A Healthy Stream Has Low Embeddedness
Rocks are buried in a highly-embedded stream on the right. Rocks are clearly visible in the low- embeddedness stream in the image on the left. (image credit: Kristen Koch)
When you spend time hiking near mountain creeks, driving by farm streams that flow through pastures, or biking greenways along urban waterways, you might notice that streams come in many different forms. Some streams have tall banks and flow in a straight line. Other streams meander around rocks and logs, and they are multi-channeled. And yet others are lined with concrete and act more like pipes than streams. All these characteristics help determine how healthy a stream is. Can it support life?
Whether there is a habitat for the aquatic bugs that live in streams is an essential measure of a stream's health. We call the measure of stream bottom habitat available between rocks and stones the stream's embeddedness. According to the Environmental Protection Agency, "embeddedness refers to the extent to which rocks (gravel, cobble, and boulders) and snags are covered or sunken into the silt, sand, or mud of the stream bottom." If it is easy to pick up or move the rocks and stones on the stream bottom, then the stream has low embeddedness. If you can't even see the rocks on the bottom because they are buried and surrounded by soil, the stream has very high embeddedness.
The layering of gravel, cobble, and boulders on a stream bottom creates space for water to flow between and around. These spaces and rock surfaces are where the aquatic bugs live. Some, like Caddisflies, build "homes" right on rock surfaces out of sand or tiny pieces of leaves. Other Caddisfly species weave webs between rocks to capture algae and plankton. Other bugs, like Mayflies and Beetles, need space to crawl around in search of food. When these spaces between rocks become full of mud, or embedded, that habitat is lost.
Bugs on land are essential food sources for birds, frogs, bats, and small rodents. In streams, insects and other bugs are food for many fish, tadpoles, and other water-dwellers. They form the basis of the aquatic food chain. So not only do the insects rely on healthy, rocky, low-embedded stream bottoms, but so do fish, birds, raccoons, bears, and people.
The next time you pass a local stream, look to the bottom. Do you see primarily rocks or mostly mud or somewhere in between? This is just one way to start determining the health of that stream and the wildlife that might be living nearby.
You can learn more about stream health through our First Investigation of Stream Health program.
