New Zealand Journal of Marine and Freshwater Research abstracts

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CHEMISTRY AND TROPHIC STATUS OF SEVEN NEW ZEALAND LAKES

R. H. S. McColl

Ecology Division, Department of Scientific and Industrial Research, c/- Soil Bureau, Taita, Private Bag, Lower Hutt, New Zealand

Abstract The chemistry of the surface and bottom waters of seven Rotorua lakes (Okataina, Rotoma, Tikitapu, Okareka, Rotokakahi, Ngapouri, and Okaro) was examined monthly between April 1970 and April 1971 in relation to the biology of the lakes. Twenty-four parameters were measured, including dissolved 0₂, major ions, silica, phosphorus, nitrogen, algal pigments, and some trace elements. All lakes were warm monomictic, second-class lakes. All lakes contained "bicarbonate waters" except Rotoma which had "chloride waters". The waters were soft and variations between lakes in composition of major cations and anions appeared to be related to catchment differences. The major cations and CT varied little with season. Sulphate varied seasonally in the hypolimnia of the most productive lakes (Okaro, Ngapouri, and Rotokakahi). Silica was abundant in all lakes, except Tikitapu where diatoms were poorly represented. Depletion of silica by diatom populations was only observed in the two most productive lakes (Okaro and Ngapouri). All lakes except Ngapouri showed anomalous silica distribution, with lower concentrations in the bottom waters at all times.

N.Z. Journal of Marine and Freshwater Research 6 (4): 399-447
(Received for publication 20th July 1972)

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