Biomonitoring of coastal areas in Tunisia: Stable isotope and trace element analysis in the Yellow-legged Gull

We used Yellow-legged Gull (YLG) chicks to monitor trace elements in Tunisian areas subject to different pollution stresses: urban contamination (Chikly), industrial pollution (Thyna) and an unpolluted area (Kneis).We measured trace element concentrations (Hg, Se and Pb) in chick feathers. We also assessed their feeding ecology by analyzing both regurgitates and stable isotopes (SIA) in chick feathers and in their prey, to determine the main entry route of pollutants. SIA revealed that YLG feed mainly on aquatic resources from the Lake of Tunis (Chikly colony) and the Gulf of Gabès (Thyna and Kneis colonies). Moreover, the enriched δ¹⁵N found in feathers from Chikly are attributed to the eutrophication of the Lake of Tunis. Hg and Se were higher in Kneis and Thyna colonies, in agreement with the higher consumption of marine resources and the greater availability of these elements resulting from the impact of the industrial activity in the area. Pb concentrations were higher in Chikly, related to the heavier traffic around the Lake of Tunis and the use of leaded gasoline.     

Driving factors for forest fire occurrence in Durango State of Mexico: A geospatial perspective

Forest fire is one of the major causes of forest loss and therefore one of the main constraints for sustainable forest management worldwide. Identifying the driving factors and understanding the contribution of each factor are essential for the management of forest fire occurrence. The objective of this study is to identify variables that are spatially related to the occurrence and incidence of the forest fire in the State of Durango, Mexico. For this purpose, data from forest fire records for a five-year period were analyzed. The spatial correlations between forest fire occurrence and intensity of land use, susceptibility of vegetation, temperature, precipitation and slope were tested by Geographically Weighted Regression (GWR) method, under an Ordinary Least Square estimator. Results show that the spatial pattern of the forest fire in the study area is closely correlated with the intensity of land use, and land use change is one of the main explanatory variables. In addition, vegetation type and precipitation are also the main driving factors. The fitting model indicates obvious link between the variables. Forest fire was found to be the consequence of a particular combination of the environmental factors, and when these factors coexist with human activities, there is high probability of forest fire occurrence. Mandatory regulation of human activities is a key strategy for forest fire prevention.     

From regional- to local-scale seismic hazard assessment: examples from Southern Spain

An approach that relates results from a regional seismic hazard assessment study with local-scale site-effect characterizations in an area of low-to-moderate seismic activity such as Andalusia (southern Spain), is presented. Results of a previous probabilistic seismic hazard analysis of Andalusia on rock conditions are disaggregated to infer hazard controlling earthquakes for different target motions. A collection of controlling magnitude-distance pairs and the corresponding site-specific response spectra at main capital cities of the region are obtained. These spectra are first-order approximations to expected seismic actions required in local earthquake risk assessments. In addition, results of independent, local-scale studies developed in Almeria City (SE Andalusia) are used to derive an updated seismic zonation of the city. These include predominant soil period estimates and shear-wave velocity profiles at different locations. If a local seismic risk assessment study or an earthquake-resistant structural design is to be developed, it may be recommended the use of different seismic actions on sites characterized by distinct response to seismic shaking (as derived from the seismic zonation). The seismic action related to worst-case scenarios may be modeled through a hazard-consistent response spectrum, obtained by hazard disaggregation at the spectral acceleration with period matching the prevailing resonant period of the target site or structure.     

On the significance of the climate-dataset time resolution in characterising wind-driven rain and simultaneous wind pressure. Part II: directional analysis

