Temperature changes

Temperature affects the number and type of animals and plants that live in a waterway.

Temperature determines the number and type of animals and plants that live in a waterway. Temperatures vary naturally with the seasons, while water is also usually colder at the bottom (due to groundwater input) and warmer on the surface (due to higher air temperature) of a stream, river, or lake. Many activities have the ability to change water temperatures, including the discharge of warmer cooling water from thermal power stations, the release of water from dams, the removal of riparian planting that shades and maintains temperatures in waterways, a reduction or increase in water levels due to abstraction or diversion of water used for irrigation, and the addition of warmer geothermal water. Most animals and plants that live in our waterways prefer a certain temperature range for optimum growth and reproduction and when temperatures change outside a preferred range they can be significantly impacted.

Potential impacts of changing temperatures on water quality and mahinga kai

• Decreases in available oxygen (DO) with increasing temperatures - reduces oxygen available for mahinga kai. 
• Increases in fish metabolic rates - sudden changes, like those found at a discharge points, are more likely to cause stress and possibly death.
• Increases in algal abundance and changes in the dominant species present - as the water gets warmer algal growth increases, often resulting in algae blooms.
• Changes in the amount and type of animals present - some animals cannot tolerate extreme changes in temperature and will avoid these areas (habitats) of a waterway if unfavourable.
• Changes in migration patterns - water temperature triggers the time of migration for breeding as mahinga kai travel to and from the sea.
• Changes in water temperature and flow throughout streams or rivers or at localised points can have significant impacts on movement of fish through the water column (deep and shallow).