BISSON and DAVIS: PRODUCTION OF JUVENILE CHINOOK SALMON 



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Heated Stream 



2Q. Control Stream 





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 1972 1973 



Figure 2. -Temperature conditions in the model streams. 

 Horizontal and vertical lines represent monthly means and 

 ranges, respectively. 



glass observation windows in the control stream to 

 break; as a result, the entire riffle substrate was 

 exposed for several days while new windows were 

 being installed and some losses of periphyton and 

 invertebrates occurred. One window was also 

 replaced in the heated stream at this time, neces- 

 sitating exposure of one riffle. 



Associated Flora 



Vegetation surrounding the streams included 

 red alder, Alnus nibra, and apple, Malus sp. These 

 trees contributed leaves, catkins, and flowers as 

 well as a variety of terrestrial invertebrates. 



Periphytic algae composed the bulk of living 

 plant material within the streams. The same plant 

 species were found in both heated and control 

 streams, although differences in biomass and 

 temporal succession occurred. The dominant 

 species from late spring to fall was Cladophora 

 glomerata, a filamentous green alga that attached 

 to large particles in the riffles and often trailed 

 into pool areas. Various diatoms also made up a 

 significant proportion of the flora. Two species 

 exhibited especially heavy seasonal blooms. In 

 early spring, filaments of a colonial diatom, Melo- 

 sira varians, covered both riffles and pools; this 

 species was noticeably more common in the control 

 than in the heated stream. In summer and fall 

 Synedra ulna became the dominant diatom, oc- 

 curring both in the water mass and among living 

 and dead algae on the bottom. Blue-green algae 

 were generally found in late spring and summer. 

 Calothrix and Nostoc were more abundant and 

 appeared earlier in the heated stream than in the 

 control. An unidentified dense moss colonized 

 some of the large cobbles in the riffles. Diatoms 



and desmids, in addition to plant materials from 

 terrestrial sources, were common in the drift. The 

 desmid Clostermm lunula was abundant in spring 

 and early summer and was found to be an impor- 

 tant food resource for filter-feeding invertebrates. 



Benthos and Drift 



Benthic plants and animals were sampled 



triweekly. Wire mesh baskets 20 x 20 x 6 cm 



painted with nontoxic paint and having wood 



bottoms were filled with substrate and placed 



against supporting blocks in the riffles. The mesh 



size (2 cm) was small enough to retain most of the 



particles and large enough to allow movement of 



invertebrates into and out of the baskets. Each 



riffle in the streams contained four baskets placed 



about 1 m apart from upstream to downstream 



end. One basket was selected from a different 



location in each riffle, the contents emptied into a 



bucket, and all large particles cleaned with a 



plastic scrub brush. The combined samples from 



four baskets (0.16 m- total) were then collected in a 



200-jam mesh bag. One sample was taken from a 



pool in each channel, and collected material was 



combined and preserved in 10% Formalin. 



Drifting organisms were collected triweekly by 

 means of 333-iLim mesh drift nets (Anderson 1967) 

 that were suspended at the downstream end of the 

 riffles. Two nets were fished in each stream (one 

 per channel) for a 24-h period. Samples were 

 removed and preserved at approximately sunrise 

 and sunset so that diel differences in drift rates 

 could be measured. Current velocity was measured 

 at each sampling position and the amount of water 

 passing through the nets during an interval was 

 determined by multiplying this velocity by the 

 cross sectional area of the water (330 cm^) at the 

 mouth of the net. During periods when considera- 

 ble masses of leaves or algae were present in the 

 drift, usually late summer and fall, some clogging 

 took place and the volume of water entering the 

 nets was overestimated. 



All samples were allowed to remain in Formalin 

 for 1 or 2 days, after which they were washed 

 briefly with water. Drift samples were transferred 

 directly to 70% ethanol prior to enumeration, while 

 bottom samples were first sorted to remove in- 

 vertebrates larger than 4 mm, and then subsam- 

 pled (10% by volume) and preserved in ethanol. All 

 organisms were measured to the nearest mil- 

 limeter by means of a metric grid placed on the 

 stage of the microscope. We assumed that no 



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