Portable X-ray fluorescence for environmental assessment of soils: Not just a point and shoot method

Portable XRF is a rapid, mobile, high throughput, and potentially cost effective instrumental analytical technique capable of elemental assessment. It is widely used for environmental assessment of soils in a variety of contexts such as agriculture and pollution both in-situ and ex-situ, to varying levels of success. Portable XRF performance for soil analysis is often validated against wet chemistry techniques but a range of factors may give rise to elementally dependent disparities affecting accuracy and precision assessments. These include heterogeneity, analysis times, instrument stability during analyses, protective thin films, incident X-rays, sample thickness, sample width, analyte interferences, detector resolution, power source fluctuations and instrumental drift. Light elements comprising water and organic matter (i.e. carbon, oxygen) also negatively affect measurements due to X-ray scattering and attenuation. The often-overlooked phenomenon of variability in both soil organic matter and water can also affect soil density (e.g. shrink-swell clays) and thus sample critical thickness which in turn affects the effective volume of sample analyzed. Compounding this, for elements having lower characteristic fluorescence energy, effective volumes of analyses are lower and thus measurements may not be representative of the whole sample. Understanding the effects and interplay between determined elemental concentrations and soil organic matter, water, and critical thickness together with the subtlety of theoretical effective volumes of analyses will help analysts mitigate potential problems and assess the applicability, advantages and limitations of PXRF for a given site. We demonstrate that with careful consideration of these factors and a systematic approach to analysis which we summarize and present, PXRF can provide highly accurate results

The Environmental Fate and Behaviour of Antimony in the Coastal Floodplain System of the Macleay Catchment, with Comparisons to Arsenic

Antimony (Sb) has been used throughout human history, but recently anthropogenic emissions and recognition of harmful effects on humans and the environment has led to concern over the lack of knowledge about the environmental fate and behaviour of this metalloid. The coastal floodplain of the Macleay Catchment in northeastern NSW, Australia, has been shown to be subject to mining related enrichment of Sb and to a lesser extent, As. The aims of this thesis were to elucidate aspects of Sb behaviour in this system, and to compare the findings with the behaviour of As. The extent of the enrichment of both metalloids in the soils of the floodplain, and the concentrations in selected pastures and surface waters were determined. Possible influences on mobility and availability of both metalloids in selected soils and under specific management regimes were also examined. In addition, the sorption behaviour of Sb (V) was investigated for 2 floodplain soils and 2 dominant soil phases. A review of the available literature indicated that the aims of this thesis had not been addressed previously

Microplastic surface retention and mobility on hiking trails

Hiking and trail running are a source of microplastic (MP) pollution on recreational trails in wilderness and conservation areas; however, the fate of MPs deposited on trails is poorly understood as MP mobility on such surfaces has not yet been examined. In this study, we simulated heavy rainfall (100 mm/h) on trail surfaces with existing MP pollution (in situ MPs) and spiked with 99 ± 2 rubber MPs (100–940 μm). Runoff was collected for 15 min and spiked and in situ MPs were quantified. Hydrological, erosional and microplastic responses were evaluated in relation to slope, bulk density, soil moisture and surface condition indicators, including amounts and types of surface cover and soil physical attributes. The MPs were largely immobile, with 85–100% of spiked MPs retained on trail surfaces. In situ MPs were detected in the trail runoff, with the majority being polyurethane, polypropylene and polyester. Microplastic movement was primarily influenced by hydrological effects, and analysis indicated the main explanatory variable was total runoff volume, followed by soil slaking. Trail sections with at least 15% herbaceous cover or a layer of loose alluvium had higher MP retention. Areas of resource accrual may be preferentially enriched, suggesting MPs from outdoor recreation may be concentrated on and adjacent to recreational trails. Microplastics deposited on trails may have long term implications for biodiversity and ecosystem functioning in wilderness and conservation areas, particularly around the trail corridor

The speciation and mobilisation of phosphorus in alkaline Vertosols

Phosphorus (P) is an essential element for all life, serving as a structural component of cells, being integral in energy transfer, and a component of genes and enzymes (Campbell and Reece, 2002; Schachtman et al., 1998). More than other nutrients, P is held tightly by the soil, so only low concentrations relative to plant requirements are in the soil solution (Holford, 1997). In alkaline soils, it is generally accepted that P is retained in the soil as calcium phosphate (CaP) minerals, limiting plant growth and agricultural production (Conyers and Moody, 2009; Holford, 1997). This research investigates factors that influence the supply of P to the soil solution of alkaline Vertosols, focusing on pH and the concentration of P itself and calcium (Ca) in the solution. The soils were taken from the Northern Grains Region (NGR), a productive agricultural region of 4 M ha in northern New South Wales and southern Queensland, Australia. The soils contain a diminishing pool of phosphorus (P) that is rapidly available to plants, and an acid-soluble P fraction that has been considered to slowly replenish the available pool. The process of replenishment is not well understood, and this may lead to inefficient use of fertiliser P. It is possible that modification of soil in the rhizosphere, particularly acidification, enables plants to directly access the acid-soluble P fraction

