One indicator of stream health is the condition of the stream bank cover.
When we talk about stream bank cover, or simply bank cover, we are talking about how much of the soil, immediately adjacent to the water, is covered by growing vegetation, stable debris, or bedrock material.
This helps determine the health of a stream because it can tell us a lot about the relative stability of that stream.
A stable stream is one that maintains the same shape and flow pattern over time. A healthy, stable stream will typically have more bank cover than an unhealthy stream.
Bank cover helps to reduce erosion by reducing the amount of soil that is exposed to passing water as it rushes into and down the stream.
The stability of a stream is important for any organisms that live in and around the stream as well as for protecting your property and nearby infrastructure (driveways, sewer lines, bridges, and more).
Bank erosion causes sediment to wash into the stream. That sediment has major impacts on stream life including a loss of wildlife habitat, higher levels of nutrients, and clouding the water.
As banks collapse or slough-off into a stream the bushes, shrubs, and grasses drop off into the stream as well. These stream-side plants, now lost, were providing shade and cover for fish, perches for birds, and habitat for many other wildlife.
Stream dwelling insects are also impacted by bank erosion. As the soils and sediment settle out on the stream bottom, they fill the rock spaces where stream-dwelling insects live, smothering the insects and taking away their feeding and breeding areas. Stream dwelling insects are an important food source for fish, birds, and other wildlife.
Excessive amounts of erosion can also introduce excess levels of soil nutrients, such as Nitrogen and Phosphorus.
Nutrients are important for plant growth, and in the water, they lead to algal growth. Excess algae causes a decrease in dissolved oxygen in the water. Many fish, shellfish, bugs, and other aquatic animals depend on that dissolved oxygen for respiration.
Depleted oxygen levels is what has led to many “dead-zones” in America’s largest fisheries.
When stream banks erode, the soil dirties the stream water. Cloudy and muddy water blocks sunlight from reaching the stream bottom. Sunlight is important for plant growth and for fish to find their food. It can also make it harder for fish to obtain oxygen through their gills.
Since plants are key to helping prevent erosion and keep stream banks stable, observing the amount of vegetation growing on stream banks can help measure the health of a stream over time.
Questions to ask when considering your stream's health
What percentage of the soil next to the stream is covered in vegetation? Are the stream banks tall and steep or do they gently slope towards the stream? Has the stream maintained its shape over time or are the banks collapsing into the water?
The more vegetation, the healthier and more stable the stream is likely to be. Adding more native plants, such as live stakes can help to increase your stream’s health, provide more habitat, and protect you from property loss.
You can learn more about assessing stream health using the First Investigation of Stream Health (FISH) protocol from Penn State Extension. The FISH protocol is based on procedures taken mostly from the PA DEP. In Stream Comprehensive Evaluation (ICE) Surveys Manual; 2013 version
(Reprinted from the June 22 Penn State Extension Watershed Winds newsletter. Click Here to sign up for your own copy.)
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[Posted: June 22, 2020] PA Environment Digest
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