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The Australian Coastal Zone and Global Change: Research Needs

Australian Academy of Science, Becker House, Canberra. Friday 16 December 1994

Discussion

Professor John Chappell: Thank you, Peter. We now have some time for questions and discussion. Are there any questions?

Professor Ralph Slatyer: Just to start the ball rolling: I am from the ANU. I could not see why sea-level change would necessarily change the salinity and anoxia levels. Accepting the fact of the redistribution of the coastal zone geomorphologically, surely those same mangrove species would find comparable habitats in the new environment with respect to salinity and anoxia?

Professor Peter Saenger: What I was suggesting is that there will, at any one particular point, be a change. With increasing sea level or greater tidal incursions, there will be changes at one particular point. If there is scope for inward movement or if there is room to move, those same conditions that had existed there before would re-establish on a more landward basis, assuming the sediments are of the same characteristic. What I did not talk about in detail was obviously that the sediment characteristics themselves may affect the salinity and certainly the anoxia of the sediments.

Professor Bruce Thom: I was just going to ask perhaps if Peter might comment on whether or not he sees any changes in the characteristics of mangroves in tropical areas as a result of, say, increasing CO2 and fertiliser effect on the plants at all?

Professor Peter Saenger: Most of the mangroves and C3 plants are such that the increase in the CO2, at least theoretically, should increase the photosynthetic production. There may well be other effects such as storminess. While productivity may increase, the actual production may be limited to destruction of plant tissue, growing tips and so on. So that that is certainly an area that needs further quantification. Certainly in terms of storminess, destruction of areas, entire zones are being removed. I think that is probably going to be fairly important as well.

In relation to possible questions of sediment stability where, for example, there is no major terrestrial input of sediments, there may well be very large-scale erosion or regression of mangrove shorelines. Any increase in productivity is probably going to be relatively small in terms of what might happen with major erosion, at least in the Australian mangrove system.

In the American systems and in the west African systems where the species are much more rapid heat producers, it may well be there that productivity at peak production in the soils may in fact allow the mangroves to keep up with most types of sea-level change.

Dr Patrick Holligan: Can I ask Gregg Brunskill: are there are any elements of your projects that deal with the impacts of changes in land use or perhaps the changes in climate, like precipitation?

Dr Gregg Brunskill: Yes and no. There are aspects of deforestation in the northern coast of New Guinea and along the north coast of Irian Jaya as well that have occurred quite recently in some cases. The entire basis of the Mamberamo River is slated for large industrial park development in the next 10 years by the Indonesian Government, including a hydro-electric dam to be constructed on the place. Are those the large-scale type of experiments you are thinking of?

There are a number of mines that come into and go out of production in the Fly River basin that the Australian Institute of Marine Science has taken advantage of in the past 10 years as a source of funding for our research there, in which case there are chemical perturbations in the system that might be thought of as used as experimental spikes.

The largest experimental spike is the Ok Tedi mining operation in the headwaters of the Fly. The delivery of that sediment load to the delta has happened already, and major models are being made of how that doubling of load transport into the delta, how that material is moving through it. For example, particulate copper is an excellent tracer in the Fly delta. I know less about the Sepik. As far as climate-related changes: I do not anticipate any climatic experiments of our own making in New Guinea.

Professor John Chappell: Could I just pursue myself that same question with Gregg. The Ok Tedi mine, as you say, has almost doubled the sediment yield of the Fly-Strickland basin. It has gone from about 10 to the 7 tonnes per year up to 1.7 times 10 to the 7 tonnes per year, and is going to run at that level for another 15 years yet.

This is the kind of anthropogenic change which has occurred in that one catchment. It is becoming visible in the delta. The same scale of change in a much smaller catchment is the Freeport Mine in Irian Jaya. This kind of thing can be multiplied either by point source mine inputs or by regional deforestation.

Against this background, do you think there is any chance whatsoever of detecting a greenhouse-related climatic effect and, if the latter is not detectable, is it likely to be important at all?

Dr Gregg Brunskill: Several of the river basins that I mentioned, specifically the Mamberamo and the Digul, I do not think have large mines on them and have very minimal development. The Sepik and the Fly definitely have disturbances. The Purari River as well has several disturbances that probably will confuse the message. Some of the sediment core and coral-related historical work on hindcasting river flow and sediment-related delivery to that zone may show the effect of this land-use change and will presumably show the variation in those kinds of parameters previous to the land disturbance.

