of metals in freshwaters. Thus, it is important to understand the main sources and sinks of ROS in freshwaters. In this study, we found that biological production and decay of hydrogen peroxide (H2O2) are ubiquitous in natural freshwaters in Colorado and Massachusetts. Dark laboratory incubations of samples from 16 sites influenced by different settings such as mountain, rural, and urban areas revealed varying spatial and temporal H2O2 biological production rates (PH2O2) and decay rates (kloss,H2O2). An example of the spatial variation is shown by a mountain lake, Barker Reservoir, which had a low PH2O2 of 3.0 � 1.0 nM hr-1 while sites influenced by agricultural or populated areas generally had higher PH2O2 (ex. suburban Crown Hill Lake 226 � 72 nM hr-1). The spatial variability trend of kloss,H2O2  was similar with low decay rates in mountain sites and generally higher kloss,H2O2  in agricultural and populated areas. Temporal fluctuations in PH2O2 and kloss,H2O2 were measured at Sloan's Lake (Denver, CO) and Mirror Lake at Big Elk Meadows (ML-BEM) in Lyons, CO. May Sloan's Lake PH2O2 was as low as 38 �12 nM hr-1 and peaked in mid-August at 259 � 83 nM hr-1. Hypertrophic ML-BEM PH2O2 fluctuated weekly during July from as low as 56 � 18 and peaked at 213 � 68 nM hr-1. Sloan's Lake kloss,H2O2 fluctuated from 0.82 � 0.13 hr-1 in May and peaked in late August at 8.87 � 1.42 hr-1. ML-BEM kloss,H2O2  varied weekly from as low as 0.87 � 0.14 hr-1 and peaking at 2.77 � 0.44 hr-1. These production rates indicate that metal reactions involving ROS are likely to occur even when photochemical ROS production is minimal.

Ubiquity of biological production of hydrogen peroxide in natural freshwater: Implication for redox cycling of metals

246th National Meeting (2013)

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