Episode 8: Scientist Jon Brodie

Jon Brodie has been studying the world’s coral reefs for more than 30 years and is a leading expert on the impacts of run-off and water quality.

Audio transcript

Introduction: The Great Barrier Reef needs to be fighting fit to cope with climate change. While the world takes action to address climate change, improving water quality is the best thing we can do to increase the Reef’s resilience. Run-off from the neighbouring catchment can cause all sorts of problems when pollutants end up in delicately balanced reef ecosystems in his podcast series we talk to farmers scientists extension officers and local experts to hear their water quality perspectives.

Jon Brodie: My name’s Jon Brodie, Iam a professorial research fellow at the Centre of Excellence for Coral Reef Studies at James Cook University in Townsville. My role and it has been for many decades is to do research and be involved in management of water quality in the Great Barrier Reef and I've been doing that through positions at universities and at the Great Barrier Reef Marine Park Authority for many years.

Vanessa: Jon can you tell us about the global challenge of water quality?

Jon: Yes the problems are similar everywhere particularly for coral reefs but for other marine systems as well. For coral reefs, the combined issues of run-off from land, discharge of sewerage, some places around big cities and climate change are affecting coral reefs everywhere no matter where it is. They are all affected whether it’s in Madagascar, Indonesia or Japan or the Red Sea in Yemen where I worked or Fiji. A similar set of issues, of course locally they vary depending whether you have a sort of run-off you have, whether it’s a big city with sewerage discharge and climate change has somewhat different effects in different places as well.

But the combined effects of land run-off, to some extent fisheries in some places as well; destructive fisheries and water quality along with this rising temperature and ocean acidification are really degrading coral reefs everywhere in the world.

This is the shallow coral reefs, I am not talking about deep coral reefs like you get down at 1,000 metres off Tasmania or Scotland. They are a very different case. But these are the shallow reefs, go down about 100 metres generally in the surface ocean in the tropics.

Vanessa: Can you get specific and talk about the water quality issues in the Great Barrier Reef catchment?

Jon: Yes essentially the big problem is the amount of fine sediment, the amount of nutrients, like nitrogen in particular and the amount of pesticides that run off the land through our rivers and into the Great Barrier Reef have increased greatly in the last 150 years. Fine sediment overall by maybe five times, nitrogen by double maybe and pesticides of course they didn't exist before.

So we can't say they've increased a hundred times or anything but they've increased an infinite times because it was zero before and that's happened just over the last hundred and fifty years and that has had dramatic effects on the Great Barrier Reef.

All of those fine sediment causes problems of turbidity in the water, lack of light for coral and for other things like seagrass. Sediments out onto the cold surface that causes coral mortality. Nutrients cause a whole range of issues like crown of thorns starfish outbreaks, like bioerosion of coral, like algal overgrowth or changes in the relationship between coral and algae, more algae, less coral. It enhances bleaching, nutrients as well. They’re just a few of the things that affect corals and seagrass.

Then pesticides while their differential effects, most of the effects are inshore in estuaries but herbicides for marine plants just like they effect terrestrial plants that they need to act on. Insecticides have the same effect on small crustaceans and so on as on the insects that were designed to kill in the first place. In addition to those major ones of course we have a whole lot of other pollutants, contaminants that are more recent if you like, which we know less about. These include plastics both macro plastics that turtles and so on eat. Micro plastics all sorts of things take up. We don't really know much about what the long-term effects of all this plastic in the oceans.

Pharmaceuticals coming out of sewerage treatment plants, personal care products food additives, caffeine, all sorts of things that don’t get trapped in sewerage treatment plants, toxic metals mobilised by dredging or discharge. So we have a range of lot of things but the main things we're still concentrating on are sediment nutrients and pesticides.

Vanessa: A lot of the stuff you've just mentioned has been reported last year in the Scientific Consensus Statement, it would be good if you could just help people understand what that document, what its intention was, its purpose?

Jon: We've had now four Scientific Consensus Statements more or less. First one in 2001, was different. I’ve been involved in all of them and then we've had more or more organised ones 2008,’13 and ‘17. Each five years roughly and they've been done really to bring the science together about what we know about water quality and the Great Barrier Reef and its interaction with things like climate change as well that focus on water quality before we did major revisions.

And so the purpose of the Scientific Consensus Statement certainly was to get the best published peer reviewed science together to tell us what was going on and what the priorities might be for management. That’s been its purpose. And it's also particularly important to report on progress. We have the report cards that also report on progress and come out every year. But the Consensus Statement tries to take an overview of how we're going as well, in management. And so make statements particularly in the conclusions of the Consensus Statement about how we're travelling.

Vanessa: Do you think there's a sort of barrier forming in society between science and lots of groups who need to understand complex information?

Jon: That’s a growing trend around the world of course we need our scientists put that down to the fact that we're telling them the situation for the environment is in desperate, we are at the end for lots of things and that hard decisions have to be made. So an easier path to making hard decisions on climate change and all sorts of things is scepticism of the science. We see that particularly in the US and other places, Australia, that it's easier to deny the science than it is to take the hard decisions. And so we're going away from evidence based policy really.

Vanessa: The Scientific Consensus Statement is a very long document out of necessity it covers a lot of ground. Could you give us a summary about the number of factors that came together to make this a consensus.

Jon: Well each of the three recent Scientific Consensus Statements have been designed in the same way to get together a group of the most published eminent scientists who work in the space of water quality in the Great Barrier Reef together.

