DETECTING CUMULATIVE EFFECTS ON HEADWATER STREAMS IN THE ROUTT-NATIONAL-FOREST, COLORADO

This study evaluated the use of a modified pebble count procedure (Bev enger and King, 1995) to detect cumulative watershed effects on headwa ter streams in the Routt National Forest in northcentral Colorado. The 42 sample reaches were stratified by disturbance (reference or distur bed) and geologic terrane (granitic or mixed sedimentary-volcanic). Wa ter surface slope was a significant control on the number of fine part icles in the reference reaches in both terranes, and the data from the disturbed reaches were adjusted accordingly. The disturbed reaches in the granitic terrane generally had a higher percentage of fine partic les, and the adjusted number of fine particles was significantly corre lated with the number of road crossings. Disturbed reaches in the sedi mentary-volcanic (s-v) terrane generally did not have significantly mo re fine particles, nor were the adjusted numbers of fine particles sig nificantly correlated with any management index. The lack of significa nt trends in the s-v streams is probably due to differences in weather ing between the two rock types, and the location of the sample reach r elative to sedimentary outcrops. Two other procedures were also used t o assess cumulative watershed effects, with the Pfankuch channel stabi lity rating yielding stronger and more consistent differences between the reference and the disturbed streams than the Tarzwell substrate ra tio. We conclude that it may be difficult to define a standard referen ce condition, and that the number of mad crossings is more strongly co rrelated with the number of fine particles than equivalent clearcut ar ea.