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Human activities create a raft of problems for braided rivers, from deliberately introduced predators and invasive plants to climate change. These are historic and/or large scale problems that require complex management strategies.
This page outlines current and future problems caused by recreational and commercial activities, all of which can be addressed through advocacy, community education, and legislation. Some but not all of these issues are being discussed and decided upon through the Canterbury Water Management Strategy.
Pollution comes from point and non-point sources. Point sources include things like industrial discharges and sewerage treatment plants and urban runoff through drains. Non-point sources are harder to define, and include farm and urban runoff over the land and through soils. In Canterbury, farm runoff is a major problem, particularly with the recent rapid growth in dairy farming and irrigation adding excess nitrogen and phosphate to the waters, along with agricultural chemicals and heavy metals such as cadmium. Excess nitrogen combined with phosphate, for example, leads to algae blooms. This reduces oxygen in the water and the amount of light getting through, starving native plants and destroying in-stream invertebrate and fish habitats. At the top of the food chain, there is less or no food for river birds.
We take a great deal of water from our rivers, for domestic use, manufacturing and other commercial reasons, to generate power, and for irrigation. Taking water from braided rivers changes their natural character and hydrology. When water levels drop, the gravel islands used by many birds to nest become joined to the land. Introduced predators including hedgehogs, cats and stoats are then easily able to reach nests. They steal eggs, kill chicks and nesting parents, and often scare away entire colonies of rare and endangered breeding birds. Low levels of water also means pollution becomes more concentrated. This is a critical problem in Canterbury, which has a naturally drier climate that other parts of the country, a situation that will be increasing challenging as the effects of climate change accelerate.
This alarming report from ECan shows that from 1990-2012, over 11,000 hectares of braided rivers were converted to intensive agriculture. A discussion of the impacts of intensive dairy farming and concurrent water abstraction and pollution in Canterbury, and the ongoing legal arguments regarding ecology vs economy, can be found here: ‘Rivers of Gold‘.
Work in riverbeds is done for many reasons, including flood control, road and bridge construction, gravel extraction, land development, and water storage and diversion. These activities can interfere with the natural character of braided rivers, in turn affecting braided river birds. For example, machinery in riverbeds during the breeding season may disturb breeding birds and destroy nests, killing eggs and chicks. Poorly managed gravel extraction and water storage may change the hydrology of the river so that it is no longer ‘braided’. In the worst cases, poorly managed gravel extraction can exacerbate erosion and flooding, cause sediment to enter waterways, leading to the degradation or destruction of ecosystems.
In contrast, well-managed riverbed works such as gravel extraction can help restore the character of rivers by removing invasive weeds, helping to create and maintain islands, and keeping waterways flowing even during minimal flow periods. Timing is often everything. In many instances it’s simply a case of avoiding a very small patch of rivers where birds nest during the breeding season. Under the Braided Rivers Partnership Project, BRaid is working with gravel extractors such as Taggarts and Fulton-Hogan who are actively assisting to create and restore braided river bird habitats as part of their day-to-day operations.
Unattended eggs and young chicks are extremely vulnerable to predation and cold temperatures. If parent birds are kept away from their nests, the eggs and young chicks quickly perish. People, and their dogs, commonly disturb nesting birds. Vehicles can run over eggs and chicks. The wash from speeding jetboats can erode banks, flood nests, kill chicks and disrupt feeding. In 2013, Samuel John Townhill pleaded guilty to Department of Conservation charges of destroying nests and disturbing a protected species when he drove into a 3000-strong black-billed gull colony on the Ashburton Hakatere. He was sentenced to one month’s imprisonment. In 2014 a single fishermen caused an entire colony of birds to abandon their nests in the Ashley Rakahuri. Microlight aircraft and kitesurfing around areas where birds breed can also disturb them.
There are very few remaining places where rare and endangered birds nest along our braided rivers. In contrast, there are many many places where we can walk dogs, drive off road vehicles, go fishing and kite-surfing, drive our boats and fly our planes. For the most part, when people learn how precious these small sections of rivers are to area and endangered birds, they celebrate their arrival and are either careful not to interfere or actively help to protect these areas. Unfortunately, some recreational users either ignorantly or purposefully set out to destroy these precious few remaining areas.