8250

• UCREFRP Catalog Number: 8250
• Author: Lamarra, V. A.
• Title: Longitudinal Variation in the Trophic Structure of the Upper Colorado River.
• USFW Year: 1999.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

A comparison of the Colorado and Gunnison river PAE values indicates that the Gunnison
had higher percent surface embeddedness than the Colorado. However, these differences
were not significant at the P=0.05 level except for riffles in fall 1995.
COLORADO RIVER-RIFFLES COLORADO RIVER-RUNS
Mean Percent Embeddedness Mean Percent Embeddedness
100% 100%

90%
90% - ................

_. ....:::::
.... ... .............

80%
w
....... .... ......_.. ..... .....
60%
• ........ .................... ......... ...
........ ...1. .........
70%

a 60%

........ -..... ....... -
o
e 60% ,.

X 40%
.... ... .._ 40%
.'. ....
30% ...... 30% ..

20% ..._. ... ....
2095
-
..... 10% .............
......... ._?
.....
-
.
Spring 1994 Fall 1994 Spring 1995 Fall 1995 Spring 1994 Fall 1994 Spring 1995 Fall 1995
PERIOD PERIOD
Figure 20. The seasonal distribution of percent to embeddedness for riffles and runs in the Colorado River (above) and the
Gunnison River (below).
The mean interstitial void volume represents the cumulative effects of the depth to
embeddedness, substrate size and the percent of the surface area that is embedded. The
comparison of the Colorado and Gunnison rivers between runs and riffles for the four sample
dates can be seen in Figure 21. Several interesting points can be made upon inspection of
these data. First, riffles had consistently more void volume than runs. There is a significant
difference (P=0.05) between habitat types, and this is evident for all sample periods.
Secondly, the void volumes for both habitats significantly decreased between the spring and
fall of 1994 and significantly increased between the spring and fall of 1995. Greatest values
for both habitats occurred in the fall of 1995. The only major difference between the
temporal distributions of the two habitats was in the spring of 1995. Void volumes increased
in riffles but decreased in runs between the fall of 1994 and the spring of 1995. The
comparison between the Gunnison and Colorado rivers for each habitat type indicated that
for a specific habitat no significant differences occurred between samples dates with the
exception of the fall of 1995 when the Colorado River had significantly higher void volumes
for both riffles and runs.
20