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

TKN fluctuated between sampling periods at all
stations.
The most frequently detected nutrient at all stations
was N03-N. There were no significant differences
(p>0.05, ANOVA) in N03-N, N02-N, TKN, and NH3-N
from upstream to downstream stations reported
during phase 1. Nutrient concentrations are reported
in tables 1 OA through 15A.
Biological Analyses
In this study, particulate organic matter analyzed
generally comprised one of four main components:
phytoplankton, zooplankton, bacteria, and detritus.
Chlorophyll analyses were used as an indicator of
phytoplankton abundance. Study results for chloro-
phyll, phytoplankton, and zooplankton as they relate
to POM are given below. Species lists and overall
distributions for phytoplankton and zooplankton
include data from phases 1 and 2.
Chlorophyll a.-Chlorophyll a was analyzed to
examine how it relates to particulate organic matter.
A linear relation may occur between chlorophyll a
and POM when phytoplankton concentrations are
high. However, when the phytoplankton biomass
comprises only a small part of POM, as in this study,
the relation cannot be assumed to be linear. Mean
chlorophyll a concentrations ranged from 0.91
Mg/M3 at Palo Verde to 3.03 mg/m3 at Yuma
(table 3). Mean chlorophyll a concentration
decreased from Davis Dam to Palo Verde Diversion
Dam and increased from Cibola to Yuma. Chlorophyll
a concentrations below Davis Dam and Parker Dam
peaked in early fall (Oct.) when river flows decreased.
Conversely, chlorophyll a concentrations were
lowest in the spring (Mar. and Apr.) when water
temperatures were low and river flows increased
(fig.3). Generally, the greatest chlorophyll a concen-
trations were found in the lower most river reaches
(Imperial Dam to Yuma), but periodically high values
were observed at Davis Dam which reflect input from
Lake Mohave. The greatest chlorophyll a concen-
trations occurred in May and June 1987, at the
Imperial Dam and Yuma stations.
Table 3 shows that the <25-µm size-fraction
comprised the greatest proportion of the total
chlorophyll a concentration. This is further reflected
in table 4 which shows that the <25-µm size-fraction
comprised from 49 to 100 percent of the total
chlorophyll a concentration during each sampling
period and at all stations. Chlorophyll a concentra-
tions,from Davis Dam downstream to Palo Verde
Diversion Dam indicated no significant differences.
Chlorophyll a concentrations were significantly
greater (p<0.05, ANOVA) at Imperial Dam and Yuma
compared to all stations (table 5). A Pearson
Table 3.-Range, mean x, and standard deviation s of
chlorophyll a concentration for phase 1 (Oct. 1986
through June 1987).
<25-µm-
Station' Total size-
fraction
mg/m3
Davis Dam Range 0.73 - 3.12 0.89 - 3.13
X 1.50 1.50
S 0.66 0.66
Park Moabi Range 0.73 - 2.65 0.60 - 2.09
X 1.43 1.21
S 0.48 0.42
Parker Dam Range 0.91 - 1.94 0.91 - 2.22
X 1.30 1.30
S 0.29 0.35
Headgate Rock Dam Range 0.77 - 1.53 0.60 - 1.47
X 1.19 1.00
S 0.22 0.27
Palo Verde Diversion Range 0.60 - 1.20 0.31 - 1.18
Dam x 0.91 0.88
S 0.19 0.24
Cibola Range 1.05 - 1.66 0.75 - 1.78
X 1.36 1.22
S 0.18 0.27
Imperial Range 1.20 - 3.27 1.06 - 3.58
X 2.16 1.93
S 0.75 0.80
Yuma Range 1.20 - 5.67 1.20 - 5.11
X 3.03 2.85
S 1.12 1.19
" Number of samples at all stations is 16.

5.0 -- --

PHASE 1, 1986-1987
E 4.5 ?
? ? DAVIS DAM I
+ PALO VERDE DIVERSION DAM
E 4.0 j p IMPERIAL D AM
3.5 p YUMA
J
= 3.0
a

2.5 a i
0
J
2.0-
_j
1.51
0
1-0

0 D J F M- A M J
Figure 3.-Total chlorophyll a concentrations at Davis
Dam, Palo Verde Diversion Dam, Imperial Dam, and
Yuma during phase 1 (Oct. 1986 to June 1987).
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