New Zealand Journal of Marine and Freshwater Research abstracts
Postulated responses of phytoplankton and bacteria to predicted increases of
inorganic suspended sediments in oligotrophic lakes
MARC SCHALLENBERG+
UDO FRIEDRICH*
CAROLYN W. BURNS
Department of Zoology
University of Otago
P. O. Box 56
Dunedin, New Zealand
email: marc.schallenberg@stonebow.otago.ac.nz
*Present address: Fachbereich Biologie/Chemie,
Universität Osnabrück, Barbarastrasse 11, D- 49076,
Osnabrück, Germany.
Abstract We establish the relationships between
concentrations of inorganic suspended sediments (ISS) on light, nutrients,
phytoplankton, and bacteria in three oligotrophic lakes (four sites) and we use
these relationships to predict the impacts of increasing concentrations of ISS
on the biomass and productivity of phytoplankton and bacteria in the lakes.
Increased concentrations of ISS contributed little available nutrient to the
lakes. The relationships between ISS and underwater light attenuation differed
among lakes because of variation in sediment size-structure, and composition.
Only at the site with the highest ISS concentrations and a relatively deep
mixing depth, were phytoplankton apparently light-limited and, thus, predicted
to decline with increased ISS concentrations. In contrast to previously
published studies, bacterial abundance and production were not highly
correlated to suspended sediment concentrations in these lakes. However,
bacterial biomass, productivity, and specific productivity were more strongly
correlated to phytoplankton production. As a result of light limitation and
stimulation of bacterial production, increases in ISS concentrations are not
predicted to significantly shift the metabolic balance in the planktonic
ecosystem of three of the sites towards greater heterotrophy. Where light
limits phytoplankton production, increases in ISS are predicted to reduce the
productivity of both phytoplankton and bacteria by direct inhibition of
phytoplankton production, again without a large shift towards greater
importance of the microbial loop. By reducing phytoplankton production and
inhibiting larger cladoceran grazers, we predict that high concentrations of
ISS will reduce available energy and its flow up the food chain.
Keywords suspended sediments; suspended solids; primary
production; phytoplankton; bacterial production; bacteria;
autotrophy:heterotrophy; lakes; oligotrophic; microautoradiography
+Author for correspondence.
M00077
Received 2
November 2000; accepted 20 February 2001
PDF file of entire paper: medium quality (1710K); (scanned from paper original: notes about this process)
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