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<br />
<br />which is about 6,2 miles downstream from the
<br />Craig Waste Water Treatment Plant, the effects of
<br />photosynthesis increased slightly, and pH rose to
<br />8,80, Respiration plus oxidation of organic matter
<br />became dominant at Yampa River at Deerlodge
<br />Park in Dinosaur National Monument, where pH
<br />was 8,51, dissolved oxygen concentration was at
<br />109 percent of saturation, and CO2 was at 189
<br />percent of saturation, Respiration plus oxidation
<br />of organic matter, though diminished, apparently
<br />extended to the mouth of the Yampa River.
<br />Diurnal measurements on the Yampa River
<br />during August 23-26,1999, show that the effects
<br />of photosynthesis and respiration plus oxidation
<br />of organic matter decreased downstream with
<br />distance from the developed urban area in the
<br />eastern part of the basin, Larger night-time values
<br />of pH in Dinosaur National Monument at Deer-
<br />lodge Park and at the mouth of the Yampa River
<br />indicate that source waters varied with respect to
<br />capacity for respiration plus oxidation and photo-
<br />synthesis, that photosynthesis was minor, and that
<br />pH was largely controlled by respiration plus
<br />oxidation of organic matter,
<br />Synoptic sampling was repeated during
<br />March 13-16, 2000, when discharge was larger in
<br />response to late-winter melting of snow and ice at
<br />lower altitudes in the basin, Concentrations of
<br />nitrite plus nitrate were about 9 times greater in
<br />the Yampa River during March 2000 than during
<br />August 1999, and the largest increase (greater
<br />than 1,200 percent) was at Yampa River below
<br />Craig, At and downstream from Steamboat
<br />Springs, Colorado, pH at Yampa River sites aver-
<br />aged 8,85 during synoptic sampling in March
<br />2000 compared to 8,70 in August 1999, with the
<br />
<br />
<br />Evaluation of Trends in pH in the Yampa River,
<br />Northwestern Colorado, 1950-2000
<br />
<br />By Daniel 1. Chafin
<br />
<br />Abstract
<br />
<br />In 1999, the V,S, Geological Survey began
<br />a study of pH trends in the Yampa River from near
<br />its headwaters to its mouth, The study was
<br />prompted by an apparent historical increase in
<br />measured pH at the Yampa River near Maybell,
<br />from an average of about 7,6 in the 1950's and
<br />1960's to about 8,3 in the 1980's and 1990's,lf
<br />real, further increase could cause more frequent
<br />exceedances of the Colorado water-quality stan-
<br />dard of 9,0 and adversely affect aquatic life in the
<br />Yampa River Basin, including Dinosaur National
<br />Monument. The principal conclusion ofthis study
<br />is that this apparent historical increase in
<br />measured pH was caused mostly by changes in
<br />measurement protocoL
<br />
<br />Synoptic sampling during August 16-19,
<br />1999, a period of relatively warm weather and
<br />base flow, showed that late afternoon pH of the
<br />Yampa River ranged from 8.46 to 9,20, The
<br />largest pH (9,20) exceeded the Colorado water-
<br />quality standard and was measured at Yampa
<br />River above Elk River, about 1.8 miles down-
<br />stream from the Steamboat Springs Regional
<br />Waste Water Treatment Plant outfall, where
<br />nutrient enrichment caused photosynthesis by
<br />algae to dominate, Here, the dissolved oxygen
<br />concentration was 161 percent of saturation and
<br />carbon dioxide (C02) was at 26 percent of satura-
<br />tion. At Yampa River downstream from a diver-
<br />sion near Hayden, 16,3 miles downstream, the
<br />effects of photosynthesis were still dominant,
<br />though attenuated by reaeration and dilution with
<br />freshwater from the Elk River. About 37,2 miles
<br />farther downstream, at Yampa River below Craig,
<br />
<br />Abstract
<br />
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