Some effects of land use on bacteriological water quality in a recreational lake

Abstract

A study was conducted to detect the source of fecal indicator bacteria and the resulting degree of bacteriological water quality impairment of Mississippi Lake, a shallow eutrophic lake in southern Ontario, Canada. The lake was intensively sampled during two 5-day periods in late May-early June, and in July of 1976. The main detectable sources of fecal coliform were cattle watering sites, farms, public beaches, some flooded and substandard septic tanks, and a bird sanctuary. The impairment of water quality was localized to shoreline locations near the suspected source of the input of bacteria. After rainfall, about a 10-fold increase was noted in the levels of fecal coliforms and fecal steptococci in all lake surface water sampled. The effect was short-lived lasting only 2 or 3 days after the main rainfall. The levels of indicator bacteria were low and did not exceed maximum levels set down for Water Quality Management in Ontario, of 1000 TC(100 ml) −1 and 100 FC(100 ml) −1 at recreational areas. For this lake and six others in southern Ontario, the LOG of spring densities of aerobic heterotrophic bacteria correlated significantly with the LOG of mean summer chlorophyll a concentration ( r = 0.80). Cottagers on Mississippi Lake were surveyed for their swimming habits and for the incidence of disease associated with swimming. The largest cause of disease associated with bathing, 57 of 67 reported infections, was infection of the ear; 3.28% of bathers at shoreline cottages suffered ear infections. The frequency of ear infections in the population of swimmers was significantly associated with the amount of swimming in the lake. Males and females were infected at equal rates. Young people suffered a significantly higher rate of ear infections than adult bathers. Frequency of water contact was probably greater in young people than in adults and may explain the greater number of ear infections in young swimmers. These studies provided the basis for recommendations designed to improve lakewater quality.