Based on these few constituents, Lakes Michigan, Erie, and Ontario were 

 similar in chemical composition (Table 2). Lake Superior's chemical levels 

 were substantially below all the others. Lake Huron receives approximately 

 41% of its inflow from Lake Superior, 31% from Lake Michigan, and 28% from 

 the Lake Huron basin. Apparently the basin is a major contributor to the 

 characteristics of the water quality, because the total dissolved solids 

 are much higher than would be expected based only on a mixture of the 

 waters from Lakes Superior and Michigan. The Lake Erie watershed apparently 

 contributed significant amounts of calcium, sulphate, chlorides, and sodium- 

 potassium to the waters flowing into Lake Ontario, because their chemical 

 characteristics are nearly identical. Although differences between lakes 

 were large compared to the range between other natural bodies of water, the 

 five Great Lakes were remarkably similar. 



Analysis of nutrient concentrations for the Great Lakes has been made 

 only in recent years; therefore, base levels are only now being established. 

 Estimates based on recent values for phosphorus and nitrogen indicate that 

 the levels in the mid-1800's were less than 10 pg/liter for phosphorus and 

 usually less than 1 mg/liter for total nitrogen in the three upper lakes 

 (Superior, Huron, and Michigan). The Great Lakes in the 1900's would have 

 been classified as oligotrophic (as defined by Hutchinson, 1957) with the 

 probable exception of Lake Erie. 



The order of the lakes, if listed from the greatest to the least 

 fishery productive potential in the 1800's, probably would be Lake Erie, 

 Lake Ontario, Lake Michigan, Lake Huron, and Lake Superior (Figure 2). 



THE INITIAL IMPACT OF SETTLEMENT (1850-1900) 



Changes in Fish Populations 



The first environmental stresses on the Great Lakes ecosystem were pri- 

 marily caused by physical alterations in the basin, particularly in the 

 lower lakes. These alterations were deforestation of the watershed and 

 siltation and blockage of streams. These changes mainly affected the 

 tributaries and consequently the obligate anadromous species. Christie 

 (1972) reported the Atlantic salmon had begun to decline as eaHy as 1830 

 in Lake Ontario and was extinct, or nearly so, by 1900. Documentation of 

 the early proliferation of mills and dams was given by Christie (1972) 

 based on data from Richardson (1944). On the Ganaraska watershed (one of 

 the larger Canadian rivers tributary to Lake Ontario) at least two sawmills, 

 two grist mills, and two dams had been constructed by 1800. Construction 

 of the mills and dams increased rapidly, reaching a maximum of 34 sawmills, 

 19 grist mills, 4 woolen mills, and 34 dams by 1860. In 1930, 15 dams 

 still remained on this single tributary. Christie (1972) considered the 

 elimination of the Lake Ontario Atlantic salmon stock as the best known 

 example of the effects of despoliation on a species habitat. 



The lake sturgeon population in all the lakes was greatly reduced 

 during this period. Prior to 1903 the annual commercial production fluctu- 

 ated between 100,000 pounds and 500,000 pounds in Lake Ontario (Baldwin and 



199 



