Analysis of seasonal variation in the Niger River interior delta using satellite data∗

The Niger River is one of the most important sources of water supply for human consumption and agriculture in Western Africa. Two Landsat‐5 Multispectral Scanner (MSS) images, corresponding to the dry and wet seasons, over a selected area of the Niger River interior delta were classified to produce a land cover/land use map that reflects the geo‐hydrological units of this area. To classify the satellite data, training statistics were generated using a clustering algorithm with parameter values that maximize the separability among spectral classes. Both dry and wet season images are required to obtain an accurate classification for evaluation of hydrological parameters. The spatial resolution of the MSS proved to be adequate for this kind of work, since all the major cover types and geographic features were correctly recognized.     

Horizontal and seasonal patterns of tropical zooplankton from the eutrophic Prado Reservoir (Colombia)

Zooplankton community analyses can reveal valuable information about the trophic status and secondary production in reservoirs. The zooplankton seasonal distribution and important physical and chemical parameters in Prado Reservoir (Tolima, Central Colombia) were studied in monthly surveys throughout a hydrological cycle (February 2000-January 2001) in order to establish seasonal patterns and the biotic and abiotic relationships for the reservoir. Surface zooplankton collections at 1 m depth were taken at six sampling stations with regard to reservoir morphometry, location of main tributaries and mixing areas of the incoming tributaries. Cladocerans numerically dominated (48.1%) the community throughout the study period followed by Copepoda (32.7%), Rotifera (19.1%), and Diptera larvae (0.01%). Among the cladocerans, there was a greater abundance of Bosmina longirostris (69.8%) than other crustaceans. Among the Rotifera, Brachionus falcatus was the most abundant with 23% and Keratella tropica was least abundant with 8%. The only cyclopoid species found was Thermocyclops decipiens. The phantom midge Chaoborus sp. was also part of the zooplankton community. Based on numbers, cladocerans represented a significant component of the zooplankton in both dry and rainy seasons. Four species (Brachionus spp., K. tropica, Diaphanosoma brachyurum, Ceriodaphnia cornuta, Moina sp., and T. decipiens) had never previously been found in the reservoir, but were recorded for other standing Colombian water bodies. The replacement of B. longirostris instead of Daphnia sp. as dominant species was observed. The results of the comparison of the different studies confirmed that the trophic state of this artificial lake may be classified as eutrophic, and in general, physical, and chemical homogeneity were observed both spatially and temporally.     

Soil moisture dynamics at high temporal resolution in a semiarid Mediterranean watershed with scattered tree cover

Subsurface water flows play a key role in the distribution of water and solutes and thereby in the water availability for plants. However, the characterization of different flow processes (i.e. matrix and preferential flow), the frequency and factors that cause them, is relatively rare. This characterization enables a better understanding of spatio‐temporal variability of water resources and allows for the design of models to be improved. Using a method based on the time derivative of soil moisture variation known as maximum wetting slope, types of soil wetting processes were classified and quantified. For this, capacitance sensors, which registered the volumetric water content at high temporal resolution (30 min) for more than two hydrological years, were installed at different depths and placed in soil moisture stations with different vegetation covers, lithology and topographic position. Results indicated that there is a general behaviour or pattern of soil moisture dynamics in the catchment with a dominant occurrence of slower soil wetting processes (>50%), caused by matrix flows, and a low occurrence of those faster processes (<30%), originated by preferential flows. Nevertheless, when the total volume of water is considered, preferential flow becomes the dominant process, so that the ecological role of both flow types becomes prominent in water‐limited environments. Statistical multivariate analyses based on data‐mining techniques proved that although both flow types depend on variables associated with precipitation and antecedent soil moisture conditions, faster soil wetting processes are mainly related to variables such as rainfall intensity and topography, while slower soil wetting processes are related to flow velocity, soils or vegetation. Copyright © 2015 John Wiley & Sons, Ltd.     

