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

• Filter-feeder utilization of POM
• Deposition/resuspension characteristics of POM
That is, POM dynamics were not as simple as
depicted in the River Continuum Concept nor were
the effects of impoundment easily predicted.
Similarly, POM dynamics in the lower Colorado River
were an involved process.
Initially, phase 1 results indicated an increase in
concentrations of POM proceeding downstream.
Because the lower Colorado River system had only
two tributaries, downstream from Davis Dam, it
appeared to be a simple process to determine the
origin of POM matter. Many phase 1 findings
regarding POM: quantity, composition, and distribu-
tion were unremarkable or similar to other studies.
For example, the mean quantity of total POM in the
lower Colorado River was less than 1.5 g/m3 which
is quite comparable to results for other Western
United States 6 and 7 order streams shown in table
9. For the tailwaters of the two reservoirs the mean
annual POM concentration was 0.80 g/m3 for Lake
Mohave and 0.89 g/m3 for Lake Havasu. Applegate
and Mullan (1967 [27]) reported mean concentra-
tions of POM in Beaver and Bull Shoals Reservoirs
(in Arkansas) to be 1.27 and 1.07 g/m3, respectively.
Birge and Juday (1934 [24]) reported mean POM
for 57 northern Wisconsin natural lakes as
0.83 g/m3. The Colorado River data showed the
greatest percentage of POM to be fine material,
generally less than 25 µm. Numerous investigators
have reported that the majority of POM transported
in all types of streams is in this smallest size-fraction
(Maciolek, 1966 [28]; Fisher and Likens, 1973 [14];
Naiman and Sedell, 1979 [29]; Webster et al., 1979
[20]?. As noted, POM concentration below Lake
Havasu increased downstream to Yuma. Ward (1975
[30]) found POM concentrations increasing with
distance downstream from Cheesman Lake on the
South Platte River, Colorado.
Phase 2 results were surprising as they did not show
the same upstream to downstream distribution
trends as in phase 1. One feature of the system that
did not seem to change between phases 1 and 2
was concentrations of POM from reservoir tail-
waters. Dance (1981 [31]) listed the presence of
lakes/impoundments as an important factor control-
ling the concentration of POM being transported
through a river system. A number of investigators
have reported that reservoirs trap POM coming into
them, thereby modifying and disrupting the natural
downstream drift (Maciolek, 1966 [28]; Armitage,
1977 [32]; Goldman and Kimmel, 1978 [26]; Walburg
et al., 1981 [33]; Ward and Stanford, 1979 [61).
Cummins (1988 [341) explains that in the River
Continuum Concept, downstream reaches depend
on processing inefficiencies in upstream reaches.
This was a major problem in the modeling effort by
Webster et al., (1979 [20]). It was assumed that the
model reservoir would increase overall processing
efficiency of POM coming into it, but the model
reduced POM output considerably. The authors
stated this effect was not evident in published studies
because of increased autochthonous (limnoplankton)
and anthropogenic (sewage) inputs. The model did
not account for the turnover nor for the material
within the spiraling action of flow from the reservoir.
POM decomposed and processed into DOM and
dissolved nutrients, within the reservoir, can be
reprocessed with sunlight by autotrophs before
leaving the reservoir.
Lind (1971 [35]) found Lake Waco had little or no
effect on the total amount of organic matter transport
in the Bosque River. POM data collected here (lower
Colorado River study) are remarkably similar to
Lind's. Like Lake Waco, Lake Havasu did not
significantly affect the average volume of POM
passing through it. Lind reported that while the total
content of organic matter moving downstream
neither increased nor decreased, by presence of the
reservoir, the nature of the material changed. POM
entering Lake Waco was primarily sestonic detritus,
but POM leaving was living and dead limnoplankton.
As noted earlier, in phase 2 results, this appears
to be the same case in Lake Havasu-particularly
in late spring and early summer.
A similar reservoir effect upon POM composition was
reported by Maciolek and Tunzi (1968 [36]). They
found the amount of fine POM in the outlet of Laurel
Lake, California was 85 percent greater than the inlet
and that the majority of material was limnoplankton.
They credit part of this to the presence of an
epilimnetic flow from the reservoir. Lake Havasu also
has an epilimnetic flow. Rol ine and Lieberman (1985
[18]) reported that the epilimnetic release from Lake
Havasu is from the top 15 meters and results in
the discharge of phytoplankton from throughout the
euphotic zone of the reservoir.
Minckley (1979 [101) recorded both the greatest
biomass and the greatest number of taxa for
macroinvertebrates from main channel reaches of
the lower Colorado River downstream of Lake
Mohave (Mohave Valley Division) and Lake Havasu
(Parker Division). Minckley stated that the presence
of many filter-feeding invertebrates below dams in
Mohave Valley and Parker Divisions attest to the
presence of finely-divided particulate organic matter
originating from the upstream reservoirs. Similarly,
Cushing (1963 [37]) reported the reservoirs in the
Montreal River lake/stream system provided
sufficient exports of both living and nonliving
plankton to support large populations of filter-feeding
macroi nvertebrates.
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