12 3 4 5 6 7 

 STATION 



Figure 13. — Average concentration of dissolved oxygen 

 at each sampling station in the lower Columbia River, 

 July 1967 through December 1968. 



Dissolved Oxygen 



Dissolved oxygen ranged from 7.7 to 11.9 

 p. p.m. (fig. 7); percentage saturation was 78 to 

 116 percent. Dissolved oxygen concentration 

 decreased slightly but steadily from station 1 

 downriver to station 7 (fig. 13). 



Phosphate 



Phosphate showed seasonal variation typical 

 of a lake --high in winter and low in summer 

 (fig. 8). The highest average concentration was 

 0.35 p.p.m. in late February; the lowest was 

 0.05 p.p.m. in late July 1967. The fall increase 

 began in late September; the spring decline 

 began in late March. 



Silicate 



Silicate was generally high in winter and low 

 in summer (fig. 8). The highest average con- 

 centration in the lower river was 15.9 p.p.m., 

 in late February; the lowest was 3.6 p.p.m., in 

 early August. Silicate concentrations tended to 

 increase progressively from station 1 down- 

 river to station 7 (fig. 2). This downriver in- 

 crease was attributed to higher silicate con- 

 centration in tributaries than in the Columbia 

 River (U.S. Geological Survey, 1964). 



Calcium and Magnesium 



Neither calcium nor magnesium varied sea- 

 sonally (fig. 9). Calcium ranged from 13 to 19 



p.p.m.; magnesium was 3.5 to 6 p.p.m. Con- 

 centrations of calcium (fig. 5a) and magnesium 

 (fig. 5b) decreased downriver, which was at- 

 tributed to the low concentrations of those ions 

 in tributaries of the lower Columbia (U.S. 

 Geological Survey, 1964). 



Sodium 



In general, sodium concentrations were 

 lower in summer than in winter (fig. 9). 

 Average concentrations for all stations varied 

 from 2.9 p.p.m. in mid-July to 9.2 p.p.m. in 

 late February. 



Chlorophyll a 



Chlorophyll a content was high in summer and 

 low in winter (fig. 10). The spring bloom was 

 in late April when the average chlorophyll a 

 content for all stations was 27.5mg./m-3. The 

 smaller fall bloom was in early October, and 

 the winter low was 1.8 mg./m 3 . 



Zooplankton 



Scarola (1968) listed the species of zooplank- 

 ton collected in McNary Reservoir, which is 470 

 km. above the mouth of the Columbia River; the 

 same species were collected in the lower river. 

 Many observations by Scarola on seasonal oc- 

 currence and abundance of specific species in 

 McNary are similar to observations in the pres- 

 ent study on the same species in the lower river. 



The largest number of zooplankton orga- 

 nisms collected was on September 10 (fig. 10). 

 Numbers thendecreased, remained low through 

 the winter, and began to increase slowly in 

 early spring with small peaks in MayandJuly. 

 This same general variation in relative abun- 

 dance was seen in the occurrence of the two 

 most abundant zooplankters, Cyclopoids and 

 Bosmina (table 8). Cyclopoids began their 

 spring increase in late February and Bosmina 

 in late March. 



Calanoids, Daphnia , and Ceriodaphnia were 

 third, fourth, and fifth in abundance, respec- 

 tively, without large differences in total num- 

 bers (table 8). The numerical peak of calanoids 

 and Ceriodaphnia occurred on September 10, 

 whereas Daphnia peaked in late July. The 



Table 8. — Abundance of zooplankton at stations 

 1 to 7, July 1967 through July 1968 



10 



