9623

• UCREFRP Catalog Number: 9623
• Author: Bails, J. B.
• Title: Streamwater Quality at Selected Sites in the Fraser Basin, Grand County, Colorado, Water Years 1991-2000.
• USFW Year: 2003.
• USFW - Doc Type: \
• Copyright Material: NO

Streamwater-Quality Results
associated inputs to the wastewater-treatment plants during
the ski season. With the onset of high flow at the end of the
ski season, loads decreased significantly. Chloride loading,
however, seems to more closely reflect streamflow condi-
tions. This scenario supports the concept that the source of
chloride in the river is a combination of a nonpoint source,
possibly from the salt and gravel applications on the road-
ways in the basin and discharges from the wastewater-
treatment plants. The reduction in loads during early spring
runoff is an indication that either most of the road salts are
removed during initial runoff or runoff from near the highway
is reduced.
Temporal Trends
The seasonal Kendall test (Helsel and Hirsh, 1992) was
used to test for trends in water quality (table 4). Trend analysis
was completed on sites 1--4 on the main stem of the Fraser
River. These sites had at least 5 years of monthly data. Trend
analysis was performed on ammonia, nitrite plus nitrate,
and orthophosphorus because these constituents are directly
related to biological responses in the river. The null hypothesis
for trend testing in this report is no change in concentration
over time when compared seasonally. The null hypothesis is
rejected, indicating that there is a trend, if the p-value (or
probability value) of the test is less than the alpha level, which
for this report is set at 0.05. This alpha level (or acceptable
error) requirement means that there is a 5-percent chance that
a trend is mistakenly identified and the null hypothesis is true
(Helsel and Hirsch, 1992). Trend analysis was done on the
raw, or unadjusted, concentrations to assess trends in ambi-
ent stream conditions, which is desirable in relation to human
or aquatic organism water use. Where applicable, a LOcally
WEighted Scatterplot Smoothing (LOWESS) procedure
(Cleveland, 1979) was used to flow-adjust concentrations
before trend analysis. This procedure will account for vari-
ability of chemical concentrations due to streamflow (flow)
and provide greater insight about the sources of nutrients to
the Fraser River. The LOWESS smoothing procedure and
recalculation of trends were performed only on data sets that
contained less than 10 percent censored (less than the labora-
tory minimum reporting level) concentrations. If a trend was
calculated on the flow-adjusted concentrations, the trend slope
(the magnitude of the trend expressed in units per year) was
listed only to indicate relative magnitude because the trend
analyses for these sites were computed on flow-adjusted con-
centrations and not the raw concentrations. Where some of the
concentrations were censored (below the laboratory reporting
level), trend analyses on the raw data were performed twice
at each site, once with the censored data set at the minimum
reporting level and again with the censored data set to zero. In
Wastewater-treatment
plant locations

020
0
0.7 . Site 4 .
Site 5
-a Ammonia 0.018
0
6 f Nitrite plus nitrate
.
Q -0- Dissolved phosphorus
0 - Orthophosphorus 0.016 Q

-0- Total phosphorus Q
w
EL 0.5
-4- Chloride
0.014 0
a

Z

0 Z
1-- 0.012 O
Z 0.4 Z
Site 3
0.010
Q d
O Site 2 Q
J 0.3 O
Lu 0.008 -J
0 Z
O Site 1 w
• 0.006
J 0.2
2 ?
U
0.004 Z
0.1
0.002
0
0
28 26 24 22 20 18 16 14 12 10
MILES UPSTREAM OF MOUTH OF THE FRASER RIVER
Figure 3. Downstream median instantaneous load of selected constituents in the Fraser
River Basin, 1991-2000.