Darwin Harbour health improves with ‘B’ rating but better monitoring of toxic metals needed

A new “report card” into the health of a key Territory waterway has painted an optimistic picture, but concerns are bubbling about growing levels of litter and toxic metals in Darwin Harbour.

Darwin Harbour’s health is on the up but toxic metal pollution and litter have been singled out as looming threats.

The last Darwin Harbour Integrated Report Card in 2021 saw a B-minus grade from the Darwin Harbour Advisory Committee, which is made up of scientists, rangers, industry and government members.

That rating has been upgraded to a B in the new report released on Tuesday, the authors judging that “the harbour is in good condition, with many of the indicator objectives being met”.

However, they also said “there are signs that the system is experiencing stress and is in need of improved management”.

Darwin Harbour received a “B” in this year’s Integrated Report Card, up from a “B-minus” in 2021. Picture: Shaana McNaught

Improvements from three years ago include water quality, mangrove health, solar energy uptake and tourism.

On the other hand, the prevalence of litter was graded a C-minus, with an average of 2.8 kgs/km of waste collected over recent years.

Indigenous food security received a D based on survey responses that found “a reduced reliance on the harbour as a primary food source”.

The authors recommended improved monitoring of key environmental data including “heavy metals in areas of high impact”.

In April, the NT News reported that lead levels across Darwin waterways had risen by 50 per cent in the last 15 years.

Twelve other monitored pollutants had also shot up including copper and chromium according to the 2022-23 Inpex report.

Environment Centre NT spokeswoman Bree Ahrens welcomed the improvements but said that the “alarmingly accelerated pace of heavy metal accumulation” shows “we can’t afford to be complacent about the harbour going into the future”.

The organisation had previously called for bioaccumulation testing to track how harmful substances move across the food chain, particularly in apex predators like barramundi.

“We welcome the scorecard’s recommendation for expanded monitoring of water quality, particularly for heavy metals including sediments and I hope that can include an evaluation of bioaccumulation,” Ms Ahrens said.

“(The findings) certainly do urge us to investigate further the source of those increases and the impact they are having on the harbour.”

Environment and Water Minister Kate Worden said the report card showed “the health of Darwin Harbour has improved”, adding that the government has “implemented more stringent measures to detect pollution”.

Sediment testing is carried out at 135 sites in the harbour according to the Minister.

“Water quality monitoring carried out by the Department of Environment, Parks and Water Security in the harbour focuses on factors which are more likely to have an impact on marine life,” Ms Worden said.

“Darwin Harbour is a vital resource for the economic development of the Northern Territory. We must balance the economic activity with the harbour’s preserving the ecological and cultural values.”

Darwin Lord Mayor Kon Vatskalis, who sits on the advisory committee, said the report reflected it was a “working harbour” rather than a “pristine marine environment”.

“You have got a population of 120,000 people, you’ve got a port, and industry, but what we have to focus on is how to minimise the impact of all this human activity,” he said.

Darwin Lord Mayor Kon Vatskalis. Picture: Alex Treacy

Mr Vatskalis said it was likely that most litter in the harbour was unintentional, but the council’s drain filtration system had caught waste items as diverse as car tyres, baby prams and even a firearm on one occasion.

“Don’t throw things out – keep it in your car and when you get home, throw it in the rubbish bin,” Mr Vatskalis said.

“You throw out a chewing gum foil and it ends up in the harbour. If everyone did the same, think about how much rubbish would end up in the water.”

THE FULL BREAKDOWN

• Water quality – A: Improvements seen in Central Harbour and West Arm, while Buffalo Creek and Myrmidon Creek graded fair to poor.

• Sediment quality – B: Sites located next to developed harbour regions more impacted.

• Park visitation at Casuarina Costal Reserve – A-plus: Surpassed previous five-year average.

• Air quality – B overall: Graded A in wet season and D-plus in dry season due to smoke.

• Litter – C-minus: 2.8kg/km/person collected over recent years.

• Indigenous food security – D: Based on survey responses about native food available near harbour.

• Future generations – B-minus: Strong desire from Aboriginal communities to transmit traditional knowledge.

• Spiritual and sacred sites – C: Survey results indicated “insufficient protection efforts for these sites in the region and varying levels of respect perceived by the community”.

• Barramundi health – B: Fish measured up to 92 cm indicating good health.

• Coastal bird health – A-minus: “Healthy levels” of diversity across harbour.

• Tourism – A: “Substation improvement” from post-Covid travel slump.

• Shipping activity – B-minus: Average of 3.65 million gross tonnes of goods moving in and out port annually.

• Mangrove health – A-plus: Net increase of 400 hectares in coverage since 2016.

• Catchment health – B: Howard River and Palmerston experienced increased disturbances since 2021, while Darwin City, Pioneer Creek and Elizabeth River saw lower levels.

• Planning preparedness – C: Indicated “initial progress but also underscoring the need for enhanced monitoring of sustainability policy implementation and impacts”.

• Urban tree cover – C-plus: “Within Darwin City, areas under NT government ownership exhibit the highest tree coverage at 29 per cent, while Australian government-owned land has the lowest at 20 per cent”.

• Solar uptake – C: More installations since 2021.