An assessment of gully erosion along major armoured roads in south-eastern region of South Africa: a remote sensing and GIS approach

An assessment of gully erosion along road drainage-release sites is critical for understanding the contribution of roads to soil loss and for informed land management practices. Considering that road-related gully erosion has traditionally been measured using field methods that are expensive, tedious and limited spatially as well as temporally, it is important to identify affordable, timely and robust methods that can be used to effectively map and estimate the volume of gullies along the road networks. In this study, gullies along major roads were identified from remotely sensed data sets and their volumes were estimated in a Geographic Information Systems environment. Also, the biophysical and climatic factors such as vegetation cover, the road contributing surface area, the gradient of the discharge hillslope and rainfall were derived from remotely sensed data sets using Geographic Information Systems techniques to find out whether they could explain the morphology of gullies that existed in this area. The results of this study indicate that hillslope gradient (R²?=?0.69, α = 0.00) and road contributing surface area (R²?=?0.63, α = 0.00) have a strong influence on the volume of gullies along the major roads in the south-eastern region of South Africa, as might have been expected. However, other factors such as vegetation cover (R² = 0.52, α = 0.00) and rainfall (R² = 0.41 and α = 0.58) have a moderately weaker influence on the overall volume of gullies. Overall, the findings of this study highlight the importance of using remote sensing and Geographic Information Systems technologies in investigating gully erosion occurrence along major roads where detailed field work remains a challenge.     

Modelling the influence of environmental and weather factors on the density of the invasive polychaete Boccardia proboscidea

The inter‐tidal zone around sewage discharges in a Southwest Atlantic shore (Mar del Plata, Argentina) is currently colonized by extensive inter‐tidal reefs of the invasive spionid Boccardia proboscidea. Understanding the links between both human and natural disturbances and the massive development of non‐indigenous species will help prevent marine bioinvasions, which are already favoured by global oceanic trade. We present herein predictive models for variations in the density of B. proboscidea around sewage discharges of Mar del Plata, using environmental (pH, turbidity, temperature, salinity and total organic matter content), weather (wind direction and storm records), spatial (sites) and temporal (season and year) variables. Density variations were modelled by generalized linear models, and model averaging (multimodel inference) was used to obtain predicted values. The highest predicted values of B. proboscidea density occurred at sites to the south of the sewage effluent in spring. These sites are more affected by urban effluent discharges and they showed increased B. proboscidea density when the north wind was predominant. In addition, B. proboscidea density values were higher in sites with 20–22 °C (seawater temperature), high total organic matter content in sediments and low salinity. The averaged model was only a good ‘predictive model’ for sites to the north of the outfall, but was useful as an ‘explanatory model’ in all sites. Such predictions may help to back up conservation and management policies and decisions.     

Prediction of the water waves generated by a potential semisubmerged landslide in La Yesca reservoir,Mexico

This paper presents a study of the effects of a potential landslide in La Yesca Reservoir, Jalisco-Nayarit, Mexico. The main purpose of the paper is to predict the maximum wave amplitude, wave run-up, and dam overtopping. The landslide is formed by an unstable slope of more than 24 Mm³ that is partially submerged for the range of the reservoir operation levels. The dynamics of the sliding mass were obtained in detail considering that it moves over a pair of failure surfaces with the potential rupture of a third surface. The paper presents results of a physical model of the reservoir based on Froude similitude (scale 1:200). Impulse waves are produced with a solid wedge shape slide as it moves on rails. The movement was calibrated to reproduce the dynamics of the landslide. Also, numerical modelling of the event was performed with a 2D implicit model that solves the two-dimensional shallow water equations. In this case, the impulse waves were generated at each time increment with the variation of the ground elevation (obtained from the dynamics of the landslide) for the mesh points where the landslide passes. The results of both studies are similar.     

The skeleton of a straight-tusked elephant,Palaeoloxodon antiquus (Falconer and Cautley, 1847) from Selsey,England, and growth and variation in Palaeoloxodon of the European Pleistocene

A partial skeleton of straight-tusked elephant (Palaeoloxodon antiquus) excavated at Selsey beach (Sussex, UK) in 1961 is one of very few from Marine Isotope Stage 7 (MIS 7), ca. 240–200 ka, in Europe. Dental morphometrics, including X-ray micro-computed tomography, confirms the species identification. Age determination through dental wear and skeletal morphology, sex determination through pelvic anatomy, and body-size measurements, together identify the individual as a female of approximately 30 years old with a live shoulder height of ca. 3 m and a body mass of ca. 5 t. Dental mesowear indicates mixed feeding with a significant proportion of grass, indicating selective feeding in a predominately forested environment. Although taphonomic conclusions are limited by the nature of the excavation, identification of 107 recovered skeletal elements indicates predominant preservation of the right side of the animal, suggesting death or burial on the right side in a shallow, slow-moving freshwater environment, with possible removal of other elements by scavenging or decay. Combining the Selsey data with 29 comparative skeletons from across Europe, we demonstrate the validity of pelvic proportions for determining sex and provide a graphical representation of variation and growth rate in males and females of this species.     

