3.2. Stream Habitat

Streams, of course, are habitats to many other forms of life other than fish. Plants, small insects and invertebrates, and small mammals live and use the water. The areas around streams, called riparian habitat, are very important to a whole host of plants and animals.

In the section called Facts on Fish we will discuss what kind of stream habitat a fish requires. Birds and animals congregate around streams. One reason this occurs is that all animals need a source of water. Many animals either eat the fish or insects or the plants growing in and around streams. The areas along streams are also commonly used for travel, nesting, and shelter. If you walk along the sheltered edge of a stream in winter you will see many animal tracks and deer beds in the snow.

Adopting a stream means you are also adopting the area around the stream, all the animals that use the stream, and its riparian zone.

In addition to improving fish habitat you may want to consider putting up nest boxes for birds (see Section Where to Go For Help). Local naturalists, birding clubs, or the regional biologist from the Department of Natural Resources may have other ideas on how to improve the area around the stream. The habitat potential of a stream is created by many different factors.

3.2.1 In-stream Cover

In-stream cover is generally provided in five ways:

- Undercut Banks: where water has eroded away the material under a stream bank. The upper portion has not slipped into the water because the root systems of trees, shrubs, and other vegetation have held the soil.

- Rocks, stones and boulders found in streams provide protection from predators, weather, and other factors. The size of a rock, its shape and location, all have an influence on what uses it for cover. Irregular rocks and boulders as well as slab sided boulders with no sand or silt under them, provide the best cover for juvenile fishes.

- Logs and trees. These are essential in streams to assist in developing pools, cleaning the bottom, and stabilizing the stream. The proper amount of large material can make the difference between poor and excellent fish habitat in many streams. Logs and stumps also provide overhead cover as an escape from predators or fast flowing water. However, too much of a good thing can be bad. Log jams, which cause water to be diverted over the stream banks, can cause severe erosion and may have to be removed.

- Low overhanging grasses and bushes also provide overhead cover under which fish can hide. This is particularly important for trout.

- Water depth, water colour, and surface turbulence also act to hide fish from land predators. The broken water surface of riffles hides young salmon and the deep water of pools hides trout. The quality of a pool is determined by depth and how much of the bottom is hidden by the cover features listed above

 
3.2.2 Bank Stability

Although erosion is a natural and dynamic process, human activities often change the stability of a stream bank, causing increased erosion. The stability of a bank gives an indication of how much erosion is taking place. Excessive erosion produces silting and encourages the stream to widen and become shallow. Banks that are actively eroding will eventually cause a decrease in the abundance of fish and invertebrates, such as insects. Stable banks have little or no erosion, are not slumping, and usually have growths of grasses, shrubs and trees. In some instances, they have been stabilized previously by artificial means. The impact on the stream of stable and eroding banks as illustrated.

3.2.3 Stream Canopy (Shading)

Shading affects life within the stream because many fish are sensitive to high temperatures. Shade keeps the air and water cool. The amount of shade depends on how many plants and trees are growing near the stream, the height of the trees, and the direction the stream is flowing (the direction is important because of where the sun is in relation to the trees. For example, a stream flowing in a north-south direction may have different amounts of sun than a stream flowing in an east-west direction. Trees overhanging the stream also provide nutrients (in the form of old fallen leaves) and food (insects dropping into the stream).

3.2.4 Stream Gradient or Slope

Stream gradient is the actual visual angle of descent or slope of the stream. Slope affects the speed of the water flow and how much of the stream will be pool or riffle. This directly affects the balance between salmon and trout and other species. For example, salmon prefer a 75:25 riffle - pool ratio while trout prefer a 50:50 ratio of pool to riffle.

3.2.5 Stream Chemistry

Nova Scotia's streams have poor levels of nutrients and minerals. This is expressed as low conductivity. To help compensate for this, leaves and litter that come from plants along the watercourse are very important, accounting for up to 90% of the food in a stream. Leaves from deciduous trees and bushes are the best

 

The chemistry of fresh water is not nearly as complex as that of salt water. However, some basic chemicals in fresh water should be mentioned. The amount of dissolved oxygen gas is a vital requirement for fish and insects living in water. Twenty percent of the earth's atmosphere is oxygen. Land animals use lungs to bring oxygen into their bodies. Many insects, amphibian tadpoles, and all fish use gills to perform the same function. The gills absorb oxygen from the water and release waste gases back to the water, but oxygen levels in the water are only 6 to 12 parts per million, far less than the air. This means the oxygen levels in water can be easily depleted. Oxygen dissolves in water depending on water temperature. The colder the water the more oxygen it can hold.

Acidity is another important component of stream chemistry. The amount of acid in the water is measured on a 14-point scale called the pH scale. Liquids like lemon juice, vinegar and battery acid are all considered "acidic" with a pH ranging from 0 - 7. Substances like baking soda, milk of magnesia, ammonia, and lye are all alkaline with a pH ranging from 7 -14. A pH of exactly 7 is neutral (milk is an example of a neutral substance).


During stream surveys you will be asked to take water samples to test for pH. The alkalinity of a water sample refers to its ability to counter the effects of acid. Alkalinity is mainly determined by the kind of rock base that forms the streambed and the watershed.

Most stream life quickly dies if the pH falls below 4.7. Vinegar has a pH of 3.0


Water also contains minerals such as calcium and magnesium, which determines how "hard or soft" the water is. Other nutrients found in the stream include phosphorus and nitrogen. Usually when stream samples are taken, the water is also examined for toxic amounts of copper, mercury, and other metals.

3.2.6 Stream Temperature

The shape of the channel, shade, the air temperature, the surrounding soil, the speed of the water flow, and the water volume, control stream temperature. If the channel is narrow and deep (with good pool development), it has a large volume of water to heat up and cool down in comparison to the water surface, so temperatures do not change much over the day. If the channel is wide and shallow it will heat and cool quickly. Following the air temperature.

Everyone knows it is cooler in the shade because there is little or no direct sun. The amount of shade along a stream affects the amount of direct sun that reaches the water. Direct sun heats the dark coloured, unshaded stream bottom, raising water temperatures. The shallower the water, the more effect it has. Shallow streams have water temperatures that follow the air temperature throughout the day. This is because there is a relatively large surface in contact with the air and a small volume of water.

Springs in the riparian area are important moderators of temperature because groundwater temperature is usually cool and stable. Water also seeps in and out of the stream and these seeps can have an important influence on temperature. If an area is cleared of vegetation (e.g. clear-cut, farm field, or parking lot), the seeps heat up in the sun. The cooler groundwater becomes hot.

In the winter the temperature situation is reversed. Shade actually warms the stream temperature by moderating cold winds and frigid temperatures. The vegetation also keeps frost from getting into the ground so that springs and seeps keep running longer in the winter and the stream bottom resists freezing. A healthy stream keeps an open passage under the snow and ice during low flow periods in winter. This insulating layer provides over-winter water for fish, prevents freezing of eggs, and keeps ice formations to a minimum. Since there is less ice, there is also less ice damage to the stream during the thaw or spring break-up
Streams fed by lakes are warmer because of the heating effect of the sun on the open water. If the stream channel is well developed and shaded, the water temperature will drop to tolerable levels within a kilometer downstream of the lake
A healthy stream can maintain temperatures within ideal ranges for fish throughout their growing season.

Tributaries that come into the stream, of course, can affect the water quality and habitat. Try to identify where and what kind of water is entering the stream you are studying.