The 2011 Lorca seismic series: Temporal evolution,faulting parameters and hypocentral relocation

The Lorca 2011 seismic series was recorded by an unprecedented set of high quality on scale broadband seismograms and strong motion accelerograms. The waveforms from permanent and temporary broadband seismic networks deployed in the region by different institutions allowed to invert regional moment tensor for the fore, main and largest aftershock of the complete seismic sequence. Using double-difference algorithm we have performed a precise relocation of the seismic series, where body wave travel times from strong ground motion accelerograms were included in the data set. Regional moment tensor inversion for the three main events show similar oblique-reverse faulting regime with a northeast-southwest fault orientation. The scalar seismic moment, moment magnitude and focal depth retrieved from the inversion yield the following values for each event: \(\hbox {Mo}=6.5\times 10^{16}\) Nm (Mw = 5.2) for the mainshock, \(\hbox {Mo}= 9.6 \times 10^{15}\) Nm (Mw = 4.6) for the foreshock and \(\hbox {Mo}=7.3\times 10^{14}\) Nm (Mw = 3.9) for the large aftershock. The centroid depths range between 4 and 6 km. The double-difference relocation of the seismic series shows significant epicentral differences with the preliminary routine location. The epicentral solutions given by this relocation show a seismic sequence distributed following a NE–SW strike, subparallel to the Alhama de Murcia fault and compatible with the faulting parameters inverted from the moment tensor analysis. The hypocenters of the series generate a subvertical trend in depth distribution, being concentrated between 2 and 6 km. The depth distribution of the main events, which range from 4.6 to 5.5 km, is in good relationship with the faulting and depth parameters deduced from the moment tensor inversion technique. The regional moment tensor solutions for the three largest earthquakes, the epicentral distribution and the focal depths show good relationship with the surface geometry and tectonic regime of the Alhama de Murcia fault. The stress drop deduced for the mainshock gives a value ranging between 58 and 85 bars, which does not support the idea of a high stress drop release as a main factor contributing to the high ground acceleration recorded at Lorca. The PGA values observed at Lorca, which contributed to the high damage independently of structural deficiencies, could be generated mainly by shallowness and proximity to the seismic source together with a directivity effect in the seismic radiation.     

Assessment of heavy metal pollution in urban topsoils from the metropolitan area of Mexico City

This study reports the degree of heavy metal pollution (Cr, Cu, Ni, Pb, Zn and V) in 135 urban topsoil samples from the metropolitan area of Mexico City. Pollution indices (PI) were calculated to identify the metal accumulation with respect to the background values. The levels of heavy metals in the analyzed samples show a wide range of variation. Lead, Zn and Cu are the elements most enriched in the analyzed area, presenting pollution indexes of up to 23.8, 21.6 and 12.4, respectively. Geochemical maps were produced to assess the spatial distribution of pollution index. It is concluded that emissions from vehicles may be the major source of Pb urban contamination; furthermore, other small or large factories are possible sources for soil pollution (Cu, Zn). The concentration of Cr, Ni, and V in most of the analyzed samples do not appear to reach pollution levels. The assessment of the soil environmental quality in the metropolitan area Mexico City in terms of PI can be used as the basis for a regular monitoring program for implementing suitable pollution control measures.     

Bivalves and oncoids as palaeoenvironmental indicators at Late Jurassic and Early Cretaceous dinosaur sites from Spain

Bivalves from the Late Jurassic and Early Cretaceous stratigraphic section at Las Zabacheras (Galve Sub-basin Teruel, northern Spain), are reviewed from both systematic and palaeoautoecological perspectives. For this study the Villar del Arzobispo Formation, well known for important dinosaur occurrences, was sampled from the boundary with the underlying Higueruelas Formation (Late Jurassic), to the first levels of the overlying El Castellar Formation (Early Cretaceous). The bivalve taxa have Late Jurassic affinity, pointing to a possible Jurassic-Cretaceous boundary towards the top of the Villar del Arzobispo Formation. We have sampled oncoids, whose nuclei are bivalves, through the section to study environment change in this lithostratigraphical formation. Geochemical trace elements and δ¹³C and δ¹⁸O stable isotope analysis of the oncoids enable us to determine the conditions in which the microbialites were formed and provide further palaeoenvironmental data from the deposits containing the bivalves. Bivalve taxa change from the lower part of the Villar del Arzobispo Formation, where Ceratomya excentrica and Unicardium cf. subregulare are characteristic of marine conditions, becoming more continental towards the top of the formation with the presence of Unionoidean bivalves, and in the “Wealden” facies of the El Castellar Formation, where Teruella gautieri, has been found. Bivalves and oncoids allow us to recognize continental conditions where the first dinosaur of Spain, the sauropod Aragosaurus ischiatus was found, in an open water system, where there was limited evaporation, and with enough energy to produce well oxygenated water.     

