In 2001 the Great Barrier Reef Management Authority (GBRMA) submitted its report to the then Reef Ministerial Council on the decline in water quality and the importance and urgency to address the issue. In August 2002, the Australian and Queensland governments announced a Memorandum of Understanding to protect the Reef from land-sourced pollutants.
Since that time, numerous reports, taskforces, independent reviews and plans have considered the impact of degrading water quality in the Reef, its causes and measures in place to address the issue. These include the Reef Water Quality Protection Plan (2003, 2009 and 2013), the Reef Report Cards (produced annually since 2009), a 2003 Productivity Commission report, independent science panels (2003, 2008, 2013 and 2017) and independent audits (2005 and 2010). More recently, the updated Reef 2050 Long-Term Sustainability Plan (Reef 2050 Plan) and Reef 2050 Water Quality Improvement Plan (Reef 2050 WQIP) have sought to establish long-term strategies to direct the protection of the Reef in the coming decades.
This chapter considers the current evidence-base on the impact of land-based run-off into the Great Barrier Reef, with specific focus on the connection between agricultural practices in the Reef's catchment regions with water quality outcomes in the Reef. Primary discussions about the scientific evidence-base revolved around the 2017 Water Quality Scientific Consensus Statement (Consensus Statement) and the use of modelling by the scientific community. This chapter then explores criticisms of the scientific process and the impact of anthropogenic sediments, pesticides (including herbicides) and nutrients on the Reef's ecosystem. This chapter proceeds to discuss the evidence relating to crown-of-thorns starfish (COTS) outbreaks, coral recovery from bleaching and extreme weather events (including overall coral cover and growth rates).
Stakeholder views on the scientific evidence base
The committee heard extensive support for the scientific evidence-base that has shown land-based anthropogenic pollutants have an adverse impact on the Reef's ecosystem, which provides the rationale for measures to reduce the amount of land-based pollutants entering the Reef's waterways. These witnesses and submitters unanimously argued the scientific process is robust and there are multiple lines of evidence to support this view. Further, this evidence has been refined over the past three to four decades, subsequently increasing scientists' confidence about the impacts of poor water quality on marine ecosystems in the Reef. This evidence has also refined management responses in the Reef's catchment.
This concept is not new or novel, having been well established since the 1980s, meaning the 'foundational evidence is very strong and well-established'. The CSIRO commented that 'there is considerable and a large amount of evidence suggesting that the [agricultural] processes we are currently using are detrimental to the Reef and will be into the future'.
Further, this phenomenon is not unique to Australia; evidence from other reefs around the world has shown that reefs adjacent to agricultural areas have either died or are dying because of land-based run-off. Further, it is not a problem that simply goes away, rather once those excess pollutants are expelled into the Reef's lagoon it becomes a legacy issue, as detailed by the Australian National University (ANU):
What they haven't evolved to is huge sediment dumps onto our reefs that come from changing catchment land use and soil erosion, and on top of that we've added chemicals, be they nutrients, nitrogen, phosphorous, pesticides or herbicides. Not only are we putting quite a toxic mix into our water; a lot of the sediment also settles down and lands on the reef and the organisms that live there…What's interesting about the legacy of polluted sediment on the reef is that the impacts can last from years to decades. It doesn't wash away with the next storm surge. If it's been deposited on the bottom of the reef, it can actually be re-suspended again and again and again. And, obviously, once it's on the reef, it's next to impossible to clean up. You needed to really prevent it entering the reef in the first place.
The urgency for improving water quality in the Reef is driven by a collective concern for the current trajectory of the Reef's ecosystem, which is primarily driven by climate change. AIMS explained the compounding effects of poor water quality and climate change has meant new approaches are needed to address the issue:
As time goes by, disturbances are occurring more often, are longer lasting and are more severe. We now know that chronic human impacts such as poor water quality, especially in near-shore areas, are superimposed on more acute long-term climate related pressures, making it harder for ecosystems to recover. The current trajectory is unsustainable. If the reef as we know it is to survive the coming decades, each of the various sources of stress that we can control will have to be reduced. The key question is how. It's time for new approaches and new solutions. Clearly, business as usual is not working.
The committee heard that the impact of this current trajectory wouldn't just be confined to the environment. Those communities and businesses that rely on the Reef's natural resources will be adversely impacted too. AIMS stated that the outcome of this continual decline will be the 'reefs as we currently know and enjoy them, both from a fishing and productivity point of view but also from a tourism point of view, will be a shadow of what they are by mid-century'.
In contrast, the committee also heard views that questioned the scientific basis of the impact of poor water quality and Reef science more broadly. These submitters and witnesses argued that the effect of land-based run-off was exaggerated, that the water quality situation is the Reef is improving, and that degrading reef ecosystems are a natural, cyclical occurrence. Dr Piers Larcombe argued that the key documents that have informed policy and regulations were not 'fit for purpose' due to being poorly designed, underpinned by weak science and lack objectivity. Dr Larcombe emphasised that Australia's research institutions have ignored relevant geoscience evidence (such as geology, sediment and past natural changes) and subsequently lack the relevant expertise. This view was similar to Dr Geoffrey Stocker, who spoke of current research being based on 'perceived current events' (such as coral bleaching) but not adequately considering the reef as a natural phenomenon with a history of climate-induced sea level change.
Key discussions during this inquiry focused on the Consensus Statement and the use of modelling to support scientific research (in particular the Paddock to the Reef program). These two matters are considered in more detail below.
