433 



the average, the mean of the monthly averages (.65 cm. 3 ) being 

 63 per cent, below that of all monthly averages of Quiver Lake, 

 and but a ninth of the production in adjacent channel waters. 

 The cause of this very marked contrast is to be found in the 

 relative dominance of tributary waters of recent origin and of 

 coarse aquatic vegetation in the lake, — a dominance increas- 

 ing as levels fall, — and accordingly we find in this year of low- 

 est levels the least annual production (see table on p. 429). 

 Production is not only low on the average but also lower than 

 the average in every month of record save September, when it 

 rises 22 percent, above the mean content for that month. This 

 is a month of higher river levels, and a similar tendency to in- 

 creased production is to be found in the August flood (PI. XXVI.). 



In Dogfish Lake, production in this year averages for the 

 8 months represented 3.3 cm. 3 perm. 3 — 44 percent, less than that 

 in the adjacent channel waters and 408 per cent, more than that 

 in Quiver Lake. This is 4 per cent, more than the average 

 monthly content, and 18 per cent, less than production in the 

 same months of the following year. The deficiency below 

 channel production may be attributed to the effect of vegeta- 

 tion, and the excess over that in the contiguous waters of 

 Quiver Lake to the absence of access of tributary waters of re- 

 cent origin. Production is above the average for 4 of the 8 

 months, the exceptions being April, June, August, and October. 

 The absence of overflow is apparently the cause of the suppres- 

 sion of the vernal pulses in April and Jane, and the dominance 

 of vegetation may be responsible for the low production in 

 August and October, both low-water months. The months of 

 plankton content exceeding the monthly average are 4; July 

 and September — months of flood, and consequently of impound- 

 ing and greater extent of vegetation-free water — and Novem- 

 ber and December — times of lessened growth on the part of the 

 aquatic vegetation, of rising levels, and of some decay of organic 

 matters from the summer's growth. 



Causes of like nature are the basis for the large production 

 in Flag Lake in the late autumn months, when in October-No 



