What are Stream Habitats?

A stream is a small, shallow flowing body of water that changes constantly. Each stream habitat is shaped by water velocity and the type of material deposited on the stream bed.

Streams are high-energy habitats, especially in upland areas. Fast-moving water prevents silt and clay from settling on the stream bottom, depositing the heavier sand and gravel. As the water flows over rocks (riffles), it takes on oxygen, is cooled, and allows for food production.

High levels of oxygen allow streams to support certain organisms, such as trout. Cool water temperatures enable stream to absorb large quantities of oxygen. Stream water is cooled by evaporation, by inflows of cold spring water, and by shading from overhanging trees, bushes or banks.

Most nutrients in streams come from overhead and streamside vegetation. Needles and leaves are an important source of food for aquatic insects, which are a main source of food for young trout and salmon.

These factors and conditions make shallow streams important for several reasons. The gravelly bottom offers the right conditions for juvenile fish to spend the winter and for spawning fish to build nests (redds). Fast- flowing water that moves over and through this gravel provides an appropriate environment for developing eggs. Streams are good feeding grounds due to the presence of large quantities of insects. All of these characteristics make stream ideal fish nurseries.

How are Stream Habitats Disrupted?

Land Development Industrial Activity

Poor logging or road construction practices can cause silt to enter the stream bed, blocking the stream and preventing fish from passing to spawning grounds. Mud, silt or clay settling on the stream bottom may bury spawning beds, insect habitats or nursery areas. Large amounts of slash and sawdust in the stream can reduce oxygen in the water as they break down. The use of heavy equipment in the stream can destroy existing habitats.

Poorly-treated sewage or industrial wastes released into a stream may reduce oxygen levels in the water. Decomposer bacteria break down the effluent, using oxygen in the process.

Chemicals are sometimes spilled or leaked from storage areas or are dumped into a stream. Drifting pesticides from nearby spraying or acid rain can also have a detrimental effect on a stream.

Agricultural Activity

Livestock moving regularly through a stream can erode the stream bank. Nursery areas may also be trampled or covered by silt. Runoff from manure piles, silage pits and fertilized fields may deplete oxygen in the stream. Agricultural chemicals such as insecticides, herbicides and fungicides may inadvertently enter a stream, killing certain organisms, including fish.

Vegetation along the stream bank acts as a buffer zone and plays an important role in reducing or preventing landbased disruptions from affecting the stream directly. Logging, land clearing or town development could remove vegetation, warming the stream as more sunlight reaches the water and increasing the number of fish-eating birds, such as king fishers and mergansers

How Long Will Disruptive Effects Last?

The longer a stream is exposed to disruptions, the more severe the adverse effects will be, and the longer the stream will take to return to its original state.

A healthy stream provides a home for bacteria and fungi (decomposers), plants and algae (producers), fish and invertebrates that eat plants and algae (primary consumers), and fish and invertebrates that eat other animals (secondary consumers).

In a balanced stream community, each group in the food chain depends on the others for food. If a group is removed, the chain will be disrupted. For example, if a chemical spill kills stream insects, fish that normally eat these insects will be forced to either move to another location, change their diet, or go without food.

If a single chemical spill kills all the stream insects and moves downstream, new insects from adjacent streams or ponds will move into the insect-free habitat. The ability of a stream to recover depends on how long it takes for the insect populations to return to normal levels after the chemical has been removed from the environment.

A single release of silt or mud into a stream will act similarly to a chemical release. The silt and mud will wash down the stream gradually, smothering the stream bottom on the way. Depending on the water velocity, it may take several months for the silt slug to pass through the whole system. Once it has passed, however, recovery of the stream community will start fairly quickly.

Some of these components are more sensitive to disruption at certain times of the year and re-establishing their populations at those times would take substantially longer.

Unlike single events of short duration, disruptions that last for longer periods of time pose a much greater problem to the stream community. Recovery cannot begin until the discharge is stopped and the toxic effects from the chemicals have passed out of the stream. In addition, long-term disruption can cause the loss of the strearres, small protected pockets of organisms that would otherwise begin recolonization.

In cases where water flow is low and the amount of material deposited in the stream is high, the stream may take generations to return to its original state.