86 ILLINOIS STATE ACADEMY OF SCIENCE 



nine years has greatly diminislied the area of the lake. 

 It is not to be inferred that the eighteen food lowering of 

 the surface has been a constantly progressing process. 

 Some years the loss was through the heated summer 

 months and was restored by the melting snows and spring 

 rains. In some cases the low levels have been replaced 

 by higher stages lasting for one or more seasons. 



The physical factors which accompany the disappear- 

 ance or dying process of a lake are numerous. Natur- 

 ally the most notable features are the lowering of the 

 water level, the emergence of islands, the appearance of 

 land projections and the final separation of the main 

 body of water into lesser basins. 



With the continued evaporation of water there is, of 

 course, the attending increase in specific gravity and the 

 lift in osmotic pressure registered by the solutes upon 

 living organisms within the water. 



There is a diminution of luminosity and a precipita- 

 tion of mineral and organic matter as the lake grows old- 

 er and the dying process advances. 



With the development of the shallow basins and the 

 comparative shallowness, even in the deepest part of 

 the Lake, the effect of winds and modification of tem- 

 perature, distribution of the gases, oxygen, carbon di- 

 oxides, and nitrogen are more rapidly modified and ad- 

 justed than was the case in the younger and deeper lake. 



The chemistry of a dying lake is associated specifically 

 with a concentration in the mineral content and the re- 

 adjustment in proportion of carbon dioxide and numer- 

 ous other substances in solution. 



The physical and chemical changes incident to the dry- 

 ing up or dying process in Devils Lake are apparently 

 going forward quite rapidly at this time. In 1914 the 

 average collections of water from various parts of 

 Devils Lake showed that it was .94 of 1% saline. During 

 the last eight years, due to the excessive evaporation and 

 the attendant concentration of lake water, the salinity 

 has increased to 1K%- This indicates a rapid concentra- 

 tion of mineral solutes and complicates still further 



