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

The depth to embeddedness (Figure 28) demonstrated a bimodal distribution with distance
downstream. Peaks in DTE were observed in stratum 10 (10.6 cm) and stratum 3 (8.6 cm).
The shallowest depth was found in stratum 1 (0.37 cm) followed by strata 5 and 6 (5.7 and
5.8 cm, respectively). This distribution was similar to the D16 values previously described.
The Gunnison River stratum sampled had averages similar to strata 7 and 8 in the Colorado
River.
The percent surface area embedded (Figure 28) continually increased with distance
downstream. The lowest percent surface area embedded was found in the uppermost reaches
of the Colorado River ranging between 20 and 25 percent. From these levels, a steady
increase occurred with distance downstream. At stratum 2, PAE was 43 percent of that in
stratum 11. A dramatic increase occurred in stratum 1, where an average of 90 percent of the
surface area of the substrate was embedded. The Gunnison River stratum had an average of
24 percent embedded which corresponded to strata 8 and 7.
The spatial distribution of mean
interstitial void volumes followed that of
the D16 values by having steadily
deceasing volumes from stratum 11 to
stratum 6 followed by steadily
increasing volumes to stratum 3 (Figure
29). From stratum 3 to stratum 1 the
volumes went from their highest levels
(53,900 cm3/m2 in stratum 3) to their
lowest levels (12,500 cm3/m2 in stratum
1). As before, the Gunnison River
stratum corresponded to the middle
reaches (strata 7 and 8) of the Colorado
River.
Figure 29. The spatial distribution of void volumes within the
Colorado and Gunnison rivers.
Water Quality-Water quality parameters collected within each stratum during the spring and
fall of 1994-1995 were averaged by stratum and results are presented in Figure 30. These
data indicate that total phosphorus and turbidity remained relatively unchanged with the
exception of strata 1 and 11. Stratum 1 had the highest concentrations while stratum 11 had
the lowest. Inspection of the soluble nutrients (total inorganic nitrogen and orthophosphate)
indicated opposite spatial trends. Concentrations of total inorganic nitrogen (TIN) were low
in stratum 11 and increased in strata 8 and 9 and then further increased in stratum 7. The
average concentration remained constant from stratum 7 to stratum 1. Starting with a low
concentration (<30 mg/liter) in strata 10 and 11, orthophosphate initially increased to a
maximum in stratum 9, followed by a gradual decrease from stratum 9 to stratum 1 (Figure
30). Based upon a stoichiometric ratio (TIN/OP) of 1511, strata 9, 10 and 11 are nitrogen
limited while strata 1 through 8 are phosphate limited.
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