370 



the contiguous but impounded and current-free waters of Dog- 

 fish Lake contain 229 times as much plankton. 



The increased production following the September flood is 

 apparent in all three localities, but reaches its highest level 

 (4.65) in Dogfish Lake, the region where the impounding factor 

 is greatest, while the least increase and quickest decline is in 

 Quiver Lake, where tributary waters of recent origin are in 

 greatest proportion. The low production in October is com- 

 mon to the three localities, reaching a slightly lower level in 

 the lakes (.13 and .52) than in the river (.57). The consider- 

 able increase in production in November-December attains the 

 highest level in Dogfish Lake (5.01 and 10.57), exceeding by 100- 

 and 17-fold that in Quiver Lake (.05 and .63), and that in the 

 river (4.37 and 2.60) by 1.2- and 4-fold. Here also the effect of 

 the quieter impounding waters of Dogfish Lake is apparent in 

 this relatively greater development. The large plankton content 

 on Dec. 19 (10.57) seems to be due to a combination of several 

 favoring environmental factors. This collection was made 

 after a steady but slight rise lasting for over five weeks, fol- 

 lowed by ten days of gentle decline in levels and contracting 

 margins of the lake. The steady rise to levels which intro- 

 duced no run-off currents through the lake established the im- 

 pounding function to its fullest, and invaded a considerable 

 stretch of margins rich in dead and decaying vegetation. There 

 is also at this season of the year less growth and more decay of 

 the Elodea and CeyatopJnjlUini which abound in the lake. The 

 collection was taken when the December flood had just be- 

 gun to rise (about 2.6 feet) and with the coml)ined action 

 of wind and waves which attended the storm then raging had 

 torn loose the vegetation and dislodged many of the smaller 

 Crustacea and insect larvae which find shelter in it. There 

 were at the time 572 Al/orehestes per m.^ adventitious in the 

 plankton. A part of this large production is thus adventitious 

 owing to disturbed hydrographic conditions. Nevertheless, 

 there still remains after such contributions are deducted a con- 

 siderable plankton of normal constitution (mainly Cladocei-a), 



