Heat could cause lake to ‘die,’ tribunal told

Press, 3 May 1984, Page 3

Heat could cause lake to ‘die,’ tribunal told

A five to 10-day spell of calm, hot weather during summer would be all that was needed before Lake Ellesmere started “dying,” with many fish, invertebrates and flora being killed, a Planning Tribunal hearing was told yesterday. The secretary of the North Canterbury Acclimatisation Society, Mr B. F. Webb, said in his evidence that the estimated total nitrogen level in Lake Ellesmere was some five times greater than the “dangerous loading” levels given by an environmental directorate. The total phosphate level was twice as great. This indicated to the society that the only factors saving Lake Ellesmere from total destruction as an aquatic habitat were the shallowness of the lake itself and the prevalence of wind turbulence. The hearing concerns an appeal by the Ellesmere County Council against a North Canterbury Catchment Board decision on the discharge of treated sewage effluent into the L2 River which flows into Lake Ellesmere. The Catchment Board agreed to give the council a water right to discharge up to 1700 cu m of treated sewage effluent into the lake a day, from a primary

oxidation pond it plans to build, into the L2 River, with a provision that a treatment plant also be built. The Catchment Board believes the proposed pond alone would not sufficiently reduce the nutrient-contain-ing algae which could destroy the delicate balance of Lake Ellesmere’s water. The County Council objects to the condition being included in the water right as it considers the filtration plant would have little effect on the nutrient levels in Lake Ellesmere and would be an unnecessary financial burden on ratepayers. The present sewerage system is overloaded and subject to malfunction and high maintenance costs. Mr Webb said the proposed oxidation pond system did not appear to give any significant improvement in water quality of the kind that should reasonably be expected after so many years of discussion. “It is this society’s contention that if oxidation ponds are to be approved, with direct discharge into the L2, then some further treatment must be incorporated, such as filtration, additional Pasveer Ditch Oxidation, or activated sludge treatment so as to remove of the nutrients

from the system as possible.” Oxidation ponds, while being used throughout New Zealand, were less effective in colder months, said Mr Webb. “In the case of the Lincoln system, this coincides with the period of highest usage — the rise in the student population at Lincoln College.” Mr Webb said the society also thought that the Lincoln effluent, once properly treated, should be disposed of partially or totally by land irrigation. Under this suggestion, discharge into the L2 would be in an “emergency” situation only. “The neighbouring Leeston sewage system already has this dual disposal of effluent so even from a health viewpoint there should be no problem,” he said. Discharging effluent into natural waters was an archaic practice which, while possibly accepted 100 years ago, should now be progressively out-dated in these increasingly enlightened times of environmental protection and social awareness, said Mr Webb. “The society is not asking for a total effluent clean-up at this stage, but only that a start be made.” As a recreational'fishing area, Lake had

remained popular in the last seven years, said Mr Webb. The lake was one of the most important freshwater habitats in New Zealand for waterfowl, wading birds, and as a staging area for many species of migratory birds, he said. “The society is concerned that any future trend towards deterioration in the water of Lake Ellesmere and its inflowing rivers, should not only be curtailed but endeavours made to reverse the pollution trend and restore the lake water clarity to the pre-1970 condition.” ' With the lake being recommended as an international wetland, every opportunity should be taken to improve Ellesmere water quality. The society left the question of effluent quality and water right conditions to the Catchment Board as they had the available expertise for making such decisions, said Mr Webb. The tribunal comprised Judge Skelton, Mr R. N. McLennan and Mrs N. J. Johnson, Mr G. H. Nation appeared for the Ellesmere County Council; Mr C. B. Atkinson, Q.C., for the Catchment Board, and Mr M. D. de Goldi for the North Canterbury Acclimatisation Society.. The tribunal reserved its decision.