On May 28 2006, the Sunday morning current affairs program on Channel 9 television in Australia ran a story about salinity in the Murray-Darling Basin. Parts of the story were accurate, parts were wrong, and parts were sort of semi-right but distorted in various ways to fit the thrust of the story.

The messages of the story included that:

(a) especially during the hey-day of salinity as a hot political topic, the likely future severity of the salinity problem was grossly exaggerated by scientists;

(b) trees are at least unhelpful for salinity management, if not positively bad;

(c) the rising groundwater theory of how salinity occurs in Australia is wrong.

Throughout the story, these and other separate issues were so confounded and muddled up with each other that it is difficult to untangle them, but I’ll try.

Message (a) is true, at least in the sense that the published numbers reinforced the atmosphere of alarm that existed in the late 1990s/early 2000s. In particular, the approach taken to the salinity assessment of the National Land and Water Resources Audit led to problems. They defined salinity hazard in a way that, without studious attention to detail in the reports, gave the impression of unrealistically large areas facing salinity. In at least one state the areas were exaggerated, even relative to that unfortunate definition. On the other hand, the state agencies were in a difficult situation. One of those involved has told me, “it was a politicised process and there was a prerequisite that an Australia-wide number be derived, despite protestations. What is obvious now is that it should have been argued that it was not possible at the scale required, rather than trying too hard with too little data to satisfy an ill-considered, if simple, request.” Also, it is true that the NLWRA reports do not say that all of the land identified would become salinised. The qualifications and explanations in the reports were almost always ignored when the numbers were used in political or public arenas.

Channel 9 did effectively convey the message about the over-selling of salinity. Jennifer Marohasy’s comments about salinity levels in the Murray River were well made. It is true that salinity levels in the river have been falling, and consequently true that claims of a salinity crisis in the river are overblown. The causes of the fall in salinity are well known: extensive pumping of saline groundwater, and a long period of below-average rainfall.

Despite this positive news, it is believed that, if rainfall returns to average levels, salinity from dryland areas will eventually overtake the effects of the groundwater interception schemes – river salinity levels will rise again. Indeed, if there is even a brief period of above-average rainfall, salinity levels will probably be elevated for some time afterwards. (It is now appreciated that salinity in the river is driven to a large extent by episodic flooding.)

The reporter did well to remind us of the appalling campaign by the National Farmers Federation and Australian Conservation Foundation for a $65 billion environmental program in 2000/2001, when the profile of salinity was at its peak. If their campaign had been successful, the resulting policy program would have been wildly wasteful of public money (see some prior comments of mine on this in Pannell, 2001). It was “interesting” to see Wendy Craik (who was then the executive head of the National Farmers Federation) admitting that, as a taxpayer, she was glad they didn’t succeed in their campaign back then.

Even today, other than in Western Australia, the available predictions of future salinity impacts are pretty weak. The blame for this is not just in the public sector (which came in for a hiding on the program). Many of the analyses from the private sector that we have been reviewing recently have also been very questionable.

My final comment on message (a) is that we should not forget that the likely future area of salt-affected land is still very large (probably something of the order of 6 million ha) and that for salinity’s impacts on water resources, infrastructure, and biodiversity, area is not the issue, anyway. The lesson is that salinity investments (like other environmental investments) need to deal with the issues soberly, based on the best available evidence.

Message (b) (that trees are unhelpful for salinity management) is correct in certain places, but not others. The situations where they are a problem are where rainfall is relatively high, and ground surface slopes are relatively high, so that significant surface runoff water reaches the waterway in a fresh state. Perennials (not just trees) tend to intercept this water and as a result there is less dilution of the salts that are entering the river from other locations. In addition, in these locations, the perennials reduce the amount of water available to downstream users and the environment. This has been well known for many years, but has not been adequately recognised in a number of government programs. They certainly should do so, but they also should not throw out the baby with the bathwater. Perennials, including trees, are still highly relevant in many areas where salinity is a looming or present problem.

Message (c) (that the rising groundwater theory of salinity is wrong, and should be replaced by a theory based on soil health) is problematic, to say the least. Channel 9 interviewed almost all of the small band of scientists (the “soil-health team”) who have for some years been pushing this line, but not a single person who would be qualified to present the counter view. Now Australia is a big place, and there may well be different mechanisms in operation in different places. But for the soil-health team to claim that the rising groundwater theory is universally wrong is quite outrageous.

One of them rang me once and tried to convince me that their claim even applies in Western Australia. Since I had been working on a large number of statistical analyses of the relationship between watertable depths and rainfall (Ferdowsian et al., 2001), and since I could take him to any number of paddocks where salinity coincides exactly with shallow water tables, my caller’s arguments were not very convincing.

Contrary to the claims expressed on the program, there is copious evidence in support of the rising groundwater model, including a catchment in WA where groundwater and stream salinity levels have been monitored ever since the land was cleared. There are numerous areas where establishment of perennial vegetation has lowered watertables and thereby mitigated salinity (e.g. Burke’s Flat in Victoria, the Denmark River in WA). Powerful recent evidence in the Murray-Darling Basin has been the decline in saline discharge in many areas, due to extended periods of below-average rainfall. For example, in a site at Kamarooka (northern Victoria), there was formerly a large area of saline discharge, but the recent dry period has lowered saline groundwaters to 2 metres or more below the surface for the first time in 50 years. This widely observed recent phenomenon is completely consistent with the groundwater model of salinity, and (unless I’ve misunderstood it) completely inconsistent with the soil-health model. The same is true of the fall in salinity in the Murray River, which was rightly emphasised in the program. It was amusing to see the journalist putting forward two claims that can’t possibly both be true, but apparently failing to notice this.

I’d also be very interested to know how the alternative model explains the onset of salinity affecting roads and buildings in the middle of rural towns, or occurring within remnant native vegetation (where soil health is presumably pretty good). It seems to me that these things can only be explained by rising groundwater.

The program implied that the groundwater model represents salinity processes as occurring over very large areas (e.g. cause and effect being widely separated in space). While this can be true in some cases, in many, the opposite is true – groundwaters can rise or fall on a very local basis (Pannell et al., 2001). This is one of a number of ways in which members of the soil-health team have misrepresented the rising groundwater model or the prescriptions it gives rise to.

The proponents of the alternative theory need to subject their ideas to the standard method of quality assurance in science, by publishing their evidence in a peer-reviewed journal. They have not yet done that.

David Pannell, The University of Western Australia

Further Reading

Ferdowsian, R., Pannell, D.J., McCaron, C., Ryder, A. and Crossing, L. (2001). Explaining groundwater hydrographs: Separating atypical rainfall events from time trends, Australian Journal of Soil Research 39(4): 861-875. Full journal paper (718K pdf file)

Pannell, D.J. (2001). Public Funding for Environmental Issues: Where to Now?, SEA Working Paper 01/12, School of Agricultural and Resource Economics, University of Western Australia. Full paper (42K)

Pannell, D.J., McFarlane, D.J. and Ferdowsian, R. (2001). Rethinking the externality issue for dryland salinity in Western Australia, Australian Journal of Agricultural and Resource Economics 45(3): 459-475. Full journal paper (164K pdf file)