8132

• UCREFRP Catalog Number: 8132
• Author: Lieberman, D. and T. Burke.
• Title: Limnology and Drift of Particulate Organic Matter Through the Lower Colorado River.
• USFW Year: 1991.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

flow from the Parker Division annually. By using
carefully regulated specific gravity mediums, Sollins
et al. (1985 [541) separated streambed and flood plain
detritus into fragmented plant materials and organo-
mineral particles and found that the latter comprised
the bulk of the material. However, in this study, the
authors could not determine if the organic matter
had already been adsorbed when the particles
entered the stream or if the particles had become
coated with organics while in the streambed.
At Imperial Dam, the sluicing operation indicated that
the stirring actions resulted in increased amounts
of fine POM in both the canal water and in the river
channel below the dam. This action either ground
up the larger particles (indicated by a decrease in
>25-µm POM) or loosened organic material from
mineral particles. A relationship between stirring of
the sediments and increased fine POM levels seems
apparent.
SUMMARY
During phase 2, no single factor investigated caused
the increase in total POM at downstream stations.
Minckley (1979 [10]) stated the relative importance
of backwaters to the river system was dispropor-
tionate to backwater surface area as indicated by
the greater biomass and diversity of benthos and
fishes in these habitats. The lower Colorado River
is a fairly productive and unique system with many
species (albeit exotic) of fish and wildlife. The <25-
µm size-fraction POM comprised the greatest
proportion of total POM at all stations. The majority
of this material was detritus-an important part of
the food web. Investigators have reported that
detritus provides energy for bacterial and aquatic
fauna (Wetzel and Rich, 1973 [25]); Finenko and
Zaika, 1970 [551). Minkley (1982 [12]) reported
detritus formed the major proportion of stomach
contents of threadfin shad, red shiner, mouth-
brooder, sailfin molly, and striped mullet in the lower
Colorado River, and was common in carp, channel
catfish, and yellow bullhead. From this study,
evidence supported Minckley's findings (1979 [10];
1982 [12]) that the lower Colorado River is a detrital
based trophic system that supports detritivorous
fishes. The food habits of introduced forage fishes
of the lower Colorado River do not differ substantially
from those of the same species within their native
ranges.
Conclusions derived from this study:
1. Phase 1 indicated an increase in the concen-
tration of total POM from Davis Dam downstream
to Yuma. The mean quantity of total POM in the
lower Colorado River was less than 1.50 g/m3; it
is quite comparable to results obtained for other 6
and 7 order streams in the Western United States.
The <25-µm size-fraction POM comprised the
greatest proportion of total POW
2. During phase 1, the mean annual POM concen-
tration, g/m3, was:
- Davis Dam ................. 0.80
- Parker Dam ................ .89
- Headgate Rock Dam ........ .75
- Palo Verde Diversion Dam ... .99
- Cibola ..................... 1.88
- Imperial Dam .............. 2.15
- Yuma ...................... 3.14
At Imperial Dam and Yuma, total POM concentra-
tions were not significantly different from one
another, but both were significantly different
(p<0.05) from all other upstream stations.
3. POM was dominated by:
• Detrital material and diatoms in the <25-µm size-
fraction
• Green algae in the >25-µm size-fraction
• Macrophyte fragments in the >505-µm size-
fraction
4. Possible sources for increased POM downsteam
were:
• In-stream production by autotrophs
• Input of material from backwater marshes
• Input from agricultural drains
• Input from streambed
• Input from stream bank erosion
5. Reservoirs retained inorganic matter and
released a higher percentage of POM than other
main channel stations-particularly during spring
and summer.
• Data indicate that reservoirs neither contributed
nor were a sink for POW Increases in POM observed
in Parker Dam tailwater diminished downstream
which was possibly due to primary and secondary
consumers.
• Chlorophyll a concentrations were generally
greater in Davis Dam and Parker Dam tailwaters than
in their respective downstream stations.
• In Davis Dam and Parker Dam tailwaters, 121
and 152 phytoplankton species were collected,
respectively.
• Zooplankton concentrations were greater in Davis
Dam and Parker Dam tailwaters than at all other
main channel stations.
6. POM data were inconclusive regarding the role
of backwaters during normal flows. Only during the
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