Utah’s Jordan River, according to University of Utah professor Jennifer Follstad Shah, is a hard-working river, supporting a growing population of more than 1 million people. But underneath all of the irrigation canals and reclamation discharge, new research shows, are natural water sources that continue to shape the character of the Jordan River.

The study was published in the Journal of the American Water Resources Association and funded by the National Science Foundation, the Jordan River Farmington Bay Water Quality Council and the University of Utah Undergraduate Research Opportunities Program.

“It already is an engineered river,” Shah says. “I would say that we’re not going to get away from that. There’s a lot of really dedicated, smart people who are working to make it a more sustainable river in general that everybody can enjoy.”

A hard-working river

Running for 51 miles from Utah Lake in the south to the Great Salt Lake in the north, the Jordan River has been engineered and modified for irrigation, drinking water and waste disposal since the mid-1800s. Today it supports the booming Salt Lake Valley. Low oxygen levels in the river have landed it on the EPA’s list of impaired waters, which caught Shah’s attention. As a microbial ecologist, Shah wanted to understand the relationship between river water quality, microbes and oxygen levels.“I was interested in understanding how the microbes in the Jordan River, and other urban river systems, respond to chronic inputs of carbon and nutrients,” Shah says.

Biologist Rose Smith joined the project, looking to sample Jordan River water to understand how the river processes the many nutrients that flow into it from various sources. Geochemist Yusuf Jameel also joined the team, and analyzed the isotopes of hydrogen and oxygen in the water to understand where the water came from. Isotopes are atoms of the same element with slightly different weights from each other. In a river system like the Jordan, various sources of water can have their own distinct isotope signatures, enabling researchers to tease apart how much water comes from which sources.

“And so [Yusuf] said, ‘Well, while you’re collecting that water, I’ll run some water isotopes on it’, recognizing that we have this highly engineered system in which water sources may be shifting in space and time,” Shah says.

She expected they’d find isotope signatures from the river’s source at Utah Lake, from tributary streams and from water reclamation plants, but wondered how much groundwater may be supplying the river.

Then, in May, August and October of 2016, the team set out to collect samples from 18 sites along the river.

Multiple inputs

Some of the results weren’t surprising. Close to Utah Lake, streamflow was highest in the spring, due to snowmelt runoff in tributaries. Farther downstream, however, diversion and flood control canals kept the streamflow constant year-round. As spring stretched into summer, inflow from tributaries ebbed.

“However, and surprisingly,” the researchers write, “we found that source water inputs primarily occurring upstream (i.e., lake inputs and groundwater exchange) were evident tens of kilometers downstream, even when inputs were initially low relative to other sources.” Before this, the contribution of groundwater to the river hadn’t been considered, since groundwater is so tough for hydrologists to quantify. But the results suggested that despite more than 170 years of engineering, natural inputs including groundwater are still significant inputs to the Jordan River.

Beyond that, they found, the changing sources of water over time influenced the water chemistry. “You might expect to see influences of different water sources just by looking at the river,” Shah says. “It’s pretty turbid and in some places and looks rather green, like Utah Lake. Whereas if you’re at a [reclamation plant] discharge point, you see that the water looks much clearer, like the tributaries.”

Shah says the results update our understanding of how water moves through the Wasatch Mountains and Salt Lake Valley. “The paradigm was that we get snow that falls on the mountains, it melts and turns into stream water and runs downhill into the Jordan River without much exchange with the groundwater beforehand,” she says.“And that’s not the case; a lot of that water actually percolates into the soils, recharges the groundwater, and then can re-emerge into our surface water systems.”

Managing the nutrient load

The best application of this study, the team writes, is in managing the loads of nutrients like nitrogen and phosphorus, which come into the river from water reclamation plants as well as from surface water tributaries. Understanding the role of groundwater and how the sources of water shift throughout the year help water managers take a holistic look at managing the water quality, Shah says.

“So rather than trying to find one solution or one target problem that we need to address, we need to really think about the whole system,” she says, “and how can we use the water resources more sustainably and potentially reduce the loads of energy and nutrients into the system.”

Find the full study here.