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Wetlands, water quality, and agriculture
Wetlands slow and hold back water before it flows into rivers and downstream marine ecosystems. As water moves through, wetlands have the potential to process and break down nutrients and trap organic matter and sediment particles.
Wetlands have recently received greater attention as a potential water quality management tool – but how well do they work in agricultural landscapes?
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Wetlands can be part of the solution to improve water quality across the agricultural landscape, if they are well-managed and purposefully designed.
But to maximise their ability to act as water treatment systems depends on many factors that need on ground investigations specific to the unique characteristics of local catchments.
What are wetlands?
For more information on these ecosystem services see the WetlandInfo website.
Natural wetlands
Natural wetlands have been a stable part of our landscape for thousands of years. They come in many natural forms, including lakes, floodplains, swamps, marshes, billabongs, creeks, saltmarshes, mudflats, and mangroves.
They provide habitats rich in biodiversity of plants and animals and are shaped by complex structures, intricate water pathways, diverse vegetation, and carbon-rich soils. They also meet human values, including: social, cultural, recreational and economic.
Wetlands provide many ecosystem services, like providing food, shelter, shoreline protection and habitat for Queensland’s rich biodiversity.
Constructed wetlands
In agricultural areas, wetlands can be constructed for specific purposes, including drains, sediment basins, and treatment lagoons. These human-made wetlands have been mostly built over the past 60 years.
Constructed wetlands are designed to mimic the natural function of wetlands, like capturing, treating or reusing water. These systems vary in size and purpose, from small, pond-like structures that recycle irrigation water with limited biodiversity, to large, engineered wetlands that span several hectares to either capture and treat water or offer habitat for native plants and animals.
How have wetlands changed over the last century across coastal Queensland?
Looking back
Historically, the Queensland coastline was made up of floodplains that connected a network of swamps, lagoons, rivers and estuaries.
During heavy rain, floodwaters spread slowly across these broad, low-lying areas, holding water back from rivers for days or even weeks.
Under these conditions, water had time to soak into the ground, while sediments and nutrients from the land were mostly trapped or naturally processed and broken down within the floodplain.
Developing Queensland
Through the development of regional Queensland, there was a focus on expanding agriculture and supporting urban growth.
This included initiatives that cleared large areas of the coastal floodplains, removing natural vegetation and wetlands. The landscape was reshaped into paddocks with drainage systems designed to move water from the land quickly, making it suitable for crops to grow.
Today, this intensive farming landscape in the Great Barrier Reef catchments is largely dominated by the sugarcane, banana and grazing industries.
The flow-on effect from these changes
These changes were driven by the need to improve livelihoods by creating jobs, producing food and supporting communities.
While agriculture has thrived, these changes now send floodwaters and runoff into rivers much faster than before. There’s less time for the water to slow and soak within wetlands, to top-up groundwater and for nutrients to be processed and broken down, and for organic matter and sediment particles to be trapped.
With the added broad-scale use of synthetic fertilisers and pesticides to maintain crop production, higher levels of these products are carried into waterways and groundwater systems.
What's remaining
Many remaining wetlands across the coastal zone are scattered, disconnected from waterways or degraded. In this heavily modified landscape, the natural functions of wetlands have been reduced.
What do Queensland’s coastal wetlands look like now?
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Today, Queensland’s coastal farming zones feature a mix of natural, modified and constructed freshwater wetlands, including floodplain lagoons, swamps and drains.
What does the science say about their ability to improve water quality?
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Wetlands vary widely in the size, shape, water depth, vegetation, and soil carbon. This natural variability, combined with unique local conditions, makes it difficult to determine exactly how much individual wetlands can process and break down nutrients, and trap organic matter and sediment particles.
Until recently, most of our understanding on pollutant removal came from international studies, which show that wetlands with more vegetation, higher soil carbon, and larger, more complex shapes tend to treat water more effectively – especially as they mature.
However, in the past five years, there has been significant investment in gathering field data from Queensland’s wetlands and developing advanced modelling tools. As a result, we are now building a clearer picture of which wetland characteristics are most likely to make a meaningful contribution to water quality outcomes.
