River Clyde Fisheries Management Trust Ltd.
 

Ecology - (A study of the inter-relations between living organisms and their environment.)
 

They differ from lochs (lentic environment) in a number of ways:

• a continuous one directional flow.
• variation in velocity with change in volume of water.
• wide range of fluctuations in water level.
• as a rule, shallower in depth compared to lochs.
• water confined to narrower channel.
• can increase in width, depth and length with age.
• permanent removal of eroded materials, which erode at one point to be deposited downstream with no opportunity for return.
• absence of  prolonged stagnation.
• there is a great dependence on food materials from surrounding land.

The main difference and most significant fact is that rivers and streams are open systems whereas ponds and lochs are closed or self contained. An important point is that lochs/ponds may use their nutrient materials several times a stream/river will only be able to use the food chain temporarily.

A river can be classified in two ways:

• its physical characteristics 
• by the fish species present.

The aquatic vertebrates will indicate the differing physical, chemical and biological features of the river.

The first classification can be broken down into three sections.

• Upper or mountainous course- fast flowing waters, especially after a downpour, can move large stones. this type of course runs through a V-shaped valley and has great powers of erosion.
• Middle course- the river runs over foothills where the water velocity is less causing a slower flow, but still fast enough to carry sand and silt in suspension and can also move pebbles along its bad. dependant on the surrounding land the river/stream can erode its banks with some devastation.
• Lower course- at this level the river meanders/zig-zags slowly across the plain. It has lost much of its velocity and the ability to carry anything in suspension (silt/sand) and lays it down creating a fertile plain.

The second classification breaks the river into zones, this being based upon the fish species present.

• 
  Headstream/Highland burns, formed usually by a number of small streams derived from either a spring, marsh or glacier. The stream is small, shallow and irregular in its course. It will be torrential to some degree with no pools and low water temperatures. Plant life is generally mosses and liverworts. There are no fish in this zonal area.
• Troutbeck, larger than the headwaters and more constant. A greater volume of water in this area erodes its way into the exposed bedrock. The flowing current is usually more rapid and deeper. The typical troutbeck is a steep gradient with its sides strewn with boulder/large pebble. Sheltered parts will hold heavy grit deposits. There will be little plant life due to the water current being strong coupled with the rocky environment. The water is always cold and oxygen saturated. Fish present within this zone are the brown trout (Salmo trutta) which are powerfull swimmers, the miller's thumb (Cottus gobio) and the stone loach (Nemacheilus barbatula). Their habitat is amongst the boulders and stones.
• Minnow/ Grayling zone, less of a gradient than the trout zone, therefore a slower current, although the water can still run swiftly. Less erosion is set up in this zone with some silt depositing in the quieter areas. With the quiet areas there is plant life, the water is still well oxyginated but temperatures will very more. Fish that are generally found within this zone are the minnow (Phoxinus phoxinus)  and in some areas, the grayling (Thymallus thymallus), trout also the eel and young salmon; depending on location.

Lowland course, the final stretch of a river/stream here the river is deep and slow moving. The result of the slow current is the depositing of the suspended silt forming a muddy bottom on which plants can grow. The temperature will vary and the oxygen concentration will be less than that of the other zones. Although some of the fish from the upper regions can be present conditions are not suitable for the successful completion of their life cycle. For example, the trout and salmon require silt free gravel in which to lay their eggs, also cold and well oxygenated water for the young fish. The conditions that this zone creates is more suitable for fish such as: roach (Rutilus rutilus),chub (Leusicus cephalus) an the bream (Abramis brama).

Not all rivers have these courses as the land formation is the defining factor. There are a lot other factors that come into to the formation of a river/stream and these come under the regime of man himself.