9410

• UCREFRP Catalog Number: 9410
• Author: Wydoski, R. S. and E. J. Wick.
• Title: Ecological Value of Floodplain Habitats to Razorback Suckers in the Upper Colorado River Basin.
• USFW Year: 1998.
• USFW - Doc Type: Denver.
• Copyright Material: NO

Table 3. Mean number of aquatic organisms per liter (combined species of
zooplankton and free-swimming benthic invertebrates) collected
in five vertical tows with a 20.3 cm plankton net from three
backwaters in the lower Green River during 1997. ~/

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Date Millard Canyon Anderson Canyon Holeman Canyon
May 1 6.2 2.4 6.6
May 8 0.5 5.8 5.2
May 15 8.4 3.6 3.4
May 22 29.0 7.6 6.2
May 29 30.9 6.8 6.8
Jun 5 53.7 7.6 14.9
Jun J.2 124.1 19.2 26.2
Jul 10 95.8
~/ Data from Nance (1997) ; mean values were rounded.
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the literature of benthos in running waters (Hynes 1970; Welcomme 1985)
that document a higher species diversity and often larger numbers of
benthic macroinvertebrates occur in riffles with large rock, cobble, or
gravel substrates than river reaches with sand and silt substrates.
Benthic invertebrates that inhabit riffles colonize downstream reaches by
movement through the substrate, displacement by high streamflows, and
drift. However, upstream movement is hindered by long reaches of sand-
silt substrates and streamflows 12 cm/s or greater (Luedtke and Brusven
1970). Generally, upstream movement by benthic invertebrates is 5 to 30%
of the downstream drift (Bishop and Hynes 1969). Benthic invertebrates
produced in floodplain habitats move or are carried by currents and can
provide a substantial part of the food base for fish in the main channel
and backwaters (Eckblad et al. 1984).

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Although species diversity of benthic invertebrates in low velocity
habitats with sand and silt substrates of the Upper Colorado River Basin
is less, the numbers of certain taxa (e.g, chironomids) can be very high.
Chironomids constitute a significant part of the diets of larger larvae,
juveniles, and even adult endangered fishes in low velocity habitats of
the Upper Basin so that taxon is emphasized in this discussion of benthic
production. The upper part of the range for chironomids was 4,150 per m2
in the main channel, 31,125 per m2 in backwaters, and 23,055 per m2 in
floodplain habitats of Upper Basin rivers (Table 4). More detail of the
mean numbers of chironomids in different habitats of the Upper Basin are
summarized in Appendices 1 and 2.

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The numbers of chironomids, found in the main channel of the middle Green
River, ranged between 360 to 4,645 organisms/m2 and the numbers ranged
from 4,820 to 28,860 organisms/m2 for backwater habitats in 1987 (Appendix
1; Grabowski and Hiebert 1989). In 1988, Grabowski and Hiebert reported
the range in numbers of chironomids between 280 and 5,000 organisms/m2 for
the main channel of the river and between 3,330 and 28,890 organisms/m2 in
backwater habitats. Obviously, the backwater habitats were more

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