Lowe (1974) was also used as an ecological reference for the 

 diatoms. Bahls et al . (1984) provide autecological information 

 on important diatom species that live in the Fort Union Region of 

 Montana, including many of the diatom species found in 0' Fallon 

 Creek and tributaries. 



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) . 



Metric values for 0' Fallon Creek and tributaries were 

 compared to numeric biocriteria developed for streams in the 

 Great Plains Ecoregions of Montana (Table 3) . These criteria are 

 based on metric values measured in least -impaired reference 

 streams (Bahls et al . 1992) and on metric values measured in 

 streams that are known to be impaired by various sources and 

 causes of pollution (Bahls 1993). 



The criteria in Table 3 distinguish among four levels of 

 impairment and three levels of aquatic life use support: no 

 impairment or only minor impairment (full support) ; moderate 

 impairment (partial support) ; and severe impairment (nonsupport) . 

 These impairment levels correspond to excellent, good, fair, and 

 poor biological integrity, respectively. 



QUALTIY ASSURANCE 



Several steps were taken to assure that the study results 

 are accurate and reproducible. 



Upon receipt of the samples, station and sample information 

 were recorded in a laboratory notebook and samples were assigned 

 a unique number compatible with the Montana Diatom Database, 



