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Abstract
The role of dissolved organic matter (DOM) in aquatic systems has been associated with numerous physiochemical processes including carbon sink, contamination indicator and important component in natural geochemical and microbial processes. However, to date research into the behaviour of DOM within groundwater systems has been minimal. A developing technology for measurement of DOM in aqueous environments is fluorescence spectroscopy, which has the potential to be an economical and highly sensitive means of characterising DOM source and physiochemical activity within groundwater. However, the application of optical fluorescence as a means for measuring character and concentration of DOM in groundwater systems has to date been limited.
This study consisted of four major stages. The first stage was development of a hydrogeological conceptual model. This stage identified the influence of long-duration high-volume dam releases on downstream aquifer systems. The second stage utilised a hand held fluorometer to identify and delineate a landfill leachate plume at concentrations as low as 1%. In the third stage, fluctuations of dissolved organic carbon (DOC) were measured in groundwater during a high intensity abstraction event with concentrations fluctuating up to 3,500% during initial abstraction. Analysis of excitation emission matrices (EEMs) and absorption data demonstrated that the increased DOC and an increase in relative molecular weight of dissolved organic matter (DOM) was likely due to biofilm shearing. The fourth stage split a set of EEMs from the research site, based on interpreted hydrogeological setting. Parallel factor analysis (PARAFAC) models were developed for each data set, with results compared to a model developed using all site data. This stage of the research demonstrated the potential to characterise groundwater environments based on character and concentration of OM present, however PARAFAC model accuracy was found to increase in PARAFAC models which utilised data from less varied environmental settings.
The research has demonstrated that variations in character and composition of OM can be used to characterise a complex groundwater system. Further to this, measurement and assessment of the OM variations can be undertaken in the field or laboratory with a high level of sensitivity using Fluorescence Spectroscopy coupled with EEM PARAFAC analysis.