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
within the range of 6.5-9. Dissolved-oxygen concentrations
for all sites and samples exceeded the State standard for the
Fraser River Basin set at a minimum of 6.0 mg/L (milligrams
per liter). This is an indication that there were no detrimental
processes taking place in the streamwater that would consume
oxygen beyond a threshold that would make the water toxic to
many aquatic species.
Fecal coliform bacteria samples were collected at 9 of
the 13 study sites. The State standard for fecal coliform in the
Fraser River Basin is 200 cols/100 mL (colonies per 100 mil-
liliters), with compliance defined as when the geometric mean
of all representative water samples at a site does not exceed
the standard. The geometric mean for all nine sites ranged
from 1.6 to 10.5 cols/100 mL. A few samples exceeded the
State standard at sites 7, 8, and 9 during the summer. The
larger concentrations may be attributed to reduced streamflows
and increased recreational use, or the presence of livestock
near the headwaters of these tributaries, or both.
Un-ionized ammonia (NH3) concentrations were cal-
culated from ammonium (NH,+) concentrations for all sites
where dissolved ammonia, temperature, and pH data were
collected. The percentage of ammonium ion concentration
that is in the un-ionized form is a function of the pH and
water temperature at the time of sample collection. Because
the un-ionized form of ammonia is the most toxic to aquatic
life, it is the one on which stream standards are based. The
chronic State standard for un-ionized ammonia for the Fraser
River Basin is set at 0.2 mg/L. The acute State standard for
un-ionized ammonia is defined as a table value standard (TVS)
(Colorado Water Quality Control Commission, 2001) and is
a function of the pH and temperature of the water. The acute
TVS concentration for un-ionized ammonia was calculated
for each sample and compared to the calculated un-ionized
ammonia concentration. Un-ionized ammonia concentrations
in all streamwater samples did not exceed the calculated acute
TVS or chronic standard.
State standards for nitrite plus nitrate (as nitrogen) and
chloride in the Fraser River Basin are 10 mg/L and 250 mg/L,
respectively, and concentrations did not exceed the standards
at any site. The maximum concentration for nitrite plus nitrate
for all samples was 0.88 mg/L at site 4. The maximum concen-
tration of chloride for all samples was 75 mg/L at site 1. The
highest concentrations for chloride were at site 1 for samples
collected during the early spring. The high concentrations at
site 1 may result from spring runoff flushing salts from the
accumulated road gravel/salt applications on Berthoud Pass
during the winter.
National or local standards for total phosphorus or
orthophosphorus concentrations in streamwater have not
been established, although the U.S. Environmental Protection
Agency (USEPA) has set a recommended maximum concen-
tration of 0.1 mg/L of total phosphorus for flowing water
that does not directly discharge into a lake or reservoir
(U.S. Environmental Protection Agency, 1986). Total phos-
phorus concentrations exceeded the guideline at three sites
(sites 5, 10, and 12) during the period of record for this study
in one or two samples per site. At site 4, 58 percent (18 of
31 samples) of the samples collected exceeded the guide-
line. These large concentrations primarily happened during
February through March, before spring runoff.
Currently (2002), the USEPA is revising its guidelines on
nutrient concentrations in streams and rivers to focus on more
regionally dependent recommendations for the prevention of
eutrophication, or the excessive growth of aquatic plants.
Spatial Distribution of Selected Water-Quality
Constituents, Water Year 2000
To spatially represent the condition of the streamwater
quality in the Fraser River Basin, rankings of median concen-
trations for the nutrient constituents (ammonia, nitrite plus
nitrate, dissolved phosphorus, orthophosphorus, and total
phosphorus) and chloride were plotted in map form (fig. 2).
The median concentrations at each site were compared to the
25th, 50th, and 75th percentiles of all data collected during
the study in order to assess the spatial variance for each
constituent.
Nutrient concentrations in the Fraser River increased
downstream as water flowed through the towns of Winter
Park and Fraser. The most likely sources of these nutrients are
the three wastewater-treatment plants that discharge effluent
into the Fraser River. Some dilution and possible uptake by
biological processes of nitrite plus nitrate and dilution of total
phosphorus occurred downstream from the mouths of Ranch
and Crooked Creeks where nutrient concentrations were
lower than the Fraser River. At the most downstream site near
Granby (site 6), concentrations of nitrite plus nitrate and total
phosphorus were large, indicating that nutrient input exceeded
the physical, chemical, and biological processes that tend to
decrease nutrient concentrations and may be influenced by the
agricultural land use that is prevalent in the lower part of the
basin.
Chloride concentrations were highest in the upper
reaches of the Fraser River and tended to decrease down-
stream. Tributaries to the Fraser River had the lowest chloride
concentrations and contributed to the dilution of chloride as
water traveled downstream. A likely source for the chloride in
the upper reaches of the Fraser River is road salts applied with
gravel for traffic safety.
In addition to concentrations, chemical loading also was
evaluated for selected water-quality constituents. Although
concentration data are useful for comparison to water-quality
standards, loading data indicate the mass of a chemical trans-
ported past a site. Loading information is necessary for the
State Total Maximum Daily Load (TMDL) process and can
be useful in understanding chemical deposition in downstream
surface-water storage features. Loads only were calculated
at sites 1 through 5 on the main stem of the Fraser River.
Many possible irrigation diversions exist between sites 5
and 6 and could give rise to erroneous loading values. Values
for constituent loading were calculated by multiplying the