Souris River Dissolved Oxygen Study in Support of Total Maximum Daily Load Development

The Souris River, a slow moving praire river, originates in the Canadian
\nprovince of Saskatchewan. The Souris River enters into the United States near
\nSherwood, North Dakota. The upper portion of the Souris River, from the border with
\nSaskatchewan, Canada to Lake Darling, a total of 43 .4 miles, has been on the North
\nDakota Section 303(d) Environmental Protection Agency (EPA) list of impaired waters
\nsince 1998 (NDDoH, 2008).
\nLow dissolved oxygen (DO) concentration in the river has been problematic,
\nresulting in fish kills on the upper reach of the Souris River. The primary goal of the
\nproject is to determine source(s) of contaminations that cause seasonal variation in
\ndissolved oxygen concentration. Objectives ofthis research include: 1) studying the
\nnature and extent of the impairment using existing data, 2) executing a comprehensive
\nyear long sampling plan, and 3) analyzing sample data to identify the major sources of
\nDO impairment. Results from this study will be used by North Dakota State
\nDepartment of Health (DoH) for development of a Total Maximum Daily Load
\n(TMDL) report to the EPA.
\nThe reach was expanded into Canada, totalling 52 river miles, between Glen
\nEwen, Saskatchewan, CA and Mouse River Park, ND. This reach was sampled 29
\ntimes during the period of this study. During winter months, DO under the ice was
\nconstantly below 1 mg/L. During the summer diurnal swings of DO caused the stream to fall below the designated 5 mg/L standard in the early morning hours. Sediment
\noxygen demand was determined to be the main stressor.
\nTwo contaminant sources that contribute to DO variation on the Souris River
\nwere identified, livestock ranching practices and the physical alteration of the river.
\nRanching is the leading cause of impairment. Livestock in the riparian area contribute
\norganic inputs and stream bank erosion. Physical alterations lead to DO variation in
\ntwo ways. Upstream impoundments eliminate scouring flows allowing sediment to
\nbuild up. Downstream impoundments back up water into study reach contributing to
\nsedimentation. Low head dams create hydrologic flow issues which lead to dissolved
\noxygen depletion.

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