100% 



MAINLAND SYSTEMS 



IGUSHIK 



SNAKE 



WOOD 



NUYAKUK 



KVICHAK 



PENINSULA SYSTEMS 





 a 



A 

 O 



ALAGNAK 



NAKNEK 



UGASHIK 



CHIGNIK 



KARLUK 



MAINLAND LAKES 



PENINSULA LAKES 



Figure 3. — Relative chemical proportions of the three major cations — sodium, calcium, and magnesium — in 

 water samples from sockeye salmon lakes of southwestern Alaska. Each corner of a triangle is as- 

 signed a value of 100 percent for one of the cations. If a lake had equal equivalents of each cation, 

 the value for that lake would be plotted in the center of the triangle. As the proportion of a cation 

 increases toward 100 percent for that lake, the point is plotted closer and closer to the corresponding 

 tip of the triangle. 



mine these proportions, the concentrations of 

 the three cations in equivalents per million were 

 summed. Then the proportion of the total equiv- 

 alents contributed by each cation was calculated 

 (table 5) . The data are presented graphically in 

 iigure 3. 



The graphic analysis of the proportionate con- 

 tribution of the three cations (fig. 3) reveals a 

 similarity among the lakes of a system. Lakes 

 of several systems — Wood, Nuyakuk, Naknek, 

 and Chignik^show this grouping, which sug- 

 gests that the sources of these elements (ter- 

 re.strial and marine) influence all lakes within 

 a system similarly. Figure 3 also shows that 

 groups of lakes for systems on the mainland and 

 on the peninsula do not overlap. Lakes of the 



Mainland Systems have proportionally more 

 equivalents of calcium and less sodium than 

 lakes of the Peninsula Systems. Our last com- 

 ment on this analysis concerns lakes of the 

 Nuyakuk system. In these waters the absolute 

 concentrations of sodium were comparatively 

 low (table 3) , and the proportions of equivalents 

 of sodium in relation to magnesium and calcium 

 are also low (table 5). 



Goldman (1960) found low concentrations of 

 magnesium to be limiting to phytoplankton pro- 

 duction in Brooks Lake during the summer of 

 1957. He concluded that magnesium at a low 

 level, in comparison with other cations, was less 

 available to the plankton because of the presence 

 of relatively high quantities of sodium. 



414 



U.S. FISH AND WILDLIFE SERVICE 



