339 



uary, and to the repeated flushing of the stream in the preced- 

 ing autumn. The plankton was not therefore diminished by 

 the change in chemical conditions which had progressed up to 

 the time of the sudden rise on the 28d. The average produc- 

 tion for the month (.81 cm. ^) is the largest recorded in any 

 year. Production reaches on the 21st the unparalleled midwin- 

 ter level of 1.92 cm.' — an amount in excess of any production 

 in July-November of the preceding year. This is due, it 

 seems, to the stable conditions attending the decline of the 

 January rise, to the high levels which permitted some access of 

 plankton from backwater breeding grounds, and to the freedom 

 from stagnation. The near approach of this condition is, how- 

 ever, revealed by the direction of the changes in chemical con- 

 ditions, but its arrival was prevented by the almost equally 

 catastrophic invasion of the sudden flood of the 28d, which re- 

 duced the plankton content to a minimum of .07 cm.^ on the 

 28th. Plankton production of this volume at approximately 

 freezing point, equaling that at the summer maximum in July, 

 is a striking instance of the adaptation of the plankton to the 

 extremes of temperature. 



The March pu/se has a duration of 28+ days, — from Feb. 28 

 to Mar. 28+, — with a maximum amplitude of. 54 cm.^ per m.^ on 

 the 7th. Its mean falls on the 12th, 20 days after that of the 

 preceding pulse. In the first week the rise of the last of Feb- 

 ruary ceased at 13 ft., affording overflow^ of all but the highest 

 bottoms. Levels continued to fluctuate between 13 and 14 ft. 

 during the remainder of the month, so that we have here a 

 month of sustained overflow with repeated additions of storm 

 water. The sewage and organic materials carried into the 

 stream with the first access of flood waters decline rapidly dur- 

 ing the month, as is seen (PI. XLV.) in the rapid and consider- 

 able decline of chlorine, oxygen consumed, free ammonia, and 

 organic nitrogen. Temperatures rise but 5° during the month, 

 and the average for the month is from 5° to 10° lower than that 

 in other years. The reduction in production with the initial flood 

 and the thrice-repeated influx of storm water, combined with 



