498 



A comparison of these two lakes indicates more nitrates in 

 Quiver than in Thompson's (.68 to .53 parts per million) — a 

 phenomenon which may be explained by the proximity of the 

 former to the river and the greater invasion by its richer (.81) wa- 

 ters. In the matter of free ammonia Thompson's Lake is much 

 the richer (.352 to .138 parts per million), though it falls con- 

 siderably below the river (.95) in this particular. The striking 

 feature of the diagrams and tables is the marked reduction in 

 nitrates and free ammonia during the period of growth, from 

 June 1 to October 1, in both lakes as contrasted with that of 

 quiescence, from October 1 to June 1. The former period is 

 one of higher temperature and less flood water, thus favoring 

 the process of decay and the concentration of its products. The 

 marked decrease in both the free ammonia and nitrates during 

 this period may be explained by the utilization of these prod- 

 ucts of decay by the chlorophyll-bearing organisms, which 

 presumably are much in excess of those of the colder period. 

 In Thompson's Lake the phytoplankton would be the principal 

 consumer, while in Quiver Lake submerged vegetation assumes 

 this role. The uniformity in the nitrates throughout this period, 

 and the reduction to a similar amount (about .2 parts per mil- 

 lion) in both lakes are significant of some sort of an equi- 

 librium between the supply furnished by decay and its utiliza- 

 tion in the growth of plants. This phenomenon of reduction 

 of nitrates to a summer equilibrium is to some extent manifest 

 in the analysis of soil waters (see Palmer, '97), and may in like 

 manner be attributed to utilization of the nitrates by vegetation. 



At first thought the volume of submerged vegetation seems 

 large in comparison with that of the phytoplankton, which it 

 replaces ; but when the permanence and persistence of the con- 

 stituent cells of Ceratophyllum are contrasted with the many 

 generations of the algae and diatoms of the plankton which 

 arise during a season's growth, the difference is less evident. 

 Furthermore, a much greater proportion of the cells of the 

 phytoplankton contribute directly to the growth of the animal 

 life of the lake. 



