Browsing by Author "Van der Ley, M"
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- ItemDifferentiating recharge mechanisms and groundwater inputs in a carbonate aquifer (NW-Queensland, Australia)(18th INQUA Congress, 2011-07-21) Van der Ley, M; Cendón, DI; Graham, IT; Spencer, JThe NW of Queensland is a remote pristine and sparsely populated region with minimal groundwater monitoring infrastructure. This is a semi-arid climatic region with monsoonal fronts between December and March being the main source of precipitation. While yearly rainfall averages 580 mm, evaporation can reach 3000 mm. Only a limited number of streams flowing north into the Gulf of Carpentaria sustain flow through the year. These are exclusively maintained by groundwater discharge during the dry season. Furthermore, all perennial streams share the same headwater lithology, consisting of an ∼80 m thick Cambrian marine-platform carbonate sequence. A number of water samples have been collected from perennial spring discharges and available wells downstream. Preliminary results suggest the presence of several aquifer systems operating at different time scales. The shallow system has short residence times as indicated by 35S activities in stream waters. The very low SO4 concentrations of stream waters (∼1 mg/L) suggests that most sulfur in the shallow system is marine derived and related to the last monsoonal rainfalls events. Intermediate systems discharge into perennial springs with longer residence times, where no 3H activity is detected and 14C activities suggest sub-modern groundwater. The comparison of 87Sr/86Sr and REEs of local lithologies and water samples show the interaction between water, carbonates and Proterozic metasediments. This proves intermediate systems either expand into underlying metasedimentary formations or mix with other sources prior to discharging in the springs. The deepest regional system contains palaeowaters (ca. 9000 a) that may have been partially recharged through carbonate lithologies but mostly flow through underlying Proterozoic metasediments, generally increasing in age towards the N but also mixing with younger waters along deep faults and other regional structural controls such as the Riversleigh impact structure.
- ItemDistribution 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, JRNot available
- ItemGroundwater residence time in a dissected and weathered sandstone plateau: Kulnura–Mangrove Mountain aquifer, NSW, Australia(Taylor Francis Online, 2014-04-14) Cendón, DI; Hankin, SI; Williams, JP; Van der Ley, M; Peterson, MA; Hughes, CE; Meredith, KT; Graham, IT; Hollins, SE; Levchenko, VA; Chisari, RGroundwater residence time in the Kulnura–Mangrove Mountain aquifer was assessed during a multi-year sampling programme using general hydrogeochemistry and isotopic tracers (H2O stable isotopes, δ13CDIC, 3H, 14C and 87Sr/86Sr). The study included whole-rock analysis from samples recovered during well construction at four sites to better characterise water–rock interactions. Based on hydrogeochemistry, isotopic tracers and mineral phase distribution from whole-rock XRD analysis, two main groundwater zones were differentiated (shallow and deep). The shallow zone contains oxidising Na–Cl-type waters, low pH, low SC and containing 3H and 14C activities consistent with modern groundwater and bomb pulse signatures (up to 116.9 pMC). In this shallow zone, the original Hawkesbury Sandstone has been deeply weathered, enhancing its storage capacity down to ∼50 m below ground surface in most areas and ∼90 m in the Peats Ridge area. The deeper groundwater zone was also relatively oxidised with a tendency towards Ca–HCO3-type waters, although with higher pH and SC, and no 3H and low 14C activities consistent with corrected residence times ranging from 11.8 to 0.9 ka BP. The original sandstone was found to be less weathered with depth, favouring the dissolution of dispersed carbonates and the transition from a semi-porous groundwater media flow in the shallow zone to fracture flow at depth, with both chemical and physical processes impacting on groundwater mean residence times. Detailed temporal and spatial sampling of groundwater revealed important inter-annual variations driven by groundwater extraction showing a progressive influx of modern groundwater found at >100 m in the Peats Ridge area. The progressive modernisation has exposed deeper parts of the aquifer to increased NO3− concentrations and evaporated irrigation waters. The change in chemistry of the groundwater, particularly the lowering of groundwater pH, has accelerated the dissolution of mineral phases that would generally be inactive within this sandstone aquifer triggering the mobilisation of elements such as aluminium in the aqueous phase. © 2020 Informa UK Limited
- ItemGroundwater systems in northern Australia – are they suitable for a northern food bowl: evidence from residence times and geochemical analyses of ground and surface waters in the Lawn Hill region, northwest Queensland(Geological Society of Australia, 2014-07-07) Van der Ley, M; Cendón, DI; Graham, ITWater resources in the northern regions of Australia have become increasingly important with the possible development of a northern ‘food-bowl’. Understanding the chemistry, flow systems, and mean residence time (MRT) of groundwater systems in this region is therefore essential. The Lawn Hill region of northwest Queensland is subjected to a semi-arid monsoonal climate with an average of 542 mm/a – the majority falling in the warmer months through November–March. Due to the polarity of rainfall, most streams run dry during the dry season. However, four major perennial streams are maintained by groundwater discharge, highlighting the importance of groundwater–surface water interaction and our understanding of such systems. The