Characterisation of shallow groundwater dissolved organic matter in aeolian, alluvial and fractured rock aquifers
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Date
2020-03-15
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier
Abstract
Groundwater organic matter is processed within aquifers through transformations such as the adsorption of dissolved organic matter (DOM) to minerals and biodegradation. The molecular character of DOM varies according to its source and this can impact its bioavailability and reactivity. Whilst the character of DOM in riverine and oceanic environments is increasingly well understood, the sources, character and ultimately the fate of groundwater DOM remains unclear. Here we examine groundwater DOM from contrasting hydrogeological settings in New South Wales, Australia. For the first time, we identify the distinct molecular composition of three groundwater DOM end-members including a modern terrestrial input, an aged sedimentary peat source, and an aged stable by-product pool. We also identify and characterise the processing pathway of DOM in semi-arid, low sedimentary organic carbon (OC) environments. Based on size exclusion chromatography, ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), isotopic analyses (13C, 14C and 3H) and principle component analysis (PCA), we show that in higher rainfall temperate coastal peatland environments, large amounts of aged sedimentary organic carbon can leach into groundwater resulting in higher molecular weight (500 g mol−1 < molecular weight > 1000 g mol−1) and highly aromatic groundwater DOM with high O/C ratios and low H/C ratios. We show that in semi-arid environments with low rainfall rates and high groundwater residence times, groundwater dissolved organic carbon (DOC) is processed into increasingly low molecular weight (<350 g mol−1), low aromaticity DOM with low O/C ratios and high H/C ratios by subsurface processing mechanisms such as biodegradation and adsorption. We provide the first comprehensive study of groundwater DOM characterisation based on multiple analytical techniques, and highlight the impact of source inputs and processing on groundwater DOM composition at a molecular level. Crown Copyright © 2020 Published by Elsevier Ltd
Description
Keywords
Ground water, Carbon, Aquifers, Adsorption, New South Wales, Australia
Citation
McDonough, L. K., Rutlidge, H., O'Carroll, D. M., Andersen, M. S., Meredith, K., Behnke, M. I., Spencer, R. G. M., McKenna, A. M., Marjo, C. E., Oudone, P. & Baker, A. (2020). Characterisation of shallow groundwater dissolved organic matter in aeolian, alluvial and fractured rock aquifers. Geochimica et Cosmochimica Acta, 273, 163-176. doi:10.1016/j.gca.2020.01.022