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

- total Kjeldahl nitrogen (TKN)
- nitrate-nitrogen (NO3-N)
- nitrite-nitrogen (N02-N)
- ammonia-nitrogen (NH3-N)
- total phosphorus (TP)
- orthophosphate-phosphorus (PO4-P)
Biological Parameters
Chlorophyll a.-Duplicate samples were collected
for determination of chlorophyll a concentration. A
volume of water (750 mL) for total chlorophyll a was
filtered through GF/C 47-mm diameter glass fiber
filters. Water samples for determining the <25-µm
size-fraction chlorophyll a concentration were
collected by pumping water through a 25-µm
plankton net into a 19 liter bucket. A volume of water
(750 mL) was taken from the bucket and filtered
through GF/C 47-mm diameter glass fiber filters.
Filters were individually frozen until analyzed.
Chlorophyll a was extracted by the cold-acetone
extraction method (Strickland and Parsons, 1968
[13]). The samples were analyzed on a Beckman
model 24 dual-beam spectrophotometer. Concentra-
tions were calculated for chlorophyll a according to
Strickland and Parsons (1968 [13]).
Particulate Matter.-Particulate matter was col-
lected by using a wet filtration system. Water was
pumped through selected plankton nets to separate
the sample into various size classes. The water
passing through the smallest net was also captured
(Fisher and Likens, 1973[14]; Gurtz et al., 1980[15];
Elser and Kimmel, 1985 [161). Particulate matter was
separated into three fractions: <25 µm, >25 µm, and
>505 µm. Water samples for <25-µm size-fraction
were filtered through a 25-µm plankton net into a
bucket: Two replicates were then collected from the
filtrate. From 0.75 to 5 liters of water were filtered
through preashed Gelman 47-mm diameter glass
fiber A/E filters depending on the sediment load at
each station. Three replicate samples were collected
for the >25-µm size-fraction by pumping 40 to 89
liters of water through a 25-µm Birge-style plankton
net with bucket. Replicates were transferred from
the collection bucket into 250-mL Nalgene bottles
and preserved with 4 milliliters of 100 percent
formalin. The >25-µm size-fraction samples were
analyzed for phytoplankton, zooplankton and other
organic material using a Zeiss light microscope.
Major phytoplankton and zooplankton species were
identified and counted. Three replicate samples were
-collected for >505-µm size-fraction of particulate
material (from Jan. 1987 to June 1987) with a 505-
µm mesh nylon net. The net was 3 meters long,
mounted on 0.5 meter diameter hoop, with a rope
bridle attached to the net and a 7-meter leader. A
General Oceanics model 2030 flowmeter was
mounted one-third the diameter of the mouth of each
net to estimate volume of water filtered during the
1 to 3 minute sample period. These samples were
transferred into Nalgene bottles, preserved with
formalin and major plankton taxa were identified and
counted.
The >25-µm and >505-µm size-fractions were
filtered through glass fiber A/E filters, oven dried
at 75 °C for 24 hours, weighed to determine dry
weight, ashed at 500 °C for 1 hour and weighed
for ash weight. Dry weight, ash weight, and ash-free
dry weights were calculated according to Strickland
and Parsons (1968 [13]).
RESULTS - PHASE 1
Phase 1 primary objective was to determine the
quantity, composition, and distribution of POM
within the lower Colorado River. A wide range of
parameters were examined because of their poten-
tial to effect either the quantity, composition and/
or distribution of POM. Phase 1 results follow.
Physical-Chemical Parameters
The flow pattern for the lower Colorado River is
regulated by reservoir releases governed both
seasonally and daily by downstream water require-
ments for irrigation and power production. On an
annual basis, flows are usually higher in the
summer, lower in the winter, and of moderate
magnitude during spring and fall. Adjustments for
flood control are made quarterly (Jan., Apr., July,
Oct.) based upon run-off predictions and available
reservoir storage capacity. These adjustments were
apparent during this study. Higher flows occurred
in the summer from June through August, as
expected, but they were present again in January
and April as shown on figure 2. During the study,
peak flow was nearly 700 m3/s at Davis Dam in
January 1987. Following this peak, flow gradually
decreased for the remainder of 1987, and at Davis
Dam it was 140 m3/s in November 1987.
A general reduction in flows occurred from upstream
to downstream because of water diversions. Each
of the five dams below Davis Dam serves as head-
water for the purpose of diversion. For example, the
mean flow (in cubic meters per second) immediately
below each structure for calendar year 1987 was
as follows:
- Davis Dam ................. 443
- Parker Dam ................ 375
- Palo Verde Diversion Dam ... 310
- Imperial Dam ............... 64
At Yuma (the lower-most sampling station) flow
seldom fluctuated; flows were always the lowest of
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