ENVIRONMENTAL VARIABILITY IN THE REACTIVITY OF FRESH-WATER DISSOLVED ORGANIC-CARBON TO UV-B

Reductions in the global stratospheric ozone layer are thought to be i ncreasing the amount of ultraviolet B (UV-B) radiation reaching the pl anet's surface and may be affecting the chemistry of dissolved organic carbon (DOG) in surface waters. We studied the abundance of chromopho res in DOC collected in four different aquatic environments in southwe stern Nova Scotia using C-13 nuclear magnetic resonance (C-13 NMR) spe ctroscopy. We showed a clear seasonal pattern in the distribution of s tructural carbon related to light-sensitive chromophores. There seemed to be little variation in the UV-B related chemical structure of DOC between lakes and streams, though water from a bog pool showed large d ifferences from the other samples. These patterns of potential UV-B re activity tend to be dampened however, by variations in DOC concentrati ons which also occur seasonally.