Variable water column structure of the South Atlantic on glacial–interglacial time scales

The structure of the glacial ocean was significantly different to that of the present day with intermediate to mid-depth waters being notably more δ¹³C enriched than deep waters. This contrast was especially pronounced in the South Atlantic suggesting the development of a sharp chemical divide, or ‘chemocline’, at around 2500 m water depth between upper and lower layers, with implications for deep-ocean carbon storage [Hodell et al., 2003. Pleistocene vertical carbon isotope and carbonate gradients in the South Atlantic sector of the Southern Ocean. Geochemistry, Geophysics, Geosystems, 4(1): doi: 1004 10.1029/2002GC000367.]. We evaluate existing benthic foraminiferal δ¹³C, Cd/Ca and derived carbon isotope air–sea exchange signature (δ¹³C_as) data sets for the Atlantic during the Last Glacial Maximum (LGM), and Marine Isotope Stages (MIS) 6 and 8 in order to examine the regional extent of the chemocline in the South Atlantic. Benthic δ¹³C data north of the approximate latitude of the LGM Subantarctic Front (LGM-SAF, 43°S) linearly decrease with water depth, indicative of mixing between upper ‘well’ and lower ‘poorly’ ventilated water masses, with little evidence of the sharp chemical divide. Conversely, benthic δ¹³C data south of the LGM-SAF below 2500 m water depth are uniformly around ?0.8‰. The apparent δ¹³C gradient across the LGM-SAF suggests enhanced mid-depth ventilation north of the SAF and reduced ventilation to the south. From this pattern we conclude that the regional chemocline in the South Atlantic constituted a dominantly meridional, rather than a vertical gradient, and was developed during at least the past three glacial periods. Benthic Cd/Ca data indicate that the gradient was not nutrient related, although further data from the South Atlantic are needed for a better assessment of this suggestion. The combined benthic δ¹³C and Cd/Ca data indicate the source of well-ventilated upper waters in the South Atlantic changed from Northern Component Water (NCW) during early glacial phases to Upper Southern Component Water (USCW) during mid-to-late glacial phases when the Southern Ocean may have become isolated. USCW maintained a positive δ¹³C and δ¹³C_as signature simulating a North Atlantic origin that has been implicated in previous studies. The data demonstrate that secular imprints on δ¹³C must be taken into consideration when assessing the implications of the vertical δ¹³C gradient. This data also supports a variable water column architecture and modes of water mass formation as primary means to draw down atmospheric CO₂ and storage in the abyssal ocean by involving processes occurring on either side of the SAF in the glacial Southern Ocean.     

Evaluating Copper Behavior in Urban Surface Waters Under Anthropic Influence. A Case Study from the Igua?u River, Brazil

The goal of this work was to investigate the changes in copper behavior in Igua?u River, a body of water strongly affected by urban inputs. This work was carried out in a subtropical Brazilian watershed suffering with high loads of raw sewage discharges from the Metropolitan Region of Curitiba. A comparison between sampling sites located upstream and downstream from the urban region revealed that human inputs are able to modify the water chemistry of the river in a short distance basis, that is, approximately nine miles. Probably, the most important alterations were the creation of an anaerobic environment as well as the enhancement of humic-coated suspended solids. These two aspects were determinant to explain the high concentrations observed for particulate copper (57% of total recoverable copper) and dissolved copper sulfide species (13%) in the water column. Copper in the sediment was also higher in the downstream site, probably due to the sedimentation of the Cu-enriched particles. However, copper sulfides at the bottom sediment may also be a potential source for the metal in the water column due to the creation of anaerobic conditions in both compartments. Labile copper concentration was not affected by the changes in water chemistry. Despite the fact that sewage discharges motivate the enhancement of organic matter, but not the increase in potential complexing agents, additional ligands such as chloride, carbonates, and anthropogenic dissolved organic ligands can be now computed as a part of the labile fraction.     

The Deposition and Chronology of Cenote T’isil: A Multiproxy Study of Human/Environment Interaction in the Northern Maya Lowlands of Southeast Mexico

Cenotes (natural wells or sinkholes) comprise the most common landscape features in the northern Maya Lowlands of the Yucatán Peninsula, México. Detailed study of dated soil‐sedimentary sequences, recovered from a cenote at the archaeological site T’isil and nearby wetlands, allows a partial reconstruction of environmental variability at the site for the last 2000 years. Biogenic calcite sedimentation and Calcisol development occur during three intervals of increased inundation in cenote and wetland environments, ca. A.D. 300, A.D. 1000, and A.D. 1300. Periods of increased inundation in the cenote and wetlands correlate with wetter climatic intervals, and periods of Maya occupation at sites in the Yalahau region. Evidence for Maya modification of the cenote environment may relate to regional wetland agricultural practices.     

Hypsometry of Titan

Cassini RADAR topography data are used to evaluate Titan’s hypsometric profile, and to make comparisons with other planetary bodies. Titan’s hypsogram is unimodal and strikingly narrow compared with the terrestrial planets. To investigate topographic extremes, a novel variant on the classic hypsogram is introduced, with a logarithmic abscissa to highlight mountainous terrain. In such a plot, the top of the terrestrial hypsogram is quite distinct from those of Mars and Venus due to the ‘glacial buzz-saw’ that clips terrestrial topography above the snowline. In contrast to the positive skew seen in other hypsograms, with a long tail of positive relief due to mountains, there is an indication (weak, given the limited data for Titan so far) that the Titan hypsogram appears slightly negatively skewed, suggesting a significant population of unfilled depressions. Limited data permit only a simplistic comparison of Titan topography with other icy satellites but we find that the standard deviation of terrain height (albeit at different scales) is similar to those of Ganymede and Europa.