Water Quality Scientific Consensus Statement 2017
The 2017 Consensus Statement builds upon the previous 2013 statement and provides a review of the 'significant advances in scientific knowledge of water quality issues in the [Reef]' and establishes a 'consensus on the current understanding of the system'. The Consensus Statement was led by a multi-disciplinary group of scientists, with oversight provided by the Reef Independent Science Panel and supports the Reef 2050 WQIP 2017–2022. The purpose of the Consensus Statement is to guide Reef policy for the Australian and Queensland governments by discussing the overall status of the Reef and its catchments, the source of pollutants found in the Reef and risk and management options available to address these issues.
The Consensus Statement found the Reef's ecosystem continued to be in poor condition, largely due to the land-based 'run-off associated with past and ongoing catchment development, coastal development activities, extreme weather events and climate change impacts such as the 2016 and 2017 coral bleaching events'. Concerning water quality, the Consensus Statement found initiatives would not meet water quality targets, and measures were urgently needed to accelerate the adoption of best practice. The Consensus Statement recognised that this acceleration would 'require greater incorporation of social and economic factors, better targeting and prioritisation, exploration of alternative management options and increased support and resources'.
The committee heard a high level of support for the Consensus Statement and the underlying scientific evidence from across science, government and non-government bodies. The Great Barrier Reef Foundation (the Foundation) stated that it has 'absolute faith' in the Consensus Statement and 'the weight of evidence underpinning it'. The Independent Science Panel commented that the Consensus Statement was the 'best available summary of information around the health of the [Reef] and the water quality problem'. The committee was also advised of the robustness of the peer review process that informed the Consensus Statement. TropWATER noted that it had been extensively reviewed, 'both internally…by the independent science panel and by the independent external peer reviews as well'.
Dr Rebecca Bartly, from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), was the lead author for the second chapter of the Consensus Statement. She iterated to the committee that the review process was quite rigorous, with three levels of peer review, and was inclusive of a range of scientific views, including those views shared by Reef science critic, Dr Peter Ridd:
Internally, as a consortium of scientists reviewing the literature, we did take on a range of views, including from Peter Ridd and colleagues in the second paragraph of this chapter. We did refer to it, because they've done some brilliant work in showing that it's a highly variable system. With understanding how things have changed, we need to take all that evidence into consideration, which we have done. The peer review process is then threefold. We do internal peer review. It goes then to the independent science panel for peer review, as well as to several government reviewers independently. So it's quite rigorous and thorough.
Representatives from the Independent Science Panel explained the robust nature of the review process of the Consensus Statement. Dr Shaw explained 1,200 references were considered and resolved by the authors of each chapter, who then provided their conclusions to the Independent Science Panel for review. External peer reviewers then considered those chapters and the whole statement. Dr Shaw disagreed with the assumption that the peer review process is poor.
AIMS commented that the Consensus Statement was a 'review and synthesis of the current state of knowledge' sourced from available literature and summarised. Through this process, the Consensus Statement makes the 'really complex body of work available to other people who are not reading the original scientific literature but who, through these reviews and synthesis processes, actually gain more access to that work'.
Regarding the term consensus, AIMS clarified that it was not the consensus of the opinions of those scientists that authored the report, rather the Consensus Statement is a synthesis 'of existing information and a knitting together of it into one story'. For this reason, the use of the term consensus in the title may be misleading to some. The Australian Academy of Science explained that consensus is applied because of the convergence of accumulated evidence from across scientific disciplines:
When the accumulated evidence converges towards certain strong conclusions in the minds of diverse researchers, we call this a scientific consensus. Such a consensus represents agreement on which pieces of knowledge have endured sufficient testing to be considered reliable. A scientific consensus is not absolute – it may be revised based on new evidence – but it nevertheless represents a firm basis from which advice may be given and decisions made.
Ms Jane Waterhouse from TropWATER led and coordinated the Consensus Statement. She explained that it was an update on previous statements that brought together 'new knowledge and reiterated previous knowledge'. Ms Waterhouse pointed out that the 2017 Consensus Statement was not a 'comprehensive piece of the entire story', rather it needed to read alongside previous statements 'to see the complete story'.
Some agriculture representatives and a number of scientists were critical of the Consensus Statement. Many argued that the scientific assumptions within the statement were flawed because the underlying scientific evidence is wrong, in part due to the replication crisis that has not been adequately addressed by the scientific community and its reliance upon modelling. These individuals and groups called for further scrutiny of the statement and expressed concern because it provided the rationale for the Queensland Government's Reef regulations, despite questions remaining about its accuracy and connection to farming practices.
Dr Ridd and Dr Larcombe argued the Consensus Statement failed to recognise the naturally occurring movement of nutrients down rivers and into the Reef and the resuspension of sediment during and after cyclone events, which are far more destructive to the Reef than agricultural practices. Dr Larcombe detailed how to improve the quality of research papers that inform public policy:
…if we are to improve the quality of these reports for use by government then perhaps the writers of these reports need some training in order to ensure that they deliver the objective information decision-makers require and that there are some sort of compliance checks to ensure that that happens, and perhaps the use of what is an international best practice of an evidence transparency framework…to actually demonstrate that that quality of the report is what is required. Again, I'd repeat that any policy report related to public spending should be held to a far higher level of rigour than a mere journal paper.
The committee asked whether the Consensus Statement could be improved through a red-blue team scenario, a quality assurance mechanism introduced by AIMS to add a further layer in its 'review of large-scale, complex, multi-component projects, which might have many scientists and/or papers contributing parts of a solution to a bigger problem'. Although supportive of any steps taken to 'increase and improve our knowledge over time', AIMS stated that the Consensus Statement was 'not an opinion based analysis' rather a 'review of existing information'. AIMS maintained its view that there is no 'replication crisis in marine science' and that it has 'full confidence in the science quality control and assurance processes, as well as the competence, professionalism and integrity of [its] scientists'.
