Differences in consumption of allochthonous DOC under limnic and estuarineconditions in a watershed

A temporal study of the bacterial utilisation of allochthonous dissolved or ganic 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 bi omass yield was not significantly different between the environments, indic ating a lower growth efficiency on allochthonous DOC by the estuarine bacte rioplankton. 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 e xperimental bottles was Limited by the availability of nitrogen or phosphor us in both environments. Our results showed that the major bacterial transf ormation of DOC occurred in the estuarine rather than the Limnic environmen t, due to the shift in physicochemical milieu and bacterial assemblage. How ever, the estuarine bacteria also respired a greater fraction of the DOC ut ilised than their limnic counterparts.