Toward improved operational surge and inundation forecasts and coastal warnings

Coastal regions are vulnerable to storm surge and flooding due to tropical and extratropical storms. It is necessary to build robust resiliency of the coastal communities to these hazards. The main objectives of operational surge and inundation forecast and coastal warning systems are to protect life and to sustain economic prosperity. The National Oceanic and Atmospheric Administration of the United States has initiated an integrated effort through pilot demonstration projects, and model-based ocean and coastal forecasting systems, to build improved operational warnings and forecasts capability for storm surge and inundation. This note describes the overall strategy and progress to date, with an emphasis on forecasting extratropical storm surge.     

Site effect study in central Mexico using H/V and SSR techniques: Independence of seismic site effects on source characteristics

We study the influence of different source characteristics (depth, distance, type and azimuth) on the site effect in Acapulco and the Valley of Mexico. Site amplification was estimated by means of spectral ratios (both horizontal-to-vertical spectral ratio and standard spectral ratio techniques were applied) from earthquake recordings at soft and hard sites. In Acapulco, 125 Mexican earthquakes covering a hypocentral range of 7–290 km and a depth range (H) of 3–61 km were analyzed in three different groups of hypocentral distances. In the Valley of Mexico, we estimate site effect at five locations using recordings from shallow-coastal interplate (200?Δ?570 km; H?35 km) and normal-faulting, intermediate-depth inslab (132?Δ?738 km; 32?H?178 km) earthquakes, as well as from teleseismic events. Our results seem to point to negligible dependence of site effects on the source location and type.     

‘Palaeolago Fueguino’, a Late Pleistocene lacustrine basin located in the central sector of Tierra del Fuego: a seismostratigraphic study

At ~20 ka bp , lakes Yehuin, Chepelmut and Fagnano constituted a single, large water body in the central part of Isla Grande de Tierra del Fuego (southernmost Patagonia). The evolutionary history of this lake, known as ‘Palaeolago Fueguino’, was probably controlled by the advances, stillstands and retreats of the ‘Fagnano Palaeoglacier’, an outlet glacier that flowed eastward from the Darwin Cordillera ice sheet. A detailed analysis of high-resolution seismic reflection profiles acquired within the three lakes has allowed the identification and correlation of seven unconformities within the lacustrine sedimentary infill, three seismostratigraphic sequences in Lago Fagnano and four in Lago Yehuin. A seismic stratigraphic correlation between these sequences suggests that these basins formerly constituted a single, large lacustrine body. A lake-level curve of the evolutionary stages of each lake, derived from the seismostratigraphic analysis of the sedimentary infill is proposed here, representing a 17.5 ka-long record. It was further integrated with the glacial record of the advances and retreats of the Fagnano Palaeoglacier. This study has implications for interpreting the sedimentary history of lake basins in glaciated mountain ranges.     

Geochemistry of Neogene sedimentary rocks from Borneo Basin,East Malaysia: Paleo-weathering,provenance and tectonic setting

Multi-element geochemistry and mineralogy are used to characterize the chemical composition, degree of paleo-weathering, provenance and tectonic settings of the Neogene sedimentary rocks of Borneo Basin of east Malaysia. Sedimentary rocks are classified as extremely weathered sandstones (i.e. wacke, arkose, litharenite, Fe-sandstone and quartz arenite). Wacke, arkose, litharenite and Fe-sandstone are characterized by post-depositional K-metasomatism and zircon enrichment through sediment recycling. Geochemical characteristics suggest a mixed-nature provenance for the sandstones and the variable tectonic settings possibly mirror the complexity of the basin. Enriched Cr in quartz arenite and Fe-sandstone are related to the contribution from ophiolite or fractionation of Cr-bearing minerals.