452 
BULLETIN OF THE BUREAU OF FISHERIES 
In these two figures the annual variations of hydrogen-ion concentration are very 
striking. The lowest pH value is generally in December, when it averages about 7.8. 
In late winter it rises rapid- 
ly, reaching a maximum of 
about 8.4 usually in April 
and May, from which it 
gradually drops during the 
rest of the year. The time 
of highest pH is somewhat 
later than the time of low- 
est salinity and is probably 
due to the prolific develop- 
ment of diatoms and other 
the water which 
algae 
m 
Figure 10. — Average monthly values of salinity and pH at surface and bottom (50 
feet) off Corters Point (Oyster Bay) during 2 years. Total monthly precipitation 
(Olympia) is also shown. Compare with Mud Bay, figure 11. 
contains large amounts of 
fertilizing materials such as 
nitrates, brought in by the 
inflowing drainage water 
which is becoming warmer 
during early spring. The 
warming water and the 
brighter light, associated 
with the presence of necessary chemical substances, permit the active multiplication 
of plant life, and photosynthesis rapidly removes carbonic acid, raising the pH. 
Later, however, as available fertilizing materials become fixed by the algae and as 
the water becomes warmer 
the respiratory activity of 
marine animals, including 
oysters, crustaceans, and 
others, restores a high per- 
centage of carbonic acid to 
the water, lowering the pH. 
In this regard it is of in- 
terest to call attention to 
changes in the pH and sa- 
linity of the water in a dike 
during a complete tidal 
cycle. In figure 12 the 
depth of water in a dike is 
shown throughout a 24-hour 
period in summer as related 
to the salinity and pH of 
the water. During ebb tide 
the water level became low- 
er than the dike, leaving 
it exposed at about 1:15 p. m. At about 4:45 p. m. the flood tide came up to the dike 
level. During the time the dike was exposed the pH dropped from 8.0 to 7.9, because 
of carbonic acid excreted by oysters and other organisms, and the salinity rose slightly, 
due partly to evaporation and partly to stratification of the water permitting the less 
Figure 11. — Average monthly values of salinity and pH at surface and bottom (30 feet) 
off Maple Point (Mud Bay) during 2 years. Total monthly precipitation (Olympia) 
is also shown. Compare with Oyster Bay, figure 10. 
