Browsing by Author "Harris, SJ"
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- ItemAccumulative evidence highlighting that the Narrabri and Gunnedah formations are mythical(National Centre for Groundwater Research And Training, 2017-07-12) Kelly, BFJ; Cendón, DI; Iverach, CP; Harris, SJ; Hankin, SIThe Narrabri and Gunnedah Formations, used to describe the valley-filling sedimentary sequences in portions of the Murray-Darling Basin, have never been formally defined. The hydrogeological evidence for naming these formations is reviewed in the context of modern sedimentary models. Are we using the right architectural model? Hundreds of lithological logs from the Murrumbidgee, Namoi, and Gwydir catchments are used to examine the evolution of each alluvial aquifer. For each depth interval, the catchment-wide proportions of coarse (gravel, sand) and fine (silt, clay) sediments is determined. Sediment size distributions are then examined in the context of past climates and the conceptual inland fluvial model for distributive fluvial systems. Vertical hydraulic connectivity is examined using new hydrogeochemical data and nested groundwater hydrograph sets. All systems show the core features of aggradational distributive fluvial systems. The valley-filling sequences for all catchments examined transitioned from high energy wet environments at depth, dominated by sand and gravel deposits, through to the modern-day low-energy silt and clay dominated depositional environments. Gravel and sand deposits dominate in the proximal portion of the catchment, and low energy silt and clay deposits dominate in the distal portions. The apparent existence of the Narrabri and Gunnedah Formations is due to changing sediment grain size proportion and channel fill sand connectivity. Both the facies and hydrograph analyses show that semi-confining layers are only local. Extensive hydrogeochemical data from the Namoi catchment show continuity of mixing between basement and surface inflows. All catchments have many sedimentary architectural features consistent with the distributive fluvial system model, and reflect changing climate throughout the Neogene and Quaternary. Use of the Narrabri and Gunnedah Formation nomenclature, which has been incorporated into the National Aquifer Framework, is not supported by either the sedimentological, hydrograph or hydrogeochemical record.
- ItemFertilizers rule REYs: agricultural catchments of Eastern Australia(Goldschmidt, 2019-08-18) Cendón, DI; Harris, SJ; Kelly, BFJ; Peterson, MA; Hankin, SI; Rowling, B; Watson, J; Xiao, SLanthanides, generally named Rare Earth Elements (REE), are part of the internal transition metals forming a group of 15 elements with very similar chemical characteristics and physical properties. REEs and Yttrium (named REY) are widely used to understand geochemical processes. The increasing use of REYs in technology as well as their presence as a by-product in some fertilizers has opened new pathways for these metals to enter the water cycle, thus making REYs tracers of anthropogenic activity. In this study we investigate the concentration and distribution of REYs in two predominantly agricultural catchments of Eastern Australia: the Namoi River with a 43,000 km2 catchment, which forms part of the headwaters of the Murray- Darling Basin; and the Nogoa River with a 27,600 km2 catchment, which forms part of the Fitzroy River catchment, the largest in eastern Australia flowing into the Great Barrier Reef. Bi-monthly sampling during 18 months was conducted at seven selected sites along both rivers. The [REY] in water samples were analyzed by automated chelation pre-concentration (SeaFast, ESI), followed by ICP-MS. Samples were automatically loaded onto a loop and injected to an iminodiacetate column that chelates REY allowing matrix Na+, Cl-, Ca2+, Mg2+ and, more importantly, Ba2+ ions to be rinsed out. The pre-concentration process allowed a ~20-fold increase in concentration. Results are compared to those obtained from commonly used fertilizers in the region. REY trends suggest a link to the fertilizers used in both catchments. No regional variations were apparent, possibly due to the prevailing dry conditions during the sampling period. Stream flow was controlled by dam releases in the upper ridges for both catchments.