Within Queensland, there have been only limited field studies that have comprehensively measured a wetland's water balance – this includes measuring how water enters and exits a wetland system, how this water interacts with groundwater, and the quality of this water.
While these advances are encouraging, further research is still needed to fully understand and maximise the effectiveness of wetlands as a water quality management tool.
Wetlands as a water quality management tool
How does water treatment work?
Water flow
When water enters a wetland – either from rainfall, runoff, or groundwater – it slows down. This gives sediment and organic matter particles time to settle on the bottom, instead of rapidly being carried downstream. It also provides time for nutrient processing to occur.
Vegetation
Trees, grasses, and sedges on the banks and floating plants act like a natural sponge. They trap fine particles, stop soil from moving, and help hold water in place for longer. Some vegetation can also provide shade for animals and contribute organic matter, supporting the food web and nutrient cycling within the wetland. The type and density of vegetation also makes a difference to their effectiveness to capture and treat sediment and nutrients.
How does water treatment work?
Plants and microbes
Nutrients can be converted and broken down by microbes, such as bacteria, through processes such as denitrification, in the soil and water, and taken up by plants. The longer water stays in the wetland, the more time there is for this processing. This works best in wetlands with healthy and abundant vegetation and carbon-rich soils.
How does water treatment work?
Flood control
Wetlands reduce flood peaks by holding water temporarily, helping water soak into the ground, and slowing down the volume of water moving through the catchment.
How does water treatment work?
Constructing and managing wetlands
Can wetlands be a part of the solution to water quality?
Wetlands can process runoff and improve water quality for local ecosystems, while also providing benefits to farmers and the local community. The most important factor is ongoing management of the wetland. A well-managed wetland system can provide benefits, while a neglected system risks becoming part of the problem.
Why do wetlands need to be managed?
Whether it is a newly constructed wetland or a natural wetland that exists on a farm – wetlands that aren’t maintained can become clogged with sediment, overgrown with weeds, or damaged by pests. Poorly managed wetlands may lose their ability to slow and hold water and support the vegetation and microbes needed to process and break down nutrients.
Have a purpose
Before committing to construct a wetland, it’s important to consider its purpose, how it will be managed, and how it will deliver positive outcomes. Regular maintenance is needed for both natural and constructed wetlands, including controlling weeds, managing water levels, maintaining vegetation, repairing banks and keeping out feral pigs.
The bottom line?
Constructed wetlands can be part of the solution to help improve water quality in agricultural landscapes. If they are well-managed and purposefully designed, these wetlands can mimic a wetland’s natural functions of holding back and treating water.
It’s also important to understand how wetlands interact with the surrounding landscape, such as how much water flows from the catchment into them, how they might be affected by nearby rivers and estuaries and the way they fill and drain.
For a wetland to be effective at capturing and treating farm-scale runoff, the specific farm features need to be considered when designing the constructed wetland. Every farm is different, and the type of wetland that works best will depend on factors like location, size, soil type, upstream catchment area and climate.
There are many projects that work with farmers to find the best spots to construct new wetlands, either on-farm or in drainage areas. These efforts can help manage runoff while supporting productive farming.
For broader scientific information on wetlands and all their ecosystem services, see WetlandInfo – the Queensland Government’s repository for all scientific material regarding wetlands.
A first-stop-shop for wetland information in Queensland providing a range of tools and resources to assist with the sustainable management of wetlands.
Wetland Condition Monitoring Program
The status and condition of natural, freshwater floodplain wetlands in the Great Barrier Reef catchment area.
2025 Wetlands Synthesis Report
Report on the effectiveness of wetlands in water quality improvement, costs and cost-drivers in the Great Barrier Reef catchment area
Scientific Consensus Statement
The most comprehensive and rigorous review of water quality in the Great Barrier Reef to date.
Related content
Images sourced from Canegrowers, Cassowary Coast Reef Smart Farming, Catchment Solutions, ©emvielle, Farmacist, Great Barrier Reef Foundation, HCPSL, SRA, Nathan Waltham, and Tony Webster.
The Hub is funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation, under the Regional Water Quality Program.
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