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 Stefan Loehr
Faculty of Science, Quaternary Earth and Water Systems
Thesis Title: Environmental Geochemistry of Fe in the Forested Poona Creek Catchment, Fraser Coast, Queensland.
Project Objectives:
The main objectives of the study are to understand the source, form and transport mechanisms of Fe (iron) in the forested Poona catchment, and the potential of Fe to be discharged into the marine environment. Understanding processes controlling Fe availability in this coastal system, is important as Fe is confirmed to be a limiting nutrient for the toxic cyanobacterium Lyngbya majuscula. Increased blooms of this algae have occurred in SE Queensland coastal waters, and have been linked to increased loads of Fe due to disturbance of natural systems (i.e. land-use change). The main land-use in the study area is exotic pine plantations, and there is some concern that forestry activities in this naturally iron-rich terrain may contribute to an enhanced Fe flux into the adjacent Great Sandy Strait, a declared RAMSAR site.
In this investigation both micro-scale (µm) and macro-scale (m-km) approaches will be used to determine the range of iron phases present, their formation, and their stability (i.e. potential mobilization). The study will combine regional geochemical mapping with detailed sampling of the regolith. The formation and weathering of Fe-rich concretions and the processes of transport of Fe through the catchment to the marine environment, are being investigated. Laboratory testing will include leaching experiments, comparison of iron forms transported in surface waters and mobilized from the regolith, as well as a detailed micro-scale analysis of the physical, mineralogical and chemical characteristics of a range of samples. Samples of stream water and groundwater will also be tested.
Research is presently concentrated on the Fe concretions, which represent a major store of Fe (up to 40 wt% Fe2O3) and are significant as they are used as a road-base in the study area. This use may enhance delivery of Fe into the drainage systems. The analytical techniques employed will confirm the conditions under which Fe is mobilised, what form it will take, and which other metal species are likely to be co-released. Together with leaching column experiments and targeted water sampling in Poona Creek, this approach will contribute to an understanding of the geochemical cycle of Fe and sustainable forestry management practises in a coastal catchment.
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