Effects of lake size, water clarity, and climatic variability on mixing depths in Canadian Shield lakes

The depth of the summer mixed layer (E d ) of 21 Canadian Shield lakes in northwestern Ontario was examined in relation to lake size (surface area, A 0 ) and water clarity (extinction coefficient, K d ) for periods ranging from 2 to 23 yr (n = 1,408). The lakes range in A 0 from 4 to 4.9 x 10 5 ha, and midsummer (mid-June through mid-August mean) K d varied from 2.5 m -1 with greatest variation in small lakes that were experimentally eutrophicated or acidified or whose terrestrial basins were burned. Over the full spectrum of lake sizes, A 0 was the primary determinant of E d ; transparency significantly modified this relationship but only in small lakes (A 0 <500 ha). In noneutrophic shield lakes, transparency is controlled by the concentration of dissolved organic C (DOC). Lower DOC concentrations (a likely consequence of 2 x CO 2 climate change) would cause transparency to increase, resulting in 1-2-m-deeper epilimnia in small lakes ; there would be no similar effect in large lakes.

[1]  E. Fee.  The vertical and seasonal distribution of chlorophyll in lakes of the Experimental Lakes Area, northwestern Ontario: Implications for primary production estimates , 1976 .

[2]  G. E. Hutchinson,et al.  A treatise on limnology. , 1957 .

[3]  R. Sterner.  Lake Morphometry and Light in the Surface Layer , 1990 .

[4]  E. Gorham,et al.  Influence of Lake Surface Area and Depth Upon Thermal Stratification and the Depth of the Summer Thermocline , 1989 .

[5]  E. U. Schindler,et al.  Effects of Lake Size on Phytoplankton Photosynthesis , 1992 .

[6]  K. Patalas.  Mid-summer mixing depths of lakes of different latitudes: With 5 figures in the text , 1984 .

[7]  F. M. Boyce.  Some Aspects of Great Lakes Physics of Importance to Biological and Chemical Processes , 1974 .

[8]  H. Hengeveld.  Global Climate Change: Implications for Air Temperature and Water Supply in Canada , 1990 .

[9]  R. Hecky,et al.  Introduction to the Northwest Ontario Lake Size Series (NOLSS) , 1992 .

[10]  M. Stainton,et al.  The Chemical Analysis of Fresh Water , 1977 .

[11]  Franz Ruttner.  Fundamentals of Limnology , 1953 .

[12]  R. Davies‐Colley,et al.  Absorption of light by yellow substance in freshwater lakes , 1987 .

[13]  R. A. Ragotzkie.  Heat Budgets of Lakes , 1978 .

[14]  D. Schindler,et al.  Geography and Bathymetry of Selected Lake Basins, Experimental Lakes Area, Northwestern Ontario , 1971 .

[15]  T. T. Bannister.  Production equations in terms of chlorophyll concentration, quantum yield, and upper limit to production , 1974 .

[16]  J. Elser.  Evaluation of size-related changes in chlorophyll-specific light extinction in some north temperate lakes , 1987, Archiv für Hydrobiologie.

[17]  William D. Taylor,et al.  Thermal structure of lakes varying in size and water clarity , 1994 .

[18]  J. Koenings,et al.  Secchi disk and photometer estimates of light regimes in Alaskan lakes: Effects of yellow color and turbidity , 1991 .