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MANIPULATING THE WATER BALANCE OF VEGETATION ON BAUXITE RESIDUE STORAGE AREAS

Eastham, J., Morald, T., Lockley, I. and Cooling, D.

Maximising the water use of the vegetation cover of Alcoa’s bauxite residue storage areas is critical to minimising the volumes of alkaline leachate requiring treatment after closure of the refineries. This study aimed to investigate if vegetation water use could be enhanced by the presence of a watertable, caused by preventing drainage from the surface layer of residue which forms the medium for plant growth. We varied drainage conditions to achieve different watertable depths within the residue, and measured the impact on vegetation water use and degree of water stress.

We monitored residue water content and watertable depths to explain the measured plant responses. We found that plant water use was limited by low water availability over summer. Even vegetation with a watertable within its root zone was unable to sustain high water use. The presence of a shallow watertable enhanced vegetation water use compared with vegetation growing over a deep or no watertable. We concluded that drainage volumes from residue storage areas could be reduced by restricting drainage from the surface layer, allowing the development of watertables to enhance vegetation water use.