<br />
<br />1,000
<br />
<br />W
<br />()a: CfJ
<br />ZW ::J
<br /><(O-f--
<br />I-(I)<~
<br />()z' W
<br />::Jwffi()
<br />O:;;f-CfJ
<br />zwww
<br />O(ij:;;w
<br />()o-a:
<br />()a:~(!)
<br />u:gww
<br />-~()o
<br />()~ '"
<br />Wz C\J
<br />0-_
<br />CfJ
<br />
<br />500
<br />
<br />1
<br />." 3 6
<br />"'~IJ" 5 ____~---
<br />2- '..-----
<br />
<br />d
<br />
<br />o
<br />230 220
<br />
<br />200
<br />
<br />180
<br />
<br />160
<br />
<br />. ! ,~>
<br />
<br />10
<br />o
<br />
<br />07
<br />
<br />11 12
<br />
<br />_-------.t---------9I1J1C------------
<br />
<br />---
<br />
<br />140
<br />
<br />100
<br />
<br />20
<br />
<br />o
<br />
<br />80
<br />
<br />60
<br />
<br />40
<br />
<br />120
<br />
<br />DISTANCE FROM MOUTH OF YAMPA RIVER, IN RIVER MILES
<br />EXPLANATION
<br />
<br />-.- Specific conductance at Yampa River site
<br />D Specific conductance at tributary site
<br />Note: number by symbol is site number in tables 1 and 3
<br />
<br />Figure 3, Specific conductance at Yampa River and tributary sites, August 16-19,1999,
<br />
<br />Williams Fork at mouth (site 7), with a specific
<br />conductance of 527 ~S!cm, and Little Snake River
<br />above Yampa River (site 10), with a specific conduc-
<br />tance of 809 ~S!cm, Evaporation from the river
<br />channel, irrigation return flows, sewage effluent, and
<br />inflow of saltier ground water are other potential
<br />contributors (0 the downstream increase in salinity,
<br />
<br />Downstream trends in concentrations of calcium
<br />and alkalinity (fig, 4), important controls on pH and on
<br />the capacity of the waters to dissolve or precipitate
<br />calcite (CaC03), were similar to trends for specific
<br />conductance (fig, 3), Concentrations between Yampa
<br />River below Stagecoach Reservoir (site I) and Yampa
<br />River at Steamboat Springs (site 2) were diluted by
<br />fresher water in tributary creeks, Downstream frolll
<br />Yampa River above Elk River (site 3), concentrations
<br />of calcium and alkalinity were substantially diluted by
<br />freshwater from the Elk River (site 4), From Yampa
<br />River below diversion near Hayden (site 5) to Yampa
<br />River at mouth (site 12), concentrations of calcium
<br />increased to 40 mg/L and alkalinity increased to
<br />140 mg/L of'alkalinity as CaC03, primarily because of
<br />inflow of more alkaline water from the Williams Fork
<br />(site 7) and the Little Snake River (site 10),
<br />
<br />At Yainpa River sites, pH (fig, 5) ranged from
<br />8,46 to 9,20; pH ranged from 8,08 to 8,70 at the three
<br />tributary sites, which were sampled during early after-
<br />noon before pH would be expected to peak because of
<br />photosynthesis, The smallest measured pH value in the
<br />
<br />Yampa River (8,46) was at site I, below Stagecoach
<br />Reservoir, only about 0,25 mile downstream from the
<br />darn spillway, Because this water was released from
<br />substantial depth in the reservoir, pH had little poten-
<br />tial to be affected by the cumulative effects of photo-
<br />synthesis, However, water from this site had theJargest
<br />measured concentrations of dissolved ammonia
<br />(0,02 mg/L as N), dissolved nitrite plus nitrate
<br />(0,10 mg/L as N), dissolved ammonia plus organic
<br />nitrogen (0.36 mg/L as N), dissolved organic carbon
<br />(5,4 mg/L as C), and the second largest measured
<br />concentration of dissolved phosphorus (0,05 mg/L as
<br />Plat Yampa River and tributary-river sites, In addition,
<br />the rocky streambed was covered with aquatic vegeta-
<br />tion,
<br />
<br />The largest pH value (9.20), measured at Yampa
<br />River above Elk River (site 3), exceeded the Colorado
<br />water-quality standard of 9,0 for the upper Colorado
<br />River Basin, Site 3 is about 1.8 miles downstream
<br />from the sewage outfall from the SSRWWTP, This
<br />facility discharges about 3,9 ft3/s of treated sewage
<br />effluent during summer daylight hours (David Jarvis,
<br />Steamboat Springs Regional Waste Water Treatment
<br />Plant, oral commun" 2000), indicating a fortyfold
<br />dilution of sewage effluent at site 3 during sampling,
<br />The river channel exhibited abundant attached algae
<br />and occasional clumps of entrained algae, indicating
<br />photosynthesis induced by nutrient enrichment from
<br />sewage effluent. The large pH was accompanied by a
<br />
<br />8 Evaluation of Trends in pH in the Vampa River, NorthWestern Colorado, 1950-2000
<br />
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