Diary of a dirty river: How the Logan holds the key to saving our waterways

Scientists are turning to one of the dirtiest rivers in Queensland for answers on how to rehabilitate riverine ecosystems.

A team led by the Australian Rivers Institute at Griffith University is studying the Logan River with the hope of finding the source of unhealthy nutrients like nitrogen and phosphorus.

Heavy nutrient and sediment loads can wreak havoc on ecosystems in rivers and the estuaries they run into, causing algal blooms and preventing light from reaching key plant species.

In the case of the Logan’s poor water quality, nutrients from farming in the upper catchment, large housing developments, and all the waste that comes with the humans who move into those houses all play a role.

That rehabilitation work is necessary is not disputed, the question is where to begin, project lead Professor Michele Burford said.

“There are a lot of pressures. So, it’s a case of is the river going to just get worse and worse over time? Or is there scope to try and improve it?”

The three-year study aims to determine the origin of the most damaging nutrients by looking at water samples both in the lab and out in the field.

Those experiments will then be put through models that predict what might happen under different conditions.

“If we do this sort of restoration what would be the impact? If we get bigger rain events in future, what would be that impact?” Burford said.

She said conventional water quality monitoring focuses on the net effect of all nutrients, but cannot specify where management should be targeted.

University of Queensland expert Dr Alistair Grinham has also researched south-east Queensland’s rivers and said a study with the aim of maximising rehabilitation was a good thing.

Following the devastating 2022 floods, he found 98 per cent of Moreton Bay was covered in sediment from around the catchment.

He noted major flood events carry the most runoff into estuaries, and the need for projects that can limit these flows is urgent.

“The longer you leave it to try and fix it, the more expensive it gets,” he said.

Burford and her team are replicating their work on the Hawkesbury-Nepean River, north-west of Sydney, and are looking for a third river to add to the dataset.

The results should carry lessons for how to best care for rivers in general, and give companies using nutrient offset schemes more confidence in restoration projects, Burford said.

With the federal government working on a nature repair market and companies starting to consider the positive press of environmental work, Burford said the study could be relied upon by other investors too.

“We start to think about nutrients linking with things like carbon trading, we start to think about biodiversity offsets, it starts to all come together,” she said.

Start the day with a summary of the day’s most important and interesting stories, analysis and insights. Sign up for our Morning Edition newsletter.