Water quality science
Good water quality strengthens ecosystems
Good water quality starts on the land. Rivers and creeks are intricately woven into the landscape, capturing runoff from the land that feeds into freshwater and marine ecosystems. Decades of water quality data are helping growers improve their practices to enhance water quality while keeping their farms profitable.
The agricultural landscape
About 90% of Australia’s sugarcane is produced in Queensland, playing a significant role in our economy. It supports the livelihoods of thousands of Australians and is at the heart of many small north Queensland communities.
Many of these cane farms stretch along the narrow coastal plains adjacent to the Great Barrier Reef, among freshwater and inshore marine ecosystems. Research shows that dissolved inorganic nitrogen (a key component of fertiliser) discharged from rivers into the Great Barrier Reef has more than doubled over the past 50 years, and in some cases tripled in heavily cropped regions.
A major reason for this is due to extensive historical clearing that removed many wetlands and vegetation on floodplains. This vegetation once slowed water, retaining and filtering water while holding sediments and nutrients on the land. With less vegetation, intense rainfall flows more freely over the land. This has heightened the risk of floodwaters washing fertiliser and pesticide off the paddocks into catchment waterways.
Along with the footprint of other intensive land uses, elevated levels of sediments, nutrients and pesticides are transported through catchments to reach coastal wetlands and inshore marine habitats.
In the last decade, growers have made considerable improvements to their farming practices to reduce their water quality footprint, but more needs to be done.
Inshore marine environments
During the wet season, river plumes extend along the coast to cover inshore reefs and seagrass meadows, exposing these ecosystems to terrestrial runoff.
While inshore areas are commonly more turbid and nutrient-rich environments compared to offshore marine ecosystems, excess sediment and nutrients from runoff can reduce water clarity and disrupt the balance, which has flow-on impacts on habitats.
This can often lead to higher levels of macroalgae overgrowth on coral reefs, lower coral coverage, and less new coral growth. There's also evidence that excess nutrients can increase coral bioerosion and disease, and make corals more vulnerable to bleaching and weather-related stress events.
Freshwater wetlands
Waterways, such as drains and creeks, closest to farmlands are most impacted by excess nutrients and pesticides. Freshwater ecosystems often experience the most significant runoff impacts as the concentrations are higher. This runoff often leads to problems like excessive algae and weed growth, as well as decreased levels of dissolved oxygen in the water.
Extensive monitoring has shown that certain pesticides are often found in coastal waterways, sometimes at levels and combinations that exceed ecosystem protection guidelines. Given the nature of pesticides, these chemicals can harm plants and animals in waterways, especially those nearest to the farm.
With the help of extension providers and scientists, the farming community has made numerous positive improvements to paddock management, helping alleviate some of the water quality issues in the catchments.
Like the air we breathe, good water quality is essential for the health and resilience of freshwater wetlands, seagrass meadows and coral reefs, which support our unique plants and animals. Maintaining good water quality is essential to provide these ecosystems with the best chance for resilience and recovery.
Urban development, climate change and agriculture contribute to poor water quality in marine and freshwater ecosystems. Within this, intensive farming is recognised as a major contributor.
In the sugarcane industry, applying fertiliser is needed to enhance soil fertility, meet crop nutrient demands and promote healthy cane growth. Pesticides are also used to control and kill targeted pests. But heavy rainfall and intense irrigation can quickly wash nitrogen and phosphorus fertilisers and pesticides off the paddock and into drainage systems and waterways. This can harm ecosystems and put stress on habitats and aquatic species.
The 2022 Scientific Consensus Statement brings together the latest peer-reviewed scientific evidence to understand how land-based activities can influence water quality and ecosystem conditions in the Great Barrier Reef, and how these influences can be managed.
What are the impacts of poor water quality on ecosystems
How water quality monitoring informs practice change
Water quality monitoring is undertaken at a range of scales, from paddock-scale, creeks, drains and rivers, to wetlands, estuarine and marine waters. The purpose of monitoring is to understand fertiliser and pesticide losses, how nitrogen and pesticides moves through paddock and streams and their impacts on freshwater and marine ecosystems. Collectively, this monitoring at different scales gives us a catchment-wide understanding of paddock-to-reef water quality science.
Paddock monitoring is often conducted to benchmark and compare different management practices and to build knowledge of how applied farming products can be lost from the paddock. This includes testing the benefits of the timing, placement, product choice and application rates of fertilisers and pesticides. It also helps growers be more aware of the highest risk windows for farm losses and how to reduce runoff in these events.
Water quality science is complex. Each paddock experiences different weather patterns, soil types, irrigation use, waterlogging issues and more. Water quality monitoring captures the local differences, to show how the fertilisers and pesticides run off the paddock. It provides growers with locally relevant data to take control of management practices to reduce paddock runoff directly.
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FAQs about farming and water quality
Insecticides, including imidacloprid, are designed to kill insects like cane grubs. Herbicides, including diuron, are designed to kill weeds. Given the nature of these chemicals, plants and animals in waterways can also be harmed. If herbicides and insecticides runoff from the farm there is a risk to organisms that live in the receiving freshwater and marine ecosystems, especially those closest to farm. The highest direct risk is to downstream local waterways, freshwater wetlands and inshore seagrass meadows close to the shoreline, where pesticide concentrations are typically the highest.
