On behalf of the Government of South Australia the SA Murray-Darling Basin Natural Resources Management Board has begun the Management of Acid Sulfate Soils between Lock 1 and Wellington project. This project is working to identify the most effective methods of managing acid sulfate soils for each of the wetlands between Lock 1 and Wellington. A fact sheet has been created for the projected and can be accessed via the following link.
New report released - Management of Acid Sulfate Soils along the River Murray in SA (1mb)Acid sulfate soils fact sheet (285 kb)
The investigations underway are focused on 18 of the first 25 wetlands that will re-wet. These 18 wetlands have been identified as containing acid sulfate soils with sufficient enough acid producing capability to potentially acidify the water column. Acidification would harm the ecology of the wetland and the river channel, human health, damage structures and supply water of poor quality to off-takes.
First 25 wetlands to re-wet with rising river levels.
18 wetlands likely to present an acid sulfate soil risk:
- Riverglades
- Teal Flat Hut
- Walker Flat South Lagoon
- Wellington North
- Lake Carlet
- Devon Downs North
- Younghusband West
- Tailem Bend
- Younghusband
- Coolcha Lagoon
- Craignook
- Mannum Swamps
- Reedy Creek
- Forster Lagoon
- Henley Park
- Bow Hill
- Lake Bywaters
- Saltbush Flat
Seven wetlands unlikely to present an acid sulfate soil risk:
- Teal Flat
- Wongulla Lagoon
- Marks Landing
- Caurnamont
- Mason Rock
- Wellington Marina
- Priess Landing
Background
Severe drought and continued use of water resources have resulted in reduced River Murray flows into South Australia that are now so low they are exceeded by losses through extraction, evapotranspiration and seepage. As a consequence, water levels in the River Murray below Lock 1 have declined such that the majority of the wetlands have been disconnected and are dry. This has resulted in a significant loss of habitat for aquatic biota and other water dependant species such as water birds. At the previous pool level there were approximately 80 wetlands along with riparian vegetation within the banks of the main channel providing refuge and habitat. Only the river channel and Paiwalla wetland now contain water.
As river levels rise in the future, the river channel will reconnect to wetlands and re-wet them in sequence from the lowest to highest in elevation. It is important these wetlands are managed to ensure that water quality and ecology are maintained, particularly the first wetlands to reconnect, which will provide valuable habitat after such a long dry period.
Ecological Benefits
There are a number of ecological benefits from the re-wetting of the dried wetlands, such as:
- Germination of aquatic and riparian plant species
- The provision of habitat for frog breeding and small native fish species on initial re-wet, amongst vegetation that has established on the dry wetland bed
- Reconnection of some deeper wetlands and channels, suitable for particular species of native fish
- Habitat for water birds, providing roosting, foraging and breeding opportunities
- Provide freshwater for long-lived vegetation on the floodplains and surrounding the wetland
- Reduce the risk of further salinisation of the wetland.
As well as providing ecological benefits, the re-wetting of wetlands will reduce dust and wind erosion from the wetland and submerge acid sulfate soils, preventing any further oxidation. However, the re-wetting may pose a problem due to impacts of the ecosystem from acid and mobilised metals produced by the acid sulfate soils after such a dry spell.
Acid sulfate soils
Acid sulfate soils are soils and sediments that contain high levels of sulfides, most commonly iron sulfides such as pyrite. In an undisturbed and waterlogged state these soils are quite harmless and are known as sulfidic soils. If these soils are exposed to atmospheric oxygen through disturbance or drying, they may oxidise and form sulfuric acid. Once oxidised, they are known as sulfuric soils. The acid produced has the potential to be harmful to fauna, flora, human health and manmade structures through its acidity and mobilisation of metals such as iron, aluminium and arsenic.
Much of the sulfidic sediments and soils present around the world are a natural occurrence in areas submerged in sulfate rich waters such as seawater. As a consequence, low lying coastal areas are likely to have sulfidic soils and sediments and are likely to be receiving more even today. Ancient sea level fluctuations have also provided sources of sulfur over time, which is partially why sulfidic sediments can be found inland. Additionally inland waterways subject to high salinity are also likely areas of sulfidic deposits.
Acid sulfate soils have been identified as a natural part of the Murray Darling Basin. Before European settlement, the natural wetting and drying cycles of the River Murray oxidised smaller quantities of sulfidic material during low flow events and then flushed them from the system during high flow events. While there was still a natural accumulation of sulfidic sediments within the wetlands, wetting and drying cycles prevented the accumulation of large volumes, reducing the risk to the environment posed by acidification. After more than 80 years of river regulation, the suppression of this natural wetting/drying cycle has accumulated a significant volume of sulfidic soils in the river system.
With the drying of previously permanent wetlands between Lock 1 and Wellington, acid sulfate soils have been identified as an issue that requires further investigation and possible management. There are limited examples of remediation of acid sulfate soils for inland waterways, and as such, the work that is being undertaken is pioneering new technologies and methodologies for management. The work within this project provides an opportunity for the state and the community to successfully manage acid sulfate soils within their wetlands. This will have a wider application for other areas in the Murray-Darling Basin and other parts of Australia.
For further information on acid sulfate soils visit the CSIRO website.
Management of acid sulfate soils in wetlands while they remain dry.
In addition to investigating management options for wetlands that rewet investigations are also underway to understand what has happened to the wetlands since drying and what further impacts may occur with an extended dry period. Management options under a continued dry scenario are being developed to ensure the severity of acid sulfate soils does not increase. This will ensure the ecology of the wetlands and river channel is managed so they retain the ability to recover upon the return of water.
Community Engagement
The SA MDB NRM Board is looking to engage the community throughout this project to achieve the following goals:
- To ensure that the community has up to date information on the issues involved in the management acid sulfate soils in wetlands between Lock 1 and Wellington
- To ensure the community is involved in the management of acid sulfate soils in wetlands between Lock 1 and Wellington
- To make use of local knowledge and skills wherever possible to undertake the investigations, planning and works at each wetland