Iron and manganese dynamics in lake water

Abstract

The speciation and fractionation of iron and manganese compounds from Hinze Dam water samples (Gold Coast City, Queensland, Australia) were studied using atomic absorption spectrophotometry (AAS), electron paramagnetic resonance spectroscopy (EPRS), gel filtration, ion-exchange chromatography, ultrafiltration and various acid digestion regimes. Samples were taken at various depths and times of year, and both filtrate and particulate samples of water column profiles and sediment samples were analysed. Relevant water quality parameters such as temperature, dissolved oxygen, pH, true colour, turbidity, conductivity and alkalinity were also measured. Following heavy rainfall, dirty water and associated water treatment problems increased as catchment surface erosion and dynamic mixing of the whole water column induced by the introduction of a large volume of rainwater runoff lead to marked increases in particulate matter (mainly carbonates) in the water body. The results obtained before and during artificial aeration were compared at different depths and times of year. Artificial aeration had an initial marked reduction in the levels of soluble iron and manganese in all the dam profiles, however, the concentrations of these metals showed a steady increase over the succeeding years. Statistical analysis of data has been undertaken to correlate the changes between the various forms of iron and manganese with the advent of artificial aeration. Such analyses indicate that a number of traditionally measured water quality parameters have no long-term value for predicting the likely levels of soluble and insoluble iron and manganese, even when correlations between the parameters are calculated on a seasonal rather than on a yearly basis. These water quality parameters are not measured solely for the purpose of prediction, nevertheless, the parameters may be important for real-time treatment process control and for general water resource management. Some important implications for water resource management and water treatment processes are discussed.