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<br />1921 <br /> <br />. <br /> <br />Reservoir. Data from the two stations located downstream from John Martin Reservoir were analyzed for trends <br /> <br />that may have occurred after the implementation of a new reservoir operating plan in 1980. The nonparametric <br /> <br />Mann- Whitney- Wilcoxon rank-sum test was used for trends analysis. <br /> <br />At the upper-basin station, discharge increased significantly and specific conductance decreased signifi- <br /> <br />cantlyafter 1974 during the low-flow months of January. February, and March. Thesc trends apparently were <br /> <br />. <br /> <br />caused by the increased importation of low-specific conductance water from the Colorado River Basin into the <br /> <br />Arkansas River. At the three stations located between Pueblo Reservoir and John Martin Reservoir, discharge and <br /> <br />specific conductance were affected by Pueblo Reservoir operations and by changes in the quantity and quality of <br /> <br />inflow from the upper basin. At the two stations located 0.4 miles and 24 miles downstream from Pueblo Reservoir. <br /> <br />discharge generally increased during most months of the growing season and decreased during November through <br /> <br />February after 1974. The discharge trends at these two stations are largely attributed to the storage of water in <br /> <br />Pueblo Reservoir during the winter months and the release of that stored water during the growing season to meet <br /> <br />downstream irrigation needs. Immediately downstream from Pueblo Reservoir, specific conductance decreased <br /> <br />during most months between September and April and increased during the high-flow months of May and June. <br /> <br />This trend was caused by the mixing of low-specific conductance water and high-specific conductance water in <br /> <br />Pueblo Reservoir, thus narrowing the annual range in specific conductance in the reservoir outflow. Few trends. <br /> <br />with the exception of increased specific conductance in June, August, and December. were detected in specific con- <br /> <br />ductance at the station located 24 miles downstream from Pueblo Reservoir apparently because of increased inflow <br /> <br />of relatively high-specific conductance water from Fountain Creek. At Las Animas. located 120 miles downstream <br /> <br />from Pueblo Reservoir. discharge increased during all months after 1974. but specific conductance exhibited litTle <br /> <br />change. <br /> <br />At the two stations located downstream from John Martin Reservoir. specific conductance was affected by <br /> <br />changes in John Martin Reservoir operations and by a decrease in the specific conductance of the reservoir inflow. <br /> <br />Specific conductance decreased during October through April and exhibited no significant changes during May <br /> <br />. through August. Additionally, it appears that the timing of the minimum annual specific conductance changed from <br /> <br />2 <br />