All freshwater systems naturally flow into the inshore marine environment, particularly during high rainfall events. This brings any nutrients from the land into coastal habitats, including estuaries and seagrass meadows. Nutrients from agricultural fertiliser runoff can disrupt the natural balance in these inshore habitats. For example, it can cause algal blooms across both freshwater wetlands and marine waters and lead to excessive growth of macroalgae and phytoplankton particularly within the inner Great Barrier Reef lagoon.
While inshore reefs within the inner Great Barrier Reef lagoon are most at risk, there are important biological links between freshwater systems and outer coral reefs. Healthy freshwater and inshore aquatic systems are vital for the overall health and productivity of outer reef environments. Many species, such as eels, crabs and mangrove jack, migrate between freshwater and marine habitats at different lifecycle stages and use these areas as important breeding grounds. This connection means harmful impacts to freshwater and inshore marine habitats can also influence the health of outer reef ecosystems.
Scientists collect paddock water samples quickly after rainfall events to capture accurate nitrate levels. This can sometimes lead to the misunderstanding that nitrogen disappears in waterways.
Nitrogen exists in many forms in the environment, including solids, liquids and gases. When applied to crops as fertiliser, nitrogen can be up taken or rapidly converted to its various forms by several different processes related to parameters such as air/soil temperature, soil properties and crop stage.
Measuring these various chemical forms in farm runoff helps water quality scientists understand the specific nitrogen losses from a paddock, and how the nitrogen has been processed within this environment. When rain events occur, water samples from the resulting paddock runoff need to be collected, cooled, and sent to the laboratory within short time frames to accurately measure surface nitrogen runoff losses in rainfall and irrigation events.
It is important to note that nitrogen doesn’t disappear – it can get consumed by algae, bacteria, fungi and plants in waterways and can disrupt the ‘natural balance’ of ecosystems. In extreme cases, all available oxygen can be removed from the waterways and result in fish kills. Some nitrogen forms can be rapidly converted when exposed to warm temperatures and sunlight.Reliable measurements of the different forms of nitrogen leaving a paddock allow water quality scientists to calculate the surface runoff losses from a paddock and to quantify the benefits of improved management practices. In essence, robust water quality monitoring helps the farmer better understand losses of fertilisers and pesticides and to better plan their most effective use to retain them on the paddock.
Scientists have measured dissolved inorganic nitrogen concentrations in rainfall across the Great Barrier Reef catchments, including Babinda, Ingham, Townsville and Rockhampton. Data shows dissolved inorganic nitrogen concentrations in rainfall are very low, contributing less than 5kg of nitrogen per hectare of land it falls on annually. This nitrogen contribution to the ecosystem is naturally occurring and rainfall concentrations also vary between storm rain and monsoonal rains.
Water quality guidelines have been developed in Australia and are designed to provide protection for human health and for the environment. In that regard, they should be embraced as an important tool to inform responsible pesticide management.
These guidelines are an important tool to inform the risk to humans and to off-farm receiving ecosystems and are used to promote responsible pesticide management. It reflects the most up-to-date research of individual pesticide toxicity to a range of organisms, including algae, fish, macroinvertebrates and mammals. The pesticide guidelines are revised as new toxicity research becomes available. Historically this has included both increases and decreases to pesticide values in the guidelines.Recycle pits are designed to manage and contain smaller irrigation runoff events from parts of the farm. They are generally not designed to manage large rainfall runoff events and water volumes that fall across an entire farm at the same time. If these recycle pits overflow into downstream waterways and wetlands, they can become significant pathways in transporting pollutants. Some pesticides are highly stable in water and can persist within the pit for long periods of time.
Recycle pits can have an important role in increasing irrigation and water use efficiency for farmers and reducing off-farm irrigation tailwater losses from irrigation events reaching nearby aquatic environments.
How water quality monitoring informs practice change
Water quality monitoring is undertaken at a range of scales, from paddock-scale, creeks, drains and rivers, to wetlands, estuarine and marine waters. The purpose of monitoring is to understand fertiliser and pesticide losses, how nitrogen and pesticides moves through paddock and streams and their impacts on freshwater and marine ecosystems. Collectively, this monitoring at different scales gives us a catchment-wide understanding of paddock-to-reef water quality science.
Paddock monitoring is often conducted to benchmark and compare different management practices and to build knowledge of how applied farming products can be lost from the paddock. This includes testing the benefits of the timing, placement, product choice and application rates of fertilisers and pesticides. It also helps growers be more aware of the highest risk windows for farm losses and how to reduce runoff in these events.
Water quality science is complex. Each paddock experiences different weather patterns, soil types, irrigation use, waterlogging issues and more. Water quality monitoring captures the local differences, to show how the fertilisers and pesticides run off the paddock. It provides growers with locally relevant data to take control of management practices to reduce paddock runoff directly.
