WSP03775

• File Number: 8507
• Description: Rio Grande Project
• State: CO
• Basin: Rio Grande
• Date: 6/1/1996
• Title: Assessment of Metal Transport into and out of Terrace Rervoir/ Conejos County/ Colorado/ April 994 through March 1995
• Water Supply Pro - Doc Type: Publication

Copper

Generally, temporal variations in the percentage
of dissolved and suspended copper transported into
and out of Terrace Reservoir were similar to the
temporal variations for iron. During the pre-peak
snowmelt and peak snowmelt periods, generally
more than 80 percent of the copper was transported
into the reservoir in the suspended fraction (fig. 10).
However, the percentage of dissolved-copper fraction
increased to more than 90 percent during the post-peak
snowmelt period. As streamflow diminished during
the base-flow period, the percentage of dissolved-
copper fraction decreased. The two samples collected
upstream from the reservoir during the early spring
snowmelt period indicated that the percentage of
dissolved-copper fraction continued to decrease.
With the exception of the pre-peak snowmelt
period, the temporal variations in the percentage
of dissolved and suspended fraction of copper
downstream from Terrace Reservoir were similar
to the temporal variations that occurred upstream
from the reservoir (fig. 10). During the pre-peak
snowmelt period, the percentage of dissolved-
copper fraction ranged from about 35 to about
55 percent, more than two times greater than the
dissolved-copper fraction upstream from the reservoir.
During the peak snowmelt period, the percentage
of dissolved-copper fraction decreased to about
25 percent and, conversely, the percentage of
suspended fraction increased to about 75 percent.
These percentages were similar to those upstream
from the reservoir. During this period, when the
estimated reservoir residence times were short
(between 3 and 5 days), a large percentage of
copper was transported into and out of Terrace
Reservoir in the suspended fraction. As occurred
upstream from the reservoir, a marked increase
in the percentage of dissolved-copper fraction
occurred during the post-peak snowmelt and
the summer-flow periods. Between June 9 and
September 30 (the post-peak snowmelt, the
summer-flow, and the storm-runotfperiods),
almost all the copper was transported out of the
reservoir in the dissolved fraction.

Cadmium, Manganese, and ZInc

In general, almost all the cadmium was
transported into and out of the reservoir in the
dissolved form (fig. 10). During the pre-peak

snowmelt and peak snowmelt periods, most of
the manganese and zinc generally were transported
into the reservoir in the dissolved form. After about
June 9, almost all the manganese and zinc entering the
reservoir were in the dissolved form. Less temporal
variation occurred downstream from the reservoir.
In general, throughout the entire study period,
almost all the manganese was transported out
of the reservoir in the dissolved form; and, except
for the peak snowmelt period, zinc was predomi-
nant
y transported out of the reservoir in the
dissolved form.

Correlations of Metal Concentrations,
Streamflow, Specific Conductance,
and pH

A correlation coefficient is a statistic that is
frequently used to describe the strength of a relation
between two variables (Iman and Conover, 1983).
Correlation coefficients are always between -I and
+ I. Positive correlation coefficients indicate that one
variable increases as the other variable increases;
negative correlation coefficients indicate that one
variable increases as the other variable decreases.
A correlation coefficient of zero indicates that each
variable has no predictive ability for the other. The
closer the correlation coefficient is to either a -lor + I,
the stronger the relation. A correlation analysis was
made on the data collected between April 1994 and
March 1995 at sites AR34.5 and AR31.0. Pearson
correlation coefficients were computed using pH,
the logarithms of the concentrations of the metals
of concern, streamflow, and specific conductance.
Because the metal concentrations, streamflow, and
specific conductance were assumed not to be normally
distributed, logarithms were used to transform the
concentrations of metals, streamflow, and specific
conductance. The results of the correlation analysis
are listed in tables 3 and 4; correlations were consid-
ered significant when the correlation coefficient had
a probability less than 0.05. Significant correlations
that had correlation coefficients between 0.707 and
0.865 were considered to be moderately correlated;
the percentage of the explained variation was between
50 and 75 percent. Significant correlations that had
correlation coefficients between 0.866 and 0.999 were
considered to be strongly correlated; the percentage of
the explained variation was greater than 75 percent.

20 Assessment 01 Metal Transport Into and Out of Tarrace Raaarvolr, ConaJos County, Colorado,
April 1894 Through March t995 0031 7 7