Q&A with Steve, Mark, Zoe and Aaron
In 2023, a research paper titled Submarine Groundwater Discharge Exceeds River Inputs as a Source of Nutrients to the Great Barrier Reef was published and received widespread media attention. It caused confusion among growers, extension officers, government, and other stakeholders - raising questions about how we manage water quality on the land.
In response, Dr Stephen Lewis, Dr Mark Baird, Dr Zoe Bainbridge and Dr Aaron Davis challenged aspects of the paper’s findings with a published commentary.
To unpack the science and their response, we sat down with these scientists for a Q&A discussion about how they interpreted the findings and why they felt it was important to speak up.See the links to the documents here:
The journal article titled Submarine Groundwater Discharge Exceeds River Inputs as a Source of Nutrients to the Great Barrier Reef
The media article in The Conversation, written by authors
It's important to understand that science is a process of refining our understanding and communicating the findings in a way that is constructive and understood accurately by audiences. This Q&A discussion is part of that process. We are not questioning the data collected in the Tait et al. (2023) paper, but rather how it has been interpreted and communicated.
We respect and value the work of fellow scientists. Our focus here is on how the results of the study were framed, particularly in the media. The intent is to clarify the findings to audiences and if these findings change the way we manage and protect the Great Barrier Reef.
What is the Tait et al. (2023) paper about, and why is it a concern?
The Tait et al. (2023) paper, Discovery of invisible nutrient discharge on Great Barrier Reef raises concerns, suggested that submarine groundwater discharge is a major source of excess nutrients to the Great Barrier Reef. But our analysis – backed by decades of reef water quality science – clarifies that most of these newly delivered nutrients to the Reef come from river discharge, not fresh groundwater. The study's broad definition of submarine groundwater discharge, which includes recirculated seawater, could mislead management efforts by shifting focus away from land-based nutrient reduction strategies.
We argue that improving farming practices to reduce nutrient surface runoff remains the most effective way to protect the reef. In addition, these same practices adopted by growers already address nutrient concentrations in groundwaters.
What was the main concern about the paper, and how was it misrepresented?
Our main concern was the definition and interpretation of submarine groundwater discharge and its implications for managing water quality in the Great Barrier Reef. The study included recirculated seawater as part of submarine groundwater discharge, even though it is not linked to freshwater flowing from the land. Recirculated seawater is ocean water that moves through the seabed, interacting with sediments and organic matter, before being released back into the reef system. This process allows the water to pick up nutrients from the seabed, but it does not involve new freshwater inputs from the land. Unlike fresh groundwater discharge, which originates from the catchment and carries land-derived nutrients, recirculated seawater is part of a natural marine process that redistributes existing nutrients within the reef ecosystem.
You wrote a formal response about the paper. What does this mean, and are you doing anything else?
Yes, after the paper was published, we wrote a formal response (called a journal correspondence) to challenge and clarify parts of the original study. In addition to this, we also spoke to key government representatives about our concerns and how we would interpret the data. We focused on:
Clarifying the difference between fresh groundwater flowing from the land and the seawater that has been recirculated through sediments.
Highlighting the importance of particulate and dissolved nutrients carried by rivers and how they break down and release nutrients into the Great Barrier Reef lagoon.
Demonstrating that the volume of submarine groundwater discharge proposed in the study was greater than the total annual average rainfall volume in the Great Barrier Reef catchment, meaning their definition cannot be linked to freshwater inputs from the land.
Addressing concerns about the radium-based model used to estimate submarine groundwater discharge, given how water actually moves in the reef lagoon.
Other historical research specifically on catchment groundwater losses that suggested a very different story to the one presented in the Tait paper.
The authors of the study responded with a rebuttal. What did this include?
They acknowledged that fresh groundwater flowing from the land makes only a small contribution compared to seawater that has been recirculated through sediments.
They stated: “The comparison of total submarine groundwater discharge to rainfall by Lewis et al. correctly suggests that the total calculated submarine groundwater discharge cannot be derived from fresh groundwater inputs alone. We do not dispute this, as the total submarine groundwater discharge (recirculated seawater plus freshwater discharge) is not governed solely by the amount of freshwater discharge.”
Additionally, they recognised the importance of nutrients carried by rivers and how they may be processed on the seafloor, stating: “We do, however, agree that large exports of riverine particulate nutrients are important. Indeed, settled terrestrial particles may eventually mineralize and release nutrients to the ocean via submarine groundwater discharge.”
Does this mean groundwater is not a concern in the Great Barrier Reef catchment?
No, there are still groundwater challenges in some parts of the catchment, including rising groundwater levels, high nitrate concentrations, and occasional pesticide contamination. However, existing best management practices cover both surface runoff and water draining into groundwater, meaning the key strategies for reducing nutrient losses remain appropriate. Groundwater and land use interactions are still a major research gap in GBR water quality science and should receive increased attention.
What are the key management implications of your findings?
Our findings reinforce that the current priorities for managing nutrients under the Reef 2050 Plan remain valid. Most of the nutrients released on the seafloor in the inner shelf of the Great Barrier Reef likely come from the breakdown of nutrients carried by rivers, or from marine organic matter produced using those nutrients. This means that from a management perspective, reducing excess nutrients in river discharge remains the key priority.
Do the media articles about this paper misrepresent reef water quality science to growers?
Yes. The way the media articles were framed misrepresents reef water quality science. The paper’s findings received significant media attention. This media coverage framed submarine groundwater discharge as an overlooked and dominant nutrient source affecting the reef. The media implied that current land-based management strategies, including efforts to reduce nutrient runoff from farming, may not be targeting the biggest source of nutrients. This could create confusion about where management efforts should be focused.
Decades of reef catchment research reinforce that land-based surface runoff is the dominant contributor of new nutrient input from the land to the reef. The current management strategies under the Reef 2050 Plan, which focus on improving farming practices to reduce excess nutrient runoff, remain the most effective approach for improving water quality.
Is science often misrepresented in the media?
Science is complex, and sometimes we find research papers are not communicated correctly. It’s a tricky balance to get right. However, water quality science and cane farmers in the Great Barrier Reef catchment have been under intense scrutiny for several decades. The information presented to the public can be politicised, conflicting, confusing, or misunderstood – this has led to growers becoming confused, annoyed and at times rejecting accurate reef water quality science. It’s important the science provided is clear and accurate. This is the main goal of the Water Quality Science and Agriculture Hub – to provide clear, unbiased water quality science to those who need it.
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