Dogs and geese dirtying Avon estuary

AVON-HEATHCOTE ESTUARY: Being fouled by dog and geese faeces and toxins from cars and building materials
AVON-HEATHCOTE ESTUARY: Being fouled by dog and geese faeces and toxins from cars and building materials

Faeces are again causing problems more than four years after treated sewage stopped being emptied into Christchurch's estuary.

Now, it is sewage of a different kind - dog and geese faeces.

Avon-Heathcote Estuary Ihutai Trust chairman Bill Simpson said the estuary was essentially the drain for the entire city, with run-off from the city's two main rivers being fouled by dog and geese faeces and toxins from cars and building materials.

Trust member and Christchurch City councillor Glenn Livingstone said people might not realise the extent of damage caused by their household pet.

"Dog poo is the main contributor and it will take some individual responsibility to clean it up," he said.

"Poo from Canadian geese is also prevalent and what has given rise to them is the grass in the residential red zone. I don't think Cera [Canterbury Earthquake Recovery Authority] realised that when it planned to grass it over."

Simpson said the trust had been told it would take between 20 and 40 years to completely rebuild the stormwater infrastructure.

City councillor Phil Clearwater said both the waste and stormwater networks were affected by the earthquakes, causing them to be susceptible to cross- contamination in rain events.

A council working group headed by Cr Pauline Cotter would look at the issue, he said.

Simpson said the good news for the estuary was researchers found it was "quick to bounce back".

A joint project by the University of Canterbury and Niwa showed the estuary responded quickly when cleaned up, as demonstrated by reduced nitrogen and phosphorus levels since the installation of the ocean outfall system in 2010.

Before 2010, the city's treated sewage was pumped into the estuary. The council installed an $87.2 million system to carry it 3 kilometres out to sea into Pegasus Bay.

Niwa principal scientist marine ecology Dr John Zeldis said when Bromley discharged directly into the estuary it was responsible for 90 per cent of the nitrogen and phosphorus content.

Nitrogen and phosphorus are the troublesome duo in water quality and can cause toxic algae at the right levels.

"The amount of nitrogen in the water declined almost immediately after the diversion [ocean outfall] was put in," he said.

Nutrients in the sediment also declined "quite rapidly", which Zeldis said was significant as there were concerns over the "legacy effect" of loading from Bromley.

Waste water had been pumped for about 100 years into the estuary but the results showed the estuary was robust, he said.

The Press