Riparian vegetation and mining
What are the potential impacts of mining activities on riparian vegetation around waterways?
Mining can drastically change the face of waterways as forest is cleared and riparian vegetation removed. Mining can lead to an increase in sediments and contaminants entering a waterway by direct impact from mining activities, through development of roads and infrastructure, and by surface and stormwater runoff. When land is mined, care must be taken to reduce the impact on waterways, especially during earthworks and when using mechanical equipment close to waterways. 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.
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. (Our native freshwater fish fauna 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 kōura, 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 waterways - riparian vegetation filters contaminants and sediment from the land. (Loss of riparian vegetation may also be associated with changes in land use (e.g., farming, forestry) that increase the amount of contaminants that are present in surface water runoff.)