Modelling is a well-established scientific method used by scientists to inform their understanding of the complex systems at play within the Reef and its catchments. This complexity is in part driven by the scale of the environment and the inability for scientists to measure every part of the Reef (and its catchments)—the Burdekin catchment region is almost the size of England, whilst the Reef is almost the size of Italy. AIMS highlighted that it is 'not possible to directly measure' the entire Reef over its 348,000 km₂ area. The committee heard that modelling is not solely relied upon, instead is utilised and tested against other scientific methods, such as field data and field evidence. Griffith University added that modelling is not about finding a 'perfect fit' and as scientists they would be worried if a model produced this outcome because there:
…will always be variability in the models, but it's the way that you can adjust the input data, or complement the input data, and use multiple lines of evidence to be able to make that model useful.
Many of the scientific bodies detailed their use of modelling and its benefits. Griffith University uses computer modelling for gully erosion to assist with the understanding of its scale and 'to target rehabilitation efforts and optimising investment in rehabilitation'. The Independent Science Panel stressed the importance of the marine biogeochemical eReefs model, because it provides the 'best available knowledge of the processes that operate on the continental shelf' and addresses the issue of sparse marine environment observational records. The CSIRO, which developed the eReefs model, submitted that their models are 'thoroughly calibrated using long term datasets and grounded in rigorous testing with research collaborations and next users'. The Bureau of Meteorology (BOM) uses both direct measures and its hydro climate data to:
…model the flow of rivers that feed into the [Reef] lagoon and the amounts of sediment, nitrogen and phosphorous that are transported to the river mouths. These data are made available to third parties, who use them for a wide range of purposes.
BOM detailed the scale of its modelling, comprising of 900 gigabytes of data every year, which equates to 9,000 measurements per site for each of the seven constituents it measures for every hour. The Queensland Government also records measurements of sediments and nutrients at 17 separate sites in different river systems. These data are then provided to the Queensland Government, who is responsible for measuring the data. Regarding the accuracy of these models, BOM noted that daily time scale flow models range from 80 to 99 per cent accurate, and hourly time scales accuracy ranged from 60 to 99 per cent, which is 'set against measurements taken at 270 locations'.
Although modelling is supported by the scientific community, the committee also heard that the quality of the model is reliant upon the quality of the data being inputted into the model. Another key issue with modelling is ensuring a dataset extends for a long enough period to be inclusive of natural variability, which is needed to compare natural conditions against anthropogenic changes.
The ANU spoke of the disconnect between scientists' monitoring and the feedback of these data back to farmers and other stakeholders, and the need for farmers to be informed of the impact their efforts have on improved water quality.
Dr Walter Starck argued the reliance on modelling has resulted in scientists moving away from basic research and instead being focused on hypothetical and imaginary environmental problems. Accordingly, this shift in scientific practice has 'resulted in an entire generation of researchers whose only experience of the [Reef] has been in the context of finding, promoting and investigating these hypothetical problems'. These researchers fail to collect empirical evidence based on real-world evidence; rather, rely upon hypothetical computer models that are generally not mathematically verified, nor empirically validated. Dr Starck concluded that these models are in fact 'nothing more than just the opinion of the researcher who created them'. Dr Starck did not provide any examples to substantiate his position.
Paddock to the Reef Integrated Monitoring, Modelling and Reporting Program
One of the contested elements of this inquiry has been the Paddock to the Reef Integrated Monitoring, Modelling and Reporting Program (Paddock to the Reef program). This program provides the framework for the evaluation and reporting of farmers' progress toward the Reef 2050 WQIP's targets, which informs the Reef report cards. Established in 2009, the Paddock to the Reef program monitors and models 'across a range of attributes, from paddock scale through to sub-catchment, catchment, regional and [Reef]-wide'. The program also evaluates the adoption of BMP programs and their effectiveness, catchment conditions, land-based pollutant run-off and marine conditions.
The monitoring component under the program tracks long-term trends in water quality entering the Reef from its catchments, monitoring total suspended solids, dissolved inorganic nitrogen, particulate nitrogen and particulate phosphorous. These data are sourced from 43 sites in 20 key catchments for sediment and nutrient loads, with a further 19 monitoring sites for pesticides. These data are collected monthly during low flow, dry season conditions and 'every few hours to daily during high flow events in the wet season'. Collected data are then 'used to validate the catchment water quality models and track progress towards Reef targets'. The committee also heard that some small-scale monitoring programs conducted in partnership feed into the Paddock to the Reef program.
Canegrowers and the Australian Cane Farmers Association (ACFA) criticised the Queensland Government for its limited scope of assessing farming practices, claiming the government only looked at Paddock to the Reef modelling with its considerations of the Reef regulations. Subsidiary Canegrowers groups spoke of being ignored by the bureaucrats responsible for the program, expressing disbelief that the program revealed BMP program adoption had declined. The committee heard of flawed reporting and the program's failure to recognise BMP adoption across industries, and its inability to show the source of pollutants. The committee also heard concerns about the accessibility of data related to modelling programs, and called for more transparency of modelling data.
One of the primary concerns communicated was the Paddock to the Reef program only recognising those farmers classified as an A or B grower, whereas those C class growers are not recognised for their contribution and adoption of best management practices. Canegrowers argued that the data found in the Paddock to the Reef program, which excludes many farmers applying best practice measures, unjustly provided the Queensland Government with the rationale for pursuing a regulated model (see Chapter 5 for further details). Canegrowers subsequently asserted that the Paddock to the Reef program requires sugarcane farmers to achieve a B grower status, which necessitates a reduction in nitrogen input by 15–30 per cent over ten years.
