Soil acidity/Acid Sulfate Soils - 2004Home | Land | Land Use & Management | Soil Acidity/Acid Sulfate Soils | 2004 What does the Data tell us for 2000/2004Acid Sulfate Soils Hot Spots Program – Broughton Creek Acid Sulfate Soils – Current Projects
Coastal areas with high rainfall have naturally occurring acidic soils. EPA (1993b) reports that other soils may become acidic:
This induced acidity:
Due to the natural acidity of local soils, the extent of induced acidity is, however, largely unknown. The extent of Acid Sulfate Soils in the Shoalhaven remains as per the Department of Infrastructure Planning and Natural Resources (formally Department of Land and Water Conservation) Acid Sulfate Soil Risk Maps which can be viewed at http://gis.shoalhaven.nsw.gov.au/soemaps These soils cause productivity losses due to acidity and aluminium toxicity. The soils can also indirectly have a dramatic negative impact on receiving waters due to acidic drainage high in toxic elements. Acid sulphate soils are found mainly in lowland areas like the Shoalhaven floodplain and areas towards the rear of coastal lakes. Acid sulphate soils were formed thousands of years ago when grey clays containing sulphur and iron were deposited by higher sea levels. Bacteria converted the sulphate in the sea water to iron sulphide (pyrite), in the newly formed soils. Since the turn of the century many of the City's lowland soils have been drained to make them suitable for agriculture. This draining lowers the water table and allows oxygen to enter the soil. The oxygen allows chemical and bacterial reactions to occur in the pyrite which produces sulphuric acid. This acid can then release aluminium and other metals from the soil. When the soils are left undrained few problems arise, except in very dry years. When highly acidic drainage (often with elevated levels of the toxic element aluminium) enters waterways, the effect on fish and other aquatic life can be dramatic. In fact a number of major fish kills have been reported in the State's northern rivers such as the Tweed where acid sulphate soils are also prevalent. Acid Sulfate Soils Hot Spots Program – Broughton Creek The Shoalhaven River Acid Drainage Working Group (SRADWG) developed from the involvement of Council in cooperation with the University of Wollongong, NSW EPA, NSW Fisheries, NSW Agriculture, Department of Infrastructure, Planning and Natural Resources (Department of Land and Water Conservation), volunteer groups and landholders. SRADWG has been driving research in the Broughton Creek floodplain since the early 1990’s when, after periods of long dry weather followed by large rainfall events, problems became evident with Broughton Creek exhibiting extreme acidic conditions. During the mid-1960’s and early 1970’s a series of man-made flood drainage channels were altered and in some cases dug deeper and wider which has been the catalyst for the oxidation of pyritic material and the problem of Acid Sulfate Soil (ASS) runoff. (Pease, 1994; Buman, 1995; Blunden 2000; Glamore 2003). Within the Broughton Creek Hotspot project, SRADWG directed research, planning and strategies of the project, aiming at attaining a reduction in frequency, intensity and duration of acid discharge events in certain selected hot spot areas. A preliminary analysis of the extent of the ASS was undertaken through analysis of water and soil samples. New applications of emerging technology enabled highly detailed elevation imagery to be used in the planning process for site selection. Four original management units were selected within the Hotspot, but an additional unit was added during the course of the project to achieve the maximum benefit. The project focused on remediation works that would influence the greatest area while keeping in mind the individual site characteristics. Some new and emerging remediation applications were also trialled. Within the project four new modified floodgate or ‘Smartgates’ were installed to achieve tidal exchange, in the aim of buffering the acidic leachate from the flood mitigation drains as well as to increase groundwater levels above the potential acidic layer. The prototype Smartgate that existed with the floodplain was upgraded to a more permanent structure and standardised to exhibit the same advanced telemetry systems as the other Smartgate systems. One Self-Regulating Tilting Weir (SRTW) was installed to increase the groundwater table