Both semi-empirical methods and CFD simulations use real climate datasets as a basis for determining the building facade exposure to wind-driven rain and simultaneous wind pressure. The time resolution of these datasets and the number of variables considered (commonly rainfall intensity, wind speed and wind direction) determine the required calculation effort and the accuracy of the result. Omitting the wind direction, a former article (Part I of this research) has analysed the effect of this time resolution on two scalar exposure indices obtained by semi-empirical methods: driving rain index (aDRI) and driving-rain wind pressure (DRWP). However, the wind direction during precipitation events also causes significant exposure variations between possible facade orientations. Thus, it is also necessary to clarify the influence of the time resolution of the dataset, on the accuracy of the directional semi-empirical calculation of aDRI and DRWP. To meet this challenge, the article examines 10-min climate records collected between 2001 and 2016 at 6 Spanish locations, uses them to obtain hourly, daily, monthly and annual datasets, and analyses the accuracy of the directional exposure indices associated with each time resolution. The results show that a daily dataset would allow identifying the most exposed orientation with an error less than 45°. However, even the hourly datasets cause errors close to 10% in the exposure values identified on each facade orientation. Finally, adjustment relationships that allow estimating the maximum value of directional exposure from simple scalar indices are obtained.

     

Angola seismicity

This work describes the development of the Angolan earthquake catalog and seismicity distribution in the Southwestern African Plate, in Angola. This region is one of the least seismically active, even for stable continental regions (SCRs) in the world. The maximum known earthquake had a magnitude of 6.0 M_s, while events with magnitudes of 4.5 have return period of about 10 years. Events with magnitude 5 and above occur with return period of about 20 years. Five seismic zones can be confirmed in Angola, within and along craton edges and in the sedimentary basins including offshore. Overall, the exposed cratonic regions tend to have more earthquakes compared to other regions such as sedimentary basins. Earthquakes tend to occur in Archaic rocks, especially inside preexisting weakness zones and in tectonic-magmatic reactivation zones of Mesozoic and Meso-Cenozoic, associated with the installation of a wide variety of intrusive rocks, strongly marked by intense tectonism. This fact can be explained by the models of preexisting weakness zones and stress concentration near intersecting structures. The Angolan passive margin is also a new region where seismic activity occurs. Although clear differences are found between different areas along the passive margin, in the middle near Porto Amboim city, seismic activity is more frequent compared with northwestern and southwestern regions.     

Two new conceptual models for the formation and degradation of baymouth spits by longshore drift and fluvial discharge (Iguape,SE Brazil)

This study describes the formation of two successive baymouth spits systems on the south‐eastern Brazilian coast and the degradation of the first system. The study area includes the Jureia Beach spit, the deflected Ribeira de Iguape River mouth, the central Iguape sandy headland, the Icapara Inlet of the Mar Pequeno Lagoon and the northern end of the Comprida Island barrier spit. The wave and river flow patterns were combined with the coastline evolution and the alongshore migration rates deduced from satellite images. Initially, both spits showed convergent alongshore migration rates equal to or less than 83 m/yr. However, the extreme river flow due to high rainfall during a very strong El Niño event in 1983 eroded the inland side of the Jureia Beach spit, which finally retreated due to wave erosion. In 1989, a sand bank emerged in the river mouth, which attached to the central headland forming a recurved northeastward spit. In 1994, the high fluvial discharge associated with another very strong El Niño event caused the landward migration of the new spit and emersion of a second sand bank. This second sand bank merged with the Jureia Beach spit in 1997 at an alongshore migration rate of 1795.6 m/yr. Wave erosion of the central headland continued and the attached spit disappeared in 2000. In 2009, the headland erosion merged the river mouth and the Icapara Inlet, which resulted in flanking baymouth spits in a configuration that remains today. Therefore, two models for the formation of baymouth spits have been documented for wave‐dominated microtidal coasts in humid tropical regions with intense fluvial discharge. The convergent longshore migration of the spits is controlled by both the bidirectional longshore drift and the fluvial discharge, the latter eroding the fronting spit, supplying sediments and acting as a hydraulic blockage for longshore drift. Copyright © 2017 John Wiley & Sons, Ltd.     

Non-stationary future return levels for extreme rainfall over Extremadura (southwestern Iberian Peninsula)

Based on a previous study for temperature, a new method for the calculation of non-stationary return levels for extreme rainfall is described and applied to Extremadura, a region of southwestern Spain, using the peaks-over-threshold approach. Both all-days and rainy-days-only datasets were considered and the 20-year return levels expected in 2020 were estimated taking different trends into account: first, for all days, considering a time-dependent threshold and the trend in the scale parameter of the generalized Pareto distribution; and second, for rainy days only, considering how the mean, variance, and number of rainy days evolve. Generally, the changes in mean, variance and number of rainy days can explain the observed trends in extremes, and their extrapolation gives more robust estimations. The results point to a decrease of future return levels in 2020 for spring and winter, but an increase for autumn.     

