Riparian vegetation and energy
How do energy generation activities potentially impact riparian vegetation around a waterway?
The construction phase of the energy industry can drastically change the face of many waterways which are modified through channelisation and removal of riparian vegetation. Construction and development of the surrounding catchments lead to an increase in sediments and contaminants entering the waterway through surface and stormwater runoff. Good management is essential when land is developed to reduce the impact of the construction phase especially during earthworks for the development of roads and when using mechanised equipment close to waterways.
Care should be taken to avoid damaging existing riparian vegetation and stream banks as these complex habitats are not easy to reconstruct and it may take decades before the habitat recovers, even with replanting. Vegetated riparian buffers can help to reduce inputs of contaminants from surface runoff in industrialised areas, but the amount of impervious area in the catchment and stormwater that enters the streams in pipes can have an overiding effect on stream health.
Fluctuating water levels from hydro-dams can also impact on riparian vegetation. Previously submerged banks may become exposed when water levels fall, thereby increasing erosion of the river bank, or existing riparian vegetation may become submerged and decompose when water levels rise again.
Potential impacts of reducing or removing riparian vegetation on water quality and mahinga kai
- Increased bank erosion - the loss of roots decreases the stability of the bank, increasing its vulnerability at times of flooding.
- Increased water temperature - loss of shading from trees or overhanging streamside vegetation means waterways become more exposed and are more liable to fluctuate in temperature. (New Zealand native fish generally cannot tolerate temperatures over 25ºC and trout need temperatures to be less than 19ºC for growth.)
- Decreased dissolved oxygen through increased aquatic plant growth - plants and weeds growing within the waterway are more likely to thrive in unshaded waterways, potentially clogging and stemming flow, which can decrease oxygen levels.
- Modified channel form - erosion through loss of vegetation can lead to scouring and breakdown of stream and river banks, eventually changing the form of the channel.
- Loss of species habitat - many mahinga kai species need the protection and habitat provided by riparian vegetation growing around streams and rivers. (Trees provide wood and roots to the stream that are habitat for fish and crayfish, and loss of cover can result in loss of breeding and feeding habitat.)
- Decreased water clarity - erosion and increased sediment from bank erosion may contribute to decreased water clarity and reduced visibility for fish to find food.
- Increased nutrients in streams - riparian vegetation filters contaminants and sediment from the land. (Loss of riparian vegetation may also be associated with changes in land use that increase the amount of contaminants that are present in surface water runoff.)
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