Along a quiet, daffodil-strewn ridge within the Tennessee River Gorge, there is a smattering of granite headstones. The Baxter family cemetery dates back to the late 1800s and is bisected by Mill Creek, a skinny but steep tributary edged by mossy stones. Where the stream drops off the ridge there towers a 10-foot-tall metal mill wheel, once used to grind corn and wheat but long since rusted in place.
This land is a monument to days gone by. But dig deeper. It still brims with life.
“Mill Creek is one of our best streams for macroinvertabrates,” said Mariah Prescott, who leads the Tennessee River Gorge Trust's water quality program.
Since 2015, TRGT has monitored 13 different sections of streams throughout the Tennessee River Gorge. Each month, the sites are tested for pH, dissolved oxygen, conductivity and temperature – considered the chemical indicators of water quality. Each season, they are tested for macroinvertabrates, the tiny insects that live on the creek bottom.
It was a brisk, March morning when Mariah and I made our way to Mill Creek. Our wool hats pulled tight and our dip nets and buckets in tow, we picked our way down alongside a series of splashy, miniature waterfalls. In contrast to the solemn gray river, cutting through the gorge below, the flowing tributary appeared especially bright and lively.
What makes Mill Creek unique, aside from its rich biodiversity, is that it is a perennial stream.
“Most [streams] on the property dry up at summer, but Mill Creek flows year round,” Mariah explained.
Where the water finally leveled, forming a shallow pool, we dropped our equipment.
* * *
Last spring, Mariah and I hiked to the top of the Ritchie Hollow Trail where we chemically tested the pool beneath Blowing Wind Falls, a stunning 25-foot-tall cascade. In my blog “Why We Water Test,” detailing that experience, I wrote, “To be near water is cathartic.”
However, to macro test is something different. It is to submerge oneself into a secret world filled with strange and fascinating creatures. From the cool waters, these tiny insects tell a big story.
Many of the macros found in Southeastern streams appear unfamiliar but are actually the larvae of well-known species such as the mayfly, stonefly and dragonfly. Some of these insects are more tolerant to water pollution than others. Mayfly larvae, for example, require clean, well-oxygenated water. Worm-like midgefly larvae, however, can live under most conditions.
Depending on the species found, one can deduce the health of a stream.
As Mariah scooped pebbles from the creek bed, I pulled sodden leaf packs from the water edge – two prime macro habitats. We dumped our mucky samples into the bucket then stood back, hands on knees, and waited.
Before long, the shadowy contents came to life – a dark flash, a flutter. The bucket was breathing.
We began to sort through, uncovering multitudes of macros in every handful: slender-bodied damselfly nymphs with their large eyes and even larger jaws; aquatic sowbugs, 14-legged and flat as pancakes – two species considered somewhat tolerant to pollution. We also found one of my personal favorites, the caddisfly.
Like the mayfly, the caddisfly lives only in clean water. But what makes it most special is how this species protects itself. Using silk secreted from its salivary glands, the caddisfly laces stones and twigs into a tubular structure, which it fastens to its thin, segmented body.
For up to two years, it will crawl like a hermit crab across the creek bottom, grazing on algae and decaying matter. Then, one day, it will seal up the opening of its case and begin its transformation.
When the winged pupa finally emerges, it floats to the water's surface, glistening like a celestial being.
The adult caddisfly will live just a few weeks. After it mates and lays eggs, its wispy body returns to earth. Amid daffodils and artifacts, it soon becomes soil. But by then, its eggs will have hatched. Life will begin again, carried forth by a clean, ever-flowing stream.
