Light, Temperature, and Oxygen Regimes of Selected Lakes in the Experimental Lakes Area, Northwestern Ontario

Abstract

Light was measured in several Experimental Lakes Area (ELA) lakes in 1968 and 1969, using a Secchi disc, a standard photometer (cadmium sulfide cell), and a 16-channel spectroradiometer. The results of some checks upon the standard procedure usually used for making subsurface light measurements are presented. Light penetration at several wavelengths and total energy flux at several depths are given for a number of lakes. Oxygen and temperature isopleths, winter rates of oxygen depletion, annual heat budgets, and data on work of the wind are also presented. Vertical extinction coefficients (average of all visible wavelengths) ranged from 0.285 for lake 161 to 1.732 for lake 227, and Secchi disc visibility from 1.2 to 10.1 m. The wavelength of maximum transmittance shifted toward long wavelengths, as expected, when transmission coefficients and Secchi disc visibility decreased.Annual heat budgets ranged from 8400 to 24,200 cal/cm2. From 3700 to 16,000 cal/cm2 of this were summer heat income. Summer and annual heat budgets were larger for larger lakes. Annual and summer heat incomes were related to mean depth, surface area, and volume of the lakes by simple linear regression equations.The work of the wind and its efficiency in distributing summer heat income are discussed. The depth of the thermocline in ELA lakes was set early in the year, and did not change during the summer until well after the lake had reached maximum heat content. The temperature of the epilimnion followed the mean daily air temperature closely during the summer though remaining several degrees higher, probably as the result of radiant heating. It is concluded that wind work calculated by Birge's method (Trans. Wis. Acad. Sci. Arts Lett. 18: 341–391, 1916) is of little value, unless corrections for back-radiation and evaporation can be made.Rates of oxygen depletion under ice were compared in several lakes. Values ranged from 15.0 to 73.8 mg O2/m3∙day and from 36 to 253 mg O2/m2∙day.