FISHERY BULLETIN: VOL. 70, NO. 1 



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Figure 8. — Bacterial colonies per 100 ml surface lake 

 water (O) Station 2; (•) Station 1; (5) number of 

 samples in areal survey and range, I. 



some indication in the data that bacterial num- 

 bers increased by one or two orders of magnitude 

 during the latter part of June through to August. 

 Summer increases in bacterial flora have been 

 widely observed in lakes (e.g., Snow and Fred, 

 1926; Nauwerck, 1963) , and while nutrient level 

 could have affected this increase (e.g., see Bosset, 

 1965), we have no previous data on which to 

 judge the effect. 



PHYTOPLANKTON SPECIES 



Principal phytoplankton species from surface 

 samples at Station 1 and 2 during 1970 are shown 

 in Figure 9 on a relative scale. From these re- 

 sults it is apparent that the predominant algae 



during May and early June were Dinobryon, 

 Rhizosolenia, and Nitzschia. During June and 

 July Gymnodinium, Cyclotella, and the euglenoid 

 Phncus reached maximum numbers but tended 

 to decline by August. Predominant algae of late 

 summer and autumn were the chlorophyte Nan- 

 nochloris and the cyanophyte Chroococcus. Sec- 

 ond maxima in Dinobryon, Rhizosolenia, and 

 Cyclotella occurred during the winter together 

 with a maximum in Tabellaria. 



Two studies (May and June) on the depth 

 distribution of the principal species showed that 

 maxima in Rhizosolenia, Tabellaria, and Phaciis 

 were found at the bottom of the thermocline (ca. 

 20 m) ; Cyclotella and Gymnodinium maxima 

 occurred at the top of the thermocline (ca. 10 m) 

 while Nannochloris, Dinobryon, Nitzschia, and 

 Chroococcus showed maxima within the top 

 to 10 m. 



PRIMARY PRODUCTION 



Surface primary production values at Station 

 1 during 1969 and 1970 and at Station 2 during 

 1970 are shown in Figure 10; the mean and co- 

 efficient of variation of surface primary pro- 

 duction for the months of June to August are also 

 shown on each figure. The total average pri- 

 mary production in the water column to 30 m 

 at Stations 1 and 2 during 1970 was approxi- 

 mately 12 g C/m^/year compared with approx- 

 imately 6 g C/mVyear at Station 1 during 1969. 



Primary production per unit of chlorophyll a 

 at different depths for Station 1, 1969 and 1970, 

 and Station 2, 1970, are shown plotted against 

 the light intensity at the same depths in Figure 

 11. A considerable amount of scatter is appar- 

 ent in the data which is partly due to differences 

 in environmental factors as well as to the lack 

 of precision in attempting to establish photo- 

 synthesis versus light intensity relationships on 

 the basis of ecological rather than experimental 

 data. Polynomial curves were fitted to each set 

 of data using an IBM computer. The shape of 

 these curves is consistent with P vs. / relation- 

 ships obtained by physiologists under experi- 

 mental laboratory conditions and differences in 

 asymptotic values reflect differences in the nu- 

 trient supply (Ichimura and Aruga, 1964). 



18 



