Indicator: Soil salinity

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What the results tell us for Tumut

The most recent information about soil salinity in Tumut Shire was reported in the State of the Environment Report 1997, Which found that there were 164 hectares of land affected by dryland salinity in Tumut Shire at the time of mapping (in the late-1980s). Most of this was found on lands in the north-western third of the Shire, lands now extensively cleared and used for grazing.

The areas affected by dryland salinity generally receive less than about 800 to 900 millimetres of rainfall each year on average. There was almost no dryland salinity on lands in Kosciuszko National Park or in lands under management by New South Wales State Forests.

The seriousness of the salinity problem in Tumut Shire becomes clearer when it is recognised that the area affected by dryland salinity constitutes many of the valley floors and footslopes, which are generally the most productive part of the agricultural landscape.

About the data

Dryland salinity throughout New South Wales was mapped by the New South Wales Department of Land and Water Conservation during the late 1980's at a scale of 1:25000, or at 1:50000 if the better scale mapsheets were unavailable.

Land was mapped as saline if it was scalded (complete loss of vegetation with or without salt efflorescence), or if the plant community was dominated by so-called indicator species such as couch grass (Cynodon dactylon) or sea barley grass (Hordeum marinum). Saline sites were initially identified by aerial photography with subsequent field inspection.

Description: What does 'soil salinity' measure?

Which data are collected?

• area and proportion of land affected by dryland salinity and irrigation salinity

Why do we report this indicator?

Soil salinity is a form of land degradation characterised by increasing concentrations of salt in the soil. It is often first noticed as isolated waterlogged areas, patches of dying trees or other vegetation, crop failure, or changes in the types of plants growing in an area. Both dryland and irrigation salinity are caused by rising groundwater levels carrying salt towards the soil surface and into the plant root zone.

In the case of dryland salinity, increases in groundwater levels are caused an increase in the amount of rainfall reaching the groundwater system following the removal of deep-rooted perennial native vegetation from the landscape. It can take anywhere from 12 to 100 years for the impact of clearing to be seen on soil salinity levels. In the case of irrigation salinity, the groundwater can be highly saline before the effect of any human activities, and the increases in groundwater levels are caused by the addition of water to the groundwater system by a range of irrigation practices.

Soil salinity can reduce agricultural production to virtually zero, as only plants with increasing degrees of tolerance to salt and waterlogging can survive. Eventually, if salt levels are sufficiently high, nothing survives. Land salinisation can also cause a deterioration in the condition of road and building infrastructure, to the point of requiring expensive repairs. Further, the salinisation of water supplies presents real and high costs for downstream users (as salty water enters streams).

The proportion of land affected by dryland and irrigation salinity is of interest to State of the Environment reporting because it can indicate a significant decline in the health of the land.