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Can offsetting mitigate the damage caused by floods of nutrients from fertilizers and wastewater in our rivers?


The rivers that flow through the hearts of Australia’s major cities and towns often carry heavy loads of nutrients and sediments.

This is a problem. While nutrients such as nitrogen and phosphorus are essential to life in small amounts, they become destructive to river and ocean ecosystems in large amounts.

When rivers are pumped too full with nutrients washed away from farms or wastewater treatment plants, bacteria and algae numbers soar. We see the effects in dangerous blue-green algal blooms and in oxygen levels falling so low that millions of fish could die, as we recently saw in Menindee, New South Wales.

Solving the problem can be expensive and difficult for landowners. That’s where a new idea could help: nutrient compensation. Here, large wastewater treatment plants can meet stringent requirements to keep nutrient levels low by repairing eroded riverbanks and channels upstream, creating wetlands and preventing fertilizer runoff. The end result: cleaner rivers.

While carbon offset schemes have come under scrutiny, nutrient offset is a simpler market, with fewer participants and clear ways to measure success.

Early trials in South East Queensland by water companies have proven it can work, like ours new report shows.

Poor water quality can lead to fish kills and algal blooms.

Why are our rivers too full of nutrients?

In the early industrial period, rivers around the world were seen as dumping grounds, from factory chemicals to tannery waste. Since then, many countries have worked hard to clean up their waterways, with great success, including the River Thames in the United Kingdom.

It is relatively easy to stop chemical dumping. You can see the pipes and control who is doing it. But nutrient overload is a more difficult problem, which is why we still struggle with it.

Our cities and towns are growing. There are now nearly seven million more people living in Australia compared to the year 2000. As our population grows, we need more food and create more human waste. Our agricultural sector has also boomed, exporting more and more food. Fertilizer is needed to make our famously poor soils fertile. If too much fertilizer is applied, it can end up in rivers due to heavy rains. Erosion on river banks and in channels exacerbates the problem.

Read more: Would a wildlife recovery market really work? There are indications that it is highly unlikely

Some rivers, estuaries and coastal waters have major problems, such as parts of the Murray-Darling and some urban creeks in our capitals. We have reached their natural limit to handle the load of nutrients and have gone over it. This can lead to algal blooms, fish deaths and water that is too disgusting to drink without expensive treatment.

Queensland erosion
Erosion accelerates the runoff of nutrients from farms.

Why do we need compensation at all?

Chemical dumping can be solved with laws and enforcement. But while we can repair degraded river basins to reduce nutrient loads, this is rarely done. This is because the costs are too high to be borne by one sector, such as farmers.

Regulations on nutrients discharged from sewage treatment plants, on the other hand, set limits on the amount that can be discharged into rivers and estuaries. The cost of further upgrades to sewage treatment plants to reduce nutrients to the required low levels is prohibitive, as taxpayers would end up paying much more for water treatment.

Therefore, compensation can be useful as it offers a win-win. Urban polluters such as wastewater treatment plants can meet their regulatory requirements by restoring eroded and degraded watersheds upstream to reduce nitrogen and phosphorus flows from farmland. Better, this can be done fairly cheaply if done on a large scale. Depending on available locations, this can be done along rivers and creeks on rural properties, or on municipal land in cities and towns.

For this to be viable, a market must be used. Polluters looking for cheap ways to comply with nutrient flow regulation are associated with landowners upstream with degraded land.

This is an emerging solution, but early trials show it holds promise. The densely populated southeast of Queensland has major waterways such as the Brisbane and Logan Rivers. Sewage treatment plant operators such as Logan Water, Urban Utilities and Unity Water have replanted shrubs, grasses and trees along riverbanks and conducted engineering work to stabilize eroding banks.

This led to significant cost savings. Urban Utilities avoided spending $8 million upgrading a sewage treatment plant to reduce nutrients and got the same result by spending $800,000 on erosion control and revegetation upstream, preventing five tons of nitrogen from entering the waterways. Operating costs were also much lower, saving $5 million over ten years.

Controlling erosion keeps nutrients in the soil to help crops and grasses grow, benefiting farmers rather than being washed downstream. Healthier riverbanks create better habitats for birds, reptiles and mammals and make rivers healthier for fish and other species.

What’s next?

Nutrient compensation is still new in Australia. To gain traction across Australia, you need to make sure the systems and science are mature.

To maximize benefits and provide certainty to participants, we need to move from a fragmented trial approach to a coordinated trading schedule. Successful foreign examples typically have a third party coordinating purchases and sales and provide a robust structure to set up and review these projects.

Canada has had successes here, such as the South Nation River trading program reducing phosphorus levels in the river, while America has examples such as the Chesapeake Bay food credit trade program. In Australia, a voluntary one reef trading schedule is underway in the basins of rivers that flow into the waters of the Great Barrier Reef, involving farmers and a range of investors.

For this to work, we need detailed scientific knowledge on how to compare nutrient pollution from different sources. Nutrients discharged from watersheds are mostly bound to soil particles, while sewage treatment plants contain much more dissolved nutrients. We don’t yet know how these sources differ.

We also need to know which land management methods are best suited to prevent nutrients from entering rivers, to ensure the best outcome for the money spent.

Creative solutions are needed

Despite our efforts to clean many of our rivers, traditional approaches have not been enough to stop nutrient pollution. It’s time to explore creative new approaches to making our rivers and reefs healthier.

Read more: How did millions of fish die panting in the Darling – after three years of rain?

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