2 June 2009
At this difficult time with difficult decisions to be made on the immediate future of the Lower Lakes, there is a great deal of misinformation promulgated by those whose agendas, for whatever reason, have led them to overlook the pertinent facts – even scientists it appears, can demonstrate the very human trait of wishful thinking.
Freshwater or Saltwater? The Facts are Inescapable
For thousands of years the Lower Lakes were a natural estuarine system with a seawater/freshwater mix determined by river flows – the evidence is very clear.
With no barriers between the sea and the lakes; no locks and weirs on the river, and no storage dams upstream – river flows fell away to very little in times of drought and the estuarine mix moved even further upstream – but the lakes estuarine wetland environment flourished.
In their attempts to blame someone – preferably an incumbent government – antigovernment activists have joined extremist environmentalists to distort the facts and attribute the current water level crisis, not to the drought but to an over extraction of water upstream for irrigation and other human needs, such as taps and toilets.
The over allocation and extraction of irrigation water is acknowledged and must be fixed.
Even with average catchment intakes, reduced environmental flows have created problems for the river – but right now – in these times of unprecedented drought – with less than a third of actual ‘entitlements’ extracted last year (because it just wasn’t there) – these emptying Lower Lakes are the result of the drought and the drought alone.
They have never been empty before – and they are kept artificially empty now by human intervention – the barrages - which are holding back the tides to confound thousands of years of natural ebb and flow – built for the economic benefit of those who wanted a reliable freshwater source – and the environment came last!
There may still be valid reasons for not wanting to let seawater into the lakes but a concern for the natural environment is not one of them – there can be no doubt about that – the evidence is clear.
So what are these inescapable facts?
Paleolimnology - which identifies fossilised species of micro-organisms - in core samples of lakebed sediment taken at the northern extremes of the lakes near Pomanda Island - has indicated significant estuarine/salt water conditions at various times over the past 6,000 years. (See published work of Professor Peter Gell)
Captain Charles Sturt observed in 1830, (on his epic expedition by boat down the Murray to its mouth), that near Pomanda Island,
“The transition from fresh to saltwater was almost immediate - - -“
Near Wongulla, many kilometres upstream from the lakes, there is cliff and river bank evidence of extended pre-settlement water levels well below that needed to maintain a freshwater flow to the lakes, with further evidence of vegetative growth which could not have occurred if flow levels had been higher.
Those environmental activists promoting the ‘freshwater only’ line would have us believe that salt water has only entered the lakes since settlement and then only as a result of extractions upstream. The above hard evidence completely refutes this and refutes any computer modeling which may appear to support their views. Computer modeling makes assumptions and if the conclusions don’t fit the observable facts – the modeling is clearly flawed and the assumptions must be changed.
Further supporting evidence?
The low lands subject to inundation around the northern shores of the lakes are characterised by salinity tolerant vegetation (Samphire – Sarcocornia Quinqueflora). In contrast, the River Redgums (Eucalyptus Camaldulensis) which mark wetlands and river flats all the way down the Murray from the upper reaches to the vicinity of the lakes, are missing - nor is there any evidence of their existence in the past? The Ngarrindjeri people took their bark for canoes from the lower reaches of the Finniss, Bremer and Currency creeks where Redgums abound but clearly, where salt water did not penetrate.
When the landforms of the Lower lakes are considered together with the highly variable flow statistics of the Murray Darling Basin it is difficult to accept any other conclusion than the natural estuarine state of the Lower Lakes and Coorong. The evidence for an exclusively riverine (freshwater) state is noticeably missing – with the Sim/Muller ‘A Fresh History of the Lower Lakes’, cited by the ‘activists’ as ‘proof’ of their position, so clearly flawed and biased that it cannot be taken seriously.
The report “Murray River Barrages Environmental Flows” commissioned in 2000 by the Murray Darling Basin Commission from the South Australian Department of Environment and Natural Resources, describes the pre-settlement hydrology of the Murray and Lower Lakes as follows,
“The Murray-Darling River system discharges into a particularly large-scale terminal lakes system which would have previously (before European impact) offered a wide range of fresh, brackish, saline and hyper-saline systems. The ecological systems would have evolved to take advantage of this diverse range of salinities.”
and,
“ - - - during the low flows of summer and autumn, and throughout the year in drought, the fluctuating tide levels would have allowed a substantial tidal exchange and semi-marine conditions would have established over most of the Lower Lakes.”
Thus, the argument that the lakes must be maintained as a freshwater habitat to protect their inherent ecological values and the natural environment, can be seen to be a nonsense when matched against the evidence.
What cannot be disputed is that a lake without water is no longer a wetland – and the environmental damage caused by keeping water out is profound. Any water is infinitely better than no water, and however much we may like the idea of freshwater lakes, if sea water is all that is available – it must be allowed to return the lakes to sea level and to an ecosystem as rich and diverse as that which existed over the thousands of years before white settlement.
Political agendas must be recognised for what they are and this great natural disaster given the unbiased non-partisan attention that it sensibly warrants.
In these difficult times of drought and climate change, a permanent weir at Wellington and the barrages opened to the sea may yet be the most sensible long term response.
Trevor Harden