Fine-scale vertical distribution of coastal and offshore copepods in the Golfo de Arauco, central Chile, during the upwelling season

In order to understand the mechanism by which zooplankters from different origins co-occur during the upwelling season within Golfo de Arauco, one of the most productive areas in central Chile, we assessed short term variations in the vertical distribution of the most abundant copepod species. Fine-scale, day and night vertical zooplankton sampling was done with a pump over 12 days in summer. The water column in the gulf consisted of three layers: Equatorial Subsurface Water of low dissolved oxygen content in the deeper part of the water column, strong temperature and oxygen gradients at mid-depth (15-25 m), and a layer of warmer, more oxygenated, less saline water at the surface. Copepods within the gulf originated from offshore, from the continental shelf, and from the coastal area. Most taxa showed distinctive vertical distributions. Three copepod groups were identified by their mean weighted depths of residence. One group included shallow residents found above the thermocline/oxycline (Acartia tonsa, Centropages brachiatus, Corycaeus sp., Paracalanus parvus, Oncaea sp.). A second group was comprised by species distributed at or below the thermocline/oxycline (Oithona sp., Oncaea conifera, Lucicutia sp., Metridia sp., Heterorhabdus papilliger). The third group was composed of vertical migrators that crossed the thermocline/oxycline (Calanus chilensis, Calanoides patagoniensis, Aetideus armatus, Pleuromamma piseki). In spite of their different vertical distribution ranges, the most abundant and frequent copepod species (P. parvus, C. chilensis, C. patagoniensis, C. brachiatus) share a common capacity to withstand wide ranges of oxygen concentration and temperature. This characteristic, along with the capacity to vary their life strategies under different environmental conditions, seems to facilitate the maintenance of large numbers of copepods in coastal waters along the Humboldt Current.     

Artificial intelligence applied to floating boom behavior under waves and currents

Floating containment booms are an essential device in the fight against coastal pollution, allowing to contain the pollutant prior to its recovery. An Artificial Intelligence model is developed with the focus on the effective draft, or draft available for containment that a floating boom will provide in open waters. The dataset is obtained through an extensive laboratory campaign in which seven model booms are subjected to numerous wave and current combinations. This dataset is randomly divided into two subsets, one for training, the other for testing or validating the model. Input and output variables are selected based on dimensional analysis and laboratory results. The AI technique chosen for the model is multilayer feedforward artificial neural networks trained with the back-propagation algorithm, for their capability to apprehend higher-order patterns from the training examples and subsequently generalize them to other (validation) cases. In order to find an efficient network architecture, a comparative study involving 640 neural networks is carried out. Having selected the best performing architecture, the model is successfully validated; it is a virtual laboratory allowing to determine the effective draft that a certain boom design will provide under given wave and current conditions.     

Extraterrestrial microspherules from Bajada del Diablo,Chubut, Argentina

The Quaternary infilling of a circular structure located in Bajada del Diablo, Chubut Province, Argentina has been proposed as a crater strewn field in previous studies. Here we report the finding of about 65 microspherules collected in a trench excavated in the center of the structure. The majority of hand-picked specimens are single, but some of them exhibit compound forms. The single specimens are spherical with a mean size of 137 μm, whereas the more complex samples show peduncles and drop shapes. Dendritic crystal growth is recognized in the internal structure of some broken microspherules. Preliminary chemical composition from the surface and center of microspherules was determined by energy dispersive spectrometry employing EDS. Quantitative EMPA and XRD analysis indicate that the microspherules are mainly composed of Fe and O with magnetite, Fe0 with subordinate wüstite. Following consideration of possible anthropogenic and volcanic origins, these spherulites are ascribed to an extraterrestrial input. An accumulation rate of 47 microspherules per m²/yr is estimated for the studied sediments. This value is two orders of magnitude higher than the reference flux for cosmic dust estimated for the last 1 Ma in the Transantarctic Mountains. The microspherules might have been generated as a byproduct of asteroid entry in the atmosphere.     

Application of a statistical water-table model reveals connections between dunes and vegetation at Doñana

We present a simple statistical model of the water-table fluctuations based on a set of multiple regressions for a dune slack of the Doñana National Park, and its utility to understand some ecological processes. The variation in the coefficients of the regressions for different locations allows discrimination between different zones in the dune slack, and explains the spatial pattern of heath vegetation observed in the stabilized sands. Model simulations were compared with an existing sparse data set of water-table levels, and suggests possible mechanisms responsible for the catastrophic pine tree mortality, which happened during the drought of 1979–83.     

