What is water?

Water is made up of molecules. These molecules are made up of two hydrogen atoms (H2) and one oxygen atom (O). This is why it is scientifically called H2O.

Properties of water

Water is the most common substance found on the earth’s surface and it is the only substance found naturally in three forms:

  • solid (as ice)
  • liquid (as water)
  • gas (as water vapour).

Water exists in all these three forms at 0.01°C. Which you have to admit is cool!

The density of water is approximately 1g/cm³. As water cools it becomes increasingly dense. The maximum density of water is 4ºC. As water is cooled further becomes less dense. This property is why ice floats. This impacts the ecosystems of freshwater lakes because it is unlikely that deep lakes will completely freeze.

As water is heated the molecules become agitated, boiling at 100’C turning from a liquid into a gas. At higher altitudes due to the increased pressure the boiling point is lower.

Water temperature

The growth and biological acivity of aquactic organisms can be majorly influenced by changes in temperature.

Water temperature is the major factor determining how much dissolved oxygen there is in water. Cold water is able to hold more dissolved oxygen than warm water, and dissolved oxygen is essential for the survival of aquatic animals.

As well as the need for dissolved oxygen, aquatic animals also have preferred temperature ranges. If the temperature goes too far outside of this range for too long, it can cause a decrease in the number of species living in a waterway.

Water temperature is affected by:

  • depth
  • flow rate
  • amount of sunlight or shade
  • turbidity
  • season
  • time of day
  • run-off (e.g. stormwater that has flowed over hot surfaces in urban areas).

What is turbidity?

Turbidity is a measure of the cloudiness of water. It is caused by tiny particles, such as silt and clay, organic matter and microscopic plants and animals suspended or floating in the water.

High turbidity reduces the penetration of sunlight into water and can limit photosynthesis and hence the growth of aquatic plants. It therefore affects the animals that rely on these plants for food and shelter.

Turbidity can make it difficult for animals to breathe by clogging or damaging their gills, or making it difficult for animals that filter-feed to collect food. As the suspended particles settle to the bottom they can also smother animal habitats, eggs and larvae.

Turbid water also heats up more than clear water, which can reduce the amount of dissolved oxygen available for animals to breathe. Over time, unatural levels of turbidity can reduce the biodiversity in a waterway.

Causes of turbidity:

  • soil erosion due to heavy rainfall or floods
  • erosion of the banks of a waterway
  • sediments from building sites
  • stormwater
  • loss of vegetation cover especially within the riparian zone