Where are you going and where have you been?

Emily Eidam reviews sensor settings with colleague Ted Langhorst last October in preparation for an over-winter mooring deployment in the Tanana River (Alaska).

Emily Eidam studies how sediment moves from land to sea

By Abby P. Metzger
Spring/Summer 2023

Mud. Dirt. Sediment. It’s tempting to see these things as unchanging, the terra firma holding up humans and anchoring entire forests. But Emily Eidam knows that sediment moves. Boulders get whittled down to pebbles, carried by rivers veining their way to the sea. Glaciers grind and slough off material. Beaches build. Beaches erode. And the seafloor, the resting place for many of these inland materials, holds clues to Eidam’s most important questions about sediment: Where are you going, and where have you been?

Answering these questions is key to understanding many dynamic processes that impact humans, including how erosion could limit beach access and where people can safely live on coastlines, or whether seafloor deposition could change how waves surge onto a beach. Tracking sediment transport also tells us how harmful pollutants move through (and linger in) ecosystems.

“Sediment is an interesting part of Earth’s surface,” Eidam muses. “In some ways, it’s a resource for coastal areas. It represents a mass transfer from the land to the ocean, with implications for how nutrients and pollutants move, or the dynamics of our coastlines, and whether they are accreting or eroding.”

Eidam is a newly hired interdisciplinary oceanographer and geologist in the College of Earth, Ocean, and Atmospheric Sciences at Oregon State. She is looking at sediment transport from many different angles and collaborating with partners across the Earth sciences: with coastal engineers studying shoreline erosion; with hydrologists examining sediment flow through rivers; and with physical oceanographers and geologists studying glacial retreat and marine archives of change. Sediment has a role in every collaboration.

In some ways, Eidam’s journey to Oregon State was similar to sediment movement. She did not always follow a single, simple pathway. She grew up in southcentral Alaska, in a family that supported her professional pursuits, but didn’t see science as a common career.

“The idea of being a scientist as an occupation was not part of my family culture,” she says, “but my family was supportive of wherever I was headed, as long as it had some real-world application!”

Eidam liked math. Engineering gave her a way to apply equations to real-world problems. A chance class in public speaking inspired her to present on a topic that interested her: glacial landscapes. Instead of taking a good engineering job offered after her undergraduate degree, she stayed for a second bachelor’s in geology.

With two degrees in hand, Eidam says she Googled graduate geology programs. She discovered that you could study geology within coastal environments like her home in Cook Inlet, which inspired her to think of science in a new way. “It really wasn’t until I applied to graduate school and got accepted that I thought, maybe I would like to be a scientist,” she says.

Since receiving her Ph.D. at the University of Washington, Eidam has explored a number of sediment-related projects. One involved a tidewater glacier in Alaska called LeConte. Tidewater glaciers flow directly into the ocean and are prone to ice loss through spectacular collapses. Understanding the behavior of these ocean-bound glaciers will help scientists anticipate future changes in sea level and ice flow.

Eidam’s role in the LeConte project was to study the pile of rocks and sediments accumulated at the front of the glacier, called a moraine. As Eidam explains, “A moraine acts as a point of stability for the glacier, so if you know how the moraine is changing, physical oceanographers and glaciologists can predict how much melting is happening and if it’s becoming unstable.”

Eidam is especially interested in examining sediment transport in little-studied areas such as the Arctic. Because Arctic rivers drain 20% of global landscapes, measuring how sediments move through these systems and into the coastal zone can help answer first-order questions about rates of transport and serve as a foundation for understanding future changes as the Arctic warms.

One useful measurement in these remote Arctic watersheds is turbidity. “High turbidity, like you might see in a river during a rainstorm, lets you know that abundant sediment has been washed into the river,” Eidam says. “And if there’s a lot of sediment in the river, there are probably high levels of other particulates and dissolved substances that impact water quality and nutrients.”

Yet, getting proper measurements in harsh Arctic landscapes can be costly and challenging. Seasonal ice cover often impedes wintertime access, and ice breakup in spring creates hazardous conditions. To address these challenges, Eidam and collaborator Theodore Langhorst (a graduate student at University of North Carolina) developed their own turbidity sensor at about 2% the cost of commercial designs. In remote areas where sensors might not be recovered, these DIY instruments provide important, low-cost information about the movement of material in river and coastal zones.

Eidam is passionate about sharing her science with graduate students and K-12 communities. She recently partnered with University of Alaska Fairbanks researchers and outreach specialists to connect with the Nenana Boarding School — which provides a home for many Indigenous students from rural Alaskan communities — and a regional homeschool network. Students in both programs helped build their own DIY turbidity sensors that collected measurements in the Tanana River. In the springtime students will help researchers fly drones outfitted with the turbidity sensors to collect measurements from the river during the ice breakup season. Collaborations such as these enable communities to participate in science in their backyard while providing researchers with valuable data.

In her new role at CEOAS, Eidam is looking forward to digging deeper into her research questions and learning more about sediment — what she calls an important currency between land and water. In that light, every withdrawal made by waves eroding a sandy cliff, and every deposit made by the couriers we call rivers, is a chance to understand how material moves throughout our planet. Emily Eidam, then, is the accountant, trying to square the books and figure out where it’s all coming from and where it’s going.

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