FISHERY BULLETIN: VOL. 70, NO. 1 



14 



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STATION I A 1970 



2  1970 



STATION I o 1969 



JUNE 



JULY 



AUGUST 



Figure 4. — Secchi disc depth at Stations 1 and 2, 1970, 

 and Station 1, 1969. (Mean and standard deviation of 

 values from areal surveys shown as bars.) 



^ 0.6 



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0.2 



0.0 



STATION I A 1970 



2  1970 



STATION I o 1969 



m 

 I i 



■'A fc 



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1 A o 



JUNE 



± 



JULY 



AUGUST 



Figure 5. — Surface chlorophyll a data at Stations 1 and 

 2, 1970, and Station 1, 1969. (Mean and standard de- 

 viation of values from areal surveys shown as bars.) 



thus Station 2 chlorophyll a values from June to 

 August were generally higher than either Sta- 

 tion 1 data for 1969 or 1970; minimum mean SD 

 data (8 to 10 m) occurred between June and 

 July during a maximum in the mean chlorophyll 

 a concentration. However, 1969 chlorophyll a 

 data at Station 1 do not appear to be significantly 

 different from 1970 chlorophyll a data at the 

 same station. 



The depth distribution of chlorophyll a gen- 

 erally showed a maximum between 10 and 20 m 

 following stratification and nutrient depletion in 

 the surface layers. 



pH, CALCIUM, TOTAL CO,, AND 

 CONDUCTIVITY 



pH values were generally between 7,1 and 8.3 

 with some indication of a seasonal cycle towards 

 higher pH values in summer. Several assays 

 for calcium showed a concentration of 5 mg/liter 

 while specific conductivity was very consistent 

 at 33 ix mhos/cm, except in the immediate vi- 

 cinity of small streams entering the lake; total 

 carbon dioxide varied over a range from about 

 2.2 to 4.2 mg C/liter. 



OXYGEN 



Oxygen profiles to 200 m showed that surface 

 oxygen concentrations were between 80 and 90% 

 saturation during winter and up to 110% sat- 

 uration during summer. Deepwater oxygen 

 concentrations appeared constant at around 

 10 mg/liter or about 80% saturation. An oxy- 

 gen maximum occurred at ca. 20 m during the 

 summer. 



NITRATE, AMMONIA, PHOSPHATE, 

 AND SILICATE 



Nitrate depth profiles at Station 1 during May 

 to October, 1969 and 1970, are shown in Figure 6. 

 The general form of the two profiles is similar; 

 thus a depletion in the winter level of nitrate 

 (1.0 to 2.0 fjig at./liter) becomes apparent to- 

 wards the end of May and by the end of June 

 about 1 iJLg at. NOnN/liter has been removed from 

 the water column, to 10 m. During July and 

 August nitrate in the first 10 to 15 m is close to 

 the limit of detection, but there is a partial return 

 to winter levels during September and October. 

 Some difl["erence in the form of these events is 

 apparent between 1969 and 1970; the utilization 

 of nitrate was more rapid and apparently more 

 complete during 1970; in addition, surface ni- 

 trates did not increase in September-October 

 1970 as they did in 1969. 



Starting from a winter level of 2 yug at. NO.tN/ 

 liter, the total utilization of nitrate in the water 

 column has been determined for the periods Feb- 

 ruary to May, June, and July-August using data 

 shown in Figure 7. The accumulative amount 



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