Leaching and dilution of fertilizers in the Yucatan karstic aquifer

The application of agrochemicals in crops can cause pollution of aquifers, especially those with a shallow water table and covered by thin soils; such is the case of Yucatan, Mexico. Information about the requirements and application of fertilizers to major irrigation and rainfed crops as well as the volume of water consumed in growing were used to determine the potential amount of nitrate delivered to groundwater. The research reported in this paper was conducted in the metropolitan area of the city of Merida, in Yucatán, Mexico, where groundwater plays an important role since it is the main source of supply, due to the lack of surface water in the region. In addition, the vulnerability of this aquifer is threatened by the various activities taking place in the municipalities, which emphasize agriculture, located within the groundwater basin. This activity is analyzed as a source of contamination given the concentration of NO₃ ^? present in groundwater intended for human consumption. The results show that the contribution of farming that enriches the presence of nitrates in the aquifer is different for each municipality in the study area. For the ZMM, the average nutrient leaching is 44 % of the original mass applied; it could be diluted approximately 12 times, in the groundwater.     

Absorption and fluorescence properties of rainwater during the cold season at a town in Western Portugal

This study aims at evaluating the variability of the optical properties of chromophoric dissolved organic matter (CDOM) of rainwater during the cold season, specifically between Autumn and Winter periods. The spectroscopic characteristics of rainwater samples collected at a town (Aveiro) in western Portugal were assessed by UV-Vis absorbance and three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopies. Rainwater samples showed similar characteristics to those of natural humic substances when analysed by UV-Vis absorbance spectroscopy, but a significant difference was observed in the volume weight average (VWA) of absorbances between Autumn and Winter. In general, the EEM fluorescence spectra of the Autumn and Winter samples disclosed the presence of six fluorophores with different VWA specific fluorescence intensities: three humic-like (λ _excitation/λ _emission ≈ 230/415 nm; 290/415 nm; and 340/415 nm) and three protein-like (λ _excitation/λ _emission ≈ 230/350 nm; 280/340 nm; and 225/300 nm), but one of the humic-like peaks (≈340/415 nm) does not always appear in the EEM fluorescence spectra of the Winter samples. During the cold season, chromophoric compounds are important constituents of rainwater dissolved organic matter and the presence of these highly absorbing and fluorescing compounds may exert a determining effect in atmospheric absorption of solar radiation.     

Mapping benthic faunal communities in the shallow and deep sediments of Las Perlas Archipelago, Pacific Panama

Las Perlas Archipelago (LPA) is located off the Pacific Coast of Panama and was designated as a marine protected area (MPA) in 2007. This baseline study of the shallow and deeper sedimentary habitats of the islands partly informed the MPA designation. Ninety-two grab stations and twenty trawl stations were sampled. Sediment grab sample results were interpolated to produce a map that showed the area to be dominated by mud (1246 km², 40%) and sand/shell sediments (780 km², 25%). A total of 201 taxa were recorded and over 5800 individual specimens were processed, revealing that the sediments hold varying community compositions, with annelids being the dominant group (73%) followed by crustaceans (14%). Relationships were evident between community, feeding guilds, and sediment types, which give an indication of communities that can be expected in similar sediments in other areas of the Tropical Eastern Pacific. A study of this scale and level of detail is rare for this biogeographic region and provides a valuable, comprehensive appreciation of the LPA’s benthos.     

Bioerosion by the sea urchin Diadema mexicanum along Eastern Tropical Pacific coral reefs

