Executive Summary: Extent and Impacts of Dryland Salinity in Tasmania 2000
The following is the Executive Summary of the report, "Extent and Impacts of Dryland Salinity in Tasmania". This reports was completed under the National Land and Water Resources Audit.
The Extent of Salinity in Tasmania
- It is estimated that in 1992, 45 000 ha (30 000 - 60 000 ha) of agricultural land had moderate to severe salinity and in 2000, 53 500 ha (35 600 - 71 300 ha) .
- Analysing the 41 Land Systems identified in 1992 as containing areas of salinity and nine identified in 2000 has shown that the most frequently occurring are:
93 series (Quaternary sands and sandstones) 55%
84 series (Tertiary mudstones ) 25%
88 series (Tertiary complexes) 5%
- Analysis of ground water bore data (to 1999) for EC readings has shown:
Statewide (444 bores) 43% above 1 500 EC
Within saline areas (70 test ) 90% above 1 500 EC
- Time lapse recordings of surface water in rivers at 12 permanent monitoring sites since 1994 show that only one (the Coal River at Richmond) had readings above 800 EC at any time.
- Analysis of other surface water data (random samples to 1999) for EC readings above 800 EC has shown instances in 20 of the 25 catchments sampled. Seventeen of these catchments contained some the land systems containing areas of salinity.
Salinity Trends in Tasmania
- In 2000, it is estimated that the area of salt affected land has increased to 53 500 ha (35 600 - 71 300 ha), some of the increase being due to increased detection of land previously affected. Assuming about half is an actual increase, the average rate of increase between 1992 and 2000 was 1.5% per year.
- Based on the estimated present rate of increase in salinity of 1.5 %:
69 550 ha may be affected by 2020
93 625 ha may be affected by 2050.
- Standing water levels in 54 piezometers and bores in the two salt affected test areas measured over five years or more showed that 35% were falling, 45% flat and 20% rising, which, when combined with depth gave Salinity Risk Ratings of 2% Low, 44% Moderate, and 54% High Risk.
- Results from 2908 ground water bores showed Depth to Water Struck (DWS)
1.7% 0 - 2 m (High Risk)
8.8% 2 - 5m (At Risk if water levels rise)
89.5% > 5m.
Impacts of Salinity in Tasmania
- There are 1 900 000 ha of private and freehold land, of which 500 000 are uncleared and 1 400 000 cleared, 100 000 are irrigated and 75 000 are cropped.
- Depending on the divisor, about 3% may be salt affected (or 97% unaffected).
- Assuming salinity reduces production by 40%, an enterprise mix of 85% extensive and 15% cropping, and that the average regional gross margin for this mix is $250, then,
assuming salinity increases at 1.5% per year, production losses at a State level (2000 prices) would be:
2000 : $5 350 000
2020 : $6 955 000
2050 : $9 362 500
and assuming salinity increases at 3% per year, production losses would be
2000 : $5 350 000
2020 : $8 560 000
2050 : $13 375 000
- The only quantifiable impact is that on water in the Coal River in the South East Irrigation Scheme which is at times at EC threshold levels which make water risky to use for irrigation. Alternative water is now available from the Derwent River at $400 / Ml compared with water from the Coal River at $100 / Ml.
- The land systems known to contain areas of salinity also contain 132 wetlands, 47 of which are of National significance, six also being of International significance as well as 37 Conservation Reserves.
- They also contain 12 forest and 17 non-forest vegetation types, as well as 34 flora and 17 fauna species which are listed as "Threatened".
- The Flinders and Northern Midlands BioRegions are potentially the most affected.
- Eight Local Government Areas include land of which more than 20% comprises land systems containing areas of salinity.
- These include 5 000km of roads which cost $34 000 000 annually to maintain.
- These may be at risk but there is virtually no evidence at present and little expertise to collect it.
- There is some evidence of damage to four golf courses which is being remediated at minimal cost, and to some sports ovals which has not been addressed.
Implications for Land Use
- Land clearance, rainfall, and irrigation which is not carefully managed, are generally accepted as being two major drivers of salinity.
- The rate of land clearance on private/freehold land has dropped statewide in the last decade from about 10 000 ha/year 1989 -1993 to 4 750 ha/year 1994 - 1999.
- As most of this was in the higher rainfall areas and 40% was for plantations it is therefore unlikely to be a major driver of salinity.
- The decline of extensive agricultural enterprises, especially sheep, and the increased demand for crops such as vegetables and poppies has driven diversification and an expansion of irrigation into dryland areas.
- For agriculture, the most significant impact of rising salinity would therefore be the regional effect on diversification from marginal extensive enterprises into intensive irrigated cropping (especially into high value, salt sensitive crops) with the associated financial implications to individual landowners and agribusiness.
- It could also have an adverse effect on market perceptions of Tasmania as "Environmentally responsible" and thence affect market share in export markets.
- An increase in salinity levels in surface and ground water may lead to "no go areas" such as sources of domestic water supplies and ground and surface water for use for irrigation.
- If not addressed, increasing salinity could also lead to "no go" areas in catchments containing Wetlands of National and International Significance, have an impact on Tasmania's obligations under UN conventions and possibly have an adverse effect on future developments in ecotourism.
- Key recommendations relating to this include the need for:
- Salinity Risk Assessments to be prepared for irrigation developments in identified saline areas;
- the development of salinity assessment and identification skills in local government staff;
- research aimed at understanding salinity processes and the development of appropriate management practices for Tasmania; and
- the development of management plans for public lands, addressing the implications of salinity.
Salinity Policy Requirements
- Salinity has not been an issue in Tasmania and so at present there is no specific policy to guide its management.
- The key recommendations on policy are that the State should:
- adopt a Whole of Industry /Government approach to the issue;
- work with all key stakeholders to develop a State Salinity Management Strategy;
- allocate resources for the implementation of key strategies identified in the Strategy; and
- allocate resources for Tasmania's involvement in the National Dryland Salinity Program.
Future Assessments and Monitoring Requirements
- It is recommended that strategic monitoring should be assured to enable results to be published in four iterations of the five year cycle of the "State of the Environment" reporting framework, and a central data base be established.
- It is also recommended that, after rapid field assessment to check some of the statements made in the report, at least three Key Reference Sites should be established in which to integrate strategic monitoring and assessment.