324 



current and discharge reduced, and plankton content below the 

 normal. The effect of prolonged low water, with its attendant 

 stability, is shown in increased plankton content, and in the 

 increased contamination by sewage, which under the ice results 

 ultimately in stagnation and great reduction of production. 



1898. 



(Tables III., X.; PI. XLV., LII.) 1 



As shown on page 167, this is a year of normally located 

 spring floods of considerable amplitude followed by a disturbed 

 summer and a considerable autumnal rise. It accordingly af- 

 fords our best opportunity for tracing the vernal movement of 

 production in flood conditions, and also another chance to note 

 the effect of- floods at times of reduced flow of the stream. 

 Both vernal and autumnal changes in temperature came on 

 gradually, and chemical conditions were free from catastrophic 

 fluctuations. The collections of this year number 52, all at 

 weekly intervals excepting only in January, when the regular 

 interval is slightly varied. They are without exception pump 

 collections. The interval between collections is so brief that 

 the cyclic movement can be traced, as a rule, and this point 

 of view will continue to control the discussion, though in this 

 year the suppression of production by floods increases the ele- 

 ment of conjecture in this method of treatment. 



The January pulse has a duration of 28 days, — from Dec. 

 28 to Jan. 25, — with a maximum amplitude of .81 cm. 3 per m. 3 

 on the 21st. Its mean falls on the 22d, 37 days after that of 

 the preceding pulse, This is a period of stagnation followed 

 by a small flood which carried off the ice-sheet. A fall in tem- 

 perature immediately closed the river again, and levels fell only 

 to continue again an interrupted rise during the last fortnight, 

 carrying the imperfect ice-sheet with it, but not breaking it up 

 and carrying it out (PI. XI. and XII. ). This second rise removed 

 the stagnation conditions in the third week, producing a sharp 

 decline in chlorine and free ammonia (PI. XLV.) toward a nor- 

 mal status. There is also a fall in the several forms of organic 



