New Zealand Journal of Marine and Freshwater Research abstracts
Seasonal changes in plankton and nutrient dynamics and carbon flow in the
pelagic zone of a large, glacial lake: effects of suspended solids and physical
mixing
MARK R. JAMES
National Institute of Water & Atmospheric
Research Ltd
P. O. Box 11 115
Hamilton, New Zealand
email: m.james@niwa.cri.nz
MARC SCHALLENBERG
Department of Zoology
University of Otago
P. O. Box 56
Dunedin, New Zealand
MARK GALL
ROBERT SMITH
National Institute of Water & Atmospheric
Research Ltd
P. O. Box 8602, Riccarton
Christchurch, New Zealand
Abstract The abundance and distribution of phytoplankton and
zooplankton were followed from January 1993 to March 1994 in Lake Coleridge, a
deep oligotrophic alpine lake in the Canterbury high country of New Zealand.
Our data suggest physical processes associated with deep mixing and inputs of
suspended sediments combined to limit planktonic biomass, diversity, and
determine vertical distribution. The lake was strongly stratified in summer
with a surface mixed layer of 20 m gradually extending down to 100 m
by May. Over 50 taxa of phytoplankton were recorded. Changes in vertical
distribution of most planktonic groups coincided with changes in the depth
of vertical mixing. Phytoplankton biomass increased through summer with a
diatom-dominated peak in autumn. Cell numbers however, peaked in spring and
were dominated by small chlorophytes. Phytoplankton photosynthetic production
was highest in autumn but specific growth rates were highest in summer as a
result of greater light availability combined with warmer temperatures. We
suggest that large inputs of suspended sediments and glacial silt, may have
limited the spring phytoplankton peak which occurs in a number of other
temperate lakes. Bacteria and picophytoplankton biomass peaked in winter
following the phytoplankton peak suggesting they were relying at least in part
on scenescing phytoplankton cells for dissolved organic carbon. Diversity of
ciliated protozoa was low (11 taxa), Cladocera were absent, and the only
crustacean zooplankton found in significant numbers was
Boeckella
hamata. Ciliated protozoan abundance was low (maximum 4600
litre
-1) and peaked in summer (January-March). Copepod nauplii
peaked in August and peaks in abundance of copepodites and adults followed in
September and November-January respectively. Only two generations occurred
during the year. The peak in copepod biomass followed phytoplankton peaks but
lagged 1-2 months probably as a result of slow growth rates and the time for
response to phytoplankton peaks.
Keywords plankton; oligotrophic lake; phytoplankton;
zooplankton; suspended sediments; vertical mixing
M99055
Received 1 October 1999; accepted 15 November 2000
New Zealand Journal of Marine and Freshwater Research, 2001, Vol. 35:
239-253
0028-8330/01/3502-0239 $7.00 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (2478K); (scanned from paper original: notes about this process)
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