Restoring life in degraded streams will be speeded up by tree plantings to provide shade, and by fencing waterways to keep animals out, NIWA research has confirmed.
“Our research showed that changes to farm and riparian management can quickly improve water quality,” says Dr John Quinn, research programme leader. “Without shade, and with damage from animals, it takes longer for natural stream habitat to be restored and the sensitive stream animals to return.”
What features does a restored stream have?
Features of a restored stream include:
- an overhead tree/shrub canopy
- woody in-stream debris
- native plants rather than pasture grasses along its banks.
How long does stream restoration take?
Even with best practice, our case studies suggest that it takes more than 20 years to fully restore a native forest stream. The good news is that partial restoration can be achieved in about half that time – integrated approaches to managing catchments and restoring riparian areas can produce significant progress in 5–10 years.
“We do have to wait for the riparian trees to grow and provide stream shade and natural forest inputs of leaves and wood and for fish to swim and insects to fly or crawl from source areas But native stream life showed substantial recovery within 5-10 years of planting native riparian vegetation along small streams with native forest in their headwaters or adjacent areas. As more areas of farmland streams are restored, the sources of colonising animals will increase and the whole restoration process should speed up.”
Colonisation by desired species was more rapid in smaller than larger streams, and in streams with local sources of sensitive species as colonists.
Restoring sensitive species of stream animals was shown to depend on:
- shade, and a consequent lowering of water temperature
- reduced input of sediment and nutrients
- a build-up of wood in the stream from nearby plantings also adds to recovery, but it takes a long time for enough wood to build up enough to provide significant benefits.
Cattle damage to an unfenced stream (Stephanie Parkyn)
Forestry, and sheep and beef, better for stream restoration
Changing highly erodible land from pastoral use to forestry plantings improved stream life, by providing shade, lowering stream temperature to levels plants and animals liked better, and by removing livestock impacts on the waterways.
The pressure on the land and water in a sheep and beef farming system is not as much as that in a dairy farm. There were also better sources of colonisation on the sheep and beef farm lands, with water plants, animals, and insects able to move from other high quality streams to live in the newly-restored streams.
Contact: Dr John Quinn, NIWA Hamilton ([email protected])
Full paper – New Zealand Journal of Freshwater and Marine Research 43 (3)
