New Zealand Journal of Marine and Freshwater Research abstracts

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LIMNOLOGY OF LAKE ROTOKAWA AND ITS OUTLET STREAM

D. J. FORSYTH

Freshwater Section, Ecology Division, DSIR, P.O. Box 415, Taupo, New Zealand

Abstract The water chemistry, flora, and fauna of Lake Rotokawa (38° 37.8' S, 176° 11.2'E) was studied in 1975-76. The mean pH is 2.1 and thermal inflows may elevate the mean summer temperature of the surface waters 4.2°c above that of nearby cold water Lake Rotongaio (18.9°c). The temperature range of surface water was from 10.1 °c in winter to 23.1°c in summer. The major anions were SO,}2ô 679 g.rrr3, and Cl- 314 g.m~3. Mean concentrations of major cations were Na+ 224 g.m-3, K1 28.9 g.nr3, Ca2+ 13.3 g.nr3, and Mg2' 2.6 g.m-3. The Parariki Stream was influenced by thermal springs in its upper and lower reaches, being cooler (24-25°c) about halfway along its length than near its source (27.8-39.0°c) or confluence (26.5°-28.0°c) with the Waikato River. In the cooler stretch of the stream where unidentified benthic algae were not limited by high temperature, chlorophyll and total pigment increased from 3.9 to 377.9 mg.m-³ and from 17.5 to 534.4 mg.nr³ respectively, and nutrient levels fell (NO₃-N, 22-10.5 mg.nr³; NH_t-N, 6440-230 mg.m-3; and PO₄-P, 51-19 mg.nr³).

N.Z. Journal of Marine and Freshwater Research 11 (3) : 525-39
Received 13 October 1976; revision received 25 February 1977.

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