JULY JULY JULY AUG AUG. AUG. SEPT SEPT OCT. 

 4 I 14 I 2 4l 3 I 13 I 23 I 3 |I3.23| 3 



Station I 



„ t,. , ... U,. * ^,U ,.. / . .l„.. .. . t . |.. . . . . u.^. t.. .^ , ..ai ^. ,-,l , . . .. , M4. . . .. .H ^g 



fPOCKET 



Station n ^ " iS 



hr 5' 



.: r i / l / l / l/V 



•.fmmrmijjii.. 



•i Mm. T' v 'Mt-ir^ w OoiJOM 



a 10 



Station HI 





30 60 50 60 50 60 SO 60 50 60 50 60 50 60 50 60 SO 60 



TEMPERATURE C F.) 



Figure 35. — Brooks Lake vertical temperatures, sta- 

 tions I, II. and III, July to October 1957. 



or III. This corresponds with greater zoo- 

 plankton densities at station II over those of I 

 and III (figs. 28 and 29). It is conjectured 

 that station II Is in a region of upwelllng of 

 cold water masses originating from the depths. 

 From the bottom configuration, as indicated 

 by the contour map (fig. 34), and from the 

 action of submerged gill nets at station II, 

 such upwelling is likely when strong winds 

 sweep the lake. Further study is needed to 

 learn the reasons for the measured differences 

 between stations II and III. 



Phosphorus 



Soluble phosphorus was measured with a 

 Klett-Summerson photoelectric colorimeter 

 as described by P. R. Nelson. * Great care 

 was required in analysis because of micro- 

 quantities present and the danger of contamina- 

 tion. 



Phosphorus and nitrogen (together with car- 

 bon and hydrogen) are the principal consti- 

 tuents of living cells and are usually present 

 in extremely small quantities in lake waters. 

 It is likely that if a nutrient deficiency were 

 present, one of these would be in short supply. 



■♦Compilation of field methods for water analysis. 

 1952. [Unpublished typewritten report.] On fileatBCF 

 Biological Laboratory, Auke Bay, Alaska. 



The range of phosphorus was from to 

 0.0152 p.p.m., and amounts were quite uniform 

 at all depths and dates (table 17). These data 

 indicate that when relatively few spawners 

 are present, as was the case in 1957, car- 

 casses of spawners do not contribute a meas- 

 urable amount of phosphorus to the lake. On 

 the contrary, phosphorus declined slightly 

 through the season, with the least amounts 

 on September 3. This conclusion was also 

 reached in Cultus Lake studies by Ricker 

 (1937). 



Organic bottom sediments probably play a 

 more important part in supplying available 

 phosphorus than do salmon carcasses. Our 

 quantitative phytoplankton sampling indicates 

 that the biomass of the standing crop of 

 phytoplankton must be much greater than that 

 of salmon carcasses at any one time, and over 

 a period of a year it must be vastly greater. 

 It is probable that renewal of the supply of 

 phosphorus is not dependent on salmon car- 

 casses in a large lake such as Brooks, with 

 relatively abundant plankton and small salmon 

 runs. 



Since phosphorus is present throughout the 

 season, it is probably not a limiting factor on 

 plankton production. Phosphorus is one of the 

 principal living cell constituents and is taken 

 up and readily stored by phytoplankton (Ruttner, 

 1953). If it were a limiting factor, measure- 

 ments would be zero because phytoplankton 

 would utilize all of it as soon as it appeared. 

 Thus, if it is present in detectable quantities, 

 it may be regarded as being in adequate sup- 

 ply. 



Nitrogen 



Nitrite nitrogen was measured with a Klett- 

 Summerson photoelectric colorimeter accord- 

 ing to directions in Nelson's compilation. * As 

 with phosphorus, great care was required in 

 the analysis. 



Nitrite ranged from to 0.0050 p.p.m. and 

 was relatively uniform in quantity and vertical 



5 See footnote 4. 



52 



