Lake Growth Causes Concern

Press, Volume CVIII, Issue 31784, 14 September 1968, Page 14

Lake Growth Causes Concern

Accelerated development of the nutrient qualities of lakes was becoming a world-wide problem rather than a help in their productivity, said Dr Vida M. Stout, senior lecturer in zoology at the University of Canterbury.

She has just returned from the International Congress on Limnology at the Hebrew University at Jerusalem. This was a major aspect of congress papers, she said.

At best, such growth made lakes unpleasant for swimming, unsatisfactory for drinking, difficult for boating or fishing, and at worst, actually noxious, Dr Stout said.

Growth could range from tiny algae to rank weed. The congress issued an appeal to local authorities everywhere to stop the entry of sewage into lakes, Dr Stout said. This so improved the nutrient qualities of lakes that unwanted growth became rapid. Other wastes could have similar effects. Classic cases of the problem were Lake Geneva, some North American lakes, and even those at Rotorua. Dr Stout said various methods of controlling weed growth were described at the congress. These ranged from “cropping” (cutting and use for other purposes) to feeding weed off with certain strains of fish. The fish were then “harvested.” Dr Stout said all this gave point to the careful studies of the condition of lakes being made in New Zealand. The 15 Canterbury mountain lakes she described to the congress had an opposite problem deficiencies of nutrients caused by leeching over thousands of years. But they still needed study.

At the congress and on visits to the Universities of Melbourne, Oxford, Michigan, Georgia, and the River Laboratories in Dorset, Dr Stout discussed the new course in production ecology

she will begin next week in Canterbury. This, she said, concerned estimation of the present productive capacity of tracts of both land and water. Nutrients available, climate, plant and animal growth rates, and many other factors had to be taken into account.

Israel impressed Dr Stout Development in the last 20 years had been tremendous, she said. Desert had been turned into productive land

by irrigation and other modifications and swamps had been drained. Dr Stout said a great deal of work was being done on desalination of sea water. The only major fresh-water supply in Israel was the Sea of Galilee, which was piped north and south over almost the whole country. Even reduction of the brackishness of ground water for use in agriculture would be a major gain. However, she said, all processes were very expensive.