Social preferences regarding the delivery of ecosystem services in a semiarid Mediterranean region

The valuation of ecosystem services has primarily been conducted within the context of the economic value of these services to society. Ecosystem services research has since advanced to identify conflicts of interest between different sectors of society while prioritizing conservation actions. This approach can be important in semiarid ecosystems, where biodiversity conservation can be hindered by a lack of community awareness. In the south-eastern Iberian Peninsula, conservation is perceived by society as a barrier to the economic development provided by agricultural or tourism activities. We use the contingent valuation method to identify community perception and economic values of different ecosystem services provided by semiarid ecosystems in the south-eastern Iberian Peninsula. This method identifies the perceptions of individuals benefiting from ecosystem services and examines their willingness to pay for the maintaining of these ecosystem services. Results showed that most respondents recognized the importance of services to human well-being and were willing to conserve these services. Preferences for maintaining water and air quality showed that respondents understood the relationship between the conservation of ecosystem services and local well-being. However, responses varied greatly across categories of beneficiaries; this finding highlights a potential conflict of interest that should be considered in any decision-making processes.     

Above-ground biomass and productivity in the Montado: From herbaceous to shrub dominated communities

Our study was focused on the effect of abandonment on above-ground biomass and net primary productivity (ANPP) in a Montado in Southern Portugal. The Montado has a long history of human management and control of invasion by shrubs is achieved by clearing, ploughing and grazing. When these cease, it is invaded by Mediterranean matorral species. We hypothesized that the change in life form dominance would affect both biomass and productivity, but while the total biomass was expected to increase, the effects on ANPP were less clear. We tested our hypothesis by determining above-ground biomass and ANPP along a gradient of decreasing land use intensity, ranging from extensive grazing to 20 years of abandonment.Above-ground biomass increased with abandonment, which was related with the increase in shrub cover. In addition, we found a decrease in herbaceous ANPP that was more than compensated by an increase in shrub ANPP in plots abandoned for longer time, resulting in a significant increase in total ANPP. This increase was strongly related with the increase in the cover of Cistus ladanifer, a pioneer species that colonises degraded areas and forms one of the first stages of succession of woody communities.     

Interbasin underflow between closed Altiplano basins in Chile

Interbasin ground water movement of 200 to 240 L/sec occurs as underflow beneath a mountainous surface water divide separating the topographically higher Salar de Michincha from the topographically lower Salar de Coposa internally drained basins in the Altiplano of northern Chile. Salt-encrusted flats (salars) and saline lakes occur on the lowest parts of the basin floors and comprise the principal evaporative discharge areas for the basins. Because a surface water divide separates the basins, surface water drainage boundaries do not coincide with ground water drainage boundaries. In the region, interbasin ground water movement is usually not recognized, but occurs for selected basins, and at places is an important component of ground water budgets. With increasing development of water for mining industry and potential exportation of ground water from the Altiplano for use at coastal cities, demonstration and quantification of interbasin movement is important for assessment of sustainable ground water development in a region of extreme aridity. Recognition and quantification of interbasin ground water underflow will assist in management of ground water resources in the arid Chilean Altiplano environment.     

The stabilizing effect of Na2S on the collector coating of chrysocolla

The heterogeneous reaction between natural and sulphidized chrysocolla and potassium amyl xanthate in solution is investigated.It is found that, together with the consumption of large amounts of xanthate, particles composed of the reaction products are spontaneously released from the surface of chrysocolla giving rise to a colloidal dispersion. In principle the mechamism is related to the peptizing effect of the excess xanthate ions that are found when Cu²⁺ and X^? ions are made to react in a homogeneous phase.In sulphidized chrysocolla this phenomenon is markedly reduced, showing that Na₂S has a stabilizing effect on the collector coating.Flotation experiments performed with aqueous amyl dixanthogen emulsions show that stable adhesion occurs only on properly sulphidized chrysocolla. It is believed that the mechanism controlling adhesion in this case is similar to that which determines the stability of the collector layer.