Photoproduction of dissolved inorganic carbon in temperate and tropical lakes – dependence on wavelength band and dissolved organic carbon concentration

    loading  Checking for direct PDF access through Ovid


We have evaluated photoeffects of UV-B, UV-A and PAR radiation on dissolved organic matter (DOM). Photochemical production of dissolved inorganic carbon (DIC) was measured in sterile lake water from Sweden and Brazil after 6 hours of sun exposure. Tubes were exposed to four solar radiation regimes: Full-radiation, Full-radiation minus UV-B, Full-radiation minus UV-B and UV-A (PAR) and darkness.

In both areas, lakes with most DOC (varying between 3 and 40 mg Cl−1) were highly humic, resulting in high UV-B attenuation coefficients (Kd = 5–466 m−1). Under Full-radiation, photooxidative DIC-production varied from 0.09 to 1.7 mg Cl−1 per 6 h, without UV-B from 0.07 to 1.4 mg Cl−1 and with PAR only from 0.02 to 0.7 mg C l−1. UV-B radiation explains a minor part (17%) of the photoooxidative DIC-production, while UV-A and PAR have larger effects (39% and 44%, respectively). Photooxidation was proportional to DOC-content and DIC-production was positively related to decrease in DOC and to loss of absorbance at 250 nm. There was no significant difference in DOC and radiation normalized DIC-production between Swedish and Brazilian lakes. The UV-B dose during incubations was approximately 3 times higher in Brazil compared to Sweden, while UV-A and PAR doses were similar. We conclude that DOC from tropical and temperate freshwaters do not seem to differ with respect to sensitivity to photooxidation.

Related Topics

    loading  Loading Related Articles