Freshwater Algae 



5a 



the surface of the ponds and occupies the shallower parts of them, and it is this 

 fresh water which evaporates in the summer, thus leaving the deeper and more 

 concentrated saline layers as practically the only water to freeze at the close 

 of the summer. Like all water areas in the north, the first free water on the ice 

 in the spring owes its origin to melted snow from the surrounding slopes and 

 not to the melting of the pond ice. The pond ice melts later under the combined 



Contour interval SO feet 

 Soundints in feet made by 

 fjo/isnien, September ISIS 



Fig. 1. Map of part of Bernard harbour, Northwest Territories, showing the big lake and its 

 outlet to the sea. Survey by K. G. Chipman and J. R. Cox. 



action of the sun's rays and the erosion of the overlying fresh water. In the 

 brackish ponds under consideration there is little or no circulation of the water 

 except during the influx of the freshly melted water from outside sources, but 

 during May and early June, when this influx occurs, the deeper part which 

 contains the more saline and heavier water is one mass of ice and its subsequent 

 melting is a gradual process. By the time the conditions are favourable (no ice) 

 for a thorough mixing of the water layers in the pond, there is no influx of 

 freshly melted water and, therefore, no circulation in the pond. Consequently, 

 the heavier and more saline layers continue to be the deeper layers during the 

 summer, whilst the lighter and freshwater surface layers are subject to rapid 

 evaporation. The fresh water having evaporated during the summer, the first 

 ice formed at the beginning of the winter is brackish. The deeper and more 

 saline water freezes only as the temperature lowers with the advajice of winter. 

 . The brackish ponds just described both have an algal flora which, excluding 

 diatoms, is decidedly freshwater in character. The diatoms, which are plentiful, 

 include both freshwater and marine forms. Certain species of Pediastrum and 

 Cosmarium are very numerous in both ponds. These genera are typically fresh- 

 water, marine or brackish forms being unknown. 



From the condition of the specimens examined, I have no hesitation in 

 stating that most of them were in a healthy condition when collected. Only a 

 few individuals from bottom deposits gave the impression that they must have 

 been dead before they were preserved. Healthy specimens were collected from 

 water which was distinctly brackish when tasted. The freshwater algae found 

 in these ponds. are listed below: 



