Browsing by Author "Han, LF"

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    Evolution of chemical and isotopic composition of inorganic carbon in a complex semi-arid zone environment: consequences for groundwater dating using radiocarbon
    (Elsevier, 2016-09-01) Meredith, KT; Han, LF; Hollins, SE; Cendón, DI; Jacobsen, GE; Baker, AA
    Estimating groundwater age is important for any groundwater resource assessment and radiocarbon (14C) dating of dissolved inorganic carbon (DIC) can provide this information. In semi-arid zone (i.e. water-limited environments), there are a multitude of reasons why 14C dating of groundwater and traditional correction models may not be directly transferable. Some include; (1) the complex hydrological responses of these systems that lead to a mixture of different ages in the aquifer(s), (2) the varied sources, origins and ages of organic matter in the unsaturated zone and (3) high evaporation rates. These all influence the evolution of DIC and are not easily accounted for in traditional correction models. In this study, we determined carbon isotope data for; DIC in water, carbonate minerals in the sediments, sediment organic matter, soil gas CO2 from the unsaturated zone, and vegetation samples. The samples were collected after an extended drought, and again after a flood event, to capture the evolution of DIC after varying hydrological regimes. A graphical method (Han et al., 2012) was applied for interpretation of the carbon geochemical and isotopic data. Simple forward mass-balance modelling was carried out on key geochemical processes involving carbon and agreed well with observed data. High values of DIC and δ13CDIC, and low 14CDIC could not be explained by a simple carbonate mineral–CO2 gas dissolution process. Instead it is suggested that during extended drought, water–sediment interaction leads to ion exchange processes within the top ∼10–20 m of the aquifer which promotes greater calcite dissolution in saline groundwater. This process was found to contribute more than half of the DIC, which is from a mostly ‘dead’ carbon source. DIC is also influenced by carbon exchange between DIC in water and carbonate minerals found in the top 2 m of the unsaturated zone. This process occurs because of repeated dissolution/precipitation of carbonate that is dependent on the water salinity driven by drought and periodic flooding conditions. This study shows that although 14C cannot be directly applied as a dating tool in some circumstances, carbon geochemical/isotopic data can be useful in hydrological investigations related to identifying groundwater sources, mixing relations, recharge processes, geochemical evolution, and interaction with surface water.© 2016, Elsevier Ltd.
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    Evolution of chemical and isotopic composition of inorganic carbon in the unsaturated and saturated zones of a semi-arid zone environment
    (National Centre for Groundwater Research And Training, 2017-07-12) Meredith, KT; Han, LF; Hollins, SE; Cendón, DI; Jacobsen, GE; Baker, AA
    Estimating groundwater age is important for any groundwater resource assessment and radiocarbon (14C) dating can provide this information. However a thorough investigation of the water in the soil-plant-atmosphere continuum leading to the evolution of dissolved inorganic carbon (DIC) in groundwater is required for interpretation in a water-limited environment. In this study we trace the evolution of DIC through the unsaturated and saturated zones after prolonged drought and post-flooding of a major river system, the Darling River. In doing so, we quantified the contribution of carbon from various processes influencing the 14C content of DIC in groundwater. None of the simple 14C adjustment models could be applied for age estimation. Therefore, we used a combination of a graphical method and mass-balance calculations. It was found that the saline groundwaters evolved via carbon exchange between DIC- carbon dioxide gas (CO2(g)) in the unsaturated zone and DIC-carbonate minerals in the saturated zone with water-sediment reactions driving ion exchange on clay minerals facilitating carbonate dissolution. This study shows the problems associated with using radiocarbon dating in a semi-arid zone or water-limited environment and the required carbon measurements needed to reduce this uncertainty.
