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New Zealand Journal of Marine and Freshwater Research abstracts

Limnology of Lake Waikaremoana with special reference to littoral and pelagic primary producers

CLIVE HOWARD-WILLIAMS
KAREN LAW
CONNIE L. VINCENT
JOHN DA VIES
WARWICK F. VINCENT

Taupo Research Laboratory
Division of Marine and Freshwater Science
Department of Scientific and Industrial Research
P. O. Box 415, Taupo
New Zealand

Abstract Lake Waikaremoana, the North Island's deepest lake (248 m), lies in a natural forested catchment, but the lake itself has been modified for hydro-electric power generation and by the introduction of trout, smelt, and adventive aquatic plants. The lake is a warm monomictic water body of low conductivity (82 yS cm1) and a high seasonal water column stability. The waters are oligotrophic, with epilimnetic dissolved reactive phosphorus concentrations typically < 1 mg irr3. The concentration of NO3-N is seasonally variable but generally high in winter and spring with maximum epilimnetic values approaching 70 mg tn~3. This contrasts with other central North Island lakes. Horizontal variability in surface chlorophyll a is low as are the absolute values (< 1 -2 mg m 3). A notable feature is the formation of a deep chlorophyll maximum within the metalim-nion comprised largely of Sphaewcystis schroeteri as opposed to diatoms and flagellates which normally dominate the epilimnion. Vascular macro-phytes (maximum biomass 659 g m~2 dry weight) extended to 9 m and characeans (maximum biomass 447 gm~2 dry weight) to 16 m. Total phyto-plankton primary production was calculated as 4524 tCy~' and macrophyte production as 578 t C y '. The proportion of macrophyte to phy-toplankton production (0.14) is higher than in the other deep lakes of the central North Island.

Keywords nitrogen; phosphorus; chlorophyll; macrophytes; productivity; littoral zone; phyto-plankton; monomictic lake; light

New Zealand Journal of Marine and Freshwater Research, 1986, Vol. 20: 583-597 Received 14 February 1986, accepted 14 April 1986

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