Photo-reactivity (apparent quantum yield) of dissolved organic carbon during the freshwater transit from land to sea

• In spite of substantial greenhouse gas emissions from photo-degradation of dissolved organic carbon (DOC), little is known about the variability in DOC photo-reactivity. It has been suggested that photo-reactivity depends on the degree of DOC pigmentation. However, recent evidence suggests that also non-colored fractions can be photo-reactive. Furthermore photo-degradation processes interact with extrinsic factors such as pH and Fe concentrations. Thus, the overall changes in photo-reactivity in the aquatic network are poorly known. We measured apparent quantum yield for CO2 production normalized to 350 nm (AQY350) in water from streams, lakes and rivers in boreal Sweden. Additionally, samples were incubated for 365 days to follow AQY350 over the long-term course of microbial degradation. We found no trends of decreasing AQY350 with overall losses in DOC color across space and time. Interestingly, there was a quadratic (U-shaped) relationship between AQY and pH. Overall, in situ AQY350 increased with reductions in specific DOC absorbance and with rising autochthonous DOC contributions. We suggest that partly due to extrinsic factors, photo-reactivity of DOC is sustained during the DOC residence time in the aquatic network.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

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