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    Evolution of dissolved inorganic carbon in groundwater recharged by cyclones and groundwater age estimations using the 14C statistical approach
    (Elsevier B. V., 2018-01-01) Meredith, KT; Han, LF; Cendón, DI; Crawford, J; Hankin, SI; Peterson, MA; Hollins, SE
    The Canning Basin is the largest sedimentary basin in Western Australia and is located in one of the most cyclone prone regions of Australia. Despite its importance as a future resource, limited groundwater data is available for the Basin. The main aims of this paper are to provide a detailed understanding of the source of groundwater recharge, the chemical evolution of dissolved inorganic carbon (DIC) and provide groundwater age estimations using radiocarbon (14CDIC). To do this we combine hydrochemical and isotopic techniques to investigate the type of precipitation that recharge the aquifer and identify the carbon processes influencing 14CDIC, δ13CDIC, and [DIC]. This enables us to select an appropriate model for calculating radiocarbon ages in groundwater. The aquifer was found to be recharged by precipitation originating from tropical cyclones imparting lower average δ2H and δ18O values in groundwater (−56.9‰ and −7.87‰, respectively). Water recharges the soil zone rapidly after these events and the groundwater undergoes silicate mineral weathering and clay mineral transformation processes. It was also found that partial carbonate dissolution processes occur within the saturated zone under closed system conditions. Additionally, the processes could be lumped into a pseudo-first-order process and the age could be estimated using the 14C statistical approach. In the single-sample-based 14C models, 14C0 is the initial 14CDIC value used in the decay equation that considers only 14C decay rate. A major advantage of using the statistical approach is that both 14C decay and geochemical processes that cause the decrease in 14CDIC are accounted for in the calculation. The 14CDIC values of groundwater were found to increase from 89 pmc in the south east to around 16 pmc along the groundwater flow path towards the coast indicating ages ranging from modern to 5.3 ka. A test of the sensitivity of this method showed that a ∼15% error could be found for the oldest water. This error was low when compared to single-sample-based models. This study not only provides the first groundwater age estimations for the Canning Basin but is the first groundwater dating study to test the sensitivity of the statistical approach and provide meaningful error calculations for groundwater dating. Crown Copyright © 2017 Published by Elsevier Ltd.
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    Study of groundwater recharge using combined unsaturated‐and saturated‐zone chloride mass balance methods
    (Wiley, 2023-06-19) Jiang, SY; Rao, WB; Han, LF; Meredith, Karina T
    Understanding groundwater recharge mechanisms is essential for reliable groundwater recharge estimation for sustainable groundwater resource assessment and management, especially in arid and semiarid areas. In this study, chloride, together with stable isotopes (18O and2H), in 1‐year rainfall, soil water from representative profiles, and groundwater samples, collected in the Ordos Plateau, northern China were analysed. Groundwater recharge was estimated using unsaturated‐ and saturated‐zone chloride mass balance (CMB). An equation that describes the relationship between chloride concentrations in saturated zone water (Csz) and soil water residence time (τ) was derived. With the help of the relationship, chloride concentrations in unsaturated zone water (Cuz) and in groundwater (Csz) can be used to uncover water flow and chloride transport in the unsaturated zone. The relationship betweenCszandCuzindicates that, the groundwater was recharged mainly by intense rainfall events. Small rainfall events did not lead to groundwater recharge but contributed to the flux of chloride to soil surface. Stable isotopic compositions of18O and2H provided corroborative evidence of the recharge processes. The relationship betweenCszandτindicates further that there is no source of chloride in the groundwater other than that from precipitation. Thus,Cszcan give more reliable recharge estimates.Cuzwas influenced by heavy rainfall‐induced runoff, run‐on and bypass flow events and cannot give reliable recharge estimates. However, if used jointly withCsz,Cuzcan help to gain insights into recharge processes and yield groundwater recharge estimates with higher certainty. The outcomes of this study can assist for groundwater recharge investigation and assessment in regions where the assumptions and boundary conditions necessary for the correct application of the CMB method may not be met. © 1999-2024 John Wiley & Sons