Microbial Response of a Freshwater Benthic Community to a Simulated Diatom Sedimentation Event: Interactive Effects of Benthic Fauna |
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Authors: | W Goedkoop KR Gullberg RK Johnson I Ahlgren |
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Institution: | Institute of Limnology, Uppsala University, Norbyv?gen 20, S-752 36 Uppsala, Sweden, SE Swedish University of Agricultural Sciences, Department of Environmental Assessment, P.O. Box 7050, S-750 07 Uppsala, Sweden, SE
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Abstract: | Abstract
The response of a sediment microbial assemblage to a pulse of diatoms was studied over 36 days by measuring bacterial activity
and biomass, ATP concentration, and overall community respiration in laboratory microcosms. Also, the contribution of macrofaunal
chironomids to the decomposition of settling diatoms in benthic communities, and the relative importance of benthic meiofauna
in community metabolism, were determined.
The addition of diatoms resulted in an immediate response by sediment bacteria, with higher bacterial production recorded
after only 2 h, and a more than tenfold increase within one day. The rapid response by sediment bacteria was accompanied by
relatively high initial concentrations of dissolved organic carbon. In treatments receiving diatoms, higher bacterial production
was sustained throughout the experiment. Surprisingly, neither these elevated production estimates, nor the starvation of
controls affected bacterial abundance. Mean bacterial cell volume, however, was markedly affected by the addition of diatoms.
Combining community respiration measurements and bacterial production estimates showed that growth efficiencies for sediment
bacteria ranged from 14.6 to 34.5%. The contribution of ambient meiozoobenthos to carbon metabolism was less than 1%. Carbon
budgets showed that 1.3 mg C was cooxidized along with 4.3 mg added diatom C.
Sediment reworking by Chironomus larvae initially enhanced bacterial production, but the presence of Chironomus resulted in lower bacterial production estimates after 16 and 36 days. This was interpreted as a result of faster decomposition
of diatoms in treatments with chironomids, which was validated by a faster decline of ATP and chlorophyll a in the sediment. Our results indicate that Chironomus larvae compete with sediment bacteria for available organic substrates.
Received: 11 June 1996; Accepted: 13 August 1996 |
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