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<br />0239
<br />
<br />Nutrients
<br />
<br />Nutrients collected and analyzed as part of
<br />this study were total ammonia (hereinafter referred to
<br />as ammonia), total nitrite plus nitrate lhereinafter
<br />referred to as nitrate), and total phosphorus (herein-
<br />after referred to as phosphorus). Water samples for
<br />analysis of ammonia and nitrate concentrations were
<br />collected 24 to 28 times at all 20 main-stem sites.
<br />Samples for phosphorus were collected 24 to 28 times
<br />at \ 3 main-stem sites. Tributaries generally were
<br />sampled less frequently. Different reporting limits
<br />were used for sites in the upper and lower Arkansas
<br />River Basin because nutrient samples collected in the
<br />upper Arkansas River Basin had much lower concen-
<br />trations than those in the lower basin.
<br />Potential major nutrient sources include several
<br />municipal wastewater-treatment facilities and
<br />nonpoint-source loading from agricultural return flow,
<br />domestic livestock, feedlots, and septic systems. In
<br />the upper basin, municipal wastewater sources include
<br />facilities for Leadville, Buena Vista, Salida, and the
<br />Fremont Sanitation District (Gary Soldano, Colorado
<br />Department of Public Health and Environment,
<br />written commun., 1996). The town of Leadville uses
<br />secondary wastewater treatment and discharges
<br />directly into California Gulch about one-half mile
<br />upstream from the confluence with the Arkansas River
<br />and the water-quality site on California Gulch. Buena
<br />Vista uses a lagoon system that uses evaporation and
<br />discharges to ground water. Wastewater treatment at
<br />Salida uses secondary treatment and discharges to the
<br />Arkansas River. Fremont Sanitation District uses
<br />secondary treatment for Canon City, Florence, and
<br />several penal institutions and discharges to the
<br />Arkansas River between Florence and Portland (pI. I).
<br />In the lower basin, municipal wastewater sources
<br />include wastewater-treatment facilities for Pueblo,
<br />Colorado Springs, Security Sanitation District, Wide-
<br />field, Fountain Sanitation District, Fowler, Manzanola,
<br />Rocky Ford, La Junta, Las Animas, and Lamar (Gary
<br />Soldano, Colorado Department of Public Health and
<br />Environment, written commun., 1996). The cities of
<br />Pueblo, Colorado Springs, Security, Widefield, and
<br />La Junta use secondary wastewater treatment. Colo-
<br />rado Springs has since upgraded to advanced waste-
<br />water treatment (William Vanderveer, Colorado
<br />Springs Utilities, written commun., 1996). Pueblo and
<br />La Junta discharge to the Arkansas River; Colorado
<br />Springs, Security, and Widefield discharge to Fountain
<br />
<br />Creek. Wastewater pond systems are used at the
<br />remaining locations.
<br />
<br />Ammonia
<br />
<br />Ammonia concentrations in the upper Arkansas
<br />River Basin generally increased downstream (fig. 25).
<br />Median ammonia concentrations for main-stem sites
<br />ranged from 0.010 mg/L at Leadville and Buena Vista
<br />to 0.026 mg/L at Wellsville. California Gulch, which
<br />receives wastewater discharge from Leadville, had the
<br />highest median ammonia concentration (2.15 mg/L)
<br />in the upper basin. Several other tributaries in the
<br />Leadvi lie area, including Iowa Gulch and Empire
<br />Gulch (pI. I), contributed to the elevated ammonia
<br />concentrations in the Arkansas River downstream
<br />from California Gulch. Median concentrations of
<br />ammonia increased steadily from Buena Vista to
<br />Wellsville with a significant increase (u=0.05) in
<br />concentration occurring between Salida and Wells-
<br />vi lie. Increased ammonia concentrations probably
<br />were due to discharges from wastewater facilities in
<br />the reach, although other potential sources in this
<br />reach include nonpoint-source loading from livestock
<br />and septic systems. Ammonia concentrations gener-
<br />ally decreased along the 52-mi stream reach from
<br />Wellsville to Parkdale, probably due to dilution and
<br />assimilation of nitrogen by aquatic plants. Tributary
<br />inputs, with the exception of those in the Leadville
<br />area, did not contribute substantial amounts of
<br />ammonia to the upper Arkansas River; typically,
<br />tributaries contributed less than 15 percent of the load
<br />within a stream reach.
<br />In the lower Arkansas River Basin, median
<br />ammonia concentrations at main-stem sites ranged
<br />from 0.020 mg/L at Nepesta and Las Animas to
<br />0.145 mg/L at Below John Martin Reservoir (fig. 25).
<br />Substantially larger ammonia concentrations were
<br />analyzed just downstream from Pueblo Reservoir than
<br />at Portland. Lewis and Edelmann (1994) indicated that
<br />inorganic nitrogen concentrations were larger in the
<br />deeper portions of Pueblo Reservoir because of
<br />reduced biologic uptake and releases of nitrogen from
<br />the bottom sediments. Nutrients released from the
<br />bottom sediments in deep-water withdrawal reser-
<br />voirs, like Pueblo Reservoir, may be discharged down-
<br />stream, thus increasing concentrations in the river.
<br />Ammonia concentrations decreased through the city of
<br />Pueblo, probably because of nitrification of ammonia
<br />and assimilation of ammonia by aquatic plants.
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<br />WATER QUALITY 51
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