Bioerosion is a natural process in coral reefs. It is fundamental to the health of these ecosystems. In the Eastern Tropical Pacific (ETP) coral reefs, the most important bioeroders are sponges, bivalves, sea urchins and the fish Arothron meleagris. In the 1980s, El Niño caused high coral mortality and an increase in macroalgal growth. As a result, greater sea urchin bioerosion occurred. This weakened the reef framework. Considering the high vulnerability of the ETP coral reefs, the goal of this study was to determine the current bioerosion impact of the sea urchin Diadema mexicanum along the western coasts of Mexico, El Salvador, Costa Rica and Panamá. The balance between coral bioaccretion and sea urchin bioerosion was also calculated. Between 2009 and 2010, in 12 coral reefs localities, D. mexicanum density, bottom cover and rugosity were quantified along band transects. The daily bioerosion rate was obtained from the amount of carbonates evacuated by sea urchins per unit time. The rate of coral accretion was calculated by multiplying the coral growth rate of the dominant genus by the density of their skeleton and by their specific coral cover. The localities were dissimilar (R = 0.765, P < 0.001) in terms of live coral cover, crustose calcareous algae, turf cover, rugosity index, and density and size of D. mexicanum. At all sites, with the exception of Bahía Culebra (Costa Rica), coral bioerosion was less than coral bioaccretion. Diadema mexicanum plays a dominant role in the balance of carbonates in the ETP, but this depends on reef condition (protection, overfishing, eutrophication) and so the impacts can be either positive or negative.     

The methodology of quantification of volcanic explosions from broad-band seismic signals and its application to the 2004–2005 explosions at Volcán de Colima, Mexico

A methodology is proposed for the quantification of volcanic explosions based on three parameters derived from broad-band seismic signals: the counter force of the eruption F , the power of the explosion P and the duration of the upward movement of the gas slug in the conduit to the free surface of magma, D . This methodology was applied to the 2004–2005 sequence of explosions at Volcán de Colima, Mexico. The broad-band records of more than 100 explosive events were obtained at a distance of 4 km from the crater. We determined the counter force of the eruption by modelling the low-frequency impulse of the seismic records of 66 volcanic explosions and estimated the power of 116 explosions from the spectra of the high-frequency impulse. The power of Colima explosions spans five orders of magnitude; the counter force spans four orders of magnitude. We show that the power of a volcanic explosion is proportional to the counter force of the eruption. These parameters may be used for the elaboration of a scale of volcanic explosions.     

Point defects and pre-dose requirements for sensitization of the 300°C TL peak in natural quartz

This paper discusses the structural features required to stimulate a strong thermoluminescence (TL) glow peak near 300°C in clear natural quartz. For that reason, fresh TL data taken from several specimens prepared from five single crystals with known impurity content are shown. The TL emission was measured with a test dose of 10 mGy of γ-rays in the readout intervals 50–160 and 160–320°C. The readings were carried out prior and after the administration of a pre-dose of 175 kGy of γ-rays followed by heat-treatments at 400°C. For each single specimen, the OH content and the population of inclusions were evaluated by infrared spectroscopy and optical microscopy, respectively. The darkening induced by high γ dose was evaluated by optical spectroscopy. It was observed that the absorption at 475 nm and TL responses decrease with increase of the OH. It was shown that both smoky darkening and TL signals were better explained in terms of Li/Al and Li/OH content ratios rather than the absolute values of aluminum and alkali concentrations. The sensitization with high γ dose and heating is essential to create and stabilize a class of defects sites with Li⁺ ions dislodged from [AlO₄/Li]⁰ and Li-dependent OH centers. It is suggested that the defect sites formed with Li⁺ act as electron traps during test dose irradiation, whereas electron-hole recombination occurs essentially at [AlO₄]⁰ centers during the TL output near 300°C.     

Analysis of waves observed by synthetic aperture radar across ocean fronts

Ocean Dynamics - In this study, synthetic aperture radar (SAR) imaging of waves across ocean fronts was investigated using C-band Sentinel-1 VV-polarized SAR imagery collected over the Yangtze and...     