In each of the three late recent ones there’s been about 50 people scientists who have extensive publication record research in this area and they range from economists to a social scientists, biophysical scientists, management, government people and they then have, we have rules about what information you’re going to accept, published material, it has to be peer reviewed, peer reviewed material that can be papers research papers or in reports. Then the idea is then we draw on thousands of people’s work because if we look at the reference list many thousands of people have been involved in that. So the idea here is to get a summary, consensus. Science does work by consensus and to summarise that just in to 500 pages.

For starters it looks at all different parts of the system as best we can and then summarise that into executive summary which is still a few pages and then into that final statement which is half a page. That’s quite an effort to distil that down into something - the message we want to give to the public and the politicians and so on about what management’s needed. So we try to turn it into information and knowledge. Remember science doesn't produce facts anyway, it produces probabilities and possibilities. With good stuff there will be some uncertainty. We produce facts if you like with uncertainty. Looking at just a few papers doesn't get you anywhere because this is the most well researched environment in Australia the Great Barrier Reef.

Vanessa: Could you just talk about some of the key messages for canegrowers out of that Consensus Statement and generally about water quality?

Jon: Their issues are around nitrogen. Number one. Not about sediment. Largely because of some things they did in the past which were good. They didn't do it for environmental reasons really, trash blanketing, green cane harvesting. Many of them are doing reduced tillage. So sediment is not a big issue, it probably was at one time but it’s not a big issue in cane. So that’s okay. Fertiliser use particularly nitrogen fertiliser is a huge problem, still.

Vanessa: Can you tell us about the specific problem of nitrogen in a place like Cairns?

Jon: So to grow sugarcane, you need nitrogen, phosphorus and potassium in particular. They are the fertiliser types they add to grow cane. They add a lot of nitrogen. It’s a very nitrogen hungry crop and typically they use above 100 kilograms of nitrogen per hectare per year in sugar between 100 and 250 depending where you are and that is essential for the cane growth and for the sugar development as well. You can grow cane without sugar but that’s not very useful. Now generally the cane itself needs 90 to 100 kilograms of nitrogen per hectare per year to be taken up to grow the sugarcane to get a reasonable yield of sugar. Farmers have to use quite a lot more than that because it doesn't all get into the sugarcane. Some will be lost by some other mechanism so they have to use more than the minimum amount.

And that is the problem in a sense because that difference between 100 kilos of nitrogen in the sugarcane that goes off to the mill and the 150 that was put on perhaps; 50 kilograms of nitrogen per hectare per year goes somewhere else.

The places I can go I can go into the atmosphere as nitrogen after denitrification. It can go into the atmosphere as nitrous oxide which is a greenhouse gas, which is not so good. It can run off as nitrate or ammonium in surface runoff into the rivers or it can run off subsurface into the groundwater as well which may eventually get to the rivers as well. They are the main routes if you like some of it stored in the soil from year to year. The nitrogen and some of it's in the trash that’s left on the ground so there's pools of nitrogen.

However the more nitrogen you use the more loss there is through all those pathways. So if he use more nitrogen you get more loss and you'll end up with more nitrate in the river downstream of your farm. And we've done extensive research and monitoring over decades to show that this happens anywhere you grow sugarcane it doesn't matter whether it's whether its Maryborough or Mosman or anywhere else in the world in fact Brazil same thing happens of course.

So we know a lot about nitrogen. Now if you just think about the application of nitrogen and where nitrogen might come from in the landscape. Nitrogen nitrate comes out of rainforest of course as well at very low concentrations but still it's there because it's an essential part of plant growth and everything else, nitrate comes down with the rain and rainforests hang onto their nutrients tightly but they have nitrogen and phosphorus and you get small concentrations come out of rainforest. There's a lot of rainforest and that can still add up to be a bit of nitrate.

On the other hand, in sugarcane, you're adding 150 kilos of nitrogen per hectare per year and as you'd expect that the amounts that come out of sugarcane are maybe 100 times the amount of nitrate that comes out rainforest in the same area.

And in fact we have some wonderful research done in the wet tropics that shows if you just plot how much sugarcane there is in the catchment and what the nitrogen proportion of 5 percent 10 percent 100 percent in little sub catchments on a cane farm, against nitrate, you get a perfect straight line. See that the nitrate’s coming from the sugar nitrogen. Other sorts of land uses like wet tropics grazing they don’t use much fertiliser so the amount of nitrate that comes off wet tropics grazing situations are quite small. Other crops though are big nitrogen producers. Like bananas use large amounts of nitrogen fertiliser in fact greater than sugarcane.

And we have lots of data on that. And of course from other places we have data on grain crops and macadamias and all sorts of other things as well to compare.

Vanessa: So the problem is one for canegrowers to think about what is the sort of response you get from canegrowers in general and how do they feel about this?

Jon: That depends on where you are and what's happening in the external world. If you think of the relative cost of fertiliser with respect to overall cost of growing sugar when sugar prices are low it's quite a large part of the cost overall cost and at that time they reduce nitrogen use anyway on a cost basis. Times when sugar prices are high they go back to usual again. So there's other factors that come into what they do on their farm management as well as any environmental concerns.

For coral reefs, climate change has become now the major problem for coral reefs around the world and in the Great Barrier Reef.

That doesn't mean that other issues such as crown of thorns starfish, turbidity from sediment, discharge aren’t still problems they are. It's just that climate change has got so much worse. .

However the whole Great Barrier Reef is not coral reefs there are other wonderful things they too like seagrass, dugongs, turtles and so on and water quality management is of benefit to them as well. And also, we can still do something for the coral now if we do it quickly. We have to do it now and at the moment we're not doing it now. We're not doing enough. As the Consensus Statement says what we are doing now is not enough.

If we were really to do what we think should be done in the next five years I think we could still make a difference for the coral.

Vanessa: What is your call to action for water quality?

Jon: I think we have to do things quickly.

Last updated
15 February 2019