462 



In Flag Lake a current is only slightly present in high 

 water and during the run-off of impounded floods. It is per- 

 haps less noticeable here than at any other station examined, 

 owing to the sheltered location and freedom from tributary re- 

 lations. Renewal is therefore least rapid and production ac- 

 cordingly high (9.23). 



In Thompson's Lake, owing to freedom from tributaries, to 

 the large volume of the lake, and to the relatively small and 

 frequently interrupted run-off, renewal is relatively infrequent 

 and incomplete. Moreover, the water which replenishes the 

 lake is drawn frojn the channel, and has a considerable propor- 

 tion of old and plankton-rich contributions from impounding 

 areas up-stream. Production is accordingly high in this area 

 (8.26). 



In Phelps Lake, current, other than that of run-off of con- 

 tained waters, is absent at levels below 10 ft., above which Spoon 

 River flood waters of recent origin find their way through the 

 lake and depress production. At other seasons current is in- 

 considerable and soon ceases, and replacement no longer occurs. 

 Impounding and production (22.35) are at their maximum 

 here. 



The net effect of the continued run-off and renewal of the 

 water in a stream or lake upon the fertility of the locality will 

 depend largely upon the inflow and discharge of nitrogenous 

 and other food materials or living organisms developed at their 

 expense. It is evident from the chemical data contained in 

 this paper that a vast amount of organic matter is continually 

 carried away from the drainage basin of the Illinois, and that 

 the amount in the streams is usually greater than that in the 

 backwaters. In general, production is less where this impov- 

 erishing process is facilitated by continuous and relatively rapid 

 replacement (Spoon River, Quivei' Lake, and the Illinois), is 

 greater where the rate of renewal and total run-off is less (Dog- 

 fish, Flag, and Thompson's lakes), and is greatest when and 

 where impounding is most complete (Phelps Lake at low wa- 

 ter) and the organic matter in suspension and solution is re- 



