Soil reconstruction after mining fails to restore soil function in an Australian arid woodland

The biogeochemical properties of soils drive ecosystem function and vegetation dynamics, and hence soil restoration after mining should aim to reinstate the soil properties and hydrological dynamics of remnant ecosystems. The aim of this study is to assess soil structure in two vegetation types in an arid ecosystem, and to understand how these soil properties compare to a reconstructed soil profile after mining. In an arid ecosystem in southeast Australia, soil samples were collected at five depths (to 105 cm) from remnant woodland and shrubland sites, and sites either disturbed or totally reconstructed after mining. We assessed soil physico-chemical properties and microbial activity. Soils in the remnant arid ecosystem had coarse-textured topsoils that overlay clay horizons, which allows water to infiltrate and avoid evaporation, but also slows drainage to deeper horizons. Conversely, reconstructed soils had high sand content at subsoil horizons and high bulk density and compaction at surface layers (0–20 cm). Reconstructed soils had topsoils with higher pH and electrical conductivity. The reconstructed soils did not show increased microbial activity with time since restoration. Overall, the reconstructed soil horizons were not organized in a way that allowed rainfall infiltration and water storage, as is imperative to arid-zone ecosystem function. Future restoration efforts in arid ecosystems should focus on increasing sand content of soils near the surface, to reduce evaporative water loss and improve soil quality and plant health. © 2020 Society for Ecological Restoratio

Uncovering erosion effects on magnetic flux rope twist

Context. Magnetic clouds (MCs) are transient structures containing large-scale magnetic flux ropes from solar eruptions. The twist of magnetic field lines around the rope axis reveals information about flux rope formation processes and geoeffectivity. During propagation MC flux ropes may erode via reconnection with the ambient solar wind. Any erosion reduces the magnetic flux and helicity of the ropes, and changes their cross-sectional twist profiles. Aims. This study relates twist profiles in MC flux ropes observed at 1 AU to the amount of erosion undergone by the MCs in interplanetary space. Methods. The twist profiles of two clearly identified MC flux ropes associated with the clear appearance of post eruption arcades in the solar corona are analyzed. To infer the amount of erosion, the magnetic flux content of the ropes in the solar atmosphere is estimated, and compared to estimates at 1 AU. Results. The first MC shows a monotonically decreasing twist from the axis to the periphery, while the second displays high twist at the axis, rising twist near the edges, and lower twist in between. The first MC displays a larger reduction in magnetic flux between the Sun and 1 AU, suggesting more erosion than that seen in the second MC. Conclusions. In the second cloud the rising twist at the rope edges may have been due to an envelope of overlying coronal field lines with relatively high twist, formed by reconnection beneath the erupting flux rope in the low corona. This high-twist envelope remained almost intact from the Sun to 1 AU due to the low erosion levels. In contrast, the high-twist envelope of the first cloud may have been entirely peeled away via erosion by the time it reaches 1 AU.Peer reviewe

Spatial coherence of interplanetary coronal mass ejection sheaths at 1 AU

The longitudinal spatial coherence near 1 AU of the magnetic field in sheath regions driven by interplanetary coronal mass ejection (ICME) is studied by investigating ACE and Wind spacecraft measurements of 29 sheaths. During 2000-2002 Wind performed prograde orbits, and the non-radial spacecraft separation varied from 0.001 to 0.012 AU between the studied events. We compare the measurements by computing the Pearson correlation coefficients for the magnetic field magnitude and components and estimate the magnetic field coherence by evaluating the scale lengths that give the extrapolated distance of zero correlation between the measurements. The correlation is also separately examined for low- and high-pass filtered data. We discover magnetic fields in ICME sheaths have scale lengths that are larger than those reported in the solar wind but that, in general, are smaller than the ones of the ICME ejecta. Our results imply that magnetic fields in the sheath are more coherently structured and well correlated compared to the solar wind. The largest sheath coherence is reported in the GSE y-direction that has the scale length of 0.149 AU while the lengths for B-x, B-z, and vertical bar B vertical bar vary between 0.024 and 0.035 AU. The same sheath magnitude ordering of scale lengths also apply for the low-pass filtered magnetic field data. We discuss field line draping and the alignment of preexisting discontinuities by the shock passage giving reasoning for the observed results.Peer reviewe

Endotoxin as a Marker for Water Quality

This article belongs to the Special Issue Environmental Microbiology: Perspectives for Medicine and Public Health.Background: Water quality testing is vital to protect human health. Current testing relies mainly on culture-based detection of faecal indicator organisms such as Escherichia coli (E.coli). However, bacterial cultures are a slow process, taking 24-48 h and requiring specialised laboratories and trained personnel. Access to such laboratories is often sparse in developing countries and there are many fatalities deriving from poor water quality. Endotoxin is a molecular component of Gram-negative bacterial cell walls and can be used to detect their presence in drinking water. Method: The current study used a novel assay (BacterisK) to rapidly detect endotoxin in various water samples and correlate the results with E. coli content measured by culture methods. The data generated by the BacterisK assay are presented as an 'endotoxin risk' (ER). Results: The ER values correlate with E. coli and thus endotoxin can be used as a marker of faecal contamination in water. Moreover, the BacterisK assay provides data in near real-time and can be used in situ allowing water quality testing at different spatial and temporal locations. Conclusion: We suggest that BacterisK can be used as a convenient risk assessment tool to assess water quality where results are required quickly or access to laboratories is lacking.info:eu-repo/semantics/publishedVersio

