Muri Lagoon concerns clarified

Friday November 16, 2018 Published in Letters to the Editor

Dear Editor,

In response to the November 14 letter to the editor titled, “Algal bloom issue due to groundwater”,

The Mei Te Vai Ki Te Vai project team (PMU) would like to thank the anonymous, concerned environmentalist who wrote in support of our recent environmental study.


However, there are a few critical points in the letter that we would like to clarify for the community.

Firstly, we would like to clarify that our results confirmed that nutrients from both residential and commercial on-site wastewater systems are harming the sensitive Muri Lagoon environment, and even well-managed systems are contributing to the problem.

Unfortunately, the wastewater issue is one of density of systems, rather than their quality. While septic tank upgrades of all existing systems would lower the level of nutrients entering the sensitive areas of the lagoon, this would not be enough to solve the problem.

Secondly, our results show that there are three key changes that will help to restore the lagoon’s health:

1.A reticulated wastewater system to service the highly-developed areas along the coastline:

This system will require land for a treatment plant, to treat waste before disposing of it. There are two options for disposing of the treated wastewater - onto land, or into the ocean beyond the reef. Either option will also leave solid waste to be disposed of, just as is the case currently with septic tank systems.

2.Protect and enhance swamps and the edges of streams:

Swamps act as natural filters, removing sediment and nutrients from water before it enters the lagoon. Streams carry nutrients into the lagoon. Planting stream banks and keeping animals out of streams reduces the amount of nutrients in streams.

3. Regularly harvest the seaweed:

This will help remove nutrients from the environment, because it will disrupt the seaweed’s “self-feeding” process and remove it as a source of nutrients.

The third and final point we would like to highlight is that covered in point one above – the sewage treatment plant mentioned in the writer’s letter will be needed, regardless of whether the treated water is distributed onto land, or into the ocean.

The land-based option for disposing of treated wastewater would require an additional 20-30 hectares of land (50 to 75 acres), for the Muri area alone. To future-proof the system, additional land would be needed to enable the system to service properties built in the coastal coral sands zone around the island.

The feedback we received from the presentations we gave to the community indicate that land-based disposal is favoured by many. We are keen to hear from landowners interested in offering land to support the feasibility of this option. Without this land being made available, an ocean outfall is the only remaining option.

The PMU team

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