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New Zealand Journal of Marine and Freshwater Research abstracts

Aspects of the limnology of Lake Rotongaio

D. J. FORSYTH

M. T. DOWNES

M. M. GIBBS

L. KEMP

I. McCALLUM

L. MacKENZIE

G. PAYNE

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

Abstract Lake Rotongaio, a warm monomictic lake, was sampled at monthly intervals for 1 year to investigate water temperature, transparency, chemistry, zooplankton, and benthic macroinver-tebrates. Phytoplankton composition and standing crop represented by concentration of chlorophyll a, were measured for 6 months. Secchi disc values were always less than 2 m because of the large standing crops of algae dominated throughout the year by Anabaena oscillarioides. The major ion composition of the lake water indicated a source typical of a pumice aquifer. The average concentration of dissolved reactive phosphorus during the circulation period was 275 mg m 3and the average reactive N:P ratio was 0.55. The decline in concentration of inorganic N during the breakdown of thermal stratification could not be accounted for by mixing, and 606 kg or 6.71 mg m 3d ' of inorganic N was lost from the lake. The zooplankton comprised rotifers (57%), crustaceans (34%), and ciliates (9%). There was 1 species of calanoid cope-pod, 2 species of cladocera, and 6 species of rotifer. Ninetyone percent of the benthic rnacroinverte-brates were chironomids; the rest were other insects, oligochaete worms, and molluscs.

Keywords Lake Rotongaio; limnology; thermal stratification; water temperature; water chemistry; water clarity; phytoplankton; zooplankton; benthic macroinvertebrates

New Zealand Journal of Marine and Freshwater Research, 1983, Vol. 17: 423-435 0028-8330/83/1704-0423$2.50/0 © Crown copyright 1983 15 June 1983

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