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<br /> <br />ammonia plus organic nitrogen, nitrite plus nitrate, <br />phosphorus, and orthophosphorus were collected by <br />the equal-width-increment method (Horowitz and <br />others, 1994) to ensure sample representativeness, <br />Samples were analyzed by the USGS National Water- <br />Quality Laboratory in Denver, Colorado, using <br />methods described by Fishman and Friedman (1989), <br />Water-quality data resulting from synoptic sampling <br />are presented in table 3 in the "Supplemental Informa- <br />tion" section at the back of this report, These data are <br />discussed in a section titled "Synoptic Sampling" in <br />the "Summer 1999" section and in the "Winter 2000 <br />Synoptic Sampling" section, <br />Diurnal measurements of temperature, specific <br />conductance, measured pH, and dissolved oxygen <br />concentrations were measured from the bank of five <br />sites on the Yampa River during August 23-26,1999, <br />This period was chosen to represent streamflow condi- <br />tions that existed during summer synoptic sampling, <br />The Yampa River sites (fig, I) measured diur- <br />nally were: <br />1, Above Elk River, 402936106565000, site 3, <br />2, Below Craig, 09247600, site 6, <br />3, Near Maybell, 09251000, site 8, <br />4, At Deerlodge Park, 09260050, site II, and <br />5, At mouth (Echo Park), 403136108585900, site 12. <br />Results of diurnal measurements are presented <br />graphically and discussed in the subsection titled <br />"Diurnal Measurements" in the section titled <br />"Summer 1999:' <br />Reconnaissance measurements of temperature, <br />specific conductance, pH, and dissolved oxygen <br />concentration were measured during August 30- <br />September 3, 1999, along the Yampa River between <br />Deerlodge Park and the mouth of the river (Echo <br />Park), Results of these measurements are discussed in <br />the subsection titled "Reconnaissance Measurements <br />in Dinosaur National Monument" in the section titled <br />"Summer 1999," except for dissolved oxygen <br />measurements, which were discarded because of <br />equipment malfunction, <br /> <br />Acknowledgments <br /> <br />Gratitude is extended to the people who made <br />possible the successful completion of this study and <br />report. Dan Beyer (Colorado State University) noticed <br />the apparent historical increase in measured pH at <br />Yampa River near Maybell and approached the <br /> <br />, <br />, ': <br /> <br />National Park Service with his concerns, Roy Irwin <br />(National Park Service, Fort Collins, Colorado) and <br />Steve Petersburg (National Park Service, Dinosaur <br />National Monument) were itlstrumental in initiating <br />and conceiving the scope of the study and providing <br />access and logistical support in the National Monu- <br />ment. Michael McHale (National Park Service, Dino- <br />saur National Monument) took time away from his <br />pressing duties during the flood-prone summer of <br />1999 to make water-quality measurements at the <br />mouth of the Yampa River. Timothy Modde, Mark <br />Fuller, and David Beers (U,S, Fish and Wildlife <br />Service, Vernal, Utah) graciously allowed the author to <br />join them on a fish-study float trip through Yampa <br />Canyon in Dinosaur National Monument to make <br />reconnaissance water-quality measurements for this <br />study, Paul von Guerard (USGS, Grand Junction, <br />Colorado) worked hard to promote, develop, and <br />review the progress of this study and offered valuable <br />technical insights, John Turk (USGS, Lakewood, <br />Colorado) was instrumental in establishing the scope <br />and approach of the study and authoring the study <br />proposal. Robert Boulger, Joseph Sullivan, Jeffrey <br />Foster, Patricia Solberg, and Kenneth Butcher (USGS, <br />Grand Junction, Colorado), along with Richard Neam, <br />Dennis Smits (USGS, Lakewood, Colorado), and <br />Joseph Dungan (USGS, Meeker, Colorado), collected <br />water-quality and hydrologic data for this study, <br /> <br />INTERPRETATION OF DATA COLLECTED <br />FOR THIS STUDY <br /> <br />Data from collection of synoptic samples during <br />August 16-19, 1999, and March 13-16, 2000, and <br />from diurnal measurements during August 23-26, <br />1999, provide a framework to interpret water-quality <br />data historically collected at the Yampa River near <br />Maybell, including pH. In addition, reconnaissance <br />field measurements taken on the Yampa River between <br />Deerlodge Park and the mouth of the river (Echo Park) <br />during August 30 through September 3, 1999, give an <br />estimate of the maximum pH expected on the Yampa <br />River in Dinosaur National Monument during low <br />flow and warm weather, <br /> <br />6 Evaluation of Trends in pH in the Vamps River, Northwestern Colorado, 1950-2000 <br />