Browsing by Author "Watson, J"

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    Fertilizers 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, S
    Lanthanides, 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.
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    Nitrogen 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, BFJ
    The 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.