Conservatism of mineral magnetic signatures in farm dam sediments in the South African Karoo: the potential effects of particle size and post-depositional diagenesis

Purpose: A methodology was developed to evaluate and mitigate the impacts of particle size and post-depositional diagenesis when using mineral magnetic signatures to trace the sources of historically deposited sediment in farm dams in the South African Karoo. Materials and methods: Samples from a range of potential sediment sources were sieved to different particle size fractions, and the relationships between pairs of tracer signatures were established for each fraction. Non-conservatism of the magnetic signatures was determined by identifying whether the magnetic signatures of the farm dam sediments were within the range of those of the fractionated source samples. By fractionating the sediment source samples, the core samples were able to be traced using appropriately sized sources. Results and discussion: It was found that strong relationships existed between the pairs of tracer signatures at all particle size fractions. Relationships in the <32 μm fraction were significantly different to that of coarser fractions. It was also found that particle size had a large effect on all magnetic signatures and would prove to be a large source of uncertainty if not accounted for within any methodology developed for quantitative source discrimination and source apportionment. There was very little non-conservatism caused by diagenetic or biogenic processes in six of the seven dams sampled. In one dam, there was evidence to suggest that dissolution had probably caused the loss of almost all small superparamagnetic and stable single-domain grains. The other signatures associated with coarser magnetic grains in this dam were generally unaffected by the dissolution processes. Conclusions: The good preservation of magnetic signatures suggests that they can make reliable tracers over historical timescales (up to 164 years) in the Karoo and similar semi- arid catchments. However, the mitigation of particle size effects and screening for post-depositional alteration is an essential part of their use. The methodology presented in this paper is a potential way of recognising tracer non-conservatism and limiting its effects in future studies

Composite shell spacecraft seat

A two-part seat (10) providing full body support that is specific for each crew member (30) on an individual basis. The two-part construction for the seat (10) can accommodate many sizes and shapes for crewmembers (30) because it is reconfigurable and therefore reusable for subsequent flights. The first component of the two-part seat construction is a composite shell (12) that surrounds the crewmember's entire body and is generically fitted to their general size in height and weight. The second component of the two-part seat (10) is a cushion (20) that conforms exactly to the specific crewmember's entire body and gives total body support in more complex environment

The dynamics of sediment-associated contaminants over a transition from drought to multiple flood events in a lowland UK catchment

Fine sediment in suspended form, recently deposited overbank and in temporary storage on or in channel beds, was collected in the Nene basin during a period of drought through to a period of four high flows. The sediment was analysed for arsenic, copper, lead, phosphorus and zinc concentrations with the aim of investigating their sources, movement, temporary storage and potential for environmental harm. Copper, lead and zinc probably originated from urban street dusts, phosphorus (originally in dissolved form) from sewage effluent and arsenic from natural soils developed over ironstone. There was little difference in the metal or arsenic concentrations in the sediment under different flow conditions; instead, proximity to pollutant sources appeared to control their concentrations. Phosphorus in tributary sub-catchments probably adsorbed to sediment during periods of low flow but these sediments were flushed away during high flows and replaced by sediment with lower concentrations. However, concentrations of all pollutants in overbank sediments along the Nene's main channel were not reduced in successive flood events, suggesting no first flush effect. Only phosphorus accumulated on sediment at concentrations exceeding those of its catchment-based sources (e.g. street dusts, channel banks and catchment soils). This scavenging of aqueous phosphate by sediment explained the difference in behaviour between phosphorus, arsenic and heavy metals. The surface area and organic matter content were shown to have a small effect on contaminant concentrations. Street dust contaminants only exceeded predicted effect levels in close proximity to urban areas, suggesting a small potential for harm to the aquatic environment. Arsenic concentrations exceeded predicted effect levels in most sediment samples. However, it has been shown to be largely non-bioavailable in previously published research on the Nene, limiting its potential for significant environmental harm. Phosphorus concentrations in river sediments are high in comparison to the soils in the catchment and in comparison with sediment–P concentrations in other published lowland catchment studies, indicating a large potential for eutrophication should the Phosphorus be, or become, bioavailable

Neuronal Activity Within the Ventral Tegmental Area Is Correlated with Cocaine-Seeking Behavior in Male, But Not Female, Rats

The objective of this study was to begin to determine the neurobiological underpinnings of psychosocial stress-induced cocaine seeking. Social defeat stress, achieved using the well-established resident-intruder procedure, is an ecologically-valid psychosocial stressor in rodents that may more closely recapitulate those psychosocial experiences that elicit cocaine craving and relapse in human cocaine users. Our laboratory has developed a model of psychosocial stress-induced relapse in rats in which extinguished cocaine seeking is reinstated by re-exposure to a discrete cue that signals impending social defeat stress. We previously reported that an individual rat’s predilection towards the display of active coping behaviors during prior social defeat stress exposures was positively correlated with levels of psychosocial stress-induced cocaine seeking. The current study’s goal was to expand upon these initial findings by assessing and comparing patterns of neural activation within the ventral tegmental area (VTA) during stress-induced cocaine seeking triggered by psychosocial stress-predictive or foot shock stress-predictive cues. The VTA was selected for investigation in the present study because of its known role in the manifestation of stress-induced reinstatement of cocaine seeking. We postulated that neural activation in this brain region would be associated with the magnitude of observed psychosocial stress-induced cocaine seeking, thus providing important insights into the neurobiological underpinnings of this phenomenon

