New Zealand Journal of Marine and Freshwater Research abstracts
External forcing by wind and turbid inflows on a deep glacial lake and
implications for primary production
MARC SCHALLENBERG*
MARK JAMES
IAN HAWES
CLIVE HOWARD-WILLIAMS
National Institute of Water & Atmospheric
Research Ltd
P. O. Box 8602
Christchurch, New Zealand
*Present address: Department of Zoology, University of Otago, P. O.
Box 56, Dunedin, New Zealand. email: marc.schallenberg@stonebow.otago.ac.nz
Abstract Lake Coleridge is a deep monomictic lake in the
Southern Alps of New Zealand which is affected by strong adiabatic winds. It
receives significant inputs of inorganic suspended solids from rivers diverted
into the lake for hydro-electric generation. External inputs of wind energy and
suspended solids to Lake Coleridge were quantified throughout 1 year and their
impacts on hydrodynamics and the light climate were analysed. During
stratification, the lake had a deep mixed layer, underlain by a complex
metalimnion. High wind energy inputs caused large internal waves which resulted
in the upwelling of hypolimnetic water, horizontal density gradients, and
significant currents. Calculated vertical diffusivity and exchange coefficients
were similar to those of much larger lakes. Analyses indicated that mixing in
the metalimnion was often a result of shear stresses arising from vertical
gradients in horizontal velocities. Whole lake total suspended solids (TSS)
burdens were significantly correlated with the previous 13-week integrated TSS
loading from inflows. A seasonal pattern was observed where TSS from inflows
entered either below, within or above the metalimnion. Evidence of effects of
sediment resuspension from the marginal lake bottom was observed only when the
lake level was low and the resulting impacts on the light climate were minimal.
The synergistic effects of climate, thermal structure, and inflows resulted in
the apparent light-limitation of phytoplankton photosynthesis in winter months.
Keywords hydrodynamics; mixing; suspended solids;
phytoplankton; turbulence; wind energy; internal waves; Wedderburn number;
light climate; lake; turbidity
M98025
Received 20 May 1998; accepted 7 January 1999
PDF file of entire paper: medium quality (2062K); (scanned from paper original: notes about this process)
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