Inter-annual changes in fish communities of a tropical bay in southeastern Brazil: What can be inferred from anthropogenic activities?

We assessed inter-annual changes in fish assemblages of a tropical bay which experienced a heavily industrialized process in the last decades. A highly significant difference in community structure among the bay zones, and a decrease in fish richness and abundance over time were found. Changes in fish richness and abundance between the two first (1987–1988 and 1993–1995) and the two latter time periods (1998–2001 and 2012–2013) were sharpest in the inner bay zone, the most impacted bay area, and in the middle zone, whereas the outer zone remained comparatively stable over time. These changes coincided with increased metal pollution (mainly, Zn and Cd) in the bay and with the enlargement of the Sepetiba Port. Spatial changes in the fish community structure among the bay zones were related to differences in salinity, transparency and depth with this latter variable acting as a buffer stabilizing temporal community changes.     

Monitoring Sea Level in the Coastal Zone with Satellite Altimetry and Tide Gauges

We examine the issue of sustained measurements of sea level in the coastal zone, first by summarizing the long-term observations from tide gauges, then showing how those are now complemented by improved satellite altimetry products in the coastal ocean. We present some of the progresses in coastal altimetry, both from dedicated reprocessing of the radar waveforms and from the development of improved corrections for the atmospheric effects. This trend towards better altimetric data at the coast comes also from technological innovations such as Ka-band altimetry and SAR altimetry, and we discuss the advantages deriving from the AltiKa Ka-band altimeter and the SIRAL altimeter on CryoSat-2 that can be operated in SAR mode. A case study along the UK coast demonstrates the good agreement between coastal altimetry and tide gauge observations, with root mean square differences as low as 4 cm at many stations, allowing the characterization of the annual cycle of sea level along the UK coasts. Finally, we examine the evolution of the sea level trend from the open to the coastal ocean along the western coast of Africa, comparing standard and coastally improved products. Different products give different sea level trend profiles, so the recommendation is that additional efforts are needed to study sea level trends in the coastal zone from past and present satellite altimeters. Further improvements are expected from more refined processing and screening of data, but in particular from the constant improvements in the geophysical corrections.     

The application of GPR and ERI in combination with exposure logging and retrodeformation analysis to characterize sinkholes and reconstruct their impact on fluvial sedimentation

This work illustrates the practicality of investigating sinkholes integrating data gathered by ground penetrating radar (GPR), electrical resistivity imaging (ERI) and trenching or direct logging of the subsidence‐affected sediments in combination with retrodeformation analysis. This mutidisciplinary approach has been tested in a large paleosinkhole developed during the deposition of a Quaternary terrace on salt‐bearing evaporites. The subsidence structure, exposed in an artificial excavation, is located next to Puilatos, a village that was abandoned in the 1970s due to severe subsidence damage. Detailed logging of the exposure revealed that the subsidence structure corresponds to an asymmetric sagging and collapse paleosinkhole with no clear evidence of recent activity. The sedimentological and structural relationships together with the retrodeformation analysis indicate that synsedimentary subsidence controlled channel location, the development of a palustrine environment and local changes in the channel pattern. GPR profiles were acquired using an array of systems with different antenna frequencies, including some recently developed shielded antennas with improved vertical resolution and penetration depth. Although radargrams imaged the faulted sagging structure and provided valuable data on fault throw, they did not satisfactorily image the complex architecture of the fluvial deposit. ERI showed lower resolution but higher penetration depth when compared to GPR, roughly capturing the subsidence structure and yielding information on the thickness of the high‐resistivity alluvium and the nature of the underlying low‐resistivity karstic residue developed on top of the halite‐bearing evaporitic bedrock. Data comparison allows the assessment of the advantages and limitations of these complementary techniques, highly useful for site‐specific sinkhole risk management. Copyright © 2016 John Wiley & Sons, Ltd.