Stream Substrate
The materials that sit within a stream channel are referred to as “stream substrate” and the size, make-up and abundance of substrate are important factors for habitat structure. Cobble, gravel and boulders provide habitat for macroinvertebrates and fish. Riffles are areas, often downstream of a pool, where the water breaks over rocks or other debris, causing surface agitation. Riffles are critical for maintaining high diversity and abundance of insects in most streams, and for serving as spawning and feeding grounds for some fish species. The term “embeddedness” refers to the degree to which gravel and cobble substrate are surrounded by fine sediment. Sedimentation occurs as a result of construction near a stream, streambank erosion or runoff.
The next time you walk along a stream, look to see how embedded it is. Pick up pieces of gravel or cobble sitting within the fine sediments in the stream with your fingers. Pull the particle out of the bed and estimate what percent of the particle was buried. Some sand and silt is acceptable; however, if it looks like the embeddedness is more than 40 percent, then sedimentation is a problem.
Today's photo was taken by Jennifer Bennett, WPC Watershed Technician II, in the Shenango River watershed. It shows a good mixture of cobble and gravel, and consequently, good habitat diversity.
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