NUTRIENT AND METAL CONTENT OF WATER, SEDIMENT AND SOILS AMENDED WITH BAUXITE RESIDUE IN THE CATCHMENT OF THE PEEL INLET AND HARVEY ESTUARY,WESTERN-AUSTRALIA

The Peel Inlet and Harvey Estuary in Western Australia are susceptible to algal blooms fed by phosphorus in run-off. The surrounding catchme nt is dominated by sandy soils which do not retain phosphorus. Bauxite residue, the alkaline by-product from the extraction of alumina from bauxite with caustic soda, has been applied to the soil to increase th e phosphorus retention and improve the soil. This study examines the e ffectiveness of bauxite residue in retaining phosphorus and also the i mpact of bauxite residue on other water quality parameters. Water, sed iment and soils from sites amended or not amended with bauxite residue were analysed to establish the effect of bauxite residue and the back ground levels of heavy metals. Bauxite residue was applied at 20tha(-1 ) to 1600ha of a 4300ha catchment and the phosphorus concentration in drainage water dropped by more than 30% in the first year. A 32ha sand y catchment was treated with 80th(-1) of bauxite residue and it mainta ined a 75% lower phosphorus concentration of phosphorus than an adjace nt untreated catchment over a period of four years. The phosphorus con centration in the effluent from a domestic sewage treatment plant was reduced by an average of 88% over two years after infiltration through a sand bed amended with bauxite residue, No difference was detected b etween the water quality of catchments amended with bauxite residue an d comparable catchments, based on concentrations of a number of heavy metals. High levels of heavy metals were found in some areas unrelated to bauxite residue, mainly in the downstream receiving waters of the catchment. This was probably related to by-products of combustion and motor vehicle emissions. (C) 1997 Elsevier Science B.V.