7729

• UCREFRP Catalog Number: 7729
• Author: Valdez, R. A., W. J. Masslich and A. Wasowicz.
• Title: Annual Summary Report - 1990\
• USFW Year: 1991.
• Copyright Material: NO

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IDS

Levels of total dissolved solids (IDS) in the Dolores River ranged from 226 - 6,320 mgIL during
1990. IDS were generally much higher on Trip 1 due to low flows which concentrated dissolved
solids. IDS decreased below the confluence of the San Miguel River on Trip 1, due to dilution of
dissolved solids by the flows of the San Miguel River. High IDS above the confluence of the San
Miguel are related to saline groundwater inflow into the Dolores River across the Paradox Valley.
The San Miguel River also had a noticeable diluting effect on IDS on trips 2 and 3. Maximum levels
of IDS recorded below the confluence of the San Miguel were 2,595 mg/L on trip 1 in 1990,
compared to 3,822 mg/L in 1975 and 3,020 mg/L in 1960 (Miller 1976, USPHS 1961). Rawson and
Moore (1944) found that several common freshwater fish species survived exposure to 10,000 mg/L
IDS. Pimentel and Bulkley (1983) determined that Colorado squawfish avoid IDS concentrations
greater than 4,400 mg/l. No Criteria has been set for IDS by the EP A

Ammonia

Ammonia values varied from 0.10 mg NH3-N fL on Trip 2 to 0.963 on Trip 1. Again, high values
associated with Trip 1 were probably related to the extremely low flows during this period. No
pattern was found between study reaches, although increases in ammonia concentrations below the
San Miguel River on Trips 1 and 3 suggest that the San Miguel River is contributing to the increased
ammonia concentrations in the Dolores River, dependent on dilution flows. Ammonia levels appear
to have declined in the Dolores River within the last 15 years. Levels up to 9.0 mg NH3fL below the
San Miguel confluence were observed by Miller (1976) in 1975. Levels of <0.2 to 0.963 mg/L were
observed during 1990. Ammonia levels as high as 23.5 mg NH3fL were observed in the San Miguel
River below Uravan in 1975. Ammonia was reported to be acutely toxic to freshwater organisms at
concentrations ranging from 0.53 to 22.8 mg/L NH3 for 19 invertebrate species representing 14
families and 16 genera, and from 0.083 to 1.09 mg/L NH3 for 29 fish species from 9 families and 18
genera (EP A 1986). Among fish species, reported 96-hr LC50 for salmonids ranged from 0.083 to
1.09 mg/L and from 0.14 to 4.60 mg/L NH3 for non-salmonids. Ammonia toxicity varies with
temperature and pH, but based on conditions in the Dolores in 1990 the EPA Water Quality Criteria
for a one-hour average concentration of ammonia would range from about 2.3 to 11.4 mg/L NH3.

Nitrate

Nitrate values ranged from 0.03 and 1.26 mg N03.N fL in the Dolores River during 1990.
Consistently high levels of nitrates found above the confluence of the San Miguel suggest that nitrates
may be entering the system across the Paradox Valley. Highest nitrate values were observed during
Trip 1 and were probably associated with the poor dilution during base flows. The highest nitrate
concentration measured on the Dolores River in 1960 was 3.6 mg N03fL near Slick Rock (USPHS
1961). On the San Miguel River near the confluence, nitrate levels were 0.70 and 0.16 mg NcYfL
in 1960 and 1990, respectively. The 7-day LCSO for fingerling rainbow trout was 1,060 mg NcY-N
fL (Westin 1974), and Knepp and Arkin (1973) concluded that levels of nitrate nitrogen at or below
90 mg/L would have no adverse effects on warmwater fish. No EP A criteria have been established.

Phosphate

Concentrations ranged from 0.01 - 3.19 mg P04.p fL on trips 1 and 3, respectively. On trips 2 and
3 phosphate levels were lowest near Slick Rock and highest at the station above the confluence of

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