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 (H(2)O(2)) in lake waters. Here we assessed the patterns of H(2)O(2) using three approaches: (i) H(2)O(2) levels 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 H(2)O(2) were tracked in a pair of lakes with contrasting DOC regimes (coloured vs. noncoloured DOC); and (iii) buildup of H(2)O(2) was tracked in experimental microcosms of lake water exposed to manipulated UV levels. H(2)O(2) levels were highest at the solstice and in intermittently flooded lakes. During 24 h daylight, lakes with contrasting DOC regimes showed cumulative build up of H(2)O(2) during multiple cloudless days. Cumulatively, H(2)O(2) was highest in the Delta lake with a higher DOC concentration and low in colour. H(2)O(2) buildup 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 H(2)O(2) production.