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

that both divisions functioned similarly. Inorganic
nutrients and phytoplankton data also indicate a
similarity and tend to agree with the chlorophyll
results. More species of phytoplankton were
recorded at downstream stations (Havasu Delta and
Imperial Dam) than at upstream stations (Park Moabi
and DR3). More taxa of zooplankton were found
below than above Imperial Division backwaters,
although more zooplankton taxa were above the
backwater complex at Park Moabi than below at
Havasu Delta. (This latter observation may reflect
interference from reservoir releases from Davis
Dam.)
POM data were inconclusive regarding the role of
backwaters during normal flows. Only during the
August 1988 severe storm event did backwaters play
a major role. In general, these data suggest when
the river stays within its natural levee that the
backwaters remain lateral habitats and contribute
little to POM; but when the flow is increased-so
that the rivers run into and throughout the backwater
complexes-these complexes filter and collect large
materials and release fine POM back into the river
system.
Agricultural Drains
The four dams downstream from Parker Dam are
all diversion points for irrigation water, and while
some of the diverted water is removed from the valley
(e.g., All-American Canal deliveries to Imperial
Valley) much is used locally. Agricultural drains
collect and return some of this irrigation water to
the river. As noted earlier, few natural tributaries
occur along the lower river, but agricultural drains
could be considered as tributaries. Stations added
during phase 2 isolated one such irrigation return
flow, the Palo Verde Irrigation Drain, to investigate
the effects of drains on POM within the lower river
system.
Table 15 shows the mean values (during Phase 2)
for a number of parameters measured in the river
above the drain at Cibola, in the river below the drain
at DR3, and in the Palo Verde Irrigation Drain. The
above and below values are similar, but in all cases
values in the Palo Verde Irrigation Drain are
noticeably higher or lower than the other two
stations. The drain was warmer and more turbid,
had higher specific conductance, higher concentra-
tions of nitrogen and phosphorus, greater concen-
trations of chlorophyll a, and fewer phytoplankton
and zooplankton taxa as shown on figure 14. The
Palo Verde Irrigation Drain had a higher summer
water temperature, which exceeded 30.0 °C, than
any other station. The drain had a discernible effect
on- the specific conductance immediately down-
stream from the drain. Mean specific conductance,
Table 15.-Mean values for various parameters above,
in, and below Palo Verde Irrigation Drain during
phase 2 (Jan. through Aug. 1988).

Parameter Palo Verde Irrigation
Cibola Drain DR3
(above) (in-drain) (below)
Temperature °C 20.0 23.8 20.7
Turbidity, NTU 9.3 24.6 13.6
Conductivity, µS/cm 878 2268 1003
N03-N, mg/L 0.399 0.614 0.450
Total phosphorus, mg/L 0.007 0.096 0.013
Chlorophyll a, mg/m3 1.58 9.98 1.97
Phytoplankton, No. taxa 185 151 165
Zooplankton, No. taxa 9 3 8
Total dry weight, g/m3 23.71 41.88 22.97
Inorganic, g/m3 22.00 37.13 21.10
Organic, g/m3 1.71 4.75 1.87
16
PHASE 2,1988
® CLADOCERAN
M ROTIFER
0 COPEPOD
13
I
a 10
9
O
w B
f 7
6
DAVIS PARK HAVASU PARKER PALO CIROLA PALO DR3 IMPERIAL ALL LAGUNA YUMA
DAM MOA81 DELTA DAM VERDE VERDE DAM AMERICAN
DIVERSION IRRIGATION CANAL
DAM DRAIN
Figure 14.-Number of zooplankton taxa collected in
each major group during phase 2 (Jan. through Aug.
1988).
above and below the drain at Cibola and DR3, were
878 and 1003 µS/cm, respectively. Turbidity in the
Palo Verde Irrigation Drain was generally higher than
in the main channel and contributed to greater
turbidity downstream at DR3.
Concentrations of nitrogen and phosphorus in the
drain were significantly greater than concentrations
in the main river stations.
• In the Palo Verde Irrigation Drain mean P04-P
was 0.021 mg/L, mean N03-N was 0.614 mg/L,
mean NH3-N was 0.058 mg/L, and mean TKN was
0.553 mg/L.
• In the main channel mean P04-P above the drain
at Cibola and below the drain at DR3 was not
detected and 0.003 mg/L, respectively. The mean
N03-N was 0.399 and 0.450 mg/L, respectively;
20