AgForce expressed its members' concern about the Paddock to the Reef program that has grown in complexity, with the industry's voice being 'smothered in layers of expert opinion and bureaucracy'.
The issue of modelling and farmers' disbelief in its results prompted Reef and Rainforest Research Centre (RRRC) to consider a different approach. The RRRC explained that many farmers 'disbelieved the science and many are very concerned, confused and confronted by the end-of-catchment predictive modelling' used by the Paddock to the Reef program. For this reason, the RRRC sought to address this problem with Project 25, a farmer-led management agenda (see Chapter 7 for further details).
From the evidence received, the committee does not question the legitimacy or the accuracy of the underlying scientific evidence that formed the Consensus Statement's conclusions. The committee believes the current review process used to produce the Consensus Statement is rigorous, thorough and inclusive. However, the committee is concerned by the misunderstandings about the Consensus Statement by those stakeholders impacted by its findings. For this reason, the committee is of the view that more should be done to engage and educate stakeholders from the agricultural sector about the findings of the Consensus Statement. Through this form of outreach, the scientific community may be able to alleviate primary producers' concerns about the underlying scientific evidence that subsequently impacts on the operation of their enterprises.
The committee recommends the Australian and Queensland governments ensure adequate stakeholder engagement and education processes are integrated into future Water Quality Scientific Consensus Statement processes.
Concerning the use of modelling to inform scientific findings, the committee recognises its vital role in helping scientists understand vastly complex and expansive ecosystems. The committee does not question the validity of the modelling used by Reef scientists and, overall, is satisfied that modelling occurs alongside the collection of field data and field evidence. Accuracy of these models is an issue, but the committee accepts that the quality of this data will improve over time, as will water measuring technologies.
The committee is concerned by the disconnect between the findings made by scientists, and how this information is presented to the agricultural sector. This disconnect has been demonstrated by the reported loss of confidence in the Paddock to the Reef program. Whilst this issue can be partially addressed through citizen science (discussed further in Chapter 7), the committee is concerned about the reported gaps in the Paddock to the Reef program. The committee believes more consultation and information can be provided to the agricultural sector about the findings of the Paddock to the Reef program, in particular more accessibility and transparency of modelling data.
The committee recommends the Australian and Queensland governments improve consultation, information, accessibility and transparency of data used to inform the findings of the Paddock to the Reef Integrated Monitoring, Modelling and Reporting Program.
Criticisms of the scientific basis for human impact on the Great Barrier Reef
Numerous stakeholders from across the agricultural sector, including farmers, and a small number of academics and non-government organisations expressed concern with the Reef regulations package and Reef science more broadly.
One of the primary critics of the scientific basis for determining the impact of agriculture on the Reef is Dr Peter Ridd, who advised the committee that 'there is no proof that agriculture has any significant effect on the reef whatsoever'. His views aligned with other witnesses and submitters, including Dr Geoff Stocker, Dr Piers Larcombe, Dr Walter Starck, Dr Jennifer Marohasy, the Institute of Public Policy and the Australian Environment Foundation.
Dr Ridd's submission addressed ten 'questionable claims about the damage' human activities have on the Reef, primarily from agricultural activities. Dr Ridd argued that these questionable claims are 'important to the issue of the general quality of the scientific evidence and quality assurance systems being used to inform government policy'. These claims were supported by a number of submitters who collectively question the existing scientific evidence. The Department of Environment and Science (DES) individually addressed Ridd's claims in its submission, as did other stakeholders during the inquiry.
These claims aligned with a number of themes discussed throughout the inquiry. This included debate about the impact of land-based pollutants on the Reef, Crown-of-thorn starfish (COTS) outbreaks, degrading water quality, coral cover and growth rates and coral recovery after mass bleaching and cyclone events. Each of these themes are explored below.
Water quality of the Reef
One of the key debates concerning Reef science concerns the overall water quality issues of the Reef. There was general consensus that the primary concern and area impacted by agricultural activities are the inner reef areas; however, reports varied on the extent of the area impacted by agriculture. According to Dr Ridd, only 1.6 per cent of the Reef is under the influence of agriculture, whereas TropWATER submitted that the total area potentially influenced by land-based run-off to be approximately 91,000 km₂ or one quarter of the total area of the Reef's marine park (excluding the impact caused by large flood events). The inner shelf of the Reef, which has the highest exposure risk, accounts for 12 per cent of the total area of the Reef's marine park, including 3.6 per cent of the 'total area of coral reefs and 77 [per cent] of the area of mapped seagrass meadows and mangrove forests (which provide critical habitat and breeding grounds for many species of fish, and turtles and dugongs)'.
A key point of difference was the extent of the damage induced by poor water quality on these inner reef ecosystems. Stakeholders agreed that water quality in the mid-shelf and outer reef was largely in very good condition, with an exception for flood plumes created by significant rain events. Despite these varied impacts of poor water quality, various science representatives spoke of the interconnectedness of ecosystems. TropWATER made clear that the Reef's ecosystem is made of 'strong interconnectivity between the mangrove, seagrass and coral reef ecosystems from the catchment, and across [Reef] shelf to the outer reef', and emphasised that the Reef 'cannot be segmented into parts of relative importance'. The distinction between the quality of water in the inner and outer reefs was explained by the Independent Science Panel:
…water quality is an inshore problem. The Great Barrier Reef region, as you know, is very large. It's also regionally subdivided by the physical oceanography of the continental shelf. Peter Ridd mentioned the inflow of water from the Coral Sea. That pours over the ocean side of the marine park boundary and strongly impacts on what happens on those outer-shelf reefs. What happens inshore is different. Things come out of rivers. Rivers are fresh water. That floats on sea water; it's a buoyant plume. The prevailing winds are from the south-east and so they push the plume back against the coast and drive it northwards. So, in a sense, the material that comes out of those rivers is by and large trapped in the Great Barrier Reef lagoon. That's really why observations of very healthy reefs a hundred or more kilometres offshore have absolutely no bearing on this problem.
