River Clyde Fisheries Management Trust Ltd.
 

Water - In the beginning...

        Prior to looking at the other pages about habitats, plants and type of waters, let us overview 'water' itself.

Physical

• Buoyancy   Water is denser than air therefore giving a more buoyant medium exerting an upward push on all plants and animals. This gives way to delicate structures in the water plant world than terrestrial growth.
   

• Temperature   Water has the greatest specific heat of all substances, it can absorb a relatively large amount of heat for a small rise in temperature. Therefore giving a buffer against wide fluctuations in temperature which is why lochs and rivers
  vary relatively slowly. Cold water at 4^oC is at its densest and when the water becomes cooler in the autumn the
  upper surface sinks and displaces the warmer water from below. Water colder than 4^oC is less dense because of
  its structure change in its molecular structure and therefore floats to the surface, where further cooling creates ice.
   

• Pressure    Water is almost incompressible and there is therefore not a large increase in density with a depth increase.
  For every 10 metres that an object sinks below the surface the pressure upon it increases by one atmosphere, with plants
  and animals being able to adjust to suit their living environment and depth.
   

• Viscosity    Viscosity or internal friction of water varies with temperature. Water being twice as viscose near freezing point than at summer levels. This does affect small bodies in the rate at which they sink, and the ability to maintain their position in the water column.
   

• Surface Tension   This factor is very important physically to small plants, animals and the angler. Pond skaters can glide over the surface, snails can cling to the underside of the surface film. Hatching insects can become trapped in the surface film; especially on a flat calm day.
   

• Light      Water reflects more light than the land, furthermore light its energy diminishes with distance from the surface until there is virtually no light below a certain distance. Due to the different absorption of wave lengths by water the quality
  of light changes with depth. Water will absorb the shorter wave lengths of solar energy but within the range of visible light
  it absorbs the longer wave lengths more effectively. Light that penetrates the deeper parts of a loch is relatively poor in red and orange rays, the most effective for photosynthesis, but the light rays that do penetrate are rich in green and blue rays.