Early results from an ongoing dissolved oxygen study in the Souris River basin suggest there is not a direct relationship between water flows and the level of oxygen in water. Rather, a number of factors play a role in low oxygen conditions when they occur.
The IJC’s Souris River Board has been conducting a study on the dynamics of dissolved oxygen, or DO, in relation to water flows flow since 2019. The purpose is to specify how lower flows affect the DO dynamics in the Souris River and aid the board in its review of water quality objectives.
DO is important for a healthy ecosystem. Low concentrations can affect aquatic life like fish, mussels or insects that are a part of the food chain and result in fish kills.
Low amounts also can increase the release of nutrients and metals such as phosphate, iron and manganese from the riverbed sediment into the water column, which can cause other water quality problems. Since water flow can be managed, learning more about how it affects DO may allow water managers to ensure oxygen levels are healthy when possible.
DO measurements from the Souris River Board’s sampling program have been ongoing since the 1970s. These indicate that concentrations have been frequently below the 5 milligrams per liter objective, both during winter months when water flows are low, and in the summer during periods of stagnation.
The measurements collected at the two border sites (Sherwood and Westhope, both in North Dakota) as part of current board monitoring efforts give researchers a snapshot of conditions at a specific point in time. However, DO can fluctuate dramatically during a 24-hour period, most often with higher values in the afternoon and lower values during the night to early morning hours.
DO concentrations are affected by many factors including temperature, photosynthetic activity from plants and algae, dissolved solids, aeration from wind and turbulence in the water column and organic decomposition. Streamflow, in turn, can influence many of these factors.
Through funding from the IJC’s International Watersheds Initiative, three near-real-time continuous Aquatroll 600 DO monitors were installed at sites with corresponding US Geological Survey (USGS) flow gauges, collecting temperature, DO and specific conductance measurements every 15 minutes. These data will allow a better understanding of the duration and magnitude of low oxygen conditions and provide more information of how they match with flow conditions on the river.
The sites for this project were chosen to best capture potential influences on DO in areas below major flow control structures.
The Sherwood site, where the river leaves Saskatchewan and enters North Dakota, is below the Rafferty, Boundary and Grant Devine reservoirs in Saskatchewan. The Minot, North Dakota, site is below Lake Darling which is operated by the US Fish and Wildlife Service. The Westhope site is downstream of J. Clark Salyer National Wildlife Refuge, also operated by the Fish and Wildlife Service. The J. Clark Salyer contains a series of water control structures and pools the river passes through before flowing into Manitoba.
Data for this project is collected by USGS and publicly available at the agency’s National Water Information System website.
The Sherwood and Westhope sites have water quality objectives established by the Canadian and US governments and are monitored with discrete samples collected six to eight times a year by Environment and Climate Change Canada and USGS as part of annual sampling programs.
The year and a half of data collected so far have provided interesting results. The three sites show dramatically different diurnal (or daily) and seasonal patterns.
A variety of factors at the three sites seem to have an influence on DO. At Sherwood and Minot, cooler water temperatures showed an increase in DO, likely because colder water can hold more oxygen. In Minot, low head dams may be creating some turbulence that provides aeration to the water column under ice, increasing dissolved oxygen levels through the winter.
At Westhope, DO concentrations did not seem to follow the same pattern as streamflow for most of the year. This may be attributed to the strong influence of biological and chemical processes that occur in the upstream pools at J. Clark Salyer.
While flow may be important for DO levels at certain times, based on the data collected, it does not always determine DO levels. However, it does likely affect the variables that affect DO. The board anticipates that the additional data collected as part of this project will provide enough information to perform a rigorous statistical analysis, which in turn should help identify the primary drivers of DO depletions for each site. These data will be used to modify or supplement the current sampling program as needed.
The study is intended to continue into 2024, which should allow the researchers to collect information for a range of different flow conditions.
Heather Husband has worked in the field of natural resources for more than 32 years and is currently an environmental scientist with the North Dakota Department of Environmental Quality. Husband is US co-chair of the Souris River Board’s Aquatic Ecosystem Health Committee.