Developing new approaches to remediation for severely degraded sites benefiting local industry and communities

• Federal government
• State government
• Local government
• Farmers
• Local industry (fishing, tourism)
• Local communities impacted by ASS/MBO
• Recreational fishermen
• Environmental consultants
• Aquatic ecosystems and estuarine water

Acid sulfate soils (ASS) are “the nastiest soils in the world” (Dent and Pons 1995). ASS form naturally and pose no threat if left undisturbed or covered with water. However, when ASS are disturbed (through drought, drainage or dredging), they produce extreme adverse effects including landscape scalding, severe acidification and contamination from toxic metals. ASS mobilisation can cause fish kills and algal blooms due to low oxygen levels in water and release of nutrients. They also corrode infrastructure and can adversely impact ecosystem health and food production.

Research at Southern Cross Geoscience (SCGS) resulted in multiple breakthrough discoveries that have transformed knowledge of ASS biogeochemistry. The SCGS researchers identified elemental sulfur (S) as an important acidity-generating phase in ASS (2006), described reductive transformation of iron and S in schwertmannite-rich accumulations (2007) and explained arsenic geochemistry in ASS (2008-11). They also developed a number of innovative ASS analytical methods including a simple, inexpensive test for reduced inorganic S in ASS (2008). Their ASS knowledge and tests are used world-wide by environmental agencies and consultants, and their definition of ASS materials was adopted by the International Union of Soil Sciences in 2008. As well as making breakthrough discoveries about ASS biogeochemistry and developing innovative test methods, the team applied their knowledge to ASS sites across Australia.

From 2007-15, SCGS researchers undertook remediation at East Trinity Bay. The site had been drained for farming, and intense acidification reached deep into the soil (pH equivalent of battery acid). Conventional ASS mitigation approaches (applying lime) were expensive (estimated $300m for the East Trinity Bay site). SCGS scientists developed an innovative approach (regular tidal inundation and daily lime dosing) which cost only $10m (2007-12). Lime-Assisted Tidal Exchange (LATE) harnesses natural biogeochemical processes, activating microbial communities to generate alkalinity. The team’s discovery that 99% of remediation was attributable to in-situ microbial and tidal exchange processes and only 1% to lime, means that ASS remediation using LATE can be undertaken at a fraction of cost of conventional methods, with ongoing economic benefit for Queensland. With acidity reduced by approx. 90%, East Trinity Bay was hailed as the most effective large-scale clean-up of ASS in the world. Strong environmental benefits flowed from remediation and the site has now been transferred to Indigenous ownership.

Peel-Harvey Estuary Western Australia (WA) is a valuable ecological system (Ramsar-listed site). Peel-Harvey Estuary also has widespread occurrences of monosulfidic black ooze (MBO) in concentrations several times greater than elsewhere in the world. When disturbed (e.g. dredging) this sediment can cause severe deoxygenation of water, acidification of surface waters and release of toxic metals. SCGS researchers undertook a world-first examination of MBO’s biogeochemical cycling (2009-12). Prior to this study, there was little consensus among local or State organisations on the causes or mitigation of MBO. The research directly influenced policy on development and dredging activity, was included in WA’s environmental impact assessment requirements, and is widely cited in WA Dept. of Environment Regulation’s policy Identification and investigation of ASS and acidic landscapes 2015. The project also delivered social benefits to Peel-Harvey Estuary with amenity for canal residents and fishermen assured via sound environmental management. Other states have also used project outcomes (e.g. dredge spoil remediation Gladstone).

Between 2009 and 2014, SCGS researchers undertook Murray–Darling projects including the first comprehensive ASS risk assessment of the Murray-Darling. This research was extensively cited in the Commonwealth Government policy “National guidance for the management of ASS in inland aquatic ecosystems 2011”. The team also researched Murray Darling’s Ramsar-listed Lower Lakes where ASS sediments were exposed during the 2006-10 drought. They modelled biogeochemical cycles during periods of drought and rewetting and recommended optimal plant species for bio-remediation. The research benefitted South Australia’s Environment Protection Authority and Department of Environment and Water, providing practical information for environmental management.

During the drought, the option of opening barrages to allow seawater into the Lower Lakes was considered. This approach would have had major environmental, social and economic consequences impacting on ecology, water supply and agriculture. SCGS’s research identified negative biogeochemical consequences from seawater inundation, and the barrages were not opened. Ecosystems, local communities and farmers benefitted from the research, which also strongly influenced the environmental policy Drought Emergency Framework for Lakes Alexandrina and Albert (2014).

Over 280,000 hectares of coastal New South Wales wetlands are at risk from ASS and MBO. 54% of this land has been drained for agricultural use, and is now subject to acidification and blackwater events during flooding (rapid deoxygenisation of water via MBO mobilisation). SCGS researchers have a long history (2003-16) of advising NSW Department of Primary Industries and local councils. The team undertook a world-first examination of blackwater biogeochemistry, investigated the impact of climate change on coastal ASS and developed system-wide approaches for competing demands from agriculture, fishing, aquaculture and ecosystem health.

This research has delivered economic, social and environmental benefits to regional communities. Councils saved money with targeted remediation programs (floodgate management and drain infilling) and local fishing and tourism industries were protected from adverse ASS and MBO events. Remediation approaches also benefitted fishermen and local communities who use river systems for recreation. The research also informed local government management strategies and policy development (e.g. Cattai Wetlands Future Directions Strategy (2014).

2007-10 Discovery Project (novel insights underpin all projects): Processes controlling mackinawite oxidisation (Burton, Bush, Johnston, Sullivan, Keen (all SCU), Osterholm and Astrom).

2011-15 Management of toxic metals in ASS (Aust/EU) (Burton, Bush, Johnston, Sullivan, Keen (all SCU), Osterholm and Astrom).

2014-15 ASS/associated arsenic contamination (Burton, Bush, Johnston, Sullivan, Keen (all SCU), Osterholm (Abo Akademi Uni Finland) and Astrom (Linnaeus Uni Sweden).
 
2007-15 CRC CARE: Management of hydrology and organic matter to optimise microbial production ETB: (Bush, Johnston, Sullivan, Burton, Keene (all SCU) Slavich, Hirst, (both NSW DPI) Mitchell (UW), Hocking,(JCU),Wong(Monash), McElnea, Ahern, Powell, Martens, Smith, Stephens, Wilbraham, and van Heel (all DSITIA). SCU took a lead role in project design, planning and results interpretation.

2009-12 Linkage Project addressing: MBO biogeochemistry PHE: Bush, Sullivan, Burton (all SCU) Grice (Curtin), Greenwood (UWA), Appleyard,(DEC), Fisher (Department of Water). SCU’s contribution to the project was 95%.

2009-14 Murray-Darling: Research involving the first identification ASS sites and5 Lower Lakes’ projects. Work involved ASS monitoring, development of conceptual models and optimal vegetation and rewetting. Sullivan, Bush, Johnston, Burton, Wards, Maher, Cheetham, Fyfe, Parr, Hagan, Rosicky, Cheeseman, Watling (SCU) and Wong (Monash).

2008-10 and 2012-14 Linkage Projects examining biogeochemistry of coastal wetlands and blackwater events and in 2012-14 and 2016-18 Linkage Projects managing freshwater wetland hydrology to mitigate adverse ASS effects on water quality and to maximise net carbon sequestration on the Mid North Coast of NSW. (both studies - Johnston,  Burton, Maher, Santos (SCU 85%contribution) Slavich, Aaso, Tuckerman (Port Macquarie ,Hastings/Great Lakes Councils), Macreadie (DU), Bowen (Murray Local Land Services).