PRIMARY PRODUCTIVITY 



387 



100 



en 



E 



O 



< 



112 76 11-10-76 1-25-77 2-27-77 3-23-77 



SAMPLE DATE 



4-11-77 5-19-77 6-20-77 



Fig. 3 Carbon-14 fixation rates during temperature effect ex- 

 periments. H — H, hot samples incubated at Station 1. H — C, hot 

 samples at Station 2. C — C, cold samples at Station 2. C — H, cold 

 samples at station l.t, 2 standard deviation. 



stations incubated at cooler temperatures showed lower rates of 

 productivity. On Nov. 10, Feb. 27, and May 19, there was no 

 significant difference between the primary productivity at Stations 1 

 and 2 and no temperature effect when samples were reversed. 



Figures 4 and 5 are plots of the productivity as a function of 

 temperature for Stations 1 and 2, respectively. Regression lines and 

 equations are given for each component; r^ is a measure of variance 

 in the data, and r is the Pearson product-moment correlation 

 coefficient, a measure of how well the data fit the regression line or 

 of the "scatter" in the data. On both figures the values at 25°C were 

 included in the calculations for both components. 



DISCUSSION 



The rate of carbon fixation is affected by increased temperature, 

 as evidenced by the ANOVA for 69% of the sampling dates. The 

 maximum values in September and October for primary production 

 rates could be associated with lake turnover and vertical mixing of 

 nutrients into the epilimnion after disintegration of the thermocline, 

 but this was not reflected in the chemistry of the water. This 

 hypothesis is further supported by the concurrent decrease in 

 transparency of the water during the fall of 1976. Texas lakes are 

 generally monomictic, with mixing occurring during the cool months 

 and stratification occurring during the warmer months. 