I would hope that over a four-century record in pyrites cores, we would be able to distinguish changes related to natural variation from those to do with land-use disturbance and/or, in the case of the river basins that are not disturbed, hopefully you would see signs of the presence or absence of climate change and global change.

Professor John Chappell: Thank you. Can I invite the audience to ask any questions.

Professor Ann Henderson-Sellers: I think it was the last speaker who said: 'since storminess is correlated with sea level rise'. I thought that was a particularly provocative statement.

Professor Peter Saenger: I was speaking in terms of mangroves where we are looking at what are essentially the subtropical or latitudinal limits of mangroves. It is predicted that monsoonal storms with rising sea levels would extend further south. So in that sense, in relation to mangroves, storminess and sea-level rise are apparently correlated.

Professor John Chappell: I might just comment that the CSIRO Division of Atmospheric Research produce climatic scenario documents periodically in which changes of temperature, rainfall and other climatic variables are predicted with confidence limits. The one in which they are least willing, in the most recent issues, to make a predictions is in fact the incidence of storminess.

Dr Greg Holland: I really do think one of the problems that we have is that the incidence of storminess was so badly oversold at the beginning of the knowledge or the understanding that climate was going to change. The simple facts of life are there is no correlation between sea-level rise and storminess. If you have any doubts about that, there is an article from the tropical cyclone community with the backing of ICSU and WMO in this December volume of American Meteorological Society which states that explicitly.

There are some regional effects that not only could be, but will be, quite important. But I would like to point out that the regional changes in storminess are possibly and probably not related to greenhouse climate change. The regions simply go through cycles of storminess. If you actually look from my perspective I am not an expert on coastal zones by any means at the damage that is done to the coastal zone, the demographic damage in so many orders of magnitude larger than the storminess damage that that is where the really big danger lies in this whole exercise.

Dr Patrick Holligan: In the case of the global picture do you have any estimates for the reduction in mangroves either in terms of perhaps a biomatter or some indicator like that, or in terms of length of coastline where they now no longer are but have been in the recent past?

Professor Peter Saenger: I cannot give you any figures offhand, but certainly it depends on how far into the past you want to go in terms of where mangroves occurred. We know from fossil history that they occurred around the entire Australian coastline and that they remained as relics in certain areas. But those species that have now retreated right to the northern part of the continent, such as sonneratia and rhizophora, at least on the west coast, did occur as far south as Perth. So I am not sure whether that answers your question.

Dr Patrick Holligan: I was really thinking about the last hundred years or so.

Professor Peter Saenger: In terms of Australia, I think the general view now is that there have been no net losses, although there have been losses in certain areas. But there have been certain gains in other parts of Australia. So that in terms of what we might have had a hundred years ago, we still in a sense have more or less the same amount. That is not true in other areas and certainly there have been significant losses in places such as west Africa, for example, especially in the Sahelian part of west Africa where you have had probably about 30 years of declining rainfall now, as well as where the mangroves are confined to fairly narrow lagoonal systems in most instances which have become eroded because of sand losses. Certainly, in places such as the Caribbean where there has been massive clearing of mangroves, we are seeing quite large losses of mangroves, and in certain parts of South-East Asia: I am thinking particularly of places such as Sabah where woodchipping has been in operation.

So there is data. If you ask me whether I have actual figures, I cannot give them to you, but I know the World Conservation Monitoring Centre in Cambridge are currently compiling a mangrove world atlas which is designed to try and quantify those losses at least at a uniform scale which probably will not be adequate to map all of them, but will at least map the major ones.

Professor John Chappell: I think that is about it for this session. Before we go to afternoon tea, can I ask you to again thank the speakers. I think we are due to return at three thirty.

Professor Roger McLean: We have three speakers this afternoon in this last session, and then we will have a brief discussion. After that I will endeavour to have a wrap-up session dealing with some of the issues that have been raised in today's meeting. This is session 4. The first speaker this afternoon in this session is Dr Neville Smith from the Bureau of Meteorology Research Centre. Neville is going to speak on GOOS.