This means that land-based activities, such as agriculture, waste disposal and septic tanks, directly contribute to the lagoon’s water quality.
As previous environmental studies of Muri Lagoon did not confirm the factors contributing to the lagoon’s water quality, the PMU decided to undertake further studies to close the remaining information gaps.
The extent of connection between groundwater and the lagoon was one of these gaps.
PMU Environmental Scientist, Anthony Kirk explains how the information was gathered. “The connection between groundwater and the lagoon was found through a combination of information from monitoring wells we installed in Muri, ground surveys we conducted on Muri beach and testing of lagoon water.
“The information these methods provided shows that groundwater, even at very deep levels below the ground, responds to the lagoon tide. We also found chemical indicators of groundwater far out into the lagoon. This proves that groundwater and water in the lagoon are mixing,” explains Kirk.
He adds, “The public need to be aware of this, as it means toxic material dumped on the ground, or in streams, may make their way into groundwater and eventually into the lagoon. Examples of common products likely to cause issues are insecticides, weed killer, pharmaceuticals, paint and motor oil.” The PMU’s early findings highlight that Rarotonga’s natural environment is strongly interconnected and at risk, at least in part because of the current lack of public sanitation infrastructure, but also from everyday products that harm the environment when they end up in the water.
In addition to the planned new public sanitation infrastructure and more responsible septic tank management, the community also need to take a more conscious approach to choosing products being used on the land.
Without these changes, the current issues at Muri are likely to worsen, and develop in other areas around Rarotonga and around the Cook Islands.
The PMU will be publicly release a full report on the results of their investigations in September, but in the meantime will be sharing key findings with interested parties as work on the final report progresses.
The final results of the investigations will provide valuable information and methodology for water quality assessment, monitoring and management in other parts Rarotonga and the Cook Islands.