Professor Ove Hoegh-Guldberg criticised the narrative that improved water quality is only about corals and that inshore ecosystems are of lesser value than other areas of the Reef. He explained that seven per cent of the entire Reef is made of reef-building corals and that specialised inshore regions of the Reef, such as the heritage listed mangroves, seagrasses and soft sediment ecosystems, are also vitally important. The health of these ecosystems, such as the mangrove forests, are important because 'many organisms, including many that are commercially important to Australia, spend part of their life cycle in these inshore reef areas, and if degraded we'll see the decline of these important species and industries'. Further:
It's very clear to me that treating the inshore habitats of the Great Barrier Reef as expendable is to ignore the all-important continuity of the reef and threaten the benefits of the reef for all Australians as well as our responsibility to protect the reef under the GBR Marine Park Act and the World Heritage Convention.
The impact of poor water quality for inshore reef ecosystems is a particular concern for the region's tourism sector. Divers for Reef Conservation spoke of the noticeable deterioration of these inshore regions and the adverse impact this has on the tourism sector. These inshore areas are the most visited, and the health of these ecosystems influences people's decision whether to visit the Reef. This point was contested by Dr Ridd, who argued tourists don't travel to inshore Reefs because of their turbidity.
One critique of the existing scientific basis, in particular the Consensus Statement, is its inadequate recognition of the ocean currents flushing the Reef's lagoon. Dr Ridd explained that the amount of water that enters the Reef each eight hours is equivalent to the same amount of water from all the rivers along the Queensland coast in a whole year. For this reason, the 'water quality of the reefs is determined by the Pacific Ocean not the rivers and farms'. Dr Ridd argued that the Consensus Statement failed to appreciate the flushing of the Reef, and for this reason 'extinguishes many claims of risk, danger or damage caused by run-off from the land along the entire coastline adjacent to the [Reef]'.
In response, the DES submitted that water can rapidly flush the Reef to the Coral Sea, but evidence has also shown that 'only a small portion of fine sediment and associated nutrients that comes from catchments is exported' and that '[m]ost of the discharged sediment and nutrients are retained within the [Reef's] marine waters'.
Erosion and sedimentation of the Reef's catchments' waterways is a natural process; however, research has shown that the amount of sediments entering the Reef has substantially increased since European settlement in the region, by approximately five times the pre-European rate across the entire Reef catchment.
Techniques such as isotope tracing/fallout radio nuclides have been used by researchers to gain insights into the past. Research conducted by the CSIRO has shown changes in sediment (and nutrient) loads in the Reef's region, relative to the natural export has increased since European settlement. Griffith University's Precision Erosion Management (PrESM) Research Group produced 'incontrovertible evidence' that the acceleration of sedimentation loads since European settlement, is 'linked to land-use pressures, principally cattle grazing…from the late [19th Century] onwards'. AIMS uses 'remote sensing (satellite observations) to observe variations in water clarity (a key measure of water quality) and the amount of light reaching sea-bed habitats over the whole Reef'.
Whilst evidence has shown an increase in sediment loads since European settlement, others have questioned this research. For sediments, Dr Ridd advised the committee that it has been known for over half a century that there is 'virtually no mud/sediment from the land that reaches the [Reef]-proper which is mostly over 50 km from the coast,' and for this reason, 'there is almost no land-derived mud on these reefs'. Further, mud and sediment deposits are a naturally occurring phenomenon for inshore-reef areas that account for only one to two per cent of the Reef's coral and are not part of the Reef. In these areas, muddy water is also caused by waves that stir sea-floor sediments that have been 'deposited over the last few thousand years'. Subsequently, these inshore-reef areas have adapted and are tolerant of sediment caused by wave resuspension. Similarly, Dr Starck submitted that sediment run-off has been reduced by crops and improved pasturage, and that virgin forests have a more significant impact on sedimentation because of the absence of ground cover on the forest floor.
Further, Dr Ridd argued that plumes of river water (that carry sediments) rarely reach the Reef, and when they do (as demonstrated by the 2019 floods), 'only reach a handful of the 3,000 reefs for a few days'. Dr Ridd iterated that these flooding events are rare, and when plumes reach the Reef, 'almost all the mud has dropped out of suspension.' Although the waters may remain discoloured due to leaf tannins, Dr Ridd pointed out that this organic matter is naturally occurring and harmless, and does not settle on the Reef. Dr Ridd accused scientific bodies of failing to point out the rarity of such flood events, nor do they 'show how quickly the plumes disappear'.
In response to these issues, the DES emphasised that 'fine sediment is of greatest concern to the health' of the Reef's ecosystem because it 'travels the furthest from the coast and reduces the levels of sunlight needed to keep seagrasses and coral alive'. Further, research has shown that the main source of these sediments is in fact from agricultural land use, largely from gully and hillslope erosion caused by grazing, and from the reduction of vegetation alongside stream and creek banks. Research has shown gullies contribute approximately one-third of the total sediment load in the Reef and up to 90 per cent of the sediment load in some catchments. On average, gully erosion has been found to contribute around 40 per cent of the total sediment load of the Reef's lagoon from less than 0.3 per cent of the total land area, with 80 per cent of these sediment loads coming from gully and streambank erosion.
