Land salinity monitoring and trends
Land salinity is monitored in a series of focus areas representative of the major regional and local groundwater flow systems (GFS) in the agricultural regions of South Australia.
The long-term collection of monitoring data for each of the three main nationally agreed indicators of land salinity are required for meaningful assessment of land salinity.
- depth to groundwater
- groundwater salinity
- location, size and intensity of salt-affected areas.
Depth to groundwater is generally the most useful indicator of land salinity, as it signifies the presence or potential threat of shallow water tables. An evaluation of long-term monitoring data on the depth to groundwater in the main GFS in a region, provides an indication of salinity trends. The risk of salinity spread can be related to the type of GFS operating in the area.
Future challenges
The future impact and risk of dryland salinity will depend largely on future rainfall patterns, including climate change, the nature of the groundwater systems and the effectiveness of efforts to slow or halt rising groundwater. On-going monitoring and evaluation in focus catchments will inform adaptive management and provide a basis for future salinity assessment.
Mallee seeps have been an emerging issue over the last 10 years. Concern is growing with the formation of new seeps and existing seeps increasing in size. Mallee dune seepage is caused by water imbalances in dune-swale ‘mallee' landscapes utilised for rain-fed annual cropping. Water that drains beyond the crop root zone in sandy soils can be lost to deep drainage, or can form local perched watertables where restrictive subsoil layers limit downward movement. The perched water can discharge at the soil surface such as in lower lying areas, forming seeps. This process has the potential to result in soil salinity by accumulation of dissolved soil salts in the seepage discharge areas. Where restrictive subsoil layers are absent, deep drainage to regional water tables in the Murraylands region contributes to salts ultimately flowing into the River Murray.
Summer weeds (including deep rooted species) are now routinely controlled in more intensive cropping systems, in paddocks to be cropped the following season, to conserve stored soil moisture for the crop. This potentially allows greater leakage of ‘out of season’ summer-autumn rain to perched water-tables below the dune soils. In more traditional farming systems, particularly with longer pasture phases, summer weeds were not controlled as often.
Options to reduce the potential development of mallee seeps would need to increase overall soil water use, such as:
- Increasing productivity of current crops
- Strategic plantings of high water use, deep rooted perennial species and utilisation of pasture phases
- Amelioration of sandy soils with clay
- Winter and summer cropping
Soils with highest potential for formation of dune seepage are sand over clay soils, and deep sands. The ‘Blanchetown Clay’ geological formation commonly causes the perched water-tables in mallee dune soils in SA.
Find out more:
- Assessing Agricultural Land
- Water Table Induced Salinity factsheet
- Watertable induced salinity map
- Dry Saline Land factsheet
- Dry Saline Land map
- Saltland Pastures for South Australia Manual
- Decadal analysis of trends in depth to groundwater for dryland salinity areas of SA report
- Groundwater Flow Systems of southern South Australia map
- Impact of Perennial Vegetation on Watertables and Dryland Salinity technical report
- Mallee Seeps - Murraylands and Riverland Landscape Board website
- Mallee Seeps Decision Tree - Mallee Sustainable Farming
