146 
14. These food supplies show increase not only at the mouth of the 
river, where they are no longer available to the organisms of the stream 
itself, but also in the middle course of the Illinois, where its principal 
fisheries are found. The sum of the nitrates in spring, summer, and fall 
was greater in this part of the river in 1914 than in 1899—at Havana by 
46 per cent., at Beardstown by 39 per cent., and at Meredosia by 40 per 
cent. 
15. That this greater food supply has resulted in a greater produc- 
tion of plant and animal life in the stream was to be expected, and such 
evidence as we have supports this expectation. As we have shown in 
the earlier paper already cited, the larger plankton organisms of the IIli- 
nois River at Havana in 1909 and 1910 surpassed in quantity to the cubic 
meter of water that of 1897 and 1898 by 69 per cent., and surpassed the 
average production of the three years from 1895 to 1898 by 135 per cent., 
while the like plankton of 1909 and 1910 from Quiver Lake, a bay open- 
ing broadly into the river at all stages, surpassed that of the earlier period 
by 218 per cent. Furthermore, collections of the animal forms of the 
river bottom, so made at many points down the course of the stream as 
to give the number of specimens to a square yard, show us that the rich- 
ness of the plankton and that of the bottom sediments rise and fall 
together, the part of the river containing the largest number of organisms 
from one containing the largest number from the other also. We conse- 
quently have reason to believe that the bottom organisms, from which 
many animals, fishes especially, obtain an important part of their food, 
are more abundant now than before 1900. 
It is to be noted, however, that these foregoing data of plankton pro- 
duction were obtained at a time (August, 1909, to August, 1910) when 
only about 25,000 acres of bottom-land were under levee, and that this 
area has now been increased some five or six fold; and it will presently 
be shown that plankton production must be expected to fall off rapidly 
with the draining of lakes and a reduction of the area of overflow. It is 
quite possible, therefore, that the increased plankton production due to 
the increase of sewage has now been lost as a result of reclamation 
operations. 
16. The area in the Illinois bottom protected by levees from over- 
flow and thus reclaimed for agriculture, increased between 1899 and 1914 
from 6,700 acres to 124,205 acres, and there were at the latter date 
47,250 acres more in drainage districts whose levees were not finished at 
that time. When these newer districts are completely leveed and drained, 
the original area of overflow of every spring will be reduced by 39 per 
cent., and that subject to overflow at the high-water level of 1904 will be 
reduced by 42 per cent. The effect of this restriction of overflow upon 
some of the tendencies due to the opening of the sanitary canal must be 
considerable. The river will now rise higher than before in times of 
flood and will fall lower when rainfall is deficient, but the floods will run 
off more rapidly since the leveed areas which were formerly flooded will 
no longer help impound the waters of the overflow, giving them up 
gradually to the stream. 
ee 
