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Preliminary analysis for trends in selected water-quality characteristics, Powder River, Montana and Wyoming, water years 1952-85

Water-Resources Investigations Report 89-4050

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Abstract

Selected water-quality data from two streamflow-gaging stations on the Powder River, Montana and Wyoming, were statistically analyzed for trends using the seasonal Kendall test. Data for water years 1952-63 and 1975-85 from the Powder River near Locate, Montana, and water years 1967-68 and 1976-85 from the Powder River at Sussex, Wyoming, were analyzed. Data for the earlier period near Locate were discharge-weighted monthly mean values, whereas data for the late period near Locate and at Sussex were from periodic samples. For data from water years 1952-63 near Locate, increasing trends were detected in sodium and sodium-adsorption ratio; no trends were detected in specific conductance, hardness, non-carbonate hardness, alkalinity, dissolved solids, or sulfate. For data from water years 1975-85 near Locate, increasing trends were detected in specific conductance, sodium, sodium-adsorption ratio, and chloride; no trends were detected in hardness, noncarbonate hardness, alkalinity, dissolved solids, calcium, magnesium, potassium, or sulfate. At Sussex (water years 1967-68 and 1976-85), increasing trends were detected in sodium, sodium-adsorption ratio, and chloride, and a decreasing trend was detected in sulfate. No trends were detected in specific conductance, alkalinity, or dissolved solids. When the 1967-68 data were deleted and the analysis repeated for the 1976-85 data, only sodium-adsorption ratio displayed a significant (increasing) trend. Because the study was exploratory, causes and effects were not considered. The results might have been affected by sample size, number of seasons, heterogeneity, significance level, serial correlation, and data adjustment for changes in discharge. (USGS)

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Preliminary analysis for trends in selected water-quality characteristics, Powder River, Montana and Wyoming, water years 1952-85
Series title:
Water-Resources Investigations Report
Series number:
89-4050
Edition:
-
Year Published:
1989
Language:
ENGLISH
Publisher:
U.S. Geological Survey ; U.S. Geological Survey, Books and Open-File Reports Section,
Description:
iv, 25 p. :ill. ;28 cm.