Vegetation in an altitudinal gradient along the R?́o Loa in the Atacama Desert of northern Chile     

Julio R. Gutiérrez  Francisco López-Cortes  Pablo A. Marquet 《Journal of Arid Environments》1998,40(4):383-399

Six sites between 0 m and 4000 m were sampled for plant and soil chemical characteristics along the Río Loa, Atacama Desert, Chile. Sites located between 0 m and 1500 m showed lower species richness, higher plant cover and higher herbaceous productivity than the upper part of the altitudinal gradient. The number of species varied non-linerly with precipitation along the altitudinal gradient. Plant cover and herbaceous productivity in the lowlands is characterized by thePluchea absinthioides Distichlis spicataassociation of anthropic origin. We propose that vegetation structure along the altitudinal gradient has been affected by past and present human activities, and climatic and edaphic factors.  相似文献   

Fishery development — the Latin American model     

Julio Luna 《Marine Policy》1980,4(2):148-150

Ten years ago, the Food and Agriculture Organization (FAO) and the Inter-American Development Bank undertook an analysis of the possibilities and significance of fishery development in Latin America, formulating guidelines for action to promote development and outlining strategies and means for implementation. This report describes the evolution of fishery development in the Latin American region over the past decade.  相似文献   

Reduction of jack-up and crane vessel resistance and bow swamping     

Robert Latorre  Julio Arana 《Ocean Engineering》2006,33(14-15):2000-2011

A large bow wave forms when blunt-shaped vessels like self-propelled jack-up crane vessels (liftboats) operate at high speeds. Above a critical speed, this bow wave spills over the bow causing swamping. To investigate this phenomena, towing tank tests of a 1/25 scale model liftboat hull were done over a speed range of 3–8 kn. The test showed above 4 kn the bow wave formed and the vessel trimmed by the bow. At speeds above 8 kn the bow wave spilled over the bow (swamping). To cancel this critical bow wave a vertical bow plate was fitted ahead of the liftboat bow. This bow plate reduced the bow wave formation and achieved a 10–15% reduction in the towing resistance. The wave cancellation bow plate can reduce the liftboat power or increase its liftboat speed and operating range.  相似文献   

Seabird distribution on the Humboldt Current in northern Chile in relation to hydrography, productivity, and fisheries     

Weichler  Tanja; Garthe  Stefan; Luna-Jorquera  Guillermo; Moraga  Julio 《ICES Journal of Marine Science》2004,61(1):148-154

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Changes in the pattern of water masses resulting from a poleward slope current in the Cantabrian Sea (Bay of Biscay)     

Julio Gil 《Estuarine, Coastal and Shelf Science》2003,57(5-6):1139-1149

From September to December 1995, three hydrographic surveys were carried out in the eastern Cantabrian Sea (Bay of Biscay). Changes in the water masses pattern were examined to study the variability and main energetic features in the area. At the beginning of December, an intense Poleward Current (PC), which had come from Portuguese slopes, entered the eastern Cantabrian Sea. This current was the most energetic event in this area in winter. The PC waters increased temperature by about 2 °C (subsurface layers) and salinity by 0.2 (surface layers) in the pattern of water masses in the eastern Cantabrian Sea in winter. The core current was approximately 10 km width and 120 m depth and the water transport, estimated from geostrophic current profiles, was of about 1.3 Sv.A well-defined wavelike front with two significant ridges in the western and eastern sampling area, was observed. The variability and meandering flow of the PC were driven by dominantly baroclinic instabilities, which are due to strong vertical velocity shear. In this synoptic-scale system, the potential vorticity advection, the differential vorticity advection, and the geopotential tendency have shown to be the cause of the ageostrophic motion and the main baroclinic disturbances.One important consequence of the entrance of the PC in the eastern Cantabrian Sea was the profound effect on the pattern of nutrients. The current-induced stratification pattern drives