How has water quality changed over time in the Souris River basin?
A report that examines trends from 1970-2020 will help inform work by the International Joint Commission’s (IJC) Souris River Board.
An online StoryMap further illustrates the findings with interactive maps and other multimedia content.
Origins
A previous Souris board established water quality objectives in 1991 for two international sites in the basin, one at the Saskatchewan-North Dakota and another at the Manitoba–North Dakota border.
The latest study was done in response to concerns about changing water quality in the basin and conducted by the US Geological Survey (USGS) in cooperation with the board.
Since the 1990s, there have been sustained exceedances of the water quality objectives for total phosphorus, sodium, sulfate, total dissolved solids and total iron. The study examined 34 sites to complete a trend analysis.
Communities in Saskatchewan, North Dakota and Manitoba rely on the Souris River for their water supply; the waterway also is an important source of water for waterfowl, fish and other aquatic organisms. Exceedances of water quality objectives are a potential concern due to negative impacts on drinking water quality and aquatic life.
Findings
“I think one of the biggest things is that we did see the sulfate and the total dissolved solids increasing across most of the sites in the more-recent time period,” said the report’s co-author Rochelle Nustad, a hydrologist with the USGS Dakota Water Science Center.
Nustad said this is consistent with a trends analysis done for the Red River basin; the Souris drains into the Assiniboine River, a tributary of the Red.
An example from the StoryMap
The latest trends analysis was designed to look at how Souris water quality conditions have changed over time. Now that the study is complete, Nustad recommends an attribution analysis to help identify why they’ve changed. She also suggests a re-evaluation of the water quality objectives, due to exceedances in recent years for some parameters and ongoing exceedances for most of the last 30 years for other parameters.
“There are some things we think are contributing,” Nustad said. “One of those is the hydroclimatic system. We know that in this area, we have alternating periods of wet and dry climate states.”
Wetter climatic conditions, combined with naturally occurring sulfate minerals, can lead to increased dissolution of the minerals. This contributes to rising sulfate concentrations and higher levels of total dissolved solids.
Agricultural practices, such as fertilizer use and drainage systems, can further exacerbate these concentrations. Wetter climatic conditions also increase connectivity of streams with shallow groundwater and wetlands, which can allow more sulfate to reach the streams.
Next Steps
Eric Volkman, the board’s United States co-chair and director of the USGS Dakota Water Science Center, said rather than “sounding an alarm bell,” the study means the board will need to look at what data was used to determine the water quality objectives in the first place.
“The big benefit is that this will be the baseline moving forward.”
Dr. Bruce Davison, the board’s Canadian co-chair and head of the Boundary Waters Engineering Unit, North and West, for Environment and Climate Change Canada, added: “We’re happy that the study is done. They’ve done great work and we look forward to examining what it means for the board’s mandate.”
Nustad said there are different approaches that can be taken to answer the “why” question on exceedances of the water quality objectives. That includes looking at isotopes to parse out levels of sulfates in groundwater and surface water.
“Continued monitoring is necessary in my mind,” she said. “That is one of the biggest pieces of information. If we want to know where we’re going, we have to know where we’ve come from, and to do that we have to have the data.”
The report, “Comprehensive Water-Quality Trend Analysis for Selected Sites and Constituents in the International Souris River Basin,” is available from USGS.
The StoryMap allows viewers to view water sampling sites used in the analysis along with figures based on the data and photos from the basin.
Jeff Kart is executive editor of the Shared Waters IJC newsletter and a contractor to the US Section of the International Joint Commission in Washington, D.C.
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