core summer months (July and August) with maximum water temperatures of 65 ° F in 

 the upper reach compared with a high of 77 ° F in the lower reach (Appendix I). 



Discussion 



Compared with the laterally contained, boulder and bedrock (B and F2-3-type) 

 channels of the lower Blackfoot River, the upper Blackfoot River (upstream of Nevada 

 Creek) is a predominately a laterally extended, gravel-bed alluvial (C4-type) river 

 channel. This channel type is vegetative controlled, and much more subject to higher 

 natural sediment input and anthropogenic disturbance than the lower river (Rosgen 1996). 



The Blackfoot River from Lincoln to Nevada Creek supports a brown trout- 

 dominated salmonid community with low densities of brook trout, fluvial bull trout and 

 WSCT, and very low numbers of rainbow trout in the area of Nevada Creek. Beginning 

 below Lincoln, total trout densities (all salmonids) in this section of river decrease 

 progressively in the downstream direction from a total estimated density of 55 fish/1000' 

 at rm mid-point 95.3 (in 1999) to 12.7 fish/1000' at rm mid-point 63.1 in 2003 for fish 

 >6.0" (Pierce et al. 2000, Results Part II). Early juvenile fisheries studies found a similar 

 trend with higher abundances of Blackfoot River YOY brown trout below Lincoln (-30 

 fish/100') and progressively lower densities in the downstream direction (~5 fish/100' 

 between Nevada Creek and the North Fork) (Peters and Spoon 1 989). These downriver 

 trends towards lower densities appear to be a function of many interacting natural and 

 human-related factors occurring in the mainstem and tributaries. 



Consistent with higher juvenile trout densities, we found higher quality spawning 

 substrates in the upper portion of the river downstream of Lincoln. Consistent with 

 dovmward trends in juvenile abundance, we also found a progression towards smaller 

 particle sizes and less suitable spawning substrate in the downstream direction. 

 Excessive levels of "fines" limit not only embryo and emergence success (Weaver and 

 Fraley 1993), but also recruitment (Cederholm and Reid 1987), and instream production 

 of food organisms that salmonids in this portion of the study area rely on (Ingman et al 

 1990; McGuire 1991). We also recorded a bimodal distribution of particle sizes, with a 

 large amount of fine sediment in all bankfull samples, indicaUng non-point, upstream 

 erosion sources. Sources of sediment production, both natural and anthropogenic, have 

 been largely identified between Lincoln and Nevada Creek and calculated at 34,492 

 tons/year generated from eroding banks, of which 5,400 tons/year (16%) results from 

 anthropogenic sources such as grazing and road encroachment (Confluence 2003). 

 Further contributing to this impairment, involves reduced riparian health up and 

 downstream of Nevada Creek (Marler 1997, Marler and Schmetterling 1999). 



Alluvial rivers in forested areas are heavily dependant of on the input of organic 

 matter. Woody riparian communities not only help stabilized stream banks, they also 

 provide input of nutrients and cycling of LWD to the channel. LWD influences channel 

 morphology by creating channel features and habitat for salmonids. The occurrence of 

 LWD in the study decreases significantly among reaches in the downstream direction. 

 The downstream reduction in LWD abundance seems to relate to differences in 

 recruitment, containment (log jams), export rates and chaimel type, all of which vary 

 longitudinally and by reach. LWD recruitment is often higher in (middle and upper 

 reaches) alluvial channels than (lower reach) contained chaimels (Martin 2001). The 



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