regional geology is dominated by the Barkly Tableland, an expansive Cambrian carbonate plateau, or siliciclastic formations of the Proterozoic Mount Isa Inlier. The carbonate and siliciclastic lithologies exhibit variable influences on groundwater chemistry and flow. There are distinct differences in chemical signatures whereby the carbonate-hosted groundwater was found to be strongly influenced by carbonate dissolution with little evidence of evapotranspirative enrichment as indicated by both Cl concentrations and stable water isotopes (SWI). Conversely, major ion chemistry and SWI composition of the siliciclastic-hosted groundwaters suggest they are strongly influenced by evapotranspirative enrichment and less by later water–rock interactions (though these do impart a signature on groundwater chemistry). Importantly, the limited influence of evapotranspiration on carbonate-hosted groundwater with TDS values ranging 540–611 mg/L means these waters are classified as freshwater and represent a low–medium irrigation salinity risk. Comparatively, the siliciclastic-hosted groundwaters have much higher TDS values (599–7204 mg/L), which spans the fresh–brackish–saline classifications and represents a medium–high salinity risk. These differences highlight the fact that suitability of groundwater for irrigation purposes greatly depends on the geological controls through water–rock interactions and influence on groundwater infiltration. The mean residence time (MRT) of groundwater is an important indicator for groundwater sustainability. Again, there is a clear distinction between carbonate and siliciclastic hosted groundwaters. Both tritium and radiocarbon analyses of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) indicate a modern age for carbonate groundwaters with fast recharge indicating the carbonate groundwater is less susceptible to depletion but more susceptible to anthropogenic influences. Comparatively, measurable tritium concentrations in siliciclastic groundwaters indicate a modern system; however, DIC and DOC radiocarbon analyses indicate a much older groundwater up to ca 10 000 a (depending on the flow model applied). The differences between tritium and radiocarbon MRT may indicate more complex mixing between young and old groundwater and slower recharge, suggesting siliciclastic groundwaters may be susceptible to depletion.
- ItemHydrogeochemical processes in a monsoon dominated karst environment, NW Queensland(Australian Geosciences Council, 2012-08-05) Van der Ley, M; Cendón, DI; Graham, IT; Spencer, JThe Lawn Hill region, NW Queensland Australia, is host to perennial streams fed by springs from a large karstic aquifer with sub-modern (>50 y) groundwater, developed in Cambrian carbonate lithologies. NW Queensland is subject to semi-arid monsoon climates, and consequently the modern ground and surface waters and their interactions are greatly dependent on seasonal variability of rainfall. We have used a range of techniques to evaluate hydrogeochemical processes including geochemical analysis of host rocks, and a range of isotopic and chemical analyses of ground and surface waters. Samples were collected over multiple sampling campaigns, including during the wet season. Surface waters and groundwaters from carbonate terrains were found to be similarly Ca(Mg) HCO3 type waters as expected from interactions with the karst carbonates, which were found to be composed of primarily dolomite and minor chert. However, there are many indicators (14C, 3H and others) of a more complex system with different temporal scales. Surface waters, while showing dolomitic interactions, have compositions which suggest interaction with underlying silicic lithologies before forming springs. Also, variability in the strength and timing of the monsoon appears to have an effect on activation of different springs and groundwater flow. Additionally, there are groundwaters with much longer residence times (∼6000 a) and chemistries indicative of interaction with silicic and underlying Proterozoic sedimentary units.
- ItemRadiocarbon analysis of bulk and fractionated dissolved organic carbon from ground and surface waters in remote NW Queensland(Australian Geosciences Council, 2012-08-05) Van der Ley, M; Cendón, DI; Graham, ITRadiocarbon analysis of dissolved inorganic carbon (DIC) is prone to dilution by radiocarbon-free DIC from older hosts, particularly in carbonate-rich areas. Dissolved organic carbon (DOC) can provide a source of carbon less affected by water-rock interactions, but is rarely utilised due to more complex sample processing and potential residence time differences for specific fractions. We have developed and applied 14C methods of bulk and fractionated DOC to waters in the Lawn Hill region, remote NW Queensland. As groundwater chemistry here is largely controlled by interactions with Cambrian carbonates, analysis of 14CDIC required uncertain geochemical corrections. Additional samples were analysed from the Greater Sydney region, NSW, with greater variety of residence times and chemistries, to test the methodology. Bulk DOC was pre-concentrated in the field using a weak and non-selective resin, followed by extraction in the lab and fractionation into different DOC groups based on ultrafiltration and selective resin adsorption techniques. All samples were characterised using liquid chromatography and fluorescence to monitor the characteristics of different fractions. Comparisons of 14C activities of DIC and DOC highlight the effect of carbonate dissolution and the usefulness of DOC in radiocarbon analyses. DIC activities were consistently lower than those of DOC, particularly in carbonate-rich regions. Additionally, comparison of fractionated DOC samples showed varying 14C activities, indicating that fractionation may be required for reliable residence times.