Environmental changes, except in streams and bays near centers of high 

 human population density, were nearly undetectable in 1925 in the lakes 

 proper. Changes had occurred, however, in Lakes Michigan, Erie, and Ontario 

 in the few chemical constituents for which data are available (Table 5). 

 The absolute concentrations of these constituents, even the highest levels, 

 were well below levels of ecological or toxicological concern. The rates 

 of change, especially in total dissolved solids, sulphur, and chloride, 

 however, are staggering considering the tremendous volume of water which 

 had been changed as much as 160% in only 25 years. 



TABLE 5. ESTIMATED AVERAGE CONCENTRATION OF DISSOLVED CHEMICAL 

 CONSTITUENTS IN THE GREAT LAKES IN 1925 (EXPRESSED IN 

 MG/LITER)a WITH PERCENTAGE CHANGE AFTER 1900 IN PAREN- 

 THESES 



Total Sodium 

 Lake dissolved Calcium Sulphate Chloride and 

 solids potassium 



Superior 58 (-3) 13 (0) 4 (0) 2 (0) 3 (0) 



Michigan 143 (+12) 34 (0) 13 (+160) 4 (+100) 



Huron 108 (0) 24 (0) 9 (+50) 4 (0) 4 (0) 



Erie 146 (+3) 33 (+6) 16 (+23) II (57) 7 (0) 



Ontario 149 (+6) 34 (+10) 18 (+20) 11 (57) 7 (17) 



a From Beeton, 1969. 



The increase in population growth in the basins of the Great Lakes was 

 approximately 28% between 1900 and 1925 (Table 3). Growth in numbers was 

 greatest in the basins of Lakes Erie and Ontario. The population in the 

 Erie basin increased 93% to 5.8 million, and in the Lake Ontario basin the 

 increase was 25% to 2.5 million. Lake Michigan's basin effectively lost 

 0.8 million when the Chicago Sanitary Canal, which diverted the waste from 

 the city to the Mississippi River drainage, was completed in 1900. The in- 

 creasing urbanization and industrial expansion was the probable cause of 

 the increase in the chemically conservative ions. Undoubtedly, concentra- 

 tions of other chemical components also increased, especially the plant 

 nutrients phosphorus and nitrogen. The load of oxygen-demanding organic 

 compounds can also be assumed to have increased. 



The stresses causing the decreases in some native fish species in the 

 lower lakes by 1925 were man caused, principally by heavy exploitation. 

 The role of environmental change, especially water-chemistry change, in re- 

 duction in fish populations apparently was minor except in the tributaries 



206 



