Patterns of hydrogen peroxide among lakes of the Mackenzie Delta, western Canadian Arctic

Dissolved organic carbon (DOC) in Mackenzie Delta lakes varies in composition and concentration, ranging from low concentrations and high colour in frequently flooded lakes to high concentrations in clear lakes that are infrequently flooded. DOC is a precursor to the photochemical production of hydrogen peroxide (H2O2) in lake waters. Here we assessed the patterns of H2O2using three approaches: (i) H2O2levels were tracked in 40 lakes during the open water season from the Arctic summer solstice (24 h sunlight) to late summer; (ii) diurnal dynamics of in situ H2O2were tracked in a pair of lakes with contrasting DOC regimes (coloured vs. noncoloured DOC); and (iii) buildup of H2O2was tracked in experimental microcosms of lake water exposed to manipulated UV levels. H2O2levels were highest at the solstice and in intermittently flooded lakes. During 24 h daylight, lakes with contrasting DOC regimes showed cumulative build up of H2O2during multiple cloudless days. Cumulatively, H2O2was highest in the Delta lake with a higher DOC concentration and low in colour. H2O2buildup in lake water shielded from UVB exposure was not significantly lower from microcosms under full sunlight. UVA was the most important in coloured DOC photobleaching and H2O2production.