Browsing by Author "Mustonen, O"

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    Extent and characterisation of natural groundwater organic matter sorption onto minerals
    (Copernicus GmbH, 2019-04-08) Oudone, PP; Mustonen, O; Marjo, CE; Meredith, KT; McDonough, LK; Rutlidge, H; Andersen, MS; O'Carroll, DM; Baker, AA
    Rivers and aquifers have been proven to be physiochemically connected. Despite their interaction, organic matter (OM) concentration in groundwater is much lower than rivers. One might ask where it goes. For example, is sorption responsible for this missing fraction? If so, what components of OM are utilised by groundwater sorption to the minerals? This research aims to quantify the sorption of natural groundwater DOC over a range of groundwater and surface water environments in South East Australia. Batch experiments were set up by adding 40 ml of filtered (0.22 m) sample to a range of masses of three types of sterilised minerals: iron coated sand, quartz sand and calcium carbonate. The systems were rotated for 1 hour under controlled conditions before analysis by Liquid Chromatography-Organic Carbon Detection (LC-OCD) for the aqueous phase and X-ray Photoelectron Spectroscopy (XPS) for the solid phase. Size-exclusion chromatography using LC-OCD is used to determine the remaining chemical fractions in solution. LC-OCD separates DOC into biopolymers (»20,000 g/mol), humic substances ( 1000 g/mol), building blocks (300-500 g/mol), low molecular weight neutrals (<350 g/mol) and low molecular weight acids (350 g/mol). The technique also provides measures of humic substances aromaticity and relative molecular weight. XPS is used to characterise the surface chemistry of the adsorbed organic layer in terms of the relative carbon, nitrogen, and oxygen content, and the types of chemical bonding. The results of solid-phase XPS is compared with the remaining chemical fractions in solution characterised by LC-OCD. LC-OCD results showed that humic substances were highest in concentration in the groundwater DOC compared to other fractions (13-65%) and was the significant sorbing fraction for all mineral types and water samples. The sorption extent ranges between 4-61%. This sorption was highest for iron coated sand (8-61%) followed by calcium carbonate (10-35%) and then quartz sand (4-22%). XPS showed that more sorbed organics (O, C and N) were found on iron coated sand and calcium carbonate compared to quartz sand. The extent of humic substance sorption was found proportional to its aromaticity and molecular weight for all mineral types and water samples. In conclusion, even though sediment types influence groundwater DOC sorption, the result suggests that groundwater DOM sorption plays an important role in the missing fraction of groundwater DOC (31-9/4%). © Author(s) 2019. CC Attribution 4.0 license.
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    Natural organic matter in goundwater: carbon source or sink?
    (European Geosciences Union, 2019-04-07) Rutlidge, H; McDonough, LK; Oudone, PP; Andersen, MS; Baker, AA; Meredith, KT; O'Carroll, DM; Marjo, CE; Mustonen, O
    Carbon plays an essential role in all biological processes on the earth and hence it is important to Mustin the environment. The concentration of organic matter in groundwater, with a global median of 1.0 mg C/L, is often significantly lower than in adjacent soil and surface waters. The likely processes that are responsible for this decrease are sorption to mineral surfaces and biological processing by microbes as water travels through sediments. While these processes have been quantified individually at different sites, they have not been investigated concurrently, and hence the relative importance of each process is unknown. Therefore, the role of organic matter processes in groundwater and in the terrestrial global carbon budget is unknown. To investigate this a series of laboratory-based experiments were conducted, in conjunction with the organic matter characterization of field samples by Liquid Chromatography-Organic Carbon Detection (LC-OCD). LC-OCD is a size-exclusion based chromatography technique that separates dissolved organic carbon into five fractions based on their mass, plus a hydrophobic fraction, which remains in the column. For the laboratory-based experiments, the amount of sorption onto pure mineral surfaces (quartz sand, iron-coated sand, and calcium carbonate), desorption from natural sediments and biological degradation was investigated at a range of different locations in New South Wales, Australia. The sites covered a range of different aquifer materials (coastal sands, river alluvium and fractured meta-basalts), land cover and recharge type. At each site, groundwater samples were collected from wells located with varying distance from surface water bodies for the subsequent laboratory experiments. The results showed that predominately the humics fraction was adsorbing onto the mineral surfaces and the low-molecular weight neutrals were being biologically degraded. For the desorption experiments several fractions desorbed with the humics and hydrophobic fraction being dominant. The amount of desorption increased with increasing salinity and increasing number of cycles of drying and wetting. The LC-OCD results of field samples indicated that proportionally, sorption is more dominant than biological degradation. Hence changing environmental conditions, such as increasing salinity and/or drier conditions, could lead to a release of sorbed carbon.
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    Natural organic matter in groundwater: carbon source or sink ?
    (Copernicus GmbH, 2019-04-08) Rutlidge, H; McDonough, LK; Oudone, PP; Andersen, MS; Baker, AA; Meredith, KT; O'Carroll, DM; Marjo, CM; Mustonen, O
    Carbon plays an essential role in all biological processes on the earth and hence it is important to Mustin the environment. The concentration of organic matter in groundwater, with a global median of 1.0 mg C/L, is often significantly lower than in adjacent soil and surface waters. The likely processes that are responsible for this decrease are sorption to mineral surfaces and biological processing by microbes as water travels through sediments. While these processes have been quantified individually at different sites, they have not been investigated concurrently, and hence the relative importance of each process is unknown. Therefore, the role of organic matter processes in groundwater and in the terrestrial global carbon budget is unknown. To investigate this a series of laboratory-based experiments were conducted, in conjunction with the organic matter characterization of field samples by Liquid Chromatography-Organic Carbon Detection (LC-OCD). LC-OCD is a size-exclusion based chromatography technique that separates dissolved organic carbon into five fractions based on their mass, plus a hydrophobic fraction, which remains in the column. For the laboratory-based experiments, the amount of sorption onto pure mineral surfaces (quartz sand, iron-coated sand, and calcium carbonate), desorption from natural sediments and biological degradation was investigated at a range of different locations in New South Wales, Australia. The sites covered a range of different aquifer materials (coastal sands, river alluvium and fractured meta-basalts), land cover and recharge type. At each site, groundwater samples were collected from wells located with varying distance from surface water bodies for the subsequent laboratory experiments. The results showed that predominately the humics fraction was adsorbing onto the mineral surfaces and the low-molecular weight neutrals were being biologically degraded. For the desorption experiments several fractions desorbed with the humics and hydrophobic fraction being dominant. The amount of desorption increased with increasing salinity and increasing number of cycles of drying and wetting. The LC-OCD results of field samples indicated that proportionally, sorption is more dominant than biological degradation. Hence changing environmental conditions, such as increasing salinity and/or drier conditions, could lead to a release of sorbed carbon.