Just like humans need oxygen in the air, fish and other aquatic creatures need dissolved oxygen in the water.
But the amount of dissolved oxygen changes daily due to weather conditions, water flow, the presence of algae and other factors. This can make it difficult to get an accurate idea of what underwater oxygen is available from just a single measurement.
As part of ongoing water quality work, the IJC’s Souris River Board has teamed up with the US Geological Survey (USGS) and Environment and Climate Change Canada (ECCC) for continuous round-the-clock monitoring of dissolved oxygen at three locations in the river.
“There’s always been a concern about dissolved oxygen in the winter when there is ice cover,” said Joel Galloway, chief of the Hydrologic Investigations Section at USGS’s Dakota Water Science Center and one of the project leads. “There have been a couple incidents of fish kills in the last 10 years (in the Souris River).”
Galloway said the monitoring started in May 2019 in relation to work by the IJC Souris River Study Board to evaluate operation plans used to manage floods in the watershed. The Souris River Board also has a mandate to monitor and maintain the ecosystem health of the Souris River.
The study board is interested in how changing water flows impact water quality and dissolved oxygen in the Souris River. The dissolved oxygen monitoring by the board and two federal agencies is intended to run until 2024.
“The reason it’s a five-year period is because there is such variability in streamflow,” Galloway said. “It can be very different from year-to-year and season-to-season, and we want to capture the range of conditions in the Souris River.”
One monitoring station is at Sherwood, North Dakota, where the river crosses from Canada into the United States. The second is near Minot, North Dakota, which is the most populous city along the Souris River’s banks. Both of these are already monitored by USGS for streamflow and water quality. A third monitoring station is at Westhope, North Dakota, where the river reenters Canada and monitoring duties are split between streamflow by USGS and water quality by ECCC.
The sites were chosen for their strategic locations on the river and because existing monitoring programs are there already measuring water levels, water temperatures and flows. The sensors used to collect the dissolved oxygen data are operated continuously but removed in the winter when ice begins forming to avoid damage to the equipment.
The data is uploaded to the internet, and can be viewed at the USGS National Water Information System website.
Though one year of data isn’t enough to get a good idea of overall conditions in the Souris River, at all three locations in 2019, the sensors showed that dissolved oxygen mostly stayed above the minimum water quality objectives set by the Souris River board and the governments.
There were exceptions. Over the course of the year, dissolved oxygen fell below the objective on 47 days at the Sherwood station, below the objective on 14 days at the Minot station and below the objective for 37 days at the Westhope station. But none of these periods lasted an entire day, which should have limited the impact on fish.
The highest levels took place in the fall when water flows in the river were unusually high and water temperatures were cool.
Ice cover causes dissolved oxygen levels to drop, as do changes in “dissolved ion concentrations” due to metals (such as iron, manganese or phosphorus) in the sediment and low water flow conditions that can cause waters to stagnate. Dissolved oxygen levels can increase due to aeration caused by things such as low head dams that create turbulence.
Galloway said excessive nutrients such as phosphorus and nitrogen that enter the waterway can cause excessive algae, negatively impacting oxygen levels. Learning more about how dissolved oxygen rises and falls in the river and connecting it to other water quality and flow information can help decision-makers find ways to improve ecological conditions.
These may involve better management of nutrients that run off into the Souris River from agricultural lands or urban areas, and managing water flows through reservoirs to ensure enough water is moving. With more information, water managers and officials can have a better idea of what actions will be necessary to keep fish happy along the course of this international river.
Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.