Enrichment status of eleven lakes in the southwestern region of Ontario
In general, the eleven lakes which were sampled in the Southwestern Region of Ontario in 1974 had low to moderate Secchi disc readings and very low chlorophyll a concentrations. However, four of the lakes were too shallow to obtain accurate Secchi disc readings since light penetrated to the bottom. Also, the increased turbidity caused by construction around the new ferry dock at Tobermory Harbour occasionally resulted in reduced Secchi disc readings in this area. For lakes having two to three consecutive years of data, only minor positional changes in Secchi disc- chlorophyll a relationships were noted, indicating that evidence of accelerating eutrophy is not yet apparent. In order to maintain the excellent water quality which exists throughout much of this part of the province, every effort should be made to ensure that nutrients from sink and laundry wastes, septic tank seepage and garden fertilizers do not gain access to the lakes. To establish a clearer understanding of year to year variations in water clarity conditions and algal densities, a continuation of the study is recommended. Such information, if maintained on a long-term basis, will be extremely useful in assessing whether or not changes in the trophic condition of the lake are materializing. In this regard, a suggestion is offered to continue with Secchi disc readings and chlorophyll a sampling for three consecutive years, but to maintain Secchi disc readings only during the next three years. The following year, chlorophyll a sampling would be re-introduced to complement water clarity data. Chlorophyll a sampling could be discontinued in Chesley Lake from 1975 to 1977; however, chlorophyll a sampling should be continued in Miller Lake since accurate Secchi disc readings cannot be obtained due to the shallow nature of the lake. Ideally, data collections should be made on a weekly basis during the ice-free period of the year.
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