BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
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ation in salinity from about 19.00 to 30.00 grams per liter in the region of areas G, F, 
and E, w hil e near Balitmore at area U there is a variation from about 3.00 to 11.00 
grams per liter. So far as our records show (January, March, April, June, July, Sep- 
tember, 1916; January, March, May, July, August, October, December, 1920; Jan- 
uary, March-April, May-June, 1921; and January, March, 1922), the surface salin- 
ity never reached 31.00 at the mouth, but occasionally it was reduced to less than 
19.00 — for example 18.36 at G in March, 1922. On the other hand, at area U the 
surface salinity never reached 12.00 and sometimes dropped below 3.00— -for example 
2.26 in May, 1920. It will be seen then that the range of surface salinity from head 
to mouth may be large, for example 2.26 at U to 25.40 at F in May, 1920. 
SURFACE SALINITY FROM MOUTH TO HEAD 
A good general idea of the variation of the surface salinity from the mouth to the 
head of Chesapeake Bay may be obtained from Figure 2, which is a map 3 of the bay 
showing the surface salinity for a cruise in August, 1920. During this cruise the range 
of surface salinity was from 28.94 (area E ) at the mouth to 4.75 (area TJ ) at the head. 
The arrangement of the isohalines 4 shows clearly that the most saline surface water 
was uniformly on the east side of the bay from head to mouth. Similar maps for 
other months are shown in Figures 3, 4, 5, and 6. 
The greatest decrease per unit of distance in surface salinity took place between 
E, F, G, and D, C, B, A (from 28.94 to about 20.00 in a distance of about 15 miles) 
near the mouth, and this is indicated by the crowding of the isohalines. (August, 
1920). A similar condition was noted in the Baltic Sea by Pettersson (1894). Next 
in order was that between Y, Z, and U near the head. The decrease from the mouth 
of the Potomac River to Y, Z, as well as from D, C, B, A to the Potomac River was 
very gradual. A study of the data from the other cruises shows that while there is 
considerable variability in the rate of decrease from cruise to cruise in the regions 
mentioned, the condition during August is an average one. The amount of decrease 
in salinity per unit of distance from J, /, K into the mouth of the Potomac River at 
N, M, N' is usually rather high, but it will be noted by referring to the map (fig. 2) 
for August, 1920, that the isohalines do not show such a condition. This is probably 
due to the unusual time elapsing between the times of making the observations at 
J, I, K, and N, M, N'. 
VARIATION OF SURFACE SALINITY ACROSS BAY 
One of the most striking characteristics of part of Chesapeake Bay is the higher 
surface salinity on the eastern than on the western side of the bay (Cowles, 1925). 
Such a distribution of salinity is most marked from the region of James Island to the 
mouth, although during certain cruises — for example June 1916, January, August, 
and December, 1920 — the surface salinities obtained on the eastern side of the bay 
were highest from the mouth to the region of Baltimore. A study of the profiles 
indicates that this condition is due to the fact that the deep-water channel which 
contains the most saline bottom water lies on this side throughout most of its extent 
and to the fact that a large volume of fresh water from the rivers of the western shore 
presses the more saline water toward the eastern shore. Now, taking up in order 
3 No high degree of accuracy can be claimed for such a map, since the water samples could not be collected simultaneously at the 
stations and since the salinity fluctuates somewhat back and forth at a station with the tide. However, in the opinion of the writer 
the map presents a good general picture of the distribution of the surface salinity during the period of the cruise, 
i An isohaline is a line connecting points of the same salinity in a plane. 