- ItemIsotopic evidence for nitrate sources and controls on denitrification in groundwater beneath an irrigated agricultural district(Elsevier, 2022-04-15) Harris, SJ; Cendón, DI; Hankin, SI; Peterson, MA; Xiao, S; Kelly, BFJThe application of N fertilisers to enhance crop yield is common throughout the world. Many crops have historically been, or are still, fertilised with N in excess of the crop requirements. A portion of the excess N is transported into underlying aquifers in the form of NO3−, which is potentially discharged to surface waters. Denitrification can reduce the severity of NO3− export from groundwater. We sought to understand the occurrence and hydrogeochemical controls on denitrification in NO3−-rich aquifers beneath the Emerald Irrigation Area (EIA), Queensland, Australia, a region of extensive cotton and cereal production. Multiple stable isotope (in H2O, NO3−, DIC, DOC and SO42−) and radioactive isotope (3H and 36Cl) tracers were used to develop a conceptual N process model. Fertiliser-derived N is likely incorporated and retained in the soil organic N pool prior to its mineralisation, nitrification, and migration into aquifers. This process, alongside the near absence of other anthropogenic N sources, results in a homogenised groundwater NO3− isotopic signature that allows for denitrification trends to be distinguished. Regional-scale denitrification manifests as groundwater becomes increasingly anaerobic during flow from an upgradient basalt aquifer to a downgradient alluvial aquifer. Dilution and denitrification occurs in localised electron donor-rich suboxic hyporheic zones beneath leaking irrigation channels. Using approximated isotope enrichment factors, estimates of regional-scale NO3− removal ranges from 22 to 93% (average: 63%), and from 57 to 91% (average: 79%) beneath leaking irrigation channels. In the predominantly oxic upgradient basalt aquifer, raised groundwater tables create pathways for NO3− to be transported to adjacent surface waters. In the alluvial aquifer, the transfer of NO3− is limited both physically (through groundwater-surface water disconnection) and chemically (through denitrification). These observations underscore the need to understand regional- and local-scale hydrogeological processes when assessing the impacts of groundwater NO3− on adjacent and end of system ecosystems. © The Authors 2022, Published by Elsevier B.V. CC BY-NC-ND license
- ItemN2O isotopocule measurements using laser spectroscopy: analyzer characterization and intercomparison(European Geosciences Union, 2020-05-28) Harris, SJ; Liisberg, J; Xia, LL; Wei, J; Zeyer, K; Yu, LF; Barthel, M; Wolf, B; Kelly, BFJ; Cendón, DI; Blunier, T; Six, J; Mohn, JFor the past two decades, the measurement of nitrous oxide (N2O) isotopocules – isotopically substituted molecules 14N15N16O, 15N14N16O and 14N14N18O of the main isotopic species 14N14N16O – has been a promising technique for understanding N2O production and consumption pathways. The coupling of non-cryogenic and tuneable light sources with different detection schemes, such as direct absorption quantum cascade laser absorption spectroscopy (QCLAS), cavity ring-down spectroscopy (CRDS) and off-axis integrated cavity output spectroscopy (OA-ICOS), has enabled the production of commercially available and field-deployable N2O isotopic analyzers. In contrast to traditional isotope-ratio mass spectrometry (IRMS), these instruments are inherently selective for position-specific 15N substitution and provide real-time data, with minimal or no sample pretreatment, which is highly attractive for process studies. Here, we compared the performance of N2O isotope laser spectrometers with the three most common detection schemes: OA-ICOS (N2OIA-30e-EP, ABB – Los Gatos Research Inc.), CRDS (G5131-i, Picarro Inc.) and QCLAS (dual QCLAS and preconcentration, trace gas extractor (TREX)-mini QCLAS, Aerodyne Research Inc.). For each instrument, the precision, drift and repeatability of N2O mole fraction [N2O] and isotope data were tested. The analyzers were then characterized for their dependence on [N2O], gas matrix composition (O2, Ar) and spectral interferences caused by H2O, CO2, CH4 and CO to develop analyzer-specific correction functions. Subsequently, a simulated two-end-member mixing experiment was used to compare the accuracy and repeatability of corrected and calibrated isotope measurements that could be acquired using the different laser spectrometers. Our results show that N2O isotope laser spectrometer performance is governed by an interplay between instrumental precision, drift, matrix effects and spectral interferences. To retrieve compatible and accurate results, it is necessary to include appropriate reference materials following the identical treatment (IT) principle during every measurement. Remaining differences between sample and reference gas compositions have to be corrected by applying analyzer-specific correction algorithms. These matrix and trace gas correction equations vary considerably according to N2O mole fraction, complicating the procedure further. Thus, researchers should strive to minimize differences in composition between sample and reference gases. In closing, we provide a calibration workflow to guide researchers in the operation of N2O isotope laser spectrometers in order to acquire accurate N2O isotope analyses. We anticipate that this workflow will assist in applications where matrix and trace gas compositions vary considerably (e.g., laboratory incubations, N2O liberated from wastewater or groundwater), as well as extend to future analyzer models and instruments focusing on isotopic species of other molecules. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 Licence.
