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By Amy Edwards 31 October 2018 8 min read

Agricultural inputs such as fertiliser, herbicides and pesticides, along with eroded soil, enter waterways, making their way to the sea. Pictured is a plume from the Johnstone River near Cairns. Image: Kate Hughes

NOT all research taking place on the Great Barrier Reef involves examining beautiful coral in its natural habitat or diving to the ocean floor to eliminate the coral-eating Crown-of-thorns starfish.

In an attempt to study the full range of impacts on this global icon, which is larger in size than Italy, CSIRO researchers are busy working from “ridge to reef” and it can be all about getting their hands dirty.

Declining water quality from land-based runoff and coastal development is the second biggest threat to the Great Barrier Reef behind climate change. A key focus of protection and recovery efforts for the reef are based in the catchments adjoining its coastline.

Agricultural inputs such as fertiliser, herbicides and pesticides, along with eroded soil, enter waterways making their way to the sea and have severe impacts on water clarity and coral resilience.

CSIRO Research Scientist Dr Rebecca Bartley and her team are the experts when it comes to studying declining water quality from land-based run off.

In conjunction with government bodies and fellow research groups, they continue to work on-the-ground with agricultural extension officers and the grazing industry to develop practical and effective land management solutions for the reef.

Climate change and increasing resilience

“The first bleaching event occurred in the 1990s but it wasn’t until the major bleaching events of 2016 and 2017, that climate change became more widely accepted by communities and policy makers as the number one threat to the Reef, “ Bartley says

Despite this, scientists believe many areas of the reef still show resilience, which presents a window of opportunity to act now, while there is still enough diversity to preserve and restore it.

“We still need to address land based management in conjunction with climate change action to make the Reef as resilient as possible,” Bartley says.

“We can’t let the reef continue to be hit with multiple stresses at the same time.”

Agricultural pollution has had a major impact on the condition of coral reefs, reducing their resilience to bleaching and cyclones. In particular, fine sediment and associated particulate nutrients reduce water clarity, slowing coral growth, impairing coral recruitment and making coral more vulnerable to disease.

The big Burdekin

Much of the CSIRO’s land management research has been based in the Burdekin catchment which is more than 130 000 square kilometers and drains into the Great Barrier Reef lagoon south of Townsville on the east coast of Australia.

“The Burdekin is the largest contributor of sediments and nutrients into the reef,” Bartley says.

“It also has the largest amount of water flowing through it and is about the same size as England. The science tells us where to focus efforts to reduce sediments and nutrients, and the Burdekin is a valuable case study.”

CSIRO’s research has directly informed the location of a range of Government Programs aimed at improving water quality in the catchments draining to the reef. These programs include the Queensland Government’s Major Integrated Projects and the Australian Government’s Reef Trust investments. Together, these represent more than $50 million of funding focused on grazing management and gully and stream bank remediation across targeted areas of the GBR agricultural landscape.

This year alone Bartley and her team of researchers, technicians and a range of national and international collaborators have contributed to five published research papers on land management in the Great Barrier Reef (see full list at bottom of story) and all of them have showcased significant research in the Burdekin.

The papers range from Grazing impacts on gully erosion in northeast Australia to the Nature Scientific Reports paper on sources of nitrogen discharging into the GBR lagoon and Insights into the history of land use and its impact on erosion rates in catchments draining into the GBR.

Grazing impacts on the Great Barrier Reef

Gully erosion is the dominant source of fine sediment and excess soil attached nutrients affecting water quality to the Reef. Poor grazing practices are still considered one of the major contributors to gully erosion in northeast Australia. The “gully erosion” research and associated paper, led by Dr Scott Wilkinson from CSIRO, summarised more than a decade of measurements on gully erosion in the upper Burdekin. The research was co-funded by CSIRO, Meat and Livestock Australia (MLA), Queensland Government Paddock to Reef Program, Department of Defence and the National Environment and Science Program (NESP).

Gully erosion in the Burdekin catchment has taken place over many decades.

The study found that under long term livestock exclusion, sediment yields from gullies were 77 per cent lower than those of grazed gullies. The study suggested that reducing livestock grazing pressure within and around gullies would be a primary method of hillslope gully erosion control.

“Over the years we’ve had lots of contact with graziers and things have changed from 10 to 15 years ago; there’s a lot more awareness about improving land management practices now,” Dr Scott Wilkinson says, a lead scientist in Bartley’s team.