in the aim of reducing the rapid transport of acid out of the drain after a major rainfall event. Two new liming strategies were implemented to neutralise and prevent further oxidation of pyrite. Current water quality results collected post on-ground remediation works have been encouraging, with pH falling under ANZECC guidelines for a relatively shorter period of time than in previous rainfall events. The lime injections have also provided a slight increase in pH within the groundwater. However to understand the effectiveness of remediation works, monitoring needs to occur for a further period of time, a period long enough to encounter more than one acid event. SRADWG is committed to continuing monitoring and further research is being undertaken to find other ASS management options. SRADWG collaborative effort has guided the work of the Hotspots project from its inception to its finality and the results are beginning to indicate that the frequency, intensity and duration of acid discharge events are being reduced. Continued monitoring will help to understand and evaluate the benefits of the project. Two monitoring stations in Broughton Creek were analysed over an 18-month period from November 2002 to April 2004. Upstream and downstream pH was monitored for periods of acidity to determine the effect of tidal seawater on Broughton Creek. The comparison of the upstream and downstream results gives an indication of the effect of buffering that seawater has on the drain water entering the creek. For the logger to be recording accurately, the downstream pH must be higher at all times than the upstream logger. Graph 169 below represents this overtime and shows the decrease in pH at both upstream and downstream loggers at periods of high rainfall. In drier periods, the water table often falls below the level of which potential Acid Sulfate Soil material is exposed causing the formation of Acid Sulfate Soils. When there is an increase in rainfall after a relatively dry period, there is a dramatic fall in pH showing the system is becoming highly acidic. Figure 60 - Acid Sulfate Soil - Management Unit Locations
Graph 169 - Acid Sulfate Soils - Daily pH Upstream, Daily pH Downstream Drain P6D1 v Rainfall |
%2004.GIF)
%2004.GIF)
| Land Management Unit | Drain Identification (Common Name) | Remediation works Implemented | Length of Drain Influenced |
Total Area Remediated Hectares (Acres) Figure 61 |
% of Floodplain Remediated (2800 ha) |
| 1 | P3D7/8 (Harris) | Smartgate | 453m (195m/258m) | 240 (594) | 8.5% |
| 2 | P6D2 (Forsyth) | Smartgate | 232m | 182 (449) | 6.5% |
| 3 | P6D1G1 (Lords) | Smartgate | 336m | 241 (597) | 8.6% |
| 4 | P6D8 (Stewart) | Smartgate | 256m | 424 (1050) | 15.1% |
| 5 | P6D7 (Carolin) | Upgrade of Smartgate System for standardisation | 250m | ||
| Total | 1087 (2690) | 38.8% |
For full details of the Hot Spot Project see the:
Concept Plan, Management Plan (1.1 Mb pdf), Final Report (X.X Mb pdf)
Acid Sulfate Soils – Current Projects
Within Broughton Creek floodplain, other projects are beginning to be implemented, including an Australian Research Council (ARC) funded project that will look at research based on vertical neutralisation barriers. The University of Wollongong along with key members of SRADWG are committed to continuing research on acid sulfate soils in the Broughton Creek region, and is the custodian for the ARC project. Manildra Starches have also been involved in implementing and experimenting with various management options for the pilot Environmental Services Scheme project. This has included planting adaptable tree species, water quality monitoring, and future endeavours to implement remediation structures within flood mitigation drains.
Shoalhaven City Council has received further funding for the investigation of land affected by potential and actual sulfate soil on the southern side of the Shoalhaven River. This project titled ‘The Reduction of Acid Sulfate Soil Discharge into Shoalhaven and Crookhaven Estuaries (Stage 1)’ was authorised by the Southern Rivers Catchment Management Authority. Currently, an Airborne Laser Scanning project will include investigation of new areas on the south side of the Shoalhaven River. The knowledge, methodologies and works implemented in the Broughton Creek Hotspots project will be used to guide management of this new project.
Home | Land | Land Use & Management | Soil Acidity/Acid Sulfate Soils | 2004