Assessment of acid sulfate soil materials (Phase 2) Coolcha Lagoon (downstream) wetland, South Australia

[摘要] An initial Phase 1 acid sulfate soil investigation of the Coolcha Lagoon wetland during March 2008 showed acid sulfate soils to be a priority concern within this wetland complex. Based on Phase 1 recommendations, a Phase 2 investigation was undertaken for the Coolcha Lagoon wetland to determine the nature, severity and the specific risks associated with acid sulfate soil materials. The 24 hour reactive metals tests were undertaken to determine those metals and metalloids extractable with a moderately strong acid i.e. potentially available from binding sites on soil minerals such as iron (Fe), manganese (Mn) and aluminium (Al) oxides. Although comparisons can be made with soil and sediment quality guidelines, these are defined for total concentrations and not partial extractions. The results showed that concentrations were below the sediment quality guideline and soil ecological investigation level for those elements where guidelines are available. The concentrations for this reactive metals partial extraction are considered to be moderately high for aluminium (Al), iron (Fe) and manganese (Mn).The contaminant and metalloid dynamics tests were undertaken to assess the release of metals during a water extraction, and to assess dynamics in response to saturation over time by incubating soil materials for periods of 1, 7, 14 and 35 days. The degree to which metal and metalloid concentrations exceed ANZECC/ARMCANZ guideline values was used to characterise the degree of hazard. For Coolcha Lagoon wetland, cobalt (Co) and iron (Fe) were assigned a moderate hazard with concentrations exceeding ANZECC/ARMCANZ guidelines by more than 10 times. Arsenic (As), nickel (Ni) and zinc (Zn) were also significantly above ANZECC/ARMCANZ guideline values (3-4 times) and represent significant hazards. The dominant control on metal solubility is the pH of the extractions. All samples showed a decrease in Eh, but only one sample decreased sufficiently for iron to become soluble. The Eh was not low enough for sulfate reduction. The increase in iron was associated with the release of arsenic (As), probably due to the reductive dissolution of iron oxides/oxyhydroxides. Although pH is an initial control on most metals, longer term release of metals and particularly metalloids pose a risk to the soil materials studied.The Coolcha Lagoon wetland has been classified as medium conservation status by the SA Murray-Darling Basin Natural Resources Management Board (Miles et al. 2010). The main hazards considered in this study that may impact on wetland values are acidification, contaminant mobilisation, and deoxygenation. The wetland has been allocated a high risk rating for acidification and a high contaminant risk rating for soils. For surface waters, the risk is largely dependent on surface and sub-surface hydrology and is thus scenario dependent. Taking into account the range of likely scenarios, from very low flows (highest risk) to very high flows (lowest risk), the risk to surface waters in the wetland has been allocated a medium to high risk rating for acidification and a high risk rating for contaminant mobilisation. A risk assessment for deoxygenation was not undertaken for Coolcha Lagoon wetland as it was determined that there was no hazard associated with monosulfidic materials.In designing a management strategy for dealing with acid sulfate soils in Coolcha Lagoon wetland, other values and uses of the wetland need to be taken into account to ensure that any intervention is compatible with other management plans and objectives for the wetland.The wetland soils studied were largely dry at the time of sampling, therefore management options considered should relate to controlling or treating acidification and the protection of connected or adjacent wetlands. Due to the high risks to the wetland values associated with acidification and metal mobilisation in Coolcha Lagoon wetland, a monitoring program is strongly recommended.

[发布日期] 2011-06-30 [发布机构] CSIRO

[学科分类] 地球科学(综合)