521 
the plankton of the river, but even diminish the productivity 
of the river water by lowering the relative amount of its nutri- 
ent constituents. 
SPOON RIVER, 
In Spoon River we have a typical tributary of the larger 
type, from prairie country, with no unusual contamination by 
sewage or industrial wastes, draining 1,870 square miles, a little 
more than one tenth of the basin above its mouth, and dicharg- 
ing directly into the main channel. 
A detailed discussion of the environmental conditions in 
this stream and of its plankton production will be found on 
pages 340-350. It will suffice in this connection to recall the 
facts that the recent origin of the tributary waters, its greater 
turbidity, and burden of silt, all militate against plankton pro- 
duction in this tributary. 
A consideration of the chemical conditions in Spoon River 
and in the Illinois throws much light on the nutrition availa- 
ble for the support of the plankton in tributary and channel 
waters, a very important factor in the matter of plankton pro- 
duction. In the following table the averages of all analyses 
in these two streams and in Quiver Lake are given. 
CHEMICAL EXAMINATION OF WATER FROM THE ILLINOIS RIVER AT HAVANA, FROM 
SPOON RIVER NEAR ITS MOUTH, AND FROM QUIVER LAKE—PARTS PER MILLION.* 
Spoon Illinois Quiver 
River River Lake 
BTS ane 522.3 367.5 268.9 
issolved..... 2 
Residue on 16733 ah 2882 
evaporation) Loss on Total eee. 41.9 32.8 27.5 
ignition| Dissolved..... 24.4 25.1 25.6 
(Ch) TTR Ae sar eich ace SURO OOSEe — merce 3.8 21.6 4.8 
Oxyvpeniconsumeditcce cocuccic.isecien osc 14.1 10.4 5.9 
(PRIrees ammonia’ cece: «eis 32 .86 165 
| Albuminoid ammonia ....| .60 -48 2 
Nitrogen as Total organic............. Dei 1.03 61 
IPINTERIEES Ps erie crerotevare erecis ¢ -039 .147 02 
\GINTtTatesm acter crtse ctor eerie I.o1 1.58 .66 
*Data from Tables X., XI., and XIII. 
