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Using (14)C and (3)H to delineate a recharge 'window' into the Perth Basin aquifers, North Gnangara groundwater system, Western Australia.
MedLine Citation:
PMID:  22104381     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
The Gnangara Mound and the underlying Perth Basin aquifers are the largest source of groundwater for the southwest of Australia, supplying between 35 and 50% of Perth's potable water (2009-2010). However, declining health of wetlands on the Mound coupled with the reduction in groundwater levels from increased irrigation demands and drier climatic conditions means this resource is experiencing increased pressures. The northern Gnangara is an area where the Yarragadee aquifer occurs at shallow depths (~50m) and is in direct contact with the superficial aquifer, suggesting the possibility of direct recharge into a generally confined aquifer. Environmental isotopes ((14)C and (3)H) and hydrochemical modelling were used to assess the presence of a recharge 'window' as well as understand the groundwater residence time within different aquifers. Forty-nine groundwater samples were collected from depths ranging from 11 to 311m below ground surface. The isotopic variation observed in the superficial aquifer was found to be controlled by the different lithologies present, i.e. quartz-rich Bassendean Sand and carbonate-rich sediments of the Ascot Formation. Rainfall recharge into the Bassendean Sand inherits its dissolved inorganic carbon from the soil CO(2). Organic matter throughout the soil profile is degraded by oxidation leading to anoxic/acidic groundwater, which if in contact with the Ascot Formation leads to enhanced dissolution of carbonates. Hydrochemical mass balance modelling showed that carbonate dissolution could contribute 1-2mmolkg(-1) of carbon to groundwaters recharged through the Ascot Formation. The corrected groundwater residence times of the Yarragadee aquifer in the northern part of the study area ranged from 23 to 35ka, while waters in the southeastern corner ranged from sub-modern to 2ka. Groundwater ages increase with distance radiating from the recharge 'window'. This study delineates a recharge 'window' into the commonly presumed confined aquifers of the Perth Basin, highlighting the need for appropriate sustainable management.
Authors:
Karina Meredith; Dioni I Cendón; Jon-Philippe Pigois; Suzanne Hollins; Geraldine Jacobsen
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-11-18
Journal Detail:
Title:  The Science of the total environment     Volume:  -     ISSN:  1879-1026     ISO Abbreviation:  -     Publication Date:  2011 Nov 
Date Detail:
Created Date:  2011-11-22     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0330500     Medline TA:  Sci Total Environ     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.
Affiliation:
Australian Nuclear Science and Technology Organisation, Institute for Environmental Research, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
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