325 



nitrogen and a rise in nitrates and in the oxygen consumed,result 

 ing from the introduction of storm waters and silt. The temper- 

 atures remain at or near the winter minimum, rising slightly 

 with access of storm water. The total movement in levels is 6 

 ft., but the rise is so gradual that a considerable development of 

 the winter plankton appears. This brings the monthly aver- 

 age up to .45 cm. 3 per m. 3 , an amount over twice that record- 

 ed in 1899 and forty-five-fold greater than that in the flood 

 of 1896. The occasion for the greater production in this 

 year is, it seems, the greater enrichment of the waters (though 

 not in nitrates), the lower levels, and the slighter current, the 

 latter affording time for breeding even upon the slowly rising 

 flood. The same or even less rate of rise at higher levels — e. g. 

 1899 — would be attended by a more rapid current with lessened 

 time for production. 



The February pulse has a duration of 35 days, — from Jan. 

 25 to March 1, — with a maximum amplitude of .67 cm. 3 per m. 3 

 on the 3d. Its mean lies on the 7th, 16 days after that of the 

 preceding pulse. This is a month of almost continual rise, 

 there being only a slight cessation in the first week. The total 

 movement in levels is 5.1 ft., of which the greater part is above 

 bank height, and leads to extensive overflow. The large 

 amounts of silt carried (PI. XII.) testify to the extent of the 

 overflow and the access of flood waters of recent origin. These 

 result in a continued reduction in free ammonia and chlorine, 

 both of which reach approximately normal levels at the close 

 of the month. Nitrates rise with access of flood waters, and 

 the nitrites continue to decline, while the oxygen consumed 

 and organic nitrogen rise with the increase of silt. Tempera- 

 tures remain at the winter minimum throughout the month, 

 and an imperfect and disintegrating ice-sheet covers the stream 

 during a part of the month. The effect of the rising levels, 

 access of recent flood waters, increased current and great vol- 

 ume of silt is seen in the falling off of the plankton content 

 to a minimum of .02 cm 3 , per m. 3 on March 1. The incipient 

 pulse of production of an amplitude exceptional for this season 



