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Fencing off salt-affected land is a low risk strategy to reduce the amount of salt entering our rivers and streams, according to the research findings from the Gumble region in central NSW.
The research shows it is risky to assume that replanting perennial species in the surrounding local catchment will always fix a salinity problem.
At a recent field day at Gumble, local farmers and Catchment Management Authority advisors were told of the findings of integrated studies which examined recharge and discharge of saline water from the catchment.
One study examined how we can better manage land that has already become salinised, and the other investigated the cause of the Gumble scald.
The first study, part of the Sustainable Grazing on Saline Lands initiative of the Cooperative Research Centre for Salinity, confirmed that if a saline scald is fenced and then grazing is managed, the increased groundcover will make a big reduction in the movement of salt from the scald into the creek.
A second study found that the saline scald at Gumble is caused by groundwater which originates outside of the local catchment.
This work, undertaken as part of the NSW Department of Primary Industries’ (DPI) Key Sites project and funded through the National Action Plan, is looking into the impact of land use on salt and water movement at a paddock and farm scale.
DPI salinity researcher David Mitchell says erosion has filled up a stream at the base of the catchment and is stopping saline water from escaping.
The slopes of the small sub catchment immediately surrounding scald, which contain naturalised pasture and some annual crops, have been found to be contributing fresh water to the scalded area.
”If we do not want the scald to get worse, it is important to maintain these slopes in a similar condition”, Dr Mitchell said.
“If perennial pastures and trees were planted on them, then this is likely to reduce the runoff of fresh water and make the salt scald even more saline.”
Key Sites researchers have examined the hydrology of the catchment and found that groundwater contributing to the scald is flowing in the opposite direction to what was expected.
“If you stand near the scald it is logical to assume that the groundwater is coming from the surrounding cleared hills, but we have found that the groundwater actually flows in the opposite direction”.
“The groundwater flows from the scald towards the surrounding hills, a clear indication it is not a local system and the source of the water is outside the catchment”.
Dr Mitchell said geology is emerging as a major factor in assessing the causes of salinity in the Central West, an area known to geologists as the Lachlan foldbelt. It was formed when two tectonic plates collided.
“Because of the folding of the sediments, water tends to follow folds and the pathways are not as obvious as you’d think”, he said.
Early in the day, CMA staff and farmers were asked to look at the surrounding catchment and offer opinions as to the causes of the saline scald and the steps that could be taken to address it.
Participants agreed the findings challenge some of the commonly accepted strategies for managing salinity and that a good understanding of local hydrology is needed before funds can be invested to fix the problem.
Editor's Note: Original news release can be found here.
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