The impact of carbon addition on the organisation of rhizosheath of chickpea

Spatio-temporal development of the rhizosheath during root elongation has the potential to modify the function of the rhizosphere under abiotic stress. We quantified the impact of carbon (i.e. glucose) addition on the development and function of rhizosheath of drought tolerant and sensitive chickpea (Cicer arietinum L.) by integrating soil pore volume obtained from X-ray microtomography (µCT), soil physical and microbial respiration measures, and measurements of root traits. Structural equation modelling indicated the feedback mechanisms between added carbon, root traits, pore geometry, and soil functions differed between the cultivars in a fashion congruent with the concept of soil as a self-organising system that interacts with an introduced root system. The drought tolerant cultivar partitioned more photosynthetically fixed carbon to the roots, had more root hairs and more porous rhizosheath, as compared with the sensitive cultivar

Bromoform-assisted aqueous free radical polymerisation: a simple, inexpensive route for the preparation of block copolymers

In the quest for commercially relevant block copolymer additives, for which overall average molecular composition is key but molar mass distribution is of little importance, we present a straightforward, sulfur- and metal-free aqueous route to block copolymers using commercially available starting materials. Based on synthetic techniques first described in the 1950s for hydrophobic monomers in organic solvents, we have shown that bromoform (CHBr3) can be used to create block copolymers. Unlike common bromine-containing chain transfer agents such as carbon tetrabromide (CBr4), bromoform is partially water-miscible and relatively inexpensive. Herein, we demonstrate this new aqueous-based technology using N,N-dimethylacrylamide (DMA) and N-isopropylacrylamide (NIPAM) as exemplar monomers to synthesise PDMA-b-PNIPAM block copolymers of varying composition directly in water. This study demonstrates the potential for such a simple, inexpensive route to functional block copolymers where further research to decipher the detailed mechanism and true potential of this technique will be of great value

Visualising and Quantifying Cereal Root Responses to Phosphorus

Phosphorus (P) and nitrogen macronutrient deficiencies remain a primary constraint to global agricultural production. Expectations for decreasing fertiliser availability and increased food demand provide impetus for improving plant nutrient efficiencies. While significant genetic advances have been made based on plant shoot characteristics, the root system traits have remained largely untargeted in breeding programs. This is largely due to the difficulties in rapidly assessing root system attributes. Since the spatial distribution of the root system (root architecture) determines the edaphic resources available to plants, it is logical to target root architecture in an effort to improve plant nutrient acquisition efficiency. Characteristics such as localised root proliferation in response to high nutrient patches could be improved to increase nutrient capture from point source fertiliser applications

D'Annunzio sulla scena lirica: libretto o "Poema"?

Australia Direct Action climate change policy relies on purchasing greenhouse gas abatement from projects undertaking approved abatement activities. Management of soil organic carbon (SOC) in agricultural soils is an approved activity, based on the expectation that land use change can deliver significant changes in SOC. However, there are concerns that climate, topography and soil texture will limit changes in SOC stocks. This work analyses data from 1482 sites surveyed across the major agricultural regions of Eastern Australia to determine the relative importance of land use vs. other drivers of SOC. Variation in land use explained only 1.4% of the total variation in SOC, with aridity and soil texture the main regulators of SOC stock under different land uses. Results suggest the greatest potential for increasing SOC stocks in Eastern Australian agricultural regions lies in converting from cropping to pasture on heavy textured soils in the humid regions

Functional traits determine plant co-occurrence more than environment or evolutionary relatedness in global drylands

Plant–plant interactions are driven by environmental conditions, evolutionary relationships (ER) and the functional traits of the plants involved. However, studies addressing the relative importance of these drivers are rare, but crucial to improve our predictions of the effects of plant–plant interactions on plant communities and of how they respond to differing environmental conditions. To analyze the relative importance of – and interrelationships among – these factors as drivers of plant–plant interactions, we analyzed perennial plant co-occurrence at 106 dryland plant communities established across rainfall gradients in nine countries. We used structural equation modelling to disentangle the relationships between environmental conditions (aridity and soil fertility), functional traits extracted from the literature, and ER, and to assess their relative importance as drivers of the 929 pairwise plant–plant co-occurrence levels measured. Functional traits, specifically facilitated plants’ height and nurse growth form, were of primary importance, and modulated the effect of the environment and ER on plant–plant interactions. Environmental conditions and ER were important mainly for those interactions involving woody and graminoid nurses, respectively. The relative importance of different plant–plant interaction drivers (ER, functional traits, and the environment) varied depending on the region considered, illustrating the difficulty of predicting the outcome of plant–plant interactions at broader spatial scales. In our global-scale study on drylands, plant–plant interactions were more strongly related to functional traits of the species involved than to the environmental variables considered. Thus, moving to a trait-based facilitation/competition approach help to predict that: (1) positive plant–plant interactions are more likely to occur for taller facilitated species in drylands, and (2) plant–plant interactions within woody-dominated ecosystems might be more sensitive to changing environmental conditions than those within grasslands. By providing insights on which species are likely to better perform beneath a given neighbour, our results will also help to succeed in restoration practices involving the use of nurse plants