the Impoundiaent of 377,000 acre -feet In k 

 reservoirs built after I910. Between I9IO 

 and 1950, the population in the Deschutes 

 River watershed increased by 120 percent, 

 the irrigated acreage by 9^ percent and 

 there was no significant industrial waste 

 contribution. All water quality consti- 

 tuents increased during this time with the 

 exception of sulfates, sodium plus potas- 

 sium and nitrates. There was no change 

 in the iron content. October, November 

 an<^ December data were not collected in 

 1952-53. If these data had been collected, 

 it is possible that all constituents with 

 the exception of sulfate would have shown 

 an increase. Percentage increases were as 

 follows: Alkalinity - 19; hardness - 27; 

 dissolved solids - 2; csilcium plus magne- 

 sium - 21; silica - 7; and chlorides - 24. 

 Sodium plus potassium had a k percent 

 decrease, nitrate 11 percent and sulfate 

 36 percent. 



Nitrates and sodium plus xx^tassium 

 should have increased during the k'i year 

 period in a river basin like the Deschutes. 

 The only explanation that can be advanced 

 for their decrease is that the comparison 

 period did not extend over a full water 

 year. 



Summary : 



A compeurison of the water quality 

 data in I9IO-II with that In 1952-56 gives 

 a general rise in all constituents. The 

 Increase in all watersheds is not the same 

 because of a difference in waste discharge, 

 water Impoundment, irrigated acreage or 

 because the soil composition differs. The 

 decrease in some values is not consistent 

 and not easily explained in most instances. 

 Irrigation return flows have caused the 

 greatest increase in water quality values. 

 These return flows can normal 1 y be expected 

 to show an increase in all constituents 

 over that in the water first applied to 

 the land. Domestic sewage and industrial 

 waste discharges will increase all consti- 

 tuents (unless the water supply is of much 

 higher quality than that in the adjacent 

 stream), pajrtlculeo-ly so in the case of 

 nitrates and chlorides. Water impoundments 

 will tend to even out water quality changes, 

 increasing the values during periods of 

 high flow and reducing them during periods 

 of low flow. 



The decrease in constituents may be 

 caused by one of the following reasons in 



cases where there has been no reduction in 

 watershed pollutants: 



1. Precipitation of Iron, silica, 

 sulfates, etc. in reservoirs or 

 irrigated lands constructed since 

 1910. 



2. Rapid leeching of constituents in 

 the new irrigation developments 

 occurring eiround I910. Propor- 

 tionately speaking, very little 

 acreage was placed under irriga- 

 tion Just prior to the I952-56 

 period of data collection. The 

 large scale Columbia Basin devel- 

 opment is contributing little 

 return flow as the groxmd water 

 table has not risen sufficiently. 



3. UpteJje of silica by diatoms living 

 in the new reservoir impoundments. 

 These diatoms are either carried 

 downstream or settle to the reser- 

 voir bottom where they are covered 

 by silt. 



h. Analytical technique differences. 



5. Incomplete yearly data for con- 

 peodson. 



6. Increased river flow between I9IO 

 and 1950. 



Alkalinity increased at all locations 

 under comparison with the largest percentage 

 increase being on the Columbia River at 

 Maryhlll, the Yakima River at Kiona and in 

 the Snake River. Hardness increased at all 

 locations excepting for the Yakima River at 

 Cle Elum. The greatest percentage increase 

 in hardness was in the Snake River, the 

 Columbia River at Maryhlll, and the Yakima 

 River at Klona. Dissolved solids, calcium 

 plus magnesium, chlorides and nitrates 

 increased at all but one station with the 

 greatest increases occurring at the same 

 station €is above. 



In no case did the water quality con- 

 stituent Increase to the point that the 

 water wets nearing the upper limit for 

 acceptability as a source of public or in- 

 dustrial water supply, source of irrigation 

 water or for the propagation of fish life. 

 A subsequent chapter in this report dis- 

 cusses the probable changes in water qual- 

 ity that may occur with future river basin 

 develofment. 



86 



