Avon Heathcote Estuary: Recovery underway

A few weeks ago there was a rather muted celebration of the commissioning of the Ocean Outfall for the City's treated effluent. The Mayor and dignitaries joined the Minister of Energy and Resources, Gerry Brownlee, who officially declared the ocean outfall in action.

Some critics have suggested it was hastily arranged to give the embattled Minister a positive media event against the backdrop of his disastrous proposals for mining in national parks. Many people however will see the greater celebration, the farewell of the last discharge into the Avon Heathcote Estuary -Ihutai. But this was not always going to be the case.

Recall that proposals as late as 2002 were for the discharge to continue into the Estuary, acknowledging however, that it was to be treated to a higher standard than previously was the case.

There was a long tussle over the discharge point and it was a great relief to the supporters of the Avon Heathcote Estuary, the Ihutai Trust, when the City Council announced, on advice from the Experts Committee, that their preferred option was now to proceed with the design and construction of an ocean outfall.

This and the subsequent decision to use micro-tunnelling under the Estuary at the Avon mouth have so far proved to be the best combination of solutions.

The Avon Heathcote Estuary is an 8 square kilometre haven for migratory birds such as godwits, a sanctuary for numerous ducks during moulting, a nesting site for others. It is a feeding ground for scores of regular visitor bird species and numerous transients.

There are currently 16 species of fish in the estuary waters, areas of sea grass exposed at low tide, and two sea weeds, sea lettuce (ulva) and gracilaria. Both can be a nuisance in large quantities because they can accumulate in large smelly mats at low tide and decay. Countless buckets of worms are harvested by fishers but it remains a mystery which fish they actually catch with them.

With the ocean outfall taking the treated effluent into Pegasus Bay, the Estuary can start it's long slow recovery as the massive quantities of nutrients that have accumulated in the muddy floor are yielded up by marine plants, shellfish, snails and all the many different types of marine animals.

More immediate changes will result as the ammonia laden 'fresh' water discharges cease, allowing the Estuary to become a more saline and a safe habitat for juvenile fish. The risk of contact with pathogens will slowly be eliminated from the Estuary waters to the great relief of boaties of all sizes and persuasions as well as wind and kite surfers.

It will be some time before most of us will feel safe eating shellfish from the Estuary but that time will come.

[ Image source: http://www.flickr.com/photos/7260115@N05/4409986271 ]