BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
315 
DIATOM COUNTS AND MAXIMUM AND MINIMUM SALINITY 
During 1916 and 1920 the salinity was high on the midwinter cruise — that is, 
January. The diatom counts for the same period were low. On the spring cruises, 
for example, April, 1916, and March, 1920, the salinity was much lower than in 
January. The diatom counts for these same periods reached the maximum for the 
year so far as our records show. During the summer cruises the salinity was a little 
higher and the diatom counts were markedly lower as a rule. In the autumn the 
data did not show clearly a correlation between lower salinities and the increased 
Figure 16.— Diatoms per liter of surface water at area A indicated by black columns. Salinity 
of water from which diatom samples were taken indicated by circles 
diatom counts known as the autumnal maximum. These relations may be seen in 
Figure 16, in which the diatom counts and salinities for surface water are shown 
graphically for area A during the cruises of 1915-16 and 1920. Similar conditions 
occurred at many areas, although often not as marked, especially in the upper part 
of the bay. Usually, however, the spring diatom maximum and the decrease in 
salinity at that time showed clearly. During the cruises of most of the year the 
numbers of diatoms were usually greater in the deep layers than at the surfaces, but 
at the time of the maxima, and especially the spring maximum, large numbers were 
