Diggings logo

WSU/Pend Oreille Extension introduced the Sense of Place series in 1999, with a focus on local landscape and natural history of Pend Oreille County, Washington. A partnership with the Kalispel Tribe of Indians Natural Resources Department has allowed us to expand this program through EPA funding to include more classes, a newsletter and this website.

Beneath the Surface of a Stream

by Carol Mack

A clear mountain stream--riffles and peaceful pools, glossy spills of water over sparkling pebbles . . . Is it true that falling water generates negative ions that somehow create positive moods? Or is it just because of the tranquil setting and inspirational ambiance that we all love a quiet moment by a bubbling brook?

But not all is as tranquil as it seems. In fact, the wildest science fiction movie doesn't begin to compete with the cast of characters and melodramas happening in that rocky neighborhood of the stream bottom.

In the sunnier stretches of the creek the rocks support a slippery coating of algae. We Who Wade may curse this slime, but to the mayfly nymphs that graze there, it is the equivalent of a grassy meadow. These peaceful herbivores are easily recognized by their tails--usually three of them--and by the rows of leaf-like gills along their abdomens. Cup some water in your hands holding a mayfly and raise it to the sunlight. Watch those gills beat ever more frantically as the water warms up and oxygen dissipates. Enough! Uncle! An animal adapted to the relatively high oxygen levels of cold rushing water usually cannot survive long in warmer or less aerated water. In fact, you may find a different species mix on every side of a rock depending on its orientation to the current and preferences for protected spots versus full-on blast.

In fast-moving ripples, look for stonefly nymphs and caddisfly larvae. Popularly known as "periwinkles," many caddisfly species construct elaborate houses around their bodies to protect them while they graze. Construction ranges from lowly log cabins to cobblestone mansions worthy of an expert mason. Stonefly nymphs usually lurk between the rocks where the water flows most rapidly and can be up to two inches long. These delight children with their jet propulsion and their tendency to perform push-ups when they are stressed for oxygen. (Like a caterpillar, most aquatic insects are immature stages that lack wings, and many have no particular resemblance to their adult forms.)

These three insect families—mayflies, stoneflies, and caddisflies---are regarded as indicators of cold, clean water, and their diversity and abundance offer clues to assess a stream's water quality. More importantly, they feed the trout that favor the same habitat. But some of the most fascinating characters prefer to lurk in the murk. The giant water bug grows up to three inches long—treat these guys with respect. This predator grasps its prey and injects venom, dissolving its victim' s innards, which it then sucks out with a long beak. Even a large bullfrog is fair game. The water scorpion operates the same way. Though its tail looks like a giant stinger, it is actually just a breathing snorkel—it's the other end that needs careful watching. Dragonfly nymphs are also active predators below water, just as their adult forms are above.

Each stream microcosm has a unique pyramid of life building up from whatever energy source is available. Eaters of algae, shredders of leaves and wood, even decomposers of carcasses and excrement all play a part in maintaining stream life. Next visit, take time to look below and between the rocks, and admire the stream from a whole new perspective.

<----previous article...Diggings June 2002...next article---->