A STUDY OF RELATIONS BETWEEN PLANT GROWTH. 335 



I Few weeds at nxoiitli l)Ut the creek was choked with weeds, the dis- 

 charge of the creek is small. No sewers empty into the creek. 



K The main inlet of the lake. Water usually clear but much contami- 

 nated by discharge from septic tanks. 



M Weedy, many algae and seed plants. Im deep. 



N No weeds at mouth but the canal Avas choked with them. Flow very 

 scanty. 



O Second largest inlet. Water clear but carrying some silt. 



P Dense Potamogeton field. 3-4m deep. 



Q Dense Potamogeton field. 2-3m deep. 



T Extremely dense vegetation. Water Shallow. 



S Peaty bottom. Described in detail below. 



R Dense field of Potamogeton. 2-3 m deep. 



U Weeds sparce. Sewers empty not far away. 



V Weeds very dense, especially filamentous algae. 



Part 1. The Effect of the Vegetation Upon the Nitrogen Content. 



A In the Pelagic Region. 



Description oj Anahj.nH Station. At the deepest place in the lake (21M) a 

 barrel was anchored, and from this place the samples were taken. The posi- 

 tion of this station is indicated by the letter C upon the map. 



Discussion of the graphs.* The analyses taken in the late autumn showed 

 a low nitrogen content due to the fact that the plants growing in the lake 

 had assimilated a large amount of nitrogen during the summer previous. 

 The following March showed a rise of everything except the nitrite which was 

 practically absent. From March until May the four nitrogen compounds — 

 nitrates, nitrites, free ammonia, and albuminoid estimated as ammonia — 

 increased, reaching a maximum in late May. 



(1) Nitrogen increased during winter and early spring due to the surplus 

 of affluents and decay over effluent and fixation by plants. 



(2) Nitrogen fell during the time the plant growth was rapidly increasing 

 and profuse (after about June 10-15.) 



(3) Storms mixed the lake by bringing into the body of the lake the more 

 concentrated water of the bays. Note data taken just after the lake was 

 rough; June 21, 29, July 13, 22. 



*In all of the graphs showing a time element the horizontal spaces represent days 

 unless the graph is interrupted. The date and the number of the analysis are shown 

 just below the base line. The amounts of the diflferent compounds are represented 

 by the vertical spaces. These values are uniform throughout. In the cases of nitrate, 

 total ammonia and total nitrogen .1 part of nitrogen per million or .1 milligram of 

 nitrogen per liter is taken as the unit. In case of nitrite, however, .01 parts of nitrogen 

 per milhon is taken as the unit. This was done in order to throw the nitrite graph 

 within comparable distance to the other graphs. This change in scale must be kept in 

 mind. 



