Chapman et al: Limnology of Lake Rerewhakaait . . .

New Zealand Journal of Marine and Freshwater Research abstracts

Limnology of Lake Rerewhakaaitu

M. A. CHAPMAN

School of Science University of Waikato Private Bag Hamilton, New Zealand

V. H. JOLLY*

Zoology Department University of Auckland Private Bag Auckland, New Zealand

E. A. FLINT

33 Poynder Avenue Christchurch 1, New Zealand

Abstract The limnology of Lake Rerewhakaaitu (36°18'S, 176° 30'E) was studied at various intervals between 1971 and 1974; comparisons were made between the main lake (area 6.32 km², mean depth 7 m, maximum depth 15 m), and the smaller (0.15 km²) and deeper (mean depth 15 m, maximum 31 m) crater which are connected by a narrow, 1 m deep channel. The main lake was usually homother-mal, although temporary stratification periodically occurred, and the oxygen content of the deeper water could be as low as 2 g.m~³. The crater showed strong thermal and chemical stratification persisting well into the winter. Its heat budget and other factors related to lake stability are compared with those of some other New Zealand lakes. The failure of the crater to become fully re-oxygenated during its brief period of homothermy is believed to be related to its morphometry, since the amount of phytoplankton did not appear to be great enough to explain the low levels of dissolved oxygen in the hypolimnion. The hypolimnetic oxygen deficit in 1973-74 was 0.038 mg. cm"².day ~*. Qualitatively the phytoplankton, usually dominated by desmids, was characteristic of oligotrophic waters, but quantitatively the main lake could be rated as mesotrophic. Differences were also found in the abundance of zooplankton between the crater and the main lake: there were usually more Bosmina but considerably fewer Ceriodaphnia in the main lake which had greater numbers of Piona. Adult Calamoecia were generally more abundant in the crater.

Keywords Lake Rerewhakaaitu; freshwater lakes; zooplankton; phytoplankton; nutrients; temperatures; oxygen content; eutrophication.

New Zealand Journal of Marine and Freshwater Research, 1981, Vol. 15 : 207-224 Received 11 August 1980

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