Hydrochemical and isotopic characterisation of groundwaters to define aquifer type and connectivity in a subtropical coastal setting,Fraser Coast,Queensland |
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Authors: | Genevieve R Larsen Malcolm E Cox |
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Institution: | (1) Biogeosciences, Faculty of Science and Technology, Queensland University of Technology, Brisbane, QLD, 4001, Australia;(2) National Centre for Groundwater Research and Training, Adelaide, Australia |
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Abstract: | Physico-chemical parameters, major ion chemistry and isotope composition of surface and groundwaters were determined in forested
coastal catchments and adjacent coastal plains. Results showed obvious characterisation related to physical and hydrological
setting, and highly variable spatial differences reflecting the complexities of these areas. All these coastal waters are
dominated by Na–Cl and fall on a common dilution line; hydrochemical grouping is largely due to anionic differences (Cl, SO4 and HCO3), although Na and Mg ratios also vary. Six major hydrochemical facies were determined. For groundwaters, compositional differences
are largely related to aquifer material and level of confinement; for coastal groundwaters important are tidal effects and
proximity to the shoreline. Differentiation for surface waters is mainly by drainage morphology, flow regime plus proximity
to the coast. Connectivity between water bodies is reflected by minor base flow to catchment streams, including with flood
plain wetlands, but mostly occurs in low-lying zones where there is mixing of fresh and saline water within surface water
and subterranean estuaries, or by seawater intrusion enhanced by overuse. Oxygen and hydrogen isotopic data for confined and
semi-confined groundwaters along the coast indicates local recharge; fresh surface waters in the elevated catchments are shown
to be sourced further inland plus have experienced evaporation. |
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