Growth and production of bacterioplankton in a deep mesohumic boreal lake
Tulonen, Tiina; Kankaala, Paula; Arvola, Lauri; Ojala, Anne
published: Feb 3, 2000
ArtNo. ESP141014703003, Price: 29.00 €
Vertical distribution of bacterial biomass and production, as well as phytoplankton production, was studied in a deep, mesohumic lake in Southern Finland. In summer 1992 32-56 % of bacterial production but only ca. 17 % of biomass was found in the euphotic zone (0-5 m), which consists of 20 % of the total lake volume. In the deep central area of the lake, the production of bacteria varied between 63 and 121 mg Cm-2d-1 and that of phytoplankton 57-158 mg Cm-2 d-1 High bacterial production to primary production ratio (>0.5) indicates that the phytoplankton production alone was insufficient to sustain the total bacterial production, and that bacterioplankton utilised other carbon sources, such as allochthonous organic compounds. Factors controlling growth of bacteria in the aphotic zone (allochthonous and autochthonous dissolved organic matter (DOM), PO4-P, temperature and grazing) were studied in a laboratory experiment. The most pronounced increase in bacterial growth was achieved when allochthonous humic water originating from the catchment was added or when it was added together with PO4-P. Furthermore, PO4-P addition together with autochthonous organic carbon, resulted in higher bacterial growth rates than the addition of autochthonous DOC alone. The results suggest that despite the high concentration of dissolved organic carbon (DOC >10 mg C/L) in the lake, the quality of DOM and availability of PO4-P are the principal factors controlling the growth of bacterioplankton.