Abstract
Light degradation is very likely an important removal process for humic substances (HS) in the aquatic environment, and thus of importance for the cycling of organic carbon. For this reason, laboratory experiments under artificial conditions using UV-B radiation (λ max =313 nm) , to study light degradation of HS were carried out on natural untreated Baltic Sea water samples and, for reference, on humic (HA) and fulvic acid (FA) isolates from the Göta River. During these experiments, the molecular weight distribution, fluorescence, UV-absorbance and total organic carbon concentration were monitored over a period of 3 weeks. In the natural seawater samples the higher molecular weight part was more easily degraded than the lower molecular weight part. The results indicate that FA and HA were more resistant towards UV-B irradiation than natural seawater. Irradiation caused formation of lower molecular weight substances in the case of FA and HA whereas for natural seawater this process was less obvious.
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