Cladophora is a branched filamentous green alga that grows 

 best in cool, flowing water (15-23°C) . In Box Elder Creek, 

 Cladophora was found only in Reach 022 (Table 4) . Cladophora 

 is closely related to Rhizocloniurn, which prefers standing and 

 warmer waters (>23°C) . Rhizocloniurn was found at all sites, 

 including Reach 022 (Table 4) . 



Euglena and its cohorts Phacus and Trachelomonas generally 

 indicate elevated concentrations of organic nutrients. These 

 algae were found throughout the study section (Table 4) . Since 

 livestock are not known to concentrate in or along Box Elder 

 Creek (Amy Chadwick, RWRP, personal communication) , this loading 

 is probably internal and natural in origin (i.e., from decaying 

 aquatic vegetation) . 



An abundance of nitrogen- fixing cyanobacteria probably 

 indicates that nitrogen, rather than phosphorus, is the nutrient 

 that is in shortest supply relative to the needs of the algae of 

 Box Elder Creek, especially in the lower reaches of the study 

 section. Box Elder Creek was unusual in that it supported three 

 or more species of Ana^baeria, a planktonic and sometimes toxic 

 cyanobacterium. The abundance of AnaJbaena and the presence of 

 several other genera of planktonic algae (e.g., the euglenoid 

 algae plus Chlamydomonas , Dinohryon, and Scenedesmus) reflect the 

 pooled nature of the Box Elder Creek channel. 



DIATOMS 



The major diatom species in Box Elder Creek are somewhat to 

 very tolerant of organic pollution and nutrient enrichment (Class 

 2 and 1 diatoms, respectively; Table 5) . Nitzschia palea is a 

 nitrogen heterotroph, meaning that it can assimilate and utilize 

 forms of organic nitrogen. Some of these major species (e.g., 

 Nitzschia filiformis, Nitzschia reversa, and Synedra fasciculata) 

 also indicate elevated concentrations of dissolved solids. 



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