Browsing by Author "Zainuddin, NS"
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- ItemDissolved organic matter (DOM) concentration and quality in a coastal aquifer(Copernicus Publications, 2015-04-14) Zainuddin, NS; Andersen, MS; Baker, AA; Howley, EM; O'Carroll, DM; Jex, CN; Meredith, KT; Wells, EThis study investigates the range of fluorescence properties of natural occurring DOM in a coastal aquifer at Anna Bay, NSW, Australia. The determination of the extent to which DOM varies in coastal groundwater has been distinguished through fluorescence spectroscopy by excitation-emission matrices (EEM), and the application of parallel factor analysis (PARAFAC). In addition, DOM was characterised by a combination of DOC-LABOR Liquid Chromatography - Trace Organic Carbon Detector (LC-OCD) method and PHREEQC modelling. In general, results show an anoxic aquifer featuring calcite dissolution in the upper regions of the aquifer and organic matter degradation with redox zonation dominated by iron and sulphate reduction as well as methanogenesis. Several fluorescence EEM patterns were identified. DOM in coastal environment was variable, but mainly composed of low molecular weight compounds. On overall system two humic-like substances (C1, C2) and one fulvic-like substance (C3) were identified by the PARAFAC model. C1 and C2 exhibited same trends and were very similar. Measurement of the fluorescence excitation-emission matrices (EEM) and subsequent PARAFAC reveal different fluorescent DOM fractions and hence variable contributions by DOM to the reduction process in the coastal aquifer zones. © 2015 The Author(s).
- ItemIsotopic and chromatographic fingerprinting of the sources of dissolved organic carbon in a shallow coastal aquifer(European Geosciences Union, 2020-04-30) Meredith, KT; Baker, AA; Andersen, MS; O'Carroll, DM; Rutlidge, H; McDonough, LK; Oudone, PP; Bryan, E; Zainuddin, NSThe terrestrial subsurface is the largest source of freshwater globally. The organic carbon contained within it and processes controlling its concentration remain largely unknown. The global median concentration of dissolved organic carbon (DOC) in groundwater is low compared to surface waters, suggesting significant processing in the subsurface. Yet the processes that remove this DOC in groundwater are not fully understood. The purpose of this study was to investigate the different sources and processes influencing DOC in a shallow anoxic coastal aquifer. Uniquely, this study combines liquid chromatography organic carbon detection with organic (δ13CDOC) carbon isotope geochemical analyses to fingerprint the various DOC sources that influence the concentration, carbon isotopic composition, and character with respect to distance from surface water sources, depth below surface, and inferred groundwater residence time (using 3H activities) in groundwater. It was found that the average groundwater DOC concentration was 5 times higher (5 mg L−1) than the global median concentration and that the concentration doubled with depth at our site, but the chromatographic character did not change significantly. The anoxic saturated conditions of the aquifer limited the rate of organic matter processing, leading to enhanced preservation and storage of the DOC sources from peats and palaeosols contained within the aquifer. All groundwater samples were more aromatic for their molecular weight in comparison to other lakes, rivers and surface marine samples studied. The destabilization or changes in hydrology, whether by anthropogenic or natural processes, could lead to the flux of up to 10 times more unreacted organic carbon from this coastal aquifer compared to deeper inland aquifers. © Author(s) 2020.
- ItemLignin degradation in a coastal groundwater aquifer: a useful tracer?(American Geophysical Union, 2014-12) Howley, EM; Jex, CN; Andersen, MS; Baker, AA; Zainuddin, NS; Meredith, KT; Wells, E; McDonald, J; Kham, S; Blyth, AJ; Spencer, RGMLignin as a biomarker in soils, peat, lakes and intertidal and marine sediment cores has been widely researched in the last four decades. The biogeochemical processes controlling their distribution and composition include fractionation due to phase changes, mineral binding, and abiotic and biotic decay. However, there appears to be no studies in the literature describing the concentration and composition of lignin in groundwater aquifers, despite lignin tracing having the potential to differentiate between types of vegetation and recharge source. In the latter case aquifers could potentially be a source of old, degradation resistant lignin. In this study, we characterise the lignin composition in groundwater samples from a coastal sand aquifer, in SE Australia. We compare these data with lignin composition of fresh vegetation samples from the study site, and with lignin data from other environments in the literature. Groundwater samples were also analysed for Dissolved Organic Carbon (DOC) and inorganic chemistry (major ions, Dissolved Inorganic Carbon (DIC) and redox sensitive species) to investigate lignin fractionation processes. To achieve this, the groundwater lignin composition was compared to the total DOC and DIC in the samples and the prevailing redox reactions. The lignin composition in groundwater was found to be unrelated to the surrounding surface vegetation, indicating significant alteration by biogeochemical processes along its flow paths. We identify potential lignin degradation zones, via determination of total OC consumed through redox reactions and microbial activity. In conclusion, this study, by closely examining the correlations of lignin phenols in groundwater with lignin in surface waters, as well as biogeochemical processes in the aquifer is shedding a new light on the ability of lignin as a biomarker in these subsurface systems. To our knowledge, this is the first attempt to assess the usefulness of lignin as a tracer in groundwater. © AGU
- ItemTracing organic carbon processes in a shallow coastal sandy aquifer(American Geophysical Union (AGU), 2017-12-14) Meredith, KT; Andersen, MS; Baker, AA; O'Carroll, DM; Bryan, E; Zainuddin, NS; Rutlidge, H; McDonough, LKCoastal groundwater resources are likely to be impacted by climate change due to changes in recharge patterns, surface water flow and sea-level rise, which all have the potential to change how carbon is transported and stored within a catchment. Large quantities of carbon are currently stored within coastal wetland systems, so understanding carbon dynamics is important for climate change predictions into the future. Furthermore, dissolved organic carbon (DOC) can play a major role in weathering processes and deterioration of water quality, therefore understanding the sources, degradation pathways and its reactivity is important. Groundwater samples were collected from five nested sites (15 wells) from a shallow (0-20m) coastal sandy aquifer system located at Anna Bay, New South Wales, Australia. Surface water samples were also collected from the adjacent wetland. Waters were measured for major ion chemistry, carbon isotopes (δ13CDIC, δ13CDOC and 14CDIC) and tritium (3H). The dissolved organic matter (DOM) character was determined using optical spectroscopy and liquid chromatography. DOC was found to be elevated in the wetland (18 ppm) and had the lowest δ13CDOC value (-30.3 ‰). The shallow (3.5 m) groundwater located closest to but downgradient of the wetland (5 m) had similar characteristics to the wetland sample but contained significantly lower DOC concentrations (5 ppm) and were 1 ‰ more enriched in δ13CDOC values. This suggests that the aquifer is a sink for organic matter and the process fractionates the carbon isotopes. Higher resolution studies are underway to characterise and constrain timescales for the DOC transformation processes.