Riparian vegetation and agriculture
How may agricultural activities impact riparian vegetation around a waterway?
Fencing of riparian vegetation around a waterway prevents access by cattle and other stock animals that are attracted to water. Fencing of riparian vegetation not only prevents direct pollution from animal faeces and damage to vegetation and banks from trampling, but also intercepts microbial contaminants and nutrients that are washed down slopes toward streams. When fencing is inadequate and vegetation is cleared or sparse, the riparian area around a waterway becomes prone to stock trampling, erosion, excess nutrients, chemical contaminants, and microbial contaminants.
Good management of riparian buffers improves farm water quality, pasture management, erosion around waterways, and animal health, and reduces stock losses.
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 in the waterways.
- 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 that are habitat for fish and kōura, and reduced 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 (e.g., farming, forestry) that increase the amount of contaminants that are present in surface water runoff.)