Monitoring the Musselshell: Volunteers track salinity in Central Mont. stream

By on August 23, 2013

David Stout measures conductivity in the Musselshell with a YSI Pro30 (Image courtesy David Stout)

The Musselshell River flows for 340 miles through Central Montana, passing over a landscape that still carries the chemical signature of its past as an ancient seabed.

Sediment washing into the river and groundwater moving through soils can both carry salts into the Musselshell and boost its salinity. That’s an issue because agriculture dominates the land use along the river and supplies crucial irrigation water in a near-desert climate.

“It’s not like we have seawater levels of salinity, but there is a point at which excess salinity in your freshwater can really put crops into stress,” said David Stout, a member of the Big Sky Watershed Corps posted at the Lower Musselshell Conservation District office in Roundup, Mont. Big Sky Watershed Corps is a partnership of Montana Conservation Corps, Montana Association of Conservation Districts and the Montana Watershed Coordination Council.

Stout sometimes walks the banks of the river with landowners and ranchers who have volunteered to help out with a salinity monitoring program conducted by the conservation district with funding from the state Department of Environmental Quality. The volunteers have come together through the Musselshell Watershed Coalition. Stout, along with four volunteers spread out over a 250-mile stretch of the river, periodically measures conductivity (a salinity surrogate) with a handheld meter.

The program is new, but over time Stout says the monitoring will net long-term conductivity data that hydrologists can pair with U.S. Geological Survey flow data and build statistical relationships between the two. The goal is to use those correlations as the basis for an online tool that farmers can check before irrigating. If they find low flows and high salinity, for example, they might want to hold off.

“If we can get people to start thinking about these chemical changes in the river that are going on all the time, I think that forms this really interesting relationship with the river–this shared resource–that we haven’t really had before,” he said. “It’s those kind of real solutions that we hope to achieve through this monitoring program.”

Stout’s visits with the monitoring volunteers draw out another sort of data–local knowledge from ranchers who spend their lives in close connection with the land.

On a recent sampling trip, Stout said he was on the water with a rancher and their meter wasn’t showing them what they expected. They tested the water above the confluence with a creek and again below it, where conductivity suddenly spiked.

Stout said they weren’t sure what was going on. Then the rancher mentioned that his flood irrigation, which pumps water into fields to flow alongside crops, was running at the time.

“He starts working out the problem in his head, and he tells me, ‘Could it be that I’ve got my flood going and it could be water moving through the ground and feeding the river?’”

That was likely the case, Stout said. Irrigation can draw more groundwater through the salt-laden soils and into the river.

A rancher and monitoring volunteer test conductivity in the Musselshell with a YSI Pro30 (Credit: David Stout)

After that, the rancher started picking out more places to sample. Their readings were jumping around, and he wanted to how far downstream the numbers stabilized. And he wanted to know what the numbers were in the creek.

When they found the creek water had much lower salinity levels, the rancher recalled to Stout that the soil in the creek’s drainage doesn’t have as many salts as the rest of the Musselshell watershed.

“It’s these kind of relationships with the land that you get out of the monitoring program like this that really get us excited,” Stout said. “It just makes you happy that you drove 100 miles to drop an electrical conductivity meter in some stream somewhere.”

Top image: David Stout measures conductivity in the Musselshell with a YSI Pro30 (Image courtesy David Stout)

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