Evolution of fractality in space plasmas of interest to geomagnetic activity

We studied the temporal evolution of fractality for geomagnetic activity, by calculating fractal dimensions from the Dst data and from a magnetohydrodynamic shell model for turbulent magnetized plasma, which may be a useful model to study geomagnetic activity under solar wind forcing. We show that the shell model is able to reproduce the relationship between the fractal dimension and the occurrence of dissipative events, but only in a certain region of viscosity and resistivity values. We also present preliminary results of the application of these ideas to the study of the magnetic field time series in the solar wind during magnetic clouds, which suggest that it is possible, by means of the fractal dimension, to characterize the complexity of the magnetic cloud structure.Peer reviewe

On the Radial and Longitudinal Variation of a Magnetic Cloud: ACE, Wind, ARTEMIS and Juno Observations, Solar Physics

We present observations of the same magnetic cloud made near Earth by the Advance Composition Explorer (ACE), Wind, and the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) mission comprising the Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and THEMIS C spacecraft, and later by Juno at a distance of 1.2 AU. The spacecraft were close to radial alignment throughout the event, with a longitudinal separation of 3.6∘ between Juno and the spacecraft near Earth. The magnetic cloud likely originated from a filament eruption on 22 October 2011 at 00:05 UT, and caused a strong geomagnetic storm at Earth commencing on 24 October. Observations of the magnetic cloud at each spacecraft have been analysed using minimum variance analysis and two flux rope fitting models, Lundquist and Gold–Hoyle, to give the orientation of the flux rope axis. We explore the effect different trailing edge boundaries have on the results of each analysis method, and find a clear difference between the orientations of the flux rope axis at the near-Earth spacecraft and Juno, independent of the analysis method. The axial magnetic field strength and the radial width of the flux rope are calculated using both observations and fitting parameters and their relationship with heliocentric distance is investigated. Differences in results between the near-Earth spacecraft and Juno are attributed not only to the radial separation, but to the small longitudinal separation which resulted in a surprisingly large difference in the in situ observations between the spacecraft. This case study demonstrates the utility of Juno cruise data as a new opportunity to study magnetic clouds beyond 1 AU, and the need for caution in future radial alignment studies

On the Radial and Longitudinal Variation of a Magnetic Cloud : ACE, Wind, ARTEMIS and Juno Observations

We present observations of the same magnetic cloud made near Earth by the Advance Composition Explorer (ACE), Wind, and the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission comprising the Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and THEMIS C spacecraft, and later by Juno at a distance of 1.2 AU. The spacecraft were close to radial alignment throughout the event, with a longitudinal separation of 3.6 degrees between Juno and the spacecraft near Earth. The magnetic cloud likely originated from a filament eruption on 22 October 2011 at 00:05 UT, and caused a strong geomagnetic storm at Earth commencing on 24 October. Observations of the magnetic cloud at each spacecraft have been analysed using minimum variance analysis and two flux rope fitting models, Lundquist and Gold-Hoyle, to give the orientation of the flux rope axis. We explore the effect different trailing edge boundaries have on the results of each analysis method, and find a clear difference between the orientations of the flux rope axis at the near-Earth spacecraft and Juno, independent of the analysis method. The axial magnetic field strength and the radial width of the flux rope are calculated using both observations and fitting parameters and their relationship with heliocentric distance is investigated. Differences in results between the near-Earth spacecraft and Juno are attributed not only to the radial separation, but to the small longitudinal separation which resulted in a surprisingly large difference in the in situ observations between the spacecraft. This case study demonstrates the utility of Juno cruise data as a new opportunity to study magnetic clouds beyond 1 AU, and the need for caution in future radial alignment studies.Peer reviewe

Flux-tube-dependent propagation of Alfvén waves in the solar corona

Context. Alfven-wave turbulence has emerged as an important heating mechanism to accelerate the solar wind. The generation of this turbulent heating is dependent on the presence and subsequent interaction of counter-propagating Alfven waves. This requires us to understand the propagation and evolution of Alfven waves in the solar wind in order to develop an understanding of the relationship between turbulent heating and solar-wind parameters. Aims. We aim to study the response of the solar wind upon injecting monochromatic single-frequency Alfven waves at the base of the corona for various magnetic flux-tube geometries. Methods. We used an ideal magnetohydrodynamic model using an adiabatic equation of state. An Alfven pump wave was injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components. Results. Alfven waves were found to be reflected due to the development of the parametric decay instability (PDI). Further investigation revealed that the PDI was suppressed both by efficient reflections at low frequencies as well as magnetic flux-tube geometries.Peer reviewe