Hydrogen peroxide dynamics in an agricultural headwater stream: Evidence for significant nonphotochemical production

Abstract

Hydrogen peroxide (H 2 O 2 ) plays key roles in aquatic systems, including metal redox cycling and degradation of organic matter into bioavailable forms. Abiotic photoproduction, via photo-oxidation of chromophoric dissolved organic matter, has generally been assumed to be the most important source of H 2 O 2 to freshwater systems in the daytime. However, the significance of other H 2 O 2 sources has not been previously examined in situ. In this study, isotopically labeled H 2 O 2 (H 2 18 O 2 ) was added to in-stream mesocosms exposed to light and dark periods. By measuring total H 2 O 2 and H 2 18 O 2 in tandem, we inferred absolute rates of H 2 O 2 production and decay, which occurred simultaneously. Abiotic photoproduction rates were measured independently by exposing filtered samples to sunlight. Even in these shallow systems, total production rates greatly exceeded rates of abiotic photoproduction, and other sources of H 2 O 2 , most likely biological production, were the dominant control on the H 2 O 2 budget. Thus, H 2 O 2 and its precursor superoxide (O { 2 ) may play a greater role in biogeochemical processes, especially in the absence of light, than previously thought.

Spatial and temporal variability of widespread dark production and decay of hydrogen peroxide in freshwater

“…Decay rates in Dixon et al (2013) closed-bottom mesocosms were 2.4-2.6 h -1 , similar to those observed in the hypereutrophic Sloan's and Mirror Lakes in the present study (Fig. 2b).…”

“…Therefore, it is possible that biological production of H 2 O 2 increased gradually with increasing light exposure and then decreased after light exposure ceased. After 4 h in the dark, P H 2 O 2 values in closed-bottom Maple Creek mesocosms were approximately 100-400 nM h -1 (Dixon et al 2013) or similar to those observed in the present study.…”

“…Up to an order of magnitude faster dark P H 2 O 2 was observed in closed-bottom mesocosms (lacking a sediment-water interface, and most closely corresponding to the conditions of the present study) in the agriculturally influenced Maple Creek in Nebraska (Dixon et al 2013). However, the rates in the Maple Creek study are not directly comparable to ours because they include possible effects of prior light exposure immediately before dark P H 2 O 2 measurements were taken.…”

“…In the same study, pseudo first order decay rates coefficients (k loss;H 2 O 2 ) ranged from 0.33 to 1.7 h -1 . A second study applied the H 2 18 O 2 tracer technique to in situ mesocosms in a Nebraska agricultural headwater (Maple Creek), and showed that total production of H 2 O 2 in the stream was far greater than that expected from abiotic photoproduction alone (Dixon et al 2013).…”

“…Both Vermilyea et al (2010a) and Dixon et al (2013) attributed dark production of H 2 O 2 to biological sources, since the ability of both bacteria and algae to produce extracellular ROS in the dark has been demonstrated in culture studies. For example, dark superoxide production has been observed in a broad diversity of heterotrophic bacteria isolated from marine, freshwater, and terrestrial environments (Diaz et al 2013).…”