Whitford and Schumacher (1984) . These books also served as the 

 main references on the ecology of the soft algae . 



After the identification of soft algae, raw periphyton 

 samples were cleaned of organic matter using sulfuric acid, and 

 permanent diatom slides were prepared in a high refractive index 

 mounting medium following Standard Methods for the Examination of 

 Water and Wastewater (APHA 1998) . For each slide, between 437 

 and 496 diatom cells (874 to 992 valves) were counted at random 

 and identified to species. 



The following were used as the main taxonomic and 

 autecological references for the diatoms: Krammer and Lange- 

 Bertalot 1986, 1988, 1991a, 1991b; Patrick and Reimer 1966, 1975. 

 Lowe (1974) was also used extensively as an ecological reference 

 for the diatoms. Bahls et al . '(1984) provide autecological 

 information on important diatom species that live in the Southern 

 Fort Union Coal Region of Montana, which includes many of those 

 living in Box Elder Creek. 



The diatom proportional counts were used to generate an 

 array of diatom association metrics (Table 2) . A metric is a 

 characteristic of the biota that changes in some predictable way 

 with increased human influence (Barbour et al . 1999). 



One additional metric was calculated for this study: 

 percent of cells in the diatom family Epithemiaceae . This family 

 is represented in streams by two genera, Epithemia and 

 Rhopalodia, that commonly harbor endosymbiotic nitrogen- fixing 

 bluegreen algae (cyanobacteria) within their cells. A diatom 

 association that contains a large percentage of cells in these 

 genera may indicate nitrogen-limiting conditions, that is, low 

 nitrogen to phosphorus ratios (Stevenson and Pan 1999) . 



Metric values from Box Elder Creek were compared to numeric 



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