378 



and 22 and Aug. 15, when phenomenal declines appeared in 

 Dogfish lake. In a similar way its production exceeds that in 

 the river in every case but one, that of May 21. Thus produc- 

 tion is prevalently higher here than in Quiver Lake and the 

 river, to which it contributes its run-off, as a result of the im- 

 pounding factor and, in this year, of the relative absence of veg- 

 etation also. The impounding permits the growth of the plank- 

 ton to utilize the nutriment derived from decay of vegetation 

 and other sources before it is carried out of the lake. 



1897. 



(Table VI., PI. XXXII.) 



There are but 6 collections here in 1897, in the first six 

 months of the year, at approximately a monthly interval. The 

 average production for this period is 2.23 cm. 3 per m. 3 , with a 

 maximum of 8.18 on Apr. 27. Since the collections are coin- 

 cident in the river, Quiver Lake, and this lake, a comparison 

 of production is facilitated. The similarity noted in the previ- 

 ous year may be traced here also, and the relationship of the 

 three areas remains in the main unchanged during this half of 

 1897. Briefly, there is low production in all three under the 

 ice in midwinter, with a slight increase in all in March, a ver- 

 nal pulse in April followed by a decline in production in May 

 in the lakes but not in the river, while in June the flood reduces 

 the plankton content in the river but changes that in the lakes 

 but little. The collections throughout the period show greater 

 production in the lakes (Dogfish, 2.23, Quiver, 2.77) than in the 

 river (average, 1.91) with the exception of the May collection 

 (Dogfish, 1.94, Quiver, 1.29, river, 5.62). This drop in plankton 

 content in the lakes below that of the stream occurs at the 

 time of greatest increase in vegetation and rapid drop in levels, 

 which increases the relative occupation by vegetation — a factor 

 from which the river is relatively free. The flood of June, 

 flushing the stream, obscures the relationships of production at 

 that season. In all collections but those of May and Feb. 26 

 Dogfish Lake contains a more abundant plankton that Quiver 



