374 



lections determining the direction of the change in production 

 are given under the date of the later collection, and the posi- 

 tion of the entries also indicates the direction of the change. 



VARIATIONS IN THE MOVEMENT OF PRODUCTION IN DOGFISH AND QUIVER LAKES, 1896. 



Sept. 16 



Dog-fish Lake. 

 Quiver Lake... 



" Apr. 24 



May 8 



May 16-19 



May 21-22 



July 3 



Aug. 15 



Aug. 29 



20.35 to 

 19.50 



16.76 

 16.32 to 



13.39 to 

 13.06 



8.14 

 4.24 to 



18.40 

 13.06 to 



8.14 to 

 .51 



18. 40 to 

 .36 



.99 

 .51 to 



1.58 

 1.14 to 



.68 to 

 .49 



11.25 

 3.88 to 



4.36 to 

 3.42 



1.18 

 .75 to 



1.60 to 



.72 



3.06 

 1.18 "o 



.72 to 



.55 



In almost every case these exceptions to the precise simi- 

 larity of movement in production in the two lakes can be cor- 

 related directly with some disturbing environmental factor 

 potent in one and not equally so in the other, that is, to local 

 disturbance in the environmental similarity, as follows: The 

 exception on April 24 is due to the earlier appearance of the 

 summit of the vernal pulse of production in Dogfish Lake, and 

 this in turn is correlated with the greater proportion of shoal 

 waters in Dogfish and the greater access of spring water in 

 Quiver, both factors favoring the more rapid and complete 

 warming up of Dogfish waters. As has been repeatedly 

 pointed out, the thermal rise deflects towards itself the vernal 

 rise in production. 



Conditions on May 8, when Quiver Lake production doubles 

 and that in Dogfish Lake falls slightly, are to be explained by 

 the different effect which the hydrographic changes have at the 

 two stations. At stages existing at the first of the month 

 (7 ft.) there is not sufficient overflow to carry any considera- 

 ble current of warm backwaters to the southward down through 

 the lake to the river. The content is largely of local impound- 

 ing. The slight rise at that time (PI. XXXI.) would therefore 

 tend to increase the local reservoir action, and creek and 

 spring waters would most naturally be impounded along the 

 usual line of their run-off, in which our Quiver Lake station 

 lies (PI. II.), while the plankton-rich backwaters of Dogfish 

 Lake are held back, hence the low production in Quiver Lake 



