Episode 3: The Cold Reach

Episode summary

In spring 2024 Delia Marchetti, an environmental science major from Cedar Bluff, bolted 14 temperature loggers she built for about $38 apiece along the Millrace, the 1856 mill channel between campus and downtown. Two summers and a winter of readings later, her data show a 400-yard reach below the old Porter Woolen Mill site where groundwater seeps keep summer water four to six degrees cooler than the rest of the channel — behind a parking lot.

Dr. Grace Beaumont, a freshwater ecologist, wanted to know whether native freshwater mussels really were concentrated there, so this summer her crew ran the first season of timed snorkel and wading surveys, in 25-meter blocks along the whole Millrace in July and September. Every mussel is identified, measured, tagged and pressed back into the gravel where it was found, out of the water for less than two minutes.

First-season results, which both guests stress are preliminary: just over a hundred live mussels of four native species, close to nine in ten of them inside Marchetti’s cold reach, and a handful under 30 millimeters long that Beaumont is “not ready to say anything about yet.” This winter the crew will walk the channel on cold mornings with a thermal camera to map the seeps themselves. Also discussed: the shopping carts of the 1970s, now rare, and one intact 1950s bicycle that now lives in the Freshwater & Watershed Laboratory.

Update, April 2026: Marchetti won the 2026 Chancellor’s Undergraduate Research Prize for the logger study. Update, October 2026: after two survey seasons the team has counted 214 live mussels, 187 of them in the cold reach; the full numbers are on the research spotlight.

Chapters

Selected transcript

An excerpt, lightly edited for reading. The full speaker-labeled transcript is in your podcast app’s transcript view, or email podcast@uwporterfalls.edu for an accessible document.

Corinne Lacasse: Delia, how did a set of thermometers turn into a mussel survey?

Delia Marchetti: Honestly, by accident. I was doing temperatures because the channel was restored and nobody had good summer data. Then one logger kept reading low. I thought it was broken. I swapped it, and the new one read low too.

Grace Beaumont: And this is the part I love. She didn’t throw out the weird number. She went and stood in the water.

Delia Marchetti: It was cold. Like, noticeably. In August. And there were shells on the bottom, which nobody had written down anywhere.

Abe Tollefsrud: Grace, what does four degrees do for a mussel?

Grace Beaumont: In a hot summer, four degrees can be the difference between a stressed animal and a dead one. Mussels can’t move very far, so if their stretch of stream gets too warm, they just endure it. A cold seep is a refrigerator they happen to be sitting in.

Corinne Lacasse: So how many did you find?

Grace Beaumont: Just over a hundred live animals this first season, four native species, and close to nine in ten of them in Delia’s cold reach. One season is one season. I’d like a second summer before I put a number in a paper.

Abe Tollefsrud: And the small ones?

Grace Beaumont: We found a few under thirty millimeters. Small means young, and young means somebody reproduced. I went into this assuming we’d find old survivors. I’m not ready to say anything yet. But I said “huh” out loud in the water, and the crew hasn’t let me forget it.

Links mentioned

• Counting mussels in the cold reach of the Millrace — the research spotlight, with two-season results
• Dr. Grace Beaumont
• Dr. Everett Yoon and the Riverwatch network
• Freshwater & Watershed Laboratory
• Porter River & Millrace ecology
• How the Millrace became a stream again (magazine)
• Riverwatch monitoring grant (news)