28 



BULLETIN 61, U. S. DEPAETMENT OF AGEICULTUEE. 



sion of saline material, accounts for the variation in the analytical results often noted 

 in the reports of analyses of lake waters of the basin. The fluctuations of lake levels 

 would also produce a change in concentration and, consequently, the equilibrium 

 conditions would be changed also. The more soluble salts are accumulating in these 

 lakes while the more insoluble are precipitating out. The principal data concerning 

 the chemical content of river and lake waters of the basin are given in Table XV 

 (Appendix). 



Much detailed chemical work has been done upon the California rivers by Vaa 

 Winkle and Eaton,' and on account of the close proximity of this State to the basin 

 region the results of their analyses are of importance. They are given in the table 

 which follows: 



Mean analyses, California rivers. 



[Per cent of anhydrous residue.] 



Constituent. 



Humid (22 

 rivers); rain- 

 fall, 15+. inches. 



Semiarid (16 

 rivers); rain- 

 fall, 15— inches. 



CI 



SO4 



CO3 



Na+K 



Ca 



Mg 



Fe 



SiOs 



Solids on evaporation, parts per 100,000 



Per cent. 



8.95 



14.91 



31.27 



. 12.53 



15.52 



5.37 



0.12 



11.33 



Per cent. 



7.89 



37.02 



18.87 



12.34 



12.83 



5.76 



0.02 



5.27 



100. 00 

 16.5 



100.00 

 62.7 



From the study of the results the following conclusions are of importance to the 

 present inquiry: The total soluble salts in a river water under normal conditions 

 varies with the stream flow. They are a minimum for a maximum flow and a 

 maximum for a minimum flow. Narmal conditions may be assumed to be those for a 

 humid region. The components of the total salts also follow the above rule. If we 

 take the Yuba River as an example and apply this rule to the various soluble con- 

 stituents, we find that chlorine, the sulphate radical, carljonic acid, sodium, and 

 calcium follow this rule. Potassium fluctuates; magnesium shows little fluctuation; 

 silica remains practically constant. In an arid or semiarid region soluble salts tend 

 to accumulate duiing periods of low water. \^1ien the first floods come the river 

 water gains in total solids and sometimes to a very marked extent, due to the washing 

 out of these accumulated salts. Certain rivers, such as the Santa Ynez and the Owens 

 River, maintain the amount of total salts at practically a constant figure. Concerning 

 the comparison of the mineral content of waters in semiarid and humid regions Van 

 Winkle and Eaton state: 



First. "The average mineral content of waters in semiarid regions is, roughly, 

 four times that of waters in humid regions. 



Second. "Difference in percentage composition of the anhydrous residues shows 

 that the waters in semiarid regions contain aljout two-thirds the proportionate amount 

 of silica, less calcium; four-fifths as much carbonates, and twice as much sulphates as 

 the waters of the humid regions. Their constituents are similar in amount. In 

 regions of a1)undant rainfall disintegration of rock material can not keep pace with 

 solution, erosion, and chemical decomposition. The more soluble constituents of 

 the rocks are rapidly removed as they become exposed to the action of water, and 

 their total amount in a given quantity of the solvent water is seldom great. In arid 

 or semiarid regions, however, chemical action is frequently less marked than physical 

 disintegration. The soluble materials of the disintegrated rock masses accumulate 

 through periods of drought, allowing the water from subsequent rainfalls to take into 

 solution a greater relative amount than is found in waters from more humid regions. 



" In the waters studied the average amount of mineral in streams from the semiarid 

 regions was 627 parts per million ; in rivers of the humid regions it was 165 parts per 

 million. The greatest average mineral content, 2,412 parts per million, occurred^in 

 Santa Maria River, which flows through a sandstone country receiving barely 10 

 inches of rain a year. The smallest amount of mineral matter was found in Merced 

 River, 65 parts per million, or about one-fortieth of the amount for Santa Maria River. 



"As the silica content is apparently unaffected by the amount of the other dissolved 

 constituents, it may be expected that the percentage of silica in rivers of high dis- 



Water-Supply Paper 237, U. S. Geol. Survey. 



