Pollution Ruins Lakes

Press, Volume CVIII, Issue 31865, 18 December 1968, Page 13

Pollution Ruins Lakes

. (By ELIZABETH A. FLINT. Ph.D.) “The turning of a clear, virgin lake into a cesspool of decaying vegetation is repeated over and over where bodies of water come under the influence of human habitation and the cultivation of land.”

That was written in 1939 by the American botanist Professor G. W. Prescott. His warning went unheeded. Through ignorance or expediency, inland freshwaters are still being threatened and abused. Many have been damaged beyond repair.

While there is yet time, the serious and permanent results of interfering with the natural evolution of New Zealand lakes should be recognised. If the general public, the local authorities In pailicular, realised what was at stake, they would surely insist that lakes be protected from pollution by domestic and industrial wastes. The proposed sewerage scheme for Moana, on the shores of Lake Brunner, is a case in point. Had eutrophication of the water (that is, the process of becoming rich in dissolved nutrients) been forbidden, many lakes in Europe and America would still be delightful places to visit instead of the unpleasant and costly liabilities they have become. Pollution is now so serious and far-reaching in its effects that an international symposium on eutrophication was held last year in Wisconsin, United States of America, and was attended by specialists from Europe, America and Asia. Plant Food Increased When sewage effluents are discharged into lakes they increase the amount of nutrient material in the water, particularly the amounts of nitrogen and phosphate, both of which are essential for plants. They cause profound changes in the animals, in the microscopic algae, in the rooted vegetation and the sediments on the lake bottoms. Household sullage containing detergents is particularlydamaging, as they increase the amount of phosphate in the water.

Within a relatively short time, a clear sparkling water becomes turbid and cloudy; the shallow littoral region is clogged and overgrown by rooted aquatic plants; trout disappear; and the open water is prone to recurrent epidemics of water-blooms of free-floating algae, a few of them causing disease in animals, and all of them producing an obnoxious and

evil-smelling scum when they die and decay. When such an algal epidemic developed in Lake Wairarapa in December, 1959, the water looked like green paint. Similar epidemics are common in farm ponds in dry summers, especially when the animals have direct access to the water and pollute it. Poisonous Algae Poisonous algae have been found in ponds in Hawke’s Bay and in the Wairarapa, and there is evidence that they have killed lambs that drank heavily infected water. Some of the poisonous algae have been studied intensively in Canada, and it has been shown that in certain species toxins are not only present in the algae, but are also produced by bacteria living on the mucilage that surrounds the algae. At least six of the noxious algae have already appeared in Lakes Tarawera, Taupo, Rotomahana and Matheson. In small lakes near Kaikoura, Ashburton and Dunedin they have sometimes been very common, and have tinted the water a milky blue-green colour. Irreversible Biologists have traced the history of some lakes (the classic examples are Lake Windermere, Lake Zurich and Linsley Pond) by studying vertical cores taken from the sediment at the bottom, and they have shown that, once a lake begins to deteriorate, the quality of the water changes very rapidly. If pollution continues, the process is complete in a few decades. The change is permanent and irreversible. So far. It is impossible to restore an exploited lake to its original condition. There is a long list of polluted lakes, and the casehistories of 50 or more in Europe and America make depressing reading. Algicides and weed-killers are regularly sprayed on the water to kill

algae and rooted vegetation, but they are expensive and sometimes ineffective. Furthermore, the full effect of chemicals applied year after year is unknown, particularly if the lakes are shallow. There is every reason for saying that the emphasis should be on prevention rather than on destruction of the vegetation. Dire Consequences Occasionally, enlightened local authorities have become aware of what was happening to their lakes, and have stopped polluting them. For example, an authority in Switzerland, at great cost, diverted domestic sewage from Rotsee into less vulnerable channels. In Madison, United States, public opinion was so strong that it forced the local authority to stop discharging effluents into Lakes Waubesa and Kegonsa and to divert the waste waters elsewhere. The cost was $3 million, but the amount of phosphate in the water was reduced, and algae are less objectionable. On the other hand, Lake Zurich continues to deteriorate as the amount of phosphate increases. Legislation now being considered would require all phosphate to be removed from an effluent before it could be discharged into the lake. Authorities in New Zealand, who are fortunate in having the chance to profit by the experience of other countries, should recognise the dire consequences of polluting inland freshwaters, and be ready to protect them from misuse. If the warnings are ignored and pollution allowed, many lakes will soon be unattractive, ruined for recreational purposes such as swimming, boating or fishing, useless as potential reservoirs of industrial and domestic water supplies, and a burden to the community.