Following up on the condition of trees adjacent to the southern side of Cuttagee lake, it now appears that most if not all of the remaining Melaleucas have died. While a closer inspection is required, on this occasion some eucalyptus trees have also been affected.
As the factors leading to the death of these trees aren’t consistant with the known threat, overabundant and prolonged surface water. Another possibility is polluted groundwater.
Residents in the adjacent Murrah river catchment have known for many years that the groundwater is polluted. However, pollution that kills trees four years apart, in the same location is difficult to explain. Groundwater travels at a much slower rate that surface water. The Murray- Darling basin is a good example, where it takes some 2 million years for the groundwater to move from Queensland to South Australia.
Of course Cuttagee is quite different and a lot smaller than inland catchments. As indicated in the graphic from Council’s Rapid Catchment Assessment below, it is generally quite steep and short. The arrow is about 10 kilometers long and groundwater in these soils may travel only a ‘few centimeters a day, or even slower‘.
So rather than millions of years, a time frame of around 20 years is plausible, in the absence of other information.
As it turns out the first Melaleuca dieback, in May 2014, was exactly 16 years after rainfall that ended the first extensive dieback event in the Bio-region. The current tree deaths are 15 years after rainfall in February 2003, that punctuated the second extensive dieback event.
It is quite possible that groundwater was polluted with aluminium during these rainfall events, with subsequent negative impacts at the bottom of the catchment, in the longer term. It is also possible that the difference of one year reflects an increased ground water flow rate, due to ongoing soil dispersion and the associated reduction in soil Water Holding Capacity.
While it would be reassuring to know polluted groundwater isn’t and won’t be the cause of further environmental degradation. I expect the NSW government has no intention of restoring catchment management authorities.