Trends in lake rotorua water quality

Abstract

Fourteen determinands relating to the water quality of Lake Rotorua were examined for trend over the period 1966–1983. A linear regression package was used, but additional manipulations were performed to eliminate markedly non-normal distributions, remove seasonality, compute monthly averages, fill gaps, and correct for serial correlation. Since lake data came from 3 different organisations, with possibly different analytical techniques, trends were calculated over 3 periods separately. Lake quality deteriorated during 1967–1970 largely because meteorological conditions favoured lake stratification. During 1978–1983, despite favourable meteorological conditions, quality again deteriorated at the same time as, and probably as a result of, an increase of available nutrient input from sewage effluent. Improved sewage nutrient removal could halt this deterioration. © 1984 Taylor & Francis Group, LLC.