Bacterioplankton growth, grazing mortality and quantitative relationship to primary production in a humic and a clearwater lake |
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Authors: | Tranvik Lars J |
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Institution: | Institute of Ecology, Limnology, University of Lund Box 65, S-221 00 Lund, Sweden |
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Abstract: | Bacterial growth and grazing mortality were estimated from Mayto October in two south Swedish oligotrophic lakes, one beinga clearwater lake (water colour 510 mg Pt l1 DOC2.93.4 mg l1, Secchi disk depth 5.09.4m) and the other a humic, brownwater lake (water colour 105165mg Pt l1, DOC 13.722.7mg l1, Secchi diskdepth 1.32.1 m). Specific rates of growth and grazingmortality were generally similar for both lakes. However, theabundance of bacteria was consistently 23 times higherin the water of the humic lake, suggesting that the total productionand consumption of bacterial cells were also higher than inthe dearwater lake. The ratio of bacterial secondary productionto primary production was higher in the humic lake than in theclearwater lake, indicating that the bacterioplankton of thehumic lake utilize allochthonous substrates, in addition tosubstrates originating from autochthonous primary production.Most of the bacterial loss in both lakes could be attributedto small protozoan grazers. This implies that allochthonousand autochthonous organic carbon fixed by bacterioplankton isless important in terms of carbon flow to higher trophic levelsthan would be expected if macrozooplankton were the dominantbacterivores, providing a more direct and efficient transferof carbon to larger organisms. |
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