Using on‐nadir spectral reflectance to detect soil surface changes induced by simulated rainfall and wind tunnel abrasion

The surface susceptibility to erosion (erodibility) is an important component of soil erosion models. Many studies of wind erosion have shown that even relatively small changes in surface conditions can have a considerable effect on the temporal and spatial variability of dust emissions. One of the main difficulties in measuring erodibility is that it is controlled by a number of highly variable soil factors. Collection of these data is often limited in scale because in situ measurements are labour‐intensive and very time‐consuming. To improve wind erosion model predictions over several spatial and temporal scales simultaneously, there is a requirement for a non‐invasive approach that can be used to rapidly assess changes in the compositional and structural nature of a soil surface in time and space. Spectral reflectance of the soil surface appears to meet these desirable requirements and it is controlled by properties that affect the soil erodibility. Three soil surfaces were modified using rainfall simulation and wind tunnel abrasion experiments. Observations of those changes were made and recorded using digital images and on‐nadir spectral reflectance. The results showed clear evidence of the information content in the spectral domain that was otherwise difficult to interpret given the complicated interrelationships between soil composition and structure. Changes detected at the soil surface included the presence of a crust produced by rainsplash, the production of loose erodible material covering a rain crust and the selective erosion of the soil surface. The effect of rainsplash and aeolian abrasion was different for each soil tested and crust abrasion was shown to decrease as rainfall intensity increased. The relative contributions of the eroded material from each soil surface to trapped mixtures of material assisted the erodibility assessment. Ordination analyses within each of two important soil types explained significant amounts of the variation in the reflectance of all wavebands by treatments of the soil and hence changes in the soil surface. The results show that soil surface conditions within a soil type are an underestimated source of variation in the characterization of soil surface erodibility and in the remote sensing of soil. Copyright © 2005 John Wiley & Sons, Ltd.     

POC export from ocean surface waters by means of Th/U and Po/Pb disequilibria: A review of the use of two radiotracer pairs

²³⁴Th (T_1/2=24.1 d) and ²¹⁰Po (T_1/2=138.4 d) are particle reactive radioisotopes that are used as tracers for particle cycling in the upper ocean. Particulate organic carbon (POC) export has frequently been estimated using ²³⁴Th/²³⁸U disequilibrium. Recent evidence suggests that ²¹⁰Po/²¹⁰Pb disequilibrium may be used as an additional tool to examine particle export, given the direct biological uptake of ²¹⁰Po into cellular material. Differences in these two radioisotope pairs with regard to their half-lives, particle reactivity and scavenging affinity in seawater should provide complementary information to be obtained on the processes occurring in the water column. Here, we review eight different studies that have simultaneously used both approaches to estimate POC export fluxes from the surface ocean. Our aim is to provide a complete “dataset” of all the existing POC flux data derived from the coupled use of both ²³⁴Th and ²¹⁰Po and to evaluate the advantages and limitations of each tracer pair. Our analysis suggests that the simultaneous use of both radiotracers provides more useful comparative data than can be derived from the use of a single tracer alone. The difference in half-lives of ²³⁴Th and ²¹⁰Po enables the study of export production rates over different time scales. In addition, their different biogeochemical behaviour and preferred affinity for specific types of particles leads to the conclusion that ²³⁴Th is a better tracer of total mass flux, whereas ²¹⁰Po tracks POC export more specifically. The synthesis presented here is also intended to provide a basis for planning future sampling strategies and promoting further work in this field to help reveal the more specific application of each tracer under specific water column biogeochemistries.     

Experimental measurements of seismic velocities on core samples and their dependence on mineralogy and stress; Witwatersrand Basin (South Africa)

Physical property measurements were integrated with mineralogical analyses to better understand the nature of the seismic reflectivity of the deepest (>3.5 km depth) gold ore body (Carbon Leader Reef). The CLR lies at depths between 3.5 km and 4.5 km below the surface. Over 50 drill-core samples were selected for geochemical analyses, density and seismic velocity measurements. Ultrasonic measurements were conducted at ambient and elevated stresses, using transducers operating at 0.5 MHz. The study reveals that P-wave velocities generally increase with increasing bulk density. The CLR conglomerate, the gold-bearing reef, has slightly higher P-wave velocity (～5070–5468 m/s) and density values (～2.78 g/cm³) amongst the quartzitic units, possibly due to its massive pyrite content. The quartzite hangingwall and footwall rocks to the CLR exhibit similar P-wave velocity (～5028–5480 and ～4777–5211 m/s, respectively) and density values (～2.68 and 2.66 g/cm³, respectively). The reflection coefficients calculated at the interface between the CLR conglomerate and its hangingwall and footwall units range between ～0.02 and 0.05 which is below the required minimum reflection coefficient value of 0.06 to produce a strong reflection between two lithological boundaries. This suggests that seismic reflection methods might not be able to directly image the CLR, as observed from its poor reflectivity in the 3D seismic data. Samples were also subjected to stresses of up to 65 MPa to simulate in situ-like conditions and to investigate the dependence of seismic velocities on applied stresses. P-wave velocities increase with progressive loading, but at different rates in shale and quartzite rocks as a result of the presence of micro-defects.     

