WSP11975

• File Number: 8146.100
• Description: Pueblo Dam - Project Description
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 1/1/1986
• Author: US DoI BoR
• Title: Physical Chemical and Biological Characteristics of Pueblo Reservoir Colorado 1985 - 1986
• Water Supply Pro - Doc Type: Report/Study

2n~n
0,.),-,
0.5
Z MAY - SEPTEMBER EXPLANATION
w SURFACE
CJ
0 0.' MAXIMUM
a:
>- ~ 75TH PERCENTILE
Z
(f) 0.3
.. ME DIAN
a:
w "f /
>- ~ 25TH PERCENTILE
::J
a: 0,2 MINIMUM
w I
Il- 15 NUMBER OF
(f) 15 MEASUREMENTS
::; 0.1 8 -
..
a: BOTTOM
CJ T MAXIMUM
::J
'" 14 15 '6 ~
::; 0 75TH PERCENTILE
;;; 0.5
Z MEDIAN
w OCTOBER - APRIL
CJ 25TH PERCENTILE
0
a: 0'- MINIMUM
>-
Z '5 NUMBER OF
c;> 0,3 MEASUREMENTS
Z
..
CJ
a:
0 0.2
;;;
0
W
> 7
-' 0,'
0 7
(f)
(f) o I 7
15 7 6
38 5C 78
SITES
Figure 11, Dissolved-inorganic nitrogen concentrations in Pueblo Reservoir near the reservoir
surface and near the reservoir bottom, 1986 through 1989,

sonal differences in streamflow and subsequently in
nutrient loads.

Comparison of estimated nutrient loads in the
inflow and outflow indicate the reservoir retained about
359 tons of nitrogen and about 203 tons of phosphorus
during 1986 and 1987 (table 5). The nutrients retained
represent about 35 percent of the total nitrogen and
about 83 percent of the total phosphorus load to the res-
ervoir. Most of the total nitrogen load is in the form of
dissolved nitrogen and is less subject to removal by
sedimentation. Most of the total phosphorus load is in
the particulate form and settles from the water column
within the reservoir. About 52 percent of the total
annual nitrogen load and about 78 percent of the total
annual phosphorus load in the reservoir inflow entered
during May through September. The larger nutrient
loads during this period large]y are a function of
increased streamflow during the snowmelt- and
summer-stonn-runoff periods.

Aux of nutrients from the reservoir bottom sedi-
ments can constitute a substantial nutrient load for the
reservoir. Aux rates for inorganic nitrogen and phos-
phorus from the bollom sediments to the water column
were estimated from samples of bolt om-sediment inter-
stitial pore water that were collected from severalloca-
tions in the reservoir during ]987, 1988, and 1990.
Aux rates were calculated with the equation for Fick's
first law (Thibodeaux, 1979). In the six samples col-
lected and analyzed for inorganic nitrogen. the mean
concentration of inorganic nitrogen in the upper 1 cm
of the sediment was ].8 mgIL. The mean inorganic
nitrogen concentration in the overlying hypolimnion
was 0.03 mgIL. The mean flux rate for inorganic nitro-

gen was estimated to be about 30 mgim2/day. In four
boltom-sediment samples, the mean inorganic phos-
phorus concentration in the upper I cm of the sediment
was 0.09 mgIL. The mean inorganic phosphorus
concentration in the overlying hypolimnion was

CHEMICAL CHARACTERISTICS 31