Summary and Trend Analysis of Water-Quality Data for the Oakes Test Area, Southeastern North Dakota, 1984-2004

Scientific Investigations Report 2007-5056

Prepared in cooperation with the Bureau of Reclamation, U.S. Department of the Interior



The Oakes Test Area is operated and maintained by the Garrison Diversion Conservancy District, under a cooperative agreement with the Bureau of Reclamation, to evaluate the effectiveness and environmental consequences of irrigation. As part of the evaluation, the Bureau of Reclamation collected water-quality samples from seven sites on the James River and the Oakes Test Area. The data were summarized and examined for trends in concentration. A nonparametric statistical test was used to test whether each concentration was increasing or decreasing with time for selected physical properties and constituents, and a trend slope was estimated for each constituent at each site. Trends were examined for two time periods, 1988-2004 and 1994-2004. Results varied by site and by constituent. All sites and all constituents tested had at least one statistically significant trend in the period 1988-2004. Sulfate, total dissolved solids, nitrate, and orthophosphate have significant positive trends at multiple sites with no significant negative trend at any site. Alkalinity and arsenic have single significant positive trends. Hardness, calcium, magnesium, sodium, sodium-adsorption ratio, potassium, and chloride have both significant positive and negative trends. Ammonia has a single significant negative trend. Fewer significant trends were identified in 1994-2004, and all but one were positive. The contribution to the James River from Oakes Test Area drainage appears to have little effect on water quality in the James River.

Additional publication details

Publication type:
Publication Subtype:
USGS Numbered Series
Summary and Trend Analysis of Water-Quality Data for the Oakes Test Area, Southeastern North Dakota, 1984-2004
Series title:
Scientific Investigations Report
Series number:
Year Published:
Geological Survey (U.S.)
Contributing office(s):
North Dakota Water Science Center
iv, 118 p.
Online Only (Y/N):