- ItemNitrogen cycling dynamics in a humid subtropical climate: insights from the Nogoa River sub-catchment, central Queensland, Australia(Copernicus Publications, 2019-04-07) Harris, SJ; Cendón, DI; Peterson, MA; Hankin, SI; Watson, J; Xiao, S; Kelly, BFJThe Nogoa River sub-catchment, Queensland, Australia, supports a multimillion-dollar agricultural sector. For the last decade, efforts have been made to monitor river nitrate loads (Fitzroy partnership for River Health, 2017), which may affect sensitive ecosystems downstream, such as the World Heritage-listed Great Barrier Reef (Brodie et al. 2012). Research into nitrous oxide, which arises from both the oxidation of ammonium fertilisers and/or reduction of subsequent nitrate, is also very important due to its increasing impact on the atmosphere. An integrated approach that considers the interactions between atmosphere, river water and groundwater nitrogen compounds is thus integral to closing the nitrogen cycle in the region. Nitrogen fertiliser contributions to greenhouse gas emissions, riverine environments and aquifers remain uncertain for several reasons: (1) ad-hoc river water sampling frequency and infrequent shallow groundwater sampling; (2) a lack of isotopic evidence for attributing sources and highlighting attenuation processes; (3) poor understanding of groundwater recharge pathways, residence times, and contributions to the Nogoa River; and (4) a lack of quantification of river water and groundwater nitrous oxide concentrations and emissions. In this poster, we present hydro-geochemical data (major ions, N2O-N, δ2H-H2O and δ18O-H2O, δ15N-NO-3 and δ18O-NO- 3, and natural radioactive tracers) from seven sites along the Nogoa River that were repeatedly sampled over a 1-year period, and from 24 shallow groundwater bores sampled in October 2018. A comparison with historical major ion groundwater data reveals that nitrate concentrations have increased due to continued fertiliser input over the past ∽ 20 years, reaching up to 25 mg L-1 NO- 3 -N. Dual nitrate isotopes (δ15N and δ18O) reveal that denitrification occurs in both the shallow groundwater and Nogoa River samples, and suggest a predominant fertiliser source of nitrate. The data will be placed in the wider context of recharge pathways, residence times and contributions to the Nogoa River, and will be used to understand the interplay between the river and alluvial aquifer nitrate and nitrous oxide emissions. © Author(s) 2019. CC Attribution 4.0 license.
- ItemOccurrence and controls on N2O accumulation in the lower Namoi alluvial aquifer, Australia(Copernicus Publications, 2018-04-08) Harris, SJ; Cendón, DI; Hankin, SI; Kelly, BFJThe lower Namoi alluvial aquifer (LNAA) in northwest Australia supports a multibillion-dollar agricultural sector focused around cotton growing established in the 1960s. Investigations into N2O emissions from the LNAA and possible perturbations from agriculture and natural processes are lacking. To determine groundwater N2O concentrations and production processes in the LNAA, we sampled groundwater from 23 bores (8.4 – 33.6 m depth) in the lower Namoi catchment. To the best of our knowledge, this is the first study to quantify N2O in groundwater at a catchment scale in Australia. Dissolved N2O-N concentrations ranged from 1.2 – 11.9 μg L-1, and NO3-N concentrations ranged from <0.02 – 5.1 mg L-1. N2O-N and NO3-N concentrations were weakly, yet positively, correlated (r2 = 0.2, p = 0.01). The highest concentrations measured in groundwater were beneath intensely cropped farms (N2O-N ranging from 1.9 – 11.9 μg L-1; and NO3-N ranging from 1.3 – 5.1 mg L-1). An exception to this occurred along a groundwater transect within cropped farmland, where both N2O-N and NO3-N concentrations were lower (1.2 – 2.0 μg L-1 and 0.02 – 0.3 mg L-1, respectively). Spatially, this groundwater transect is located where the Great Artesian Basin (GAB), the largest artesian basin in the world, discharges into the LNAA (Iverach et al. 2017). Here, GAB input causes the groundwater to have low dissolved oxygen (0.2 – 0.4 mg L-1) and warmer temperatures (23 – 26 ºC), which promotes the reduction of NOǯ 3 to gaseous N2O and N2via denitrification. Mean emission factors for indirect N2O emissions (EF5g; N2O-N / NO3-N) from groundwater bores located on farm (EF5g = 0.2%) were lower than IPCC default EF5g (EF5g = 0.25%), while estimates from riparian zone groundwater (EF5g = 3.0%) were higher. Importantly, EF5g values from groundwater affected by GAB discharge (EF5g = 3.4%) were also significantly greater than the IPCC default EF5g, despite being located beneath intensely cropped farmland and having low N2O-N contents. The proximity of GAB discharge to major basement faults (FrogTech 2006) suggests these geological features may act as principal conduits for GAB input into the LNAA. By extension, this highlights a fundamental geological control on N2O emissions and nitrogen cycling – a concept that has been largely ignored in the literature. © Author(s) 2018. CC Attribution 4.0 license.