“Our next challenge is to partner with graziers on how to convert the scientific knowledge into practical changes that landholders can make on the ground. This is a challenging area that requires the integration of social, economic and biophysical science – and crosses many research areas for CSIRO.”

All of the government funded programs are focused on achieving cleaner water through direct remediation and better land management practices.

The CSIRO researchers identified “hot spots” in the Burdekin catchment where the remediation programs were most needed and would be most effective. This was based on research led by CSIRO that used tracers to identify the key hot spot locations and processes driving the erosion.

Meanwhile, the National Environmental Science Program (NESP) involves monitoring five properties in the Burdekin catchment (in Upper Burdekin, Bowen, Bogie and Don sub-catchments) where researchers are collecting land condition, terrain and water quality data. This data will demonstrate whether on-ground investment programs are actually improving measured water quality, and help determine the cost-effectiveness of the various approaches.

Nitrogen runoff from fertiliser

Reducing levels of nitrogen runoff to the Great Barrier Reef is also major objective for water quality managers as excess nitrogen can cause algal growth (which reduces water clarity affecting coral and seagrass growth), impact coral reproduction and trigger outbreaks of crown of thorns starfish (COTS).

Nitrogen is a major component of the fertilisers that are added to crops such as sugarcane and bananas. It can also be delivered from soil erosion. Understanding the sources of nitrogen is important for developing mitigation strategies to reduce nitrogen loads from large river basins draining to the Great Barrier Reef.

The recent “colloidal nitrogen” research and subsequent paper was led by Dr Jonathan Judy (formerly of CSIRO but now with the University of Florida, USA).

It found that some of the material that is currently measured as dissolved nitrogen is actually very small particles derived from soil and this is known as colloidal nitrogen.

“For many years we have been perplexed by the relatively high levels of dissolved inorganic nitrogen (DIN) in water running off non-fertilised grazing lands” Bartley says.

“Now we know that much of this nitrogen is not dissolved but is actually attached to very small soil particles that are less than 0.45 µm in diameter. This finding has implications for establishing and evaluating water quality targets, and also for how we prioritise investment in catchment remediation” Dr Bartley says. “It appears that managing soil erosion can reduce the amount of what is typically regarded as dissolved nitrogen.”

What history tells us

Bartley believes understanding the history of land use in the catchments draining into the reef is critical to improving current land management practices. She further explained this in her recent history and timing of post-European land use disturbance paper published in the Marine Pollution Bulletin in May this year.

“There can be a tendency to assume that today’s industries and land holders are entirely responsible for causing water quality impacts, however, a lot has gone on in the past that has contributed to the current condition of the land and water quality - Mining over 100 years ago continues to have an impact on erosion in some areas, and a lot of gully erosion was initiated in droughts long ago which current land holders have inherited. Variable changes in climate have also impacted. Trying to un-tangle each of these impacts is hard to do. Using a range of different approaches, such as sediment dating and historical analysis and linking that to coral data has helped to piece the story together,” she says.

“Grazing practices are still considered the biggest contributor of sediment in the Burdekin. However to treat the symptoms properly, we need to understand all the causes. It’s important to ensuring further prevention, as well as for cost effective remediation of highly erosive areas.”

Moving forward

With our partners that include James Cook University, Australian Institute of Marine Science, the North Queensland Dry Tropics and the Queensland Departments of Environment and Science; Agriculture and Fisheries as well as Natural Resources and Mines, CSIRO has defined the system of erosion and sediment transport processes connecting agricultural land with water quality in the Reef. We have assisted the industry, agricultural communities and the Australian Government to be more targeted in their programs to reduce sediment and nutrient delivery.

Our research continues to support the current Reef 2050 Long-Term Sustainability Plan, through the Reef 2050 Water Quality Improvement Plan 2017–2022.

A huge amount of effort is going into protecting this global icon and often the effort is occurring kilometres away from where the coral is actually living.

Wherever the research is taking place, protecting this world heritage listed ecosystem will continue to be a massive collaborative effort for many years to come.

Read more from papers published in 2018:

Grazing impacts on gully dynamics indicate approaches for gully erosion control in northeast Australia.

Colloidal nitrogen is an important and highly mobile form of nitrogen discharging into the GBR lagoon

Fine sediment and particulate organic matter: A review and case study on ridge to reef transport, transformations, fates and impacts on marine ecosystems.

Making management decisions in the face of uncertainty: a case study using the Burdekin catchment in the GBR

Insights into the history and timing of post-European land use disturbance on sediment rates in catchments draining into the GBR.

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