| Summary: | Lakes in the Mackenzie Delta have complex patterns of dissolved organic carbon (DOC) ranging from low levels of coloured DOC in lakes frequently flooded with riverwater to high levels of non-coloured DOC in infrequently flooded lakes. Hydrogen peroxide (H202) levels measured in 40 lakes at three times, ranging from summer solstice to late summer were highest around the solstice and in lakes of intermediate flood-frequency. Diurnal dynamics of H202, tracked for 40 hours during 24-hour sunlight in two lakes with contrasting DOC, showed cumulative build-up of H202 during multiple cloudless days. Build-up of H202, in experimental enclosures where exposure to UVirradiance was manipulated, responded to both UVA and UVB. The effect of modestly elevated H202 levels and DOC substrate on bacterial production in enclosures from six differing lakes appeared weak during late summer and suggests a trade-off between UVB-inhibition (direct effect) and photolyzed-DOC as an additional food substrate.
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