What are the impacts of geothermal energy generation activities on water temperatures?
Once geothermal water has been used, it is disposed of by discharging into surface waters or by injecting it straight back into the geothermal system or into deep groundwater. Discharging geothermal water into surface waters can impact water quality and mahinga kai by changing the acidity (pH) of the water, adding high levels of chemical contaminants (like arsenic), and increasing river temperatures.
Most animals and plants that live in 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 streams or rivers or at localised points can have significant impacts on movement of fish through the water column (deep and shallow).