Browsing by Author "Chen, JY"

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    Distribution and temporal variations in palaeo-groundwater on the Australian continent
    (International Association of Hydrogeologists in Canada, 2012-09-16) Cendón, DI; Markowska, M; Chen, JY; Van der Ley, M; Hughes, CE; Larsen, JR
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    Few-layer graphene under high pressure: raman and x-ray diffraction studies
    (Elsevier, 2013-01-01) Clark, SM; Jeon, KJ; Chen, JY; Yoo, CS
    The effect of pressure on the structure of few-layer graphene has been investigated to 50 GPa in both quasi-hydrostatic and non-hydrostatic conditions, using X-ray diffraction and Raman spectroscopy. The results indicate that few-layer graphene loses its long-range order at the critical interlayer distance of ∼2.8 Å (or above ∼18 GPa), while maintaining the local sp2 hybridization in the layer to 50 GPa. This suggests that graphene not only has the highest stability of all graphitic layer structures, but also becomes one of the most healable structures under large stress. © 2012, Elsevier Ltd.
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    Groundwater and global palaeoclimate signals (G@GPS)
    (International Union of Geological Sciences, 2016-12-01) Haldorsen, S; van der Ploeg, MJ; Cendón, DI; Chen, JY; Ben Jemâa, NC; Gurdak, JJ; Purtschert, R; Tujchneider, O; Vaikmäe, R; Perez, M; Zouari, K
    Groundwater sources supply fresh drinking water to almost half of the World’s population and are a main source of water for irrigation across world. Characterization of groundwater resources, surfacegroundwater interactions and their link to the global water cycle and modern global change are important themes in hydrogeological research, whereas little attention has been given to the relation between groundwater and past climate variations. A groundwater system’s history is vital to assess its vulnerability under future and potentially adverse climatic changes. The scientific initiative Groundwater and Global Palaeoclimate Signals (G@GPS) investigates major recharge periods of large groundwater aquifers worldwide. We describe the findings for a major basin on each permanently inhabited continent and one with coastal influences in Australia. As palaeo-signals in groundwater are inherently low-resolution records, they can only be related to considerable amounts of recharge. Long periods with substantial groundwater recharge ought to be well identifiable in terrestrial records. Correlation with regional and global climate records may give ideas of the conditions under which such large amounts of recharge were initiated. © The Authors - This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial Licence (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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    Hydrogeochemical aquifer characterization and its implication for groundwater development in the Maputo district, Mozambique
    (Elsevier B. V., 2020-05-10) Cendón, DI; Haldorsen, S; Chen, JY; Hankin, SI; Nogueira, GEH; Momade, F; Achimo, M; Muiuane, E; Mugabe, J; Stigter, TY
    Quaternary sand dunes and underlying Pliocene-Oligocene materials host the key groundwater resources that provide the only source of drinking water for a large proportion of Maputo district (Mozambique). This resource is at risk due to potential over exploitation, pollution and salinization. Few hydrogeochemical studies have been conducted in the region, with generally poor quality assurance and availability of datasets. This study provides the first isotopic results to calculate groundwater residence times in the region. Analysis in monitoring bores included major ions, selected minor ions and trace elements, water stable isotopes (δ18O, δ2H), carbon stable isotopes in dissolved inorganic and organic carbon (δ13CDIC, δ13CDOC), strontium isotopes (87Sr/86Sr), radiocarbon (14CDIC) and tritium (3H). Elevated sand dunes are parallel to the coast and constitute recharge “windows” into a phreatic (unconfined) aquifer. The presence of confining clay-rich layers below sand dunes is not continuous, favouring groundwater flow and potential transport of pollutants into a deeper semi-confined aquifer locally. Recharged water evolves from a Na-Cl-type to Na-HCO3-type groundwater with depth. This change in water chemistry is triggered by interaction with carbonate cements in underlying calcarenites and ion exchange processes. Recharge is provided by major rainfall events with smaller rains showing strong evaporation effects on water stable isotopes and limited or no influence on recharge. Groundwater residence times within Quaternary sand dunes are of a few decades as supported by measurable tritium. Deeper portions of the semi-confined aquifer (e.g. 23PZ) have no tritium and could have residence times of up to 1000 yr. Groundwater recharged through Quaternary sand dunes north of Marracuene show low major ion concentrations, low dissolved organic carbon and low nitrate concentrations suggesting a fairly healthy groundwater system. However, closer to the city centre the combined effect of large pollution sources and thinner or absent confining layers have exposed sections of the semi-confined aquifer to nitrate levels above international guidelines. Crown Copyright © 2019 Published by Elsevier Ltd