TABLE 21. — Secchi disk visibility, July 4 to September 2, 1957, Brooks Lake 



[In meters] 



varied little seasonally and ranged from 10.5 

 to 16.7 m. (table 21). These high readings are 

 within the range for large subalpine lakes in 

 Europe (Hutchinson, 1957) but are almost 

 double those at Karluk Lake (Juday, Rich, 

 Kemmerer, and Mann, 1932) and more than 

 double those of Great Slave Lake (Rawson, 

 1956). Great Slave Lake is not directly com- 

 parable, however, because of the possible in- 

 fluence of a large turbid tributary that adds 

 inorganic silt to the lake. 



Oxygen 



Oxygen in parts per million was determined 

 by the unmodified Winkler method (American 

 Public Health Association, American Water 

 Works Association, 1946). 



Oxygen was abundant at all depths and 

 stations on all dates, suggesting that the lake's 

 water mass was in constant circulation (table 

 22). Percentage saturation values (Lagler, 

 1949: fig. 51) were always high, and most 

 samples were supersaturated even at 65 m. 

 The lowest saturation was 88 percent at 5 m. 

 on July 14. These facts would place Brooks 

 Lake in the extreme (or a -orthograde) classi- 

 fication typical of oligotrophic lakes (Hutchin- 

 son, 1957). Abundance of oxygen at all depths 

 was consistent with small vertical temperature 

 gradients (fig. 35). 



Hydrogen Ion Concentration (pH) 



A limited number of pH measurements were 

 made with a Hellige colorimetric comparator 

 at all regular sampling depths on July 14 and 

 24 and on August 3, and at 0, 7, and 15 m. 

 on September 6. The range for all samples 

 was only 7.1 to 7.3, again indicating thorough 



circulation of the lake at all depths throughout 

 the summer and uniform distribution of dis- 

 solved nutrients. 



Alkalinity and Total Hardness 



Methyl-orange alkalinity was determined 

 according to the method specified by the 

 American Public Health Association and Amer- 

 ican Water Works Association (1946: p. 31-32). 

 Total hardness from all sources was measured 

 with a standard chemical testing kit. 



Alkalinity and total hardness were each 

 determined because hardness of natural water 

 is an index of productivity. Generally, moder- 

 ately hard waters are more biologically pro- 

 ductive than soft waters (Lagler, 1952). Methyl- 

 orange (normal carbonate, CO3) hardness and 

 total hardness were measured, the former 

 being the major component of total hardness 

 in Brooks Lake. Water samples were tested 

 several times for phenolphthalein alkalinity 

 (hydroxide); none was ever detected, so it was 

 not measured regularly. 



Methyl-orange alkalinity was quite uniform 

 through the season at all depths, ranging 

 from 28.0 to 35.6 p.p.m. (table 23). Values 

 found in 1957 agree closely with those meas- 

 ured from 1947 to 1955, indicating that the 

 hardness of Brooks Lake has remained stable 

 for the past 10 years. On the basis of these 

 data. Brooks may be classified as a soft-water 

 lake, of rather low productivity. 



Primary Productivity 



The measurement of primary productivity 

 of Brooks lake through the summer by the 

 Carbon technique described by Nielsen 

 (1952) was a major phase of the overall Brooks 



56 