Concerning wave resuspension along the coast and the difficulty determining a human versus natural impact, the Independent Science Panel acknowledged that those inland shore areas 'have always been turbid and life has adapted over a long period of time to live in such extreme conditions'; however, from their experience, those are not the areas to look for the 'signals of human impact', rather:
The area to look for it is in the extent of the flood plumes—that's on the margin between the terrestrial and the oceanic influences. In other words, it's sort of on the outer edges of the flood plumes.
The Independent Science Panel added that whilst fresh water does impact reefs located close to river systems, these flood plumes extend out and float at the surface over the Reef's lagoon. The fresh water doesn't sink and impacts the ecosystem below by reducing light penetration. Flood plumes events can impact the inner 30 per cent of the continental shelf, and seagrasses are known to take eight to ten years to recover from these major events. Over the last reporting period, the reduction in sediment levels was only 0.5 per cent.
The impact of pesticides on the Reef's ecosystem was discussed at length during the inquiry. Of all the land-based pollutants in the Reef's waterways, pesticides are the most easily measured because they are not natural and can be easily tracked back to the land. TropWATER stated that the 'evidence that it comes from agricultural industries is unequivocal', nor is it an issue that's unique to the Reef—it is a known agricultural pollutant found in 'catchment and downstream ecosystems around the world'.
Overall, there was general agreement that the detection of pesticides (including herbicides and fungicides) typically occurs in waters adjacent to areas of their use, and occasionally in river mouths and inshore reef regions. These chemicals are rarely detected in the waters of mid-shore and outer reefs, with possible low-level exposure during significant wet season events. CropLife Australia clarified the detection of a pesticide in an 'environment doesn't necessarily or automatically assume that the chemical would be posing a risk to the environment', rather risk is a product of the level of exposure through concentration levels and duration of exposure.
Despite the minimal detection of pesticides throughout the Reef, it was reiterated pesticides pose the greatest risk to the ecosystems closest to the source, namely freshwater inlands, rivers and estuaries, followed by coral ecosystems, seagrass and coral. Further, that the Reef's marine ecosystem and adjacent catchment regions are all interconnected. DES submitted that the 'conditions of all parts of the system, including the catchment, is important for the long-term health of the [Reef]'. This point was also made by the Independent Science Panel, which added that despite its low risk to the Reef it should also be of concern for those catchment ecosystems. For this reason, the WQIP seeks to protect 99 per cent of the Reef's catchment waterways but 'some catchments that only get to 55 per cent or 70 per cent. So there are a number of pesticides that are getting out into that close inshore area that are exceeding the guidelines required by World Heritage area'.
The committee asked about the impact pesticides have on coral growth rates. AIMS explained that it had conducted studies using its Sea Simulator to look at the effects of pesticides and herbicides on corals, seagrasses and other marine plants, such as microalgae. The research found that seagrasses were most vulnerable, although corals are affected by chemicals impacting on symbiotic algae. On notice, AIMS outlined the history of its research into pesticides (including herbicides). Research has found certain types of herbicides affect the 'photosynthetic efficiency of the algal symbionts of corals and at higher enough concentrations and long enough exposure times cause corals to expel their algal symbionts and bleach'. Follow-on effects from this herbicide exposure include reduced growth and reduced reproduction output.
The pesticide chemical industry has in place numerous best practice programs to support farmers with on-farm management of their pesticide usage. These programs include container management systems, pollinator protection initiatives and a spray application best practice program. CropLife Australia highlighted its strong outcomes through its programs and called for other input sectors to take inspiration and lessons from the pesticide industry for the best way to achieve environmental outcomes.
Concerning nutrients linked to farm practices, the committee heard that whilst phosphorous and nitrogen are essential for plant growth, these nutrients have detrimental and damaging effects on the water ecosystems. In excess, these nutrients continue to stimulate growth in aquatic plants, and in extreme circumstances, can create dead zones. These dead zones are created due to nutrients propelling the growth of aquatic plants, which then decompose and remove oxygen from the ocean. In the Gulf of Mexico, these dead zones caused by pollutants carried by the Mississippi River can extend for 7,000 square miles. Although the Reef's exposure to nutrients is 30 times less than the Gulf of Mexico, it is still impacted by excess nutrients in the same way.
As noted in Chapter 1, the Reef's lagoon is naturally a 'low-nutrient and high-light environment', which has enabled corals, seagrasses and the entire ecosystem to flourish. However, natural competitors to corals and seagrass, such as macro and micro algae (phytoplankton), flourish in high-nutrient and low-light environments. According to the AIMS, long-term excessive nutrient conditions can disrupt the natural balance between algae and corals and lead to an algal dominated ecosystem. An excessive nutrient environment does not disappear once a river plume dissipates, rather microalgae and those excessive nutrients move through the ecosystem's food chain, and 'have the potential to 'cycle' through the [Reef's] ecosystem on long time-scales'.
The need to address excess nutrients within the Reef's catchment regions has been of ongoing concern, with calls for the regulation of fertiliser first made in the 2003 Joe Baker report. The committee heard that the overall reduction of Dissolved in-organic nutrients (DIN) in the Reef for the last reporting period was only 0.3 per cent. It is estimated up to 50 per cent of applied fertiliser ends up as run-off, or not being available for plant growth, which according to the ANU is an 'unnecessary expense for the farmer in apply that fertiliser'.
