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Aquatic Microbial Ecology

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AME 19:47-56 (1999)  -  doi:10.3354/ame019047

Photochemically induced changes in bioavailable carbon and nitrogen pools in a boreal watershed

Stefan Bertilsson1, Ramunas Stepanauskas2, Rocio Cuadros-Hansson3, Wilhelm Granéli2, Johan Wikner3, Lars Tranvik4,*

1Dept. of Water and Environmental Studies, Linköping University, 58183 Linköping, Sweden
2Dept. of Ecology, Limnology, Lund University, 22362 Lund, Sweden
3Umeå Marine Science Center, Box 10124, 90010 Umeå, Sweden
4Dept. of Limnology, Uppsala University, Norbyvägen 20, 75236 Uppsala, Sweden
*Addressee for correspondence. E-mail:

ABSTRACT: In several recent studies, a net stimulation of bacterial growth has been demonstrated after exposing humic surface waters to solar radiation or artificial ultraviolet radiation. This stimulation has been attributed to a photochemical release of bioavailable carbon or nitrogen compounds (ammonium). In a synoptic experiment, we exposed 0.2 μm filtered water from 12 different habitats in a river system, dominated by allochthonous carbon input, to mild artificial UV radiation. A significant photochemical release of carboxylic acids of low molecular weight occurred. Furthermore, the exposure increased carbon-limited bacterial yield on average by a factor of 1.7. No photochemical production of free ammonium could be detected, which was in accordance with the lack of effects of radiation on bacterial growth yield under nitrogen-limited conditions. We conclude that, in boreal systems dominated by allochthonous carbon input, photochemical production of bioavailable carbon rather than nitrogen compounds is likely to positively influence the total substrate pool available for bacterial utilization.s

KEY WORDS: UV radiation · DOC · DON · Bacterial bioassays · Carboxylic acids · Ammonium

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