ABSTRACT: A temporal study of the bacterial utilisation of allochthonous dissolved organic carbon (DOC) was performed in a lake and estuary situated in the same boreal watershed. A greater utilisation of allochthonous DOC was observed under estuarine as compared to limnic conditions. However, the bacterial biomass yield was not significantly different between the environments, indicating a lower growth efficiency on allochthonous DOC by the estuarine bacterioplankton. The largest fraction of the allochthonous DOC utilised (20%) was observed under estuarine conditions and coincided with the spring flood. The utilisation of allochthonous DOC and bacterial biomass yield in the experimental bottles was limited by the availability of nitrogen or phosphorus in both environments. Our results showed that the major bacterial transformation of DOC occurred in the estuarine rather than the limnic environment, due to the shift in physicochemical milieu and bacterial assemblage. However, the estuarine bacteria also respired a greater fraction of the DOC utilised than their limnic counterparts.

KEY WORDS: River · Limnic · Marine · Organic carbon · Bacteria · Seasonal · Utilisation · Growth efficiency

Published in AME Vol. 17, No. 3 (1999) on June 18
ISSN: 0948-3055. Copyright © Inter-Research, Oldendorf/Luhe, 1999