Algae Problem In Cook Islands Lagoon Likely Caused By Groundwater Runoff

Reduction of excessive nutrient content in Muri Lagoon will not be quick or cheap

By Losirene Lacanivalu

RAROTONGA, Cook Islands (Cook Islands News, Nov. 21, 2016) –Scientific data is pointing to ground water nutrient discharge being responsible for 81 per cent of Disolved Inorganic Nitrogen (DIN) in Muri Lagoon.

With so many ongoing issues of algae and weed growth in the lagoon, a group of Geo-science scientists from the Pacific Community (SPC) were down at Muri last week to conduct a survey of their own.

Presenting their data results to the Ministry of Marine Resources staff, SPC representative Herve Damiamian said high discharge of ground water meaning high nutrient discharge is the cause of increase in algae in the lagoon.

“What this data has also showed is that phosphorous compounds are mainly driven by land run-off and data suggests that the current ground water discharge only reflects pollution that occurred 10 to 90 years ago,” Damiamian said.

He said the results do not show pollution for the past 10 years. MMR Secretary Ben Ponia said the ministry will need to change their perception about phosphate, knowing that the Cook Islands are volcanic islands and that the discharge to the lagoon is from underground water - meaning human usage of detergents.

Damiamian said in the days they visited the lagoon they considered some mitigation factors that could be helpful to Rarotonga.

“Any mitigation solution needs to be joined with an enforced policy around controlled nutrient discharge.

“The mitigation would be in order to improve the flushing of the lagoon.  We need to remove the fish trough, remove some boulders on eastern side to start with,” he said.

He said a lot of issues may still arise - and even dredging maybe a solution - but will decrease the water level in the lagoon and the water temperature may also decrease, causing another issue in the tourist attraction.

 “Any measure to control the nutrient discharge will take decades to positively impact on Muri lagoon’s water quality.”

He said the lagoon does need nutrients, but too much causes an algal bloom.

Ponia says the ground water discharges means they are coming from creeks, streams and drains during rainy days.

Noting that the pollution and nutrient discharge are more than a decade old, Ponia said there is need to have a broad and long-term solution.

“There is the suggestion of fish trough removal and it is not much of solution, boulder removal too and this could all become more of a contribution than a solution.

 “Lagoon dredging  could be a solution, but we need to be mindful of erosion and the impacts it could have on properties around the area.”

Ponia said pollution in the ground water is more than a decade old and pollution from the past is still draining out. Looking at enforcing regulations, he said to enforce regulations in controlling nutrients in the lagoon will take a few decades to see a great benefit.

“The approach to have individual sanitation plans and reticulation systems in homes, this will be addressed in the next two years for full compliance, but it is difficult to know if we see full changes.”

Meanwhile, Damiamian said SPC received a formal request from Ministry of Foreign affairs to check the lagoon and to give some technical advice. He said there are different ways to read the data in lagoon areas and, as in Aitutaki, an instrument was deployed for more than a month and the information was more efficient creating a numerical model of water movement around the lagoon. Ponia said they have been monitoring the lagoon in Muri using a buoyant; this is used in Manihiki as well. He said they are very expensive and are purchased from Australia for $73,283.82 and maintenance is $20,000.

“Technology is available, but the cost is high.”

He said when the European Union funding is available next February they will then create a budget and continue to monitor the lagoon.

Cook Islands News
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