New Zealand Journal of Marine and Freshwater Research abstracts

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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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