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Dynamics of dissolved organic carbon lability in a eutrophic lake
Søndergaard, M.; Hansen, B.; Markager, S. (1995). Dynamics of dissolved organic carbon lability in a eutrophic lake. Limnol. Oceanogr. 40(1): 46-54
In: Limnology and Oceanography. American Society of Limnology and Oceanography: Waco, Tex., etc.. ISSN 0024-3590, more
Peer reviewed article  

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Keywords
    Bacteria; Biomass; Chlorophylls; Community composition; Dissolved organic carbon; Eutrophic lakes; Freshwater lakes; Grazing; Lakes; Organic carbon; Plankton; Fresh water

Authors  Top 
  • Søndergaard, M.
  • Hansen, B.
  • Markager, S.

Abstract
    The concentration of labile dissolved organic C ([DOCL]) and the plankton community structure were measured weekly during a diatom spring bloom and the subsequent clear-water phase in a eutrophic, temperate lake. The DOCL concentration was assessed by a bacterial regrowth method based on direct measurements of the increase in bacterial biomass and its respiratory demand. [DOCL] ranged from 560 to 1,130 mu g C liter and accounted for only 5-9% of total DOC. DOCL oscillated around 800 mu g C/liter, and the amplitude over 7-d periods was within plus or minus 16% of the in situ bacterial carbon demand. One period (3 weeks) with consistently increasing [DOCL] took place concomitant with the increase in macrozooplankton and bacterial biomass. Thus, DOCL was positively related to decreases in chlorophyll and zooplankton grazing. The increase in DOCL was followed by 3 weeks with decreasing concentrations, when the relationship between DOCL and bacterial production was negative. This pattern gives support to the hypothesis that grazing is a quantitatively important process in the flow of carbon to bacteria. The variations of DOCL were analyzed with a model describing interactions among substrate, bacteria, and grazing. Short-term (days) oscillations probably result from pulses of substrate production that are followed within a few days by bacterial uptake, and long-term (weeks) variations are explained by a variable bacterial substrate affinity (Km).

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