Can channel banks be the dominant source of fine sediment in a UK river?: an example using 137Cs to interpret sediment yield and sediment source

Cultivated fields have been shown to be the dominant sources of sediment in almost all investigated UK catchments, typically contributing 85 to 95% of sediment inputs. As a result, most catchment management strategies are directed towards mitigating these sediment inputs. However, in many regions of the UK such as the Nene basin there is a paucity of sediment provenance data. This study used the 137Cs inventories of lake and floodplain cores as well as the 137Cs activities of present day sediment to determine sediment provenance. Sediment yields were also reconstructed in a small lake catchment. Low 137Cs inventories were present in the lake and floodplain cores in comparison to the reference inventory and inventories in cores from other UK catchments. 137Cs activities in the present day sediments were low; falling close to those found in the channel bank catchment samples. It was estimated that 60 to 100% of the sediment in the Nene originated from channel banks. Pre 1963 sediment yields were approximately 11.2 t km-2 yr-1 and post 1963 was approximately 11.9 t km-2 yr-1. The lack of increased sediment yield post 1963 and low sediment yield is unusual for a UK catchment (where a yield of 28 to 51 t km-2 yr-1 is typical for a lowland agricultural catchment), but is explained by the low predicted contribution of sediment from agricultural topsoils. The high channel bank contribution is likely caused by the river being starved of sediment from topsoils, increasing its capacity to entrain bank material. The good agreement between the results derived using cores and recently transported sediments, highlight the reliability of 137Cs when tracing sediment sources. However, care should be taken to assess the potential impacts of sediment particle size, sediment focusing in lakes and the possible remobilisation of 137Cs from sedimentary deposits

Sediment source fingerprinting as an aid to catchment management: a review of the current state of knowledge and a methodological decision-tree for end-users

The growing awareness of the environmental significance of fine-grained sediment fluxes through catchment systems continues to underscore the need for reliable information on the principal sources of this material. Source estimates are difficult to obtain using traditional monitoring techniques, but sediment source fingerprinting or tracing procedures, have emerged as a potentially valuable alternative. Despite the rapidly increasing numbers of studies reporting the use of sediment source fingerprinting, several key challenges and uncertainties continue to hamper consensus among the international scientific community on key components of the existing methodological procedures. Accordingly, this contribution reviews and presents recent developments for several key aspects of fingerprinting, namely: sediment source classification, catchment source and target sediment sampling, tracer selection, grain size issues, tracer conservatism, source apportionment modelling, and assessment of source predictions using artificial mixtures. Finally, a decision-tree representing the current state of knowledge is presented, to guide end-users in applying the fingerprinting approach

The potential for gamma-emitting radionuclides to contribute to an understanding of erosion processes in South Africa

Several research projects undertaken by the authors and others over the last 14 years have used fallout and geogenic radionuclides for understanding erosion processes and sediment yield dynamics in South Africa over the last 100–200 years as European settlers colonised the interior plains and plateaux of the country and imported new livestock and farming techniques to the region. These projects have used two fallout radionuclides (210Pb and 137Cs) to date sediments accumulating in reservoirs, farm dams, wetlands, alluvial fans and floodouts and have used other fallout nuclides (7Be) and long-lived geogenic radionuclides (e.g. 40K, 235U) as part of a composite fingerprint exploring contemporary sediment sources and changes to sources through time. While successful in many parts of the world, applying these techniques in Southern Africa has posed a number of challenges often not encountered elsewhere. Here we explore some of the benefits and challenges in using gamma-emitting radionuclides, especially 137Cs, in these landscapes. Benefits include the potential for discriminating gully sidewall from topsoil sources, which has helped to identify contemporary gully systems as sediment conduits, rather than sources, and for providing a time-synchronous marker horizon in a range of sedimentary environments that has helped to develop robust chronologies. Challenges include the spatial variability in soil cover on steep rocky hillslopes, which is likely to challenge assumptions about the uniformity of initial fallout nuclide distribution, the paucity of stable (non-eroding) sites in order to estimate atmospheric fallout inventories, and the limited success of 210Pb dating in some rapidly accumulating high altitude catchments where sediments often comprise significant amounts of sand and gravel. Despite these challenges we present evidence suggesting that the use of gamma-emitting radionuclides can make a significant contribution to our understanding of erosion processes and sediment yield dynamics. Future research highlighted in the conclusion will try to address current challenges and outline new projects established to address them more fully