Hydrogen peroxide formation: The interaction of ultraviolet radiation and dissolved organic carbon in lake waters along a 43-75 degrees N gradient

Hydrogen peroxide (H2O2) formation rates (nM h(-1)), photoproductive capacity (nM W-1 h(-1) m(-2)), and H2O2 formation efficiency ((H2O2)-H-phi) were measured on water samples exposed to a standard light source with a spectral composition similar to natural sunlight. Samples were from lakes and wetlands with varying levels of dissolved organic C (DOC), P, Fe, Ca, and pH. The relationship between H2O2 formation rates and DOC was a power function (H2O2 = 49.65 DOC1.71; r(2) = 0.94), whereas the relationships between formation rates and DOC fluorescence (DOCFL) (H2O2 = 118.32 + 33.06 DOCFL; r(2) = 0.98) and absorption coefficients at 310 (K-alpha 310) were linear (H2O2 = 185.0 + 55.50 K-alpha 310; r(2) = 0.91). (H2O2)-H-phi was independent of DOC (r(2) = 0.12). Apparent quantum yields decreased with increasing wavelengths (300-400 nm). However, when apparent quantum yields were corrected with solar irradiance data, values were greatest in the UV-A (320-400 nm) region. The patterns observed were consistent for samples from temperate to arctic regions.