DECREASING CHLORIDE TRENDS OBSERVED AT LAKE ERIE MUNICIPAL WATER INTAKES

Using available chloride data collected from seven municipal intakes drawing water from Lake Erie, linear trend analyses were performed to elucidate trends between the late 1960s and the early 1980s. Both seasonality and autocorrelation of the data were considered. Seasonality did not appear to significantly affect the trend. By removing the effects of autocorrelation more efficient estimates of the regression parameters were obtained and the achieved level of significance was considered valid. A decreasing chloride trend was found for all municipal intakes examined in this study. The rate of chloride decrease ranged from 0.47 to 0.88 mg/L/yr (mean: 0.7 mg/L/yr). This decreasing chloride trend in Lake Erie is believed to be the result of reduced loadings resulting from point source controls and the cessation of certain industrial operations which historically discharged high chloride loadings. Such evidence is important because of the concern for increasing chloride concentrations in Lake Erie over the past 20 years. © 1990, International Association for Great Lakes Research. All rights reserved.