Water temperature and hydro
How do hydro-electricity activities potentially influence waterway temperatures?
Changes in water flow and levels have the ability to change water temperature, especially when water is released or retained by a hydro-dam. Care must be taken to maintain the amount of water needed to support healthy ecosystems; this includes considering optimal flow and water levels and their effect on water temperature, which impacts mahinga kai survival. The amount of water needed is called environmental flow, which considers maximum and minimum flow levels to support a healthy ecosystem. Failure to provide an environmental flow can have serious consequences for water quality and mahinga kai.
The removal of any riparian planting around waterways has an especially high impact on temperatures; loss of shading means waterways become more exposed and are more liable to fluctuate in temperature during the day.
Most animals and plants that live in our waterways prefer a certain temperature range for optimum growth and reproduction. When temperatures change outside a species' preferred range, mahinga kai 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 waterways or at localised points can have significant impacts on movement of fish through the water column (deep and shallow).