Changes in Extreme Rainfall Events in South Africa

Extreme rainfall events can have severe impacts on society, so possible long-term changes in the intensity of extreme events are of concern. Testing for long-term changes in the intensity of extreme events is complicated by data inhomogeneities resulting from site and instrumentation changes. Using rainfall data from stations in South Africa that have not involved site relocations, but which have not been tested for inhomogeneities resulting from changes in instrumentation, a method of testing for changes in the intensity of extreme events is adopted. Significant increases in the intensity of extreme rainfall events between 1931–1960 and 1961–1990 are identified over about 70% of the country. The intensity of the 10-year high rainfall events has increased by over 10% over large areas of the country, except in parts of the north-east, north-west and in the winter rainfall region of the south-west. Percentage increases in the intensity of high rainfall events are largest for the most extreme events. While some inhomogeneities remain in the data used, the observed changes in the intensity of extreme rainfall events over South Africa are thought to be at least partly real.     

Windfalls for whom? The evolving notion of ‘community’ in community benefit provisions from wind farms

This paper investigates the increasing provision of ‘community benefits’ – i.e. financial or material benefits to communities affected by wind energy development – with a focus on on-shore wind projects in Wales. The paper argues that as community benefits are becoming more significant in scale, so pressures are mounting on what have hitherto been largely ad hoc arrangements for their disbursement. The paper finds that previously dominant definitions of communities as places directly affected by and within close proximity to wind farm development, are being challenged by the tendency to define ‘affected’ communities as broader entities characterised by more indirect and widely dispersed claims to benefit entitlement. This redefinition of the recipient community is causing conflict, much of it focused on debates about how community benefits should be governed. Evidence suggests that any re-scaling of relations around community benefits – from local compensation towards wider development goals – may be more consensually achieved in communities with previous experience in handling these funds, and where growing income streams allow multiple constituencies to be satisfied.     

Enteroviruses in mussels and marine sediments and depuration of naturally accumulated viruses by green lipped mussels (Perna canaliculus)

Surveys were carried out over 16 months to assess the distribution of enteroviruses of human origin in sediments and mussels near two sewage outfalls on the North Taranaki Coast, New Zealand. Enteroviruses were present in high numbers in both sediments and shellfish near the New Plymouth sewage outfall with maximum virus levels of 32 000 pfu 100 g^‐1 of wet mussel tissue and 59 pfu 100 g^‐1 of wet sediment material. Viruses were recovered occasionally from sediments and mussels near the Waitara Borough outfall. Coxsackievirus B4 was the predominant virus type isolated but CB5 and Poliovirus types 1, 2, and 3 were also recovered. Attempts to depurate virus‐contaminated New Plymouth mussels, by keeping them in water for 8 days with daily water replacement, did not achieve a significant reduction in virus numbers.     

Modification of the polyethylene glycol 6000 precipitation method for recovering human and indicator viruses from oysters and mussels

Human viruses are a common contaminant of shellfish affected by human sewage wastes. They are difficult to detect as they are not easily separated from shellfish tissue. This paper describes a modification of the polyethylene glycol (PEG) precipitation technique for recovery of enteroviruses and F‐specific bacteriophages from the Pacific oyster (Crassostrea gigas) and the green‐lipped mussel (Perna canaliculus). Modifications adopted were the use of only the digestive gland tissue for virus extraction, resuspension of the primary PEG pellet in 4 volumes of eluent, and the introduction of a secondary PEG precipitation to reconcentrate the virus containing extract. The recovery rate of the virus extraction process was not affected by introduction of the secondary concentration step (overall recovery remained at 60–70% of the virus input). The advantages of reduction of tissue residue in the extract, smaller final volume, and the ability to process 2–3 times the number of individual shellfish for the same effort, improve the practicality of the method.     

Lake sediment record of the geomagnetic secular variation in Britain during Holocene times

Summary. A palaeomagnetic record of the geomagnetic secular variation during the last 10000 years has been obtained from 10 cores of sediment from Loch Lomond, Scotland, Lake Windermere, North England, and Llyn Geirionydd, North Wales. A time-scale is provided by 30 radiocarbon age determinations and pollen analyses on several of the cores. The main swings and much fine detail of both declination and inclination records repeat well between cores and between lakes, and the overall record is much more detailed than previous European records.
The new record shows that neither declination nor inclination swings have been periodic over the past 10000 years, but that the main swings have become progressively shorter in duration during that time. Each swing is characterized by fine detail which enables use of the record as a secondary method of dating other European sediments.
The motion of the geomagnetic vector has been predominantly clockwise throughout the time period spanned, but confirms a period of anticlockwise motion from 1100 to 600 bp first discovered by British archaeomagnetic investigations. The record agrees with British and Czechoslovakian archaeomagnetic records, but not with Japanese archaeomagnetic or North American lake sediment records. This suggests that the secular changes are controlled by local growing and decaying, drifting sources, rather than by wobbling of the main geomagnetic dipole.     

Observations of SN1985G and SN1985H with the new faint-object spectrograph

Spectra of the supernovae SN1985G and SN1985H obtained with the Faint Object Spectrograph (FOS) on the 2.5 m Isaac Newton Telescope (INT) at the Observatorio del Roque de los Muchachos are presented in the wavelength range 4600 to 10 000 Å.