THE LIFE OF DKVILlS LAKE 19 



Turbidity has been determined by means of the Jackson turbid- 

 imeter described by Whipple and Jackson (1900). This ranges 

 from 70 to below 25 p p m.** of SiOg and averages sligiitly higher 

 at the surface than the bottom, the reason for which is not clear, 

 but is probably a slight excess of phytoplankton at the former level. 

 The difference, however, is slight and inconstant. The turbidity is 

 largely due to bacteria and algae (chiefly blue-greens), but consid- 

 erable quantities of amorphous matter were present in all the 

 plancton collections except in winter when only traces of it occurred. 

 This amorphous matter is probably in part the result of deteriora- 

 tion of the plancton in samples which have stood for several years, 

 and in part composed of air borne dust and more largely of the 

 flocculent ooze from the lake bottom. While I have no positive 

 evidence on this point, there is little doubt that the lake is frequent- 

 ly stirred to the bottom b}^ high winds and that the ooze thus dis- 

 turbed takes a long time to settle. 



To the action of the wind is also probably due the rather 

 uniform distribution of the plancton between surface and bottom, 

 at least at the depth of 3-4 m., where most of my collections have 

 been made, and the occasional massing of the algae along the shore 

 at certain planes, especially in the case of Nodularia, the principal 

 filamentous form in the lake. 



Horizontal currents are due to the wind, and hence are variable 

 in strength and direction. No exact measurement of these currents 

 are available but approximate determinations have been made by 

 timing the drift of submerged bottles over measured courses. 



Exact measurement of these currents would have little sig- 

 nificance unless made over a period of years to include the maxi- 

 mum, minimum and average effects of wind. To show in detail 

 wind influence it would also be necessary to make current determi- 

 nations both as to velocity and direction for all parts of the lake, 

 illustrated with chai'ts. Time and equipment have rendered such 

 detailed study impracticable, and it is further doubtful if the re- 

 sults of such a stud}^ would justify the necessary time and effort. 

 The approximate results obtained are sufficient to illustrate the im- 

 portant role which wind may play in the horizontal distribution of 

 the organisms (especially filamentous plants) in the lake. The 

 determinations were made on August 27, 1917, during a high wind, 

 and showed a current of about 13 cm. per second, or approximately 

 1.4 km. in three hours, at which rate a mass of plancton might read- 

 ily drift from one side of the lake to the other in a day. 



The determination of the penetration of light in water is a 

 matter of some difficulty. The problem has been attacked by many 

 investigators, employing several types of apparatus. The simplest 



•*In winter less than 10 ppra.. compai-ed with a silica standard. 



