Lesson 1, Topic 1
How embedded is the stream bottom? Copy
Embeddedness rates how much of the surface area of the larger rocks in the stream are surrounded by fine sediment to evaluate habitat for benthic insects, fish spawning and egg incubation. Benthic insects, the main food source for fish, make their homes on such rocks. Sediment, silt, or very fine clay can bury the rocks and reduce habitat for the bugs and, as a result, decrease the food sources for fish. Higher levels of embeddedness generally eliminate niche spaces and correlate with lower biotic productivity. The degree of embeddedness may vary in the sample depending on whether the riffle, run, or pool is being rated. Emphasis should be placed on evaluating riffle and run areas where biotic diversity of the insects will generally be the greatest.
To measure this parameter, pick up cobbles (rocks) and turn over small boulders to approximate the percent that the object has been surrounded by fine particles or sediment. Often the rocks have a discoloration on their sides which shows the line that separates the exposed and covered parts of the rock. Measure this parameter on at least 10 rocks and use the average percent for the rating.