9342

• UCREFRP Catalog Number: 9342
• Author: Wynn, K. H., N. J. Bauch and N. E. Driver.
• Title: Gore Creek Watershed, Colorado--Assessment of Historical and Current Water Quantitiy, Water Quality, and Aquatic Ecology, 1968-98.
• USFW Year: 2001.
• USFW - Doc Type: Denver.
• Copyright Material: NO

Lorch (1998) found a significant correlation
(p<O.OOOl) between chloride and manganese concen-
trations in 22 stream and runoff samples in and near
Black Gore Creek. Lorch attributed this correlation to
impurities in the salt material applied to Interstate 70
during snowstorms. Cadmium, chromium, nickel, and
zinc concentrations also were highly correlated with
chloride concentrations (p<O.OOOl), whereas copper
and lead concentrations were not as highly correlated
with chloride (p-values were equal to 0.0003 and
0.0004, respectively).
Silver concentrations exceeded the 0.08-f-lg/L
aquatic-life stream standard at two sites in Gore
Creek downstream from Red Sandstone Creek in
December 1988 (Advanced Sciences, Inc., 1990).
The concentrations were 0.2 and 0.3 f-lg/L. Silver
was detected at a concentration of 0.1 f-lg/L in four
samples in 1989. Silver has not been detected in
Gore Creek downstream from Red Sandstone Creek
in the 22 samples collected since 1989; however, the
reporting limit (0.5 and 1.0 f-lg/L) for most of those
samples was higher than all of the previous silver
detections. Trace-element sampling programs that
may be conducted for sites in Gore Creek in the future
should use analytical methods for silver analyses with
a reporting limit no higher than 0.05-0.1 f-lg/L to
determine whether silver concentrations are still
a concern in Gore Creek.

Nutrients. Distributions of concentrations for
ammonia, nitrate, total nitrogen, orthophosphate, and
total phosphorus for 30 surface-water sites are repre-
sented by boxplots in figure 15. Ammonia concentra-
tions for all sites were low, with 75 percent of the
concentrations equal to or less than 0.10 mg/L
(fig. 15). The ammonia data contained a variety of
minimum reporting limits, and no discrete median
concentration could be determined because more
than one-half the data was below one of the reporting
limits. The range of nitrate concentrations was
the largest (three orders of magnitude) of the five
nutrient constituents, and the median concentration
was 0.40 mg/L. Four nitrate concentrations in samples
collected during winter 1976-77 exceeded the USEPA
drinking-water maximum contaminant level (MCL)
of 10 mg/L. Only 53 analyses were available for total
nitrogen, which had the highest median concentration
of 0.6 mg/L. The median orthophosphate concentra-
tion was 0.01 mg/L, and 90 percent of the data were
0.10 mg/L or less. Total phosphorus concentrations
were somewhat elevated. The median concentration
was 0.05 mg/L, and 25 percent of the total phosphorus
concentrations were greater than 0.12 mg/L, which
exceeds the USEPA recommended level of 0.10 mg/L
for control of eutrophication in flowing water
(U.S. Environmental Protection Agency, 1986).

100
a: (388) (619) (53) (308) (287) EXPLANATION
W
~ (35) Number of samples
:J
a: Data value
w 10
a.. ~h ;J
Cf) 75th
~ ,
<( 50th (median) Percentiles
a:
<.9 ~!J 25th
:J 10th
...J
~ i
z ~
Z' 0.1
0
~ dm
a:
~ " " ~' '-
Z 0.01
w
U
Z
0
U
0.001
Ammonia Nitrate Total Orthophosphate Total
Nitrogen Phosphorus

Figure 15. Distribution of nutrient concentrations for all surface-water sampling sites in the Gore Creek watershed.

SURFACE WATER 31