The formation of whitings on the Little Bahama Bank

Whitings (patches of suspended fine-grained calcium carbonate) on the Great Bahama Bank (GBB) have been studied since the 1940s. The source and cause of these whitings have been hotly debated for a number of years. Recent studies have shown that resuspension of underlying sediments act as seed crystals for the slow precipitation of CaCO₃. Similar studies have not been conducted on the nearby more northerly Little Bahama Bank (LBB) where satellite photographs indicate the presence of extensive whitings north of the Grand Bahama Island. Research cruises were made to the LBB in July 2003 and May 2005. On board measurements were used to examine the distribution of the components of the carbonic acid system in LBB waters. The distribution of suspended calcium carbonate was also determined and samples of the suspended material and underlying sediments were collected for analyses, including ¹⁴C age determinations.The maximum residence time for waters on the LBB is a little over half (～ 144 d) that on the GBB. A ～ 20% decrease was found in the salinity-normalized titration alkalinity for inner bank waters. This yields a carbonate precipitation rate similar to waters on the GBB. However, unlike the waters in the whitings on the GBB where no changes in carbonic acid system parameters have been detected, large changes in the carbonic acid system parameters were found in the whiting waters of the LBB. These results clearly indicate that active precipitation was occurring in these waters. These observations are interpreted as indicating that there is a much slower mixing of waters associated with whitings and surrounding bank waters on the LBB than on the GBB. The more closed nature of whitings on the LBB makes them better targets for study of the processes taking place in whitings.Suspended carbonate mineralogy and geochemistry closely matched those of the fine-grained portion of the underlying sediments. These results support a close relationship between carbonates found in whitings and those in underlying sediments. This is further evidenced by a similar age for whiting carbonates (～ 700 y) and easily resuspended sediment carbonates (～ 1000 y) and is what was previously observed on the GBB.These observations indicate that the processes leading to whiting formation and associated calcium carbonate precipitation along with changes in water chemistry are quite similar in these two shallow carbonate bank environments in the Bahamas.     

Multi‐scale relief model (MSRM): a new algorithm for the visualization of subtle topographic change of variable size in digital elevation models

Morphological analysis of landforms has traditionally relied on the interpretation of imagery. Although imagery provides a natural view of an area of interest (AOI) images are largely hindered by the environmental conditions at the time of image acquisition, the quality of the image and, mainly, the lack of topographical information, which is an essential factor for a correct understanding of the AOI's geomorphology. More recently digital surface models (DSMs) have been incorporated into the analytical toolbox of geomorphologists. These are usually high‐resolution models derived from digital photogrammetric processes or LiDAR data. However, these are restricted to relatively small areas and are expensive or complex to acquire, which limits widespread implementation. In this paper, we present the multi‐scale relief model (MSRM), which is a new algorithm for the visual interpretation of landforms using DSMs. The significance of this new method lies in its capacity to extract landform morphology from both high‐ and low‐resolution DSMs independently of the shape or scale of the landform under study. This method thus provides important advantages compared to previous approaches as it: (1) allows the use of worldwide medium resolution models, such as SRTM, ASTER GDEM, ALOS, and TanDEM‐X; (2) offers an alternative to traditional photograph interpretation that does not rely on the quality of the imagery employed nor on the environmental conditions and time of its acquisition; and (3) can be easily implemented for large areas using traditional GIS/RS software. The algorithm is tested in the Sutlej‐Yamuna interfluve, which is a very large low‐relief alluvial plain in northwest India where 10 000 km of palaeoriver channels have been mapped using MSRM. The code, written in Google Earth Engine's implementation of JavaScript, is provided as Supporting Information for its use in any other AOI without particular technical knowledge or access to topographical data. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

HD 172189, a Cluster Member Binary System with a δ Scuti Component in the Field of View of COROT

Photometric and spectroscopic results for the star HD 172189, member of the open cluster IC 4756 in the summer field of the space mission COROT, are presented. From photometric observations in the Strömgren system carried out at various epochs, its binary nature as well as the presence of a δ Scuti-type pulsating component have been discovered. The frequency analysis of the whole dataset confirms a dominant frequency of 19.5974 c d^?1 with a maximum amplitude near 0.02 mag plus other frequencies in the range 18–20 c d^?1. A preliminary orbital solution from the light curve and from four FEROS spectra reveals two similar components of around 1.5 M _⊙ orbiting with a period of 5.702 d.