134 



THE SALTON SEA. 



The 1908 zone on the shores of Obsidian Island remained bare during that year, 

 but had been occupied by 12 species in 1909, all of which but 3 had disappeared by 

 1911. Probably a fourth is to be added to the number in 1912. The Travertine Terraces 

 were occupied or invaded at once by 8 species not identical with those found on the other 

 strands of the same year. A year later 7 species were found, 2 of the original ones having 

 disappeared and 2 new invasions having occurred. In June 1912 the plant population was 

 represented by 6 species, which were identical with those noted in October except Juncus 

 and Cyperus; but circumstances justify the assumption that both species were continuously 

 present, so that the final census here may be taken to include 6 species. 



Three species came into the 1908 zone at Mecca soon after its emersion, being followed 

 by three others, which were seen two years later. Subsequent history of this beach was 

 complicated by economic operations, but it was evident that the number of species would 

 remain small here, as at the other gently sloping beach, although the individuals would 

 be more numerous. 



REOCCUPATION OF STRANDS OF 1909. 



The year 1909 was characterized by a net recession of 48 inches in the lake. In July 

 and August there was heavy precipitation, amounting to 3.5 inches (July to October) at 

 the Salton trestle station. Nearly 3 inches of this fell in one day at this place. The run- 

 off and underflow were so great that the results of evaporation were met and the lake stood 

 nearly at constant level for a period of about six weeks, a condition very favorable for 

 sorting material in beach ridges and depositing seeds; also, the precipitation would result 

 in some leaching of salts from the surfaces of all of the exposed beaches, while unusual 

 value would be given to the washes as disseminating or invading agencies in bringing plants 

 down the slopes in lines radial to the lake. 



The conditions of evaporation and the changes in the level of the lake from midsummer 

 of 1909 to midsummer of 1910 are illustrated by the following data furnished by the U. S. 

 Weather Bureau from observations made on the northeastern part of the lake near the 

 Station at the Salt Slough. Table 32 shows evaporation from pan 500 feet from shore and 

 2 feet above the surface of the water. 



Table 32. 



June 1909 14.41 



July 1909 14.77 



August 1909 12.53 



September 1909 12.40 



October 1909 9.20 



November 1909 6.21 



December 1909 4.67 



January 1910 3.61 



February 1910 5.01 



March 1910 9.17 



April 1910 10.96 



May 1910 14.01 



Total for year 116.95 



The total evaporation from another pan, 7,500 feet from the shore, was 114.97 inches, 

 and hence for convenience the yearly evaporation from the surface of the lake will be taken 

 as about 116 inches. The level of the lake during this period, however, showed fluctuations 

 of a character more widely divergent from the curve of evaporation than at any other 

 time during which observations were carried on by the members of the Institution, as 

 denoted by the monthly recession measured by the Weather Bureau showing the altera- 

 tions in level of Salton Lake June 1909-May 1910 (table 33). 



Table 33. 



Feet. 



June 1909 0.4 



July 1909 5 



August 1909 2 



September 1909 5 



October 1909 5 



November 1909 5 



December 1909 5 



Feet. 



January 1910 o.O 



February 1910 1 



March 1910 3 



April 1910 2 



May 1910 5 



Total for year 4.3 



The total net recession of the level during twelve months was therefore less than half 

 the possible evaporation. 



