344 J. E. Hobbieetal. 



in lakes may be from 0.5x 10** ml " ' in oligotrophic water to 8x 10*^ ml " ^ 

 in eutrophic waters. The reason is that the bacteria spend most of their life 

 in an inactive or only slightly active state. They will be very active and 

 reproduce only when an algal bloom occurs or when they are in contact 

 with a detritus particle. Thus, their presence does not reflect activity and 

 their numbers do not reflect trophic states. As discussed later, bacteria are 

 also grazed upon by zooplankton which would tend to reduce the numbers 

 in rich bodies of water where animals are abundant. 



Seasonal Pattern and Growth Rates 



A characteristic seasonal pattern in populations was found in this 

 study. Three phases may be distinguished: runoff phase, growth phase, and 

 winter phase. 



There is a peak in bacterial numbers and biomass in the water during 

 the runoff phase in mid-June, a period characterized by flow of meltwater 

 from snow through the ponds. This peak is primarily a result of the input 

 of soil bacteria in the runoff water where concentrations may reach as high 

 as 4x10' cells ml"' (Boyd and Boyd 1963, Morgan and Kalff 1972). 

 Secondarily, a nutrient input from the runoff water may stimulate growth 

 of bacteria. Cell numbers in both runoff water and ponds correlate 

 significantly with volume of runoff flow during this period. As flow 

 decreases during the latter stages of this phase (late June), bacterial 

 numbers also decrease. There are two possible causes of the decrease: first, 

 the dilute pond water may be such a change for the soil bacteria that many 

 die; or second, the bacteria may be eaten by zooplankton (see later 

 discussion). Bacteria in the sediment also have an early peak which is 

 likely caused by wintertime release of nutrients. 



The growth phase encompasses the majority of the summer season. 

 During this period, beginning in late June, there is a logistic growth of the 

 population leading to a second peak in numbers in early August. An 

 average net growth constant of 4.8% day.' was calculated from standard 

 microbiological equations. This average constant does not differ 

 statistically from those of the individual planktonic populations (Table 8- 

 3). Population constants of the sediment bacteria can not be compared 

 statistically to those of the plankton but are similar (Table 8-3). 

 Comparable values recalculated from other studies include approximately 

 2.31% day"' for the bacteria at 10-m depth in Castle Lake, California 

 (Jassby 1973), and approximately 1.5, 1.7, and 1.3% day"' (spring 

 minimum to fall maximum) for the 0.5-, 4.0-, and 7.0-m depths in a 

 temperate reservoir (Francisco 1970). Because all these values are in situ 

 ones, they are minimal values that do not include the effect of predation. 



For approximately nine months of the year the ponds are totally 

 frozen and there is little bacterial activity. Total numbers decrease by an 

 order of magnitude between mid- and late August and the time of snow- 



