Limnologists Discuss Lake-water Pollution

Press, Volume CIX, Issue 32078, 28 August 1969, Page 21

Limnologists Discuss Lake-water Pollution

Although some algae species present in Lake Rotorua are the same as those found overseas in polluted waters, too few are present to provide evidence of pollution in the lake. This is the view of Dr U. V. Cassie, in a paper pre-

sented to the second conference of the New Zealand Limnological Society in Christchurch earlier this week. Dr Cassie discussed Lake Rotorua using the numbers and types of floating microscopic algae to estimate pollution. A paper on an important form of water pollution, eutrophication, using Lake Rotorua as an example, was given by Dr G. R. Fish. He discusses the annual budget of water flowing in and but of the lake and its nutrient content. Discussion supported the conclusion that in some respects agricultural development may be as important as industrial and domestic effluents in fertilising the lake waters. A further paper by Dr E. A. Flint recorded instances of blue-green algae blooms in New Zealand lakes, and discussed factors influencing their formation. Another paper by Dr J. M. A. Brown described seasonal changes of weed clumps in Lake Rotoiti (adjoining Lake Rotorua), and gave preliminary results on the accumulation of arsenic in aquatic plants growing in thermal lakes and the Waikato River. Dr I. D. Blair gave an angler’s impression of the “marked drop” in trout catches after changes in landdevelopment policy in a lowland stream, and discussed anglers’ catches in several of the Waimakariri basin lakes. The conference, which was opened on Monday by the Limnological Society’s president, Dr V. M. Stout, of the zoological department at Canterbury University, ended on Tuesday with a field excursion to the Selwyn River, Lake Ellesmere, and Lake Forsyth.