Crown-of-thorns starfish outbreaks (COTS)
A contentious part of the research about the impact of nutrients on the Reef's ecosystem is the link between COTS outbreaks and fertiliser levels in the Reef's lagoon. Those critical of this link argued that it is unresolved. Dr Ridd explained that COTS outbreaks had previously been attributed to the harvesting of Triton shells and that the most prolonged plague occurred at Swains Reefs, which is 150 km from the coast and 'completely unaffected by runoff from the land'. Dr Ridd's submission stated that COTS are a native species and evidence has shown COTS populations have reached plague proportions prior to European settlement. Walter Stark suggested that COTS play an important part and have a positive attribution to the Reef's ecosystem by maintaining coral diversity. In his appearance before the committee, Dr Ridd referred to the inadequate evidence to support the hypothesis that links nutrients and COTS outbreaks, and it was premature of the Consensus Statement to place blame on farmers for these outbreaks.
Overall, the DES disagreed with Dr Ridd's analysis, arguing that long-term water analysis has shown that 'turbidity increases are strongly related to river discharges in regions where [COTS] outbreaks originate'. The DES also made reference to the Consensus Statement, which identified waters adjacent to the Wet Tropics region were at greater risk 'because river flows with high nutrient levels occur in regions with high fertiliser use and these are areas where [COTS] outbreaks occur'. Further, laboratory research has shown that COTS larvae grow faster when exposed to increased nutrients.
The DES submitted that reports of COTS outbreaks coincided with the increase in popularity of scuba diving and tourism in the 1950s and 60s, and recognised the ongoing debate about the naturalness of COTS outbreaks. The DES made reference to COTS outbreaks in the Indo-Pacific region, which has shown the species is prone to boom-bust cycles; however, noted that it is widely assumed that outbreaks are more frequent in modern times and have a severe impact on the Reef. DES argued that controlling COTS outbreaks is vital to 'boosting the Reef's resilience to climate change and other pressures'.
AIMS advised the committee that the COTS outbreaks are a complex ecological phenomenon, and current understanding is that increased larvae survival is promoted during period of increase nutrients, in combination with reduced predation pressure. The combination of these two factors results in COTS outbreaks at regular intervals. The Great Barrier Reef Marine Park Authority (GBRMPA) clarified and concurred with the evidence that has shown nutrients exacerbate or fuel outbreaks, rather than cause the outbreaks. The GBRMPA explained the distribution of pollutants within the Reef's lagoon, in particular, as flood plumes after big rainfall events. The committee heard that these flood plumes move in a northerly direction and cover the entire Reef matrix, subsequently leading to:
…an incidence, or a coincidence, of the geographical footprint of farming, the geographical footprint of flood plumes and the initiation zone of the crown-of-thorns starfish, at least in the northern part. Also, I should emphasise that crown-of-thorns starfish outbreaks happen in different places at different times. I'm not aware of anyone who would argue that every instance of a crown-of-thorns starfish outbreak anywhere in the world is caused by exactly the same cause. It's different things in different places at different times. The nutrient connection is concerning.
The Independent Science Panel agreed that outbreaks are indeed natural and not new, but contested the view that COTS have a positive impact on the coral diversity. It stated this view was popular from 40 years ago, but 'if you look at the level of cover of coral on most coral reefs around the world, it is hardly a relevant consideration any longer'.
Coral recovery from bleaching and cyclone events
The committee heard divergent opinions about the overall health of the Reef and its recovery from major events, such as mass coral bleaching and cyclones. The 2016 and 2017 bleaching events destroyed approximately 40 to 50 per cent of the Reef's coral cover, with further declines expected as a result of the 2020 mass bleaching event. Dr Ridd submitted that although major mortality events caused by cyclones, bleaching and COTS outbreaks occur, coral reefs in every case recover strongly and rapidly. Reference is made to the increased coral cover of the southern reef area, which amounted to 250 per cent from 2010 to 2016 after Cyclone Hamish.
The DES also recognised that coral reefs can recover from major mortality events; however, recovery is highly variable and based on long-term data. Further, the DES highlighted that 'recovery is only possible if there is sufficient time between major disturbances'. Analysis has shown that overall recovery is declining on the Reef due to the short time between disturbances, which is further compounded by poor water quality. In addition, mass bleaching events are regarded as a new disturbance, having been first reported in 1983. Evidence from the 2016 and 2017 mass bleaching events has shown that there has been an 89 per cent 'decline in new coral larvae settling on the Reef, and suggests that recovery from these bleaching events may be significantly slower than other types of disturbances'.
AIMS clarified that poor water quality has 'yielded very little direct coral loss' but it influences the Reef's recovery from such events. Further, those reefs located inshore that are regularly exposed to reduced water quality 'might be much slower to recover from those events'. AIMS iterated that determining the impacts of climate change, water quality and coral cover loss is a complex ecological question.
As noted in Chapter 2, this complexity and its impact on public policy is reflected in the Great Barrier Reef Marine Park Act 1975. The precautionary principle obliges the Australian Government to refrain from postponing 'measures to prevent degradation of the environment where there are threats of serious or irreversible environmental damage', even in the circumstance of the 'lack of full scientific certainty'. This requirement under the Act was emphasised by Professor Ian Chubb, Dr Geoff Garrett and Professor Ove Hoegh-Guldberg.
A key concern shared by a number of submitters and witnesses is the evidence-base about coral cover and coral growth rates across the Reef. Dr Ridd submitted that reliable measurements had only begun in the 1980s and although coral cover has fluctuated, it remains the same today as when monitoring started. Dr Ridd identified major cyclone events being primarily responsible for coral decline. Dr Ridd contended that an Australian Coral Reef Society paper failed to mention the total recovery of the Reef between 2011 and 2016. In addition, Dr Ridd questioned a 2019 paper that reported significant reductions of coral cover on inshore reefs, stating that 'it is very likely that this decline is short-lived as many of these reefs have recently been affected by major cyclones'. Dr Ridd also argued that coral growth rates have not fallen, rather they have marginally increased in the last century based on research papers from 2013.
Evidence of coral growth rates were debated at length during the inquiry. Debate centred upon correspondence that showed AIMS advising AgForce Queensland Farmers that agricultural activities did not significantly impact coral calcification rates of the Porites species. The committee asked why this finding was not referenced in the Consensus Statement.
In response, AIMS explained Porites is a hardy and slow growing coral that is used to collect coral cores from hundreds of years ago to assist with researchers understanding of the coral's changing environment. Whereas there are other corals, such as Staghorns or Acropora, that are more fragile and fast-growing coral species. Concerning the correspondence, AIMS clarified that there are clear linkages between declining coral growth rates and water temperature, but there has been no linkage made between growth rates and agricultural activities. AIMS added that these are two separate issues were being conflated. AIMS proceeded to explain the importance of the calcification process in the Reef, as the foundation of reef building, and the Porites coral acts as a history book that has shown 'there are periods of time when calcification has reduced, and we have been able to link that with marine heatwaves and coral bleaching…[which] is not something that has anything, as far as we know at the moment, to do with water quality'.
At the committee's hearing on 27 July 2020, an assertion was made that there was 'no recorded publication that gives a Great Barrier Reef-wide average of growth data since 2005'. AIMS responded that:
'[t]he piece of evidence you are referring to here is the analysis of calcification rates in coral, of Porites coral[…]in terms of 'an entire database of growth rates for the Great Barrier Reef as a whole? No such thing exists.'
AIMS advised the committee that its Marine Monitoring Program and the Long-term Monitoring Program (the longest running coral status survey in the world) has a 35-year dataset that reveals coral cover growth and decline for the whole Reef. This data is published yearly as part of a long-term monitoring program. This monitoring maps the growth of coral communities across the entire Reef 'using the best-practice, global standard methods applicable to those species'. This data is made available via scientific journals, media releases, AIMS website, social media channels and through the AIMS Data Centre. GBRMPA and DES both cited the AIMS long-term monitoring program and the Marine Monitoring Program, which have tracked coral growth, recover and impact since 1985 in the northern, central and southern reefs. GRMPA explained that these programs have shown reefs can recover from impacts, but over the long-term 'each subsequent rebound is not reaching previous levels of coral cover'.
On notice, AIMS further explained that the Reef had over 450 species of hard (reef building) coral with 'different growth forms, life spans and traits such as their mode of feeding and reproduction'. A fundamental indicator is coral growth rate, which 'provides an understanding of coral reef recovery after disturbance events, as well as reef-building'. Due to its diversity, growth rates vary between species, years and habitats—subsequently, different methods are used to measure coral growth rates. However, AIMS noted that:
For such assessments, growth calculated from coral cover estimates is the world-wide accepted indicator. AIMS publishes annually a report on the status and trends of coral cover on the Great Barrier Reef, based on our 35-year data series of the AIMS long-term monitoring program…Assessment of the health of inshore reefs are undertaken as part of the Marine Monitoring Program, coordinated by the [GBRMPA], with reports and data freely available. AIMS long-term monitoring methods, including quality control and data management procedures, are described in regularly updated Standard Operational Procedures. Each year, about 120 reefs are being surveyed, representing reefs along the length and breadth of the GBR.
The DES also referenced evidence that coral cores have shown growth rates have slowed and that '[r]ecent coral growth trends (since 1990) show an unprecedented decline in coral growth when compared to the last 400 years'. This decline is attributed to climate change and is being expressed in coral regions throughout the world. Coral growth is also suppressed by major bleaching events, as well as increased sediment and nutrient inputs from rivers.
The committee has considered the scientific evidence that shows an impact from land-based pollutants on the Reef. Whilst the committee acknowledges those arguments made by various witnesses and submitters that the evidential base is lacking; the committee, in line with the Australian and Queensland governments, is satisfied that the evidence shows strong linkages between agricultural practices and the decline in water quality in the Reef. Although further research is required in regard to the impact of nutrients on COTS outbreaks, the committee is of the view that the scientific evidence provided that shows there are impacts on the Reef from agricultural pollutants. The committee is assured by the rigour and quality of the research regarding coral growth rates and coral cover throughout the Reef, recognising that determining the impacts of climate change, water quality and coral cover loss is a complex ecological question.
The committee also notes that the Australian Government, under the Great Barrier Reef Marine Park Act 1975, is governed by the precautionary principle, which means the 'lack of full scientific certainty should not be used as a reason for postponing a measure to prevent degradation of the environment where that are threats of serious or irreversible environmental damage'.
The committee recommends the Australian Government continue to uphold its responsibilities under the precautionary principle in the Great Barrier Reef Marine Park Act 1975.
The committee recognises the primary purpose for pursuing improved water quality is to improve the resilience of the Reef in light of more concerning projections. Namely, the increase in oceanic water temperature that causes mass coral bleaching events, such as those witnessed in 2016, 2017, and more recently, 2020. In addition to warmer waters, the Reef and adjacent catchment regions are likely to experience more severe weather events, such as cyclones, in the decades ahead. These weather events will further exacerbate the challenges faced by the Reef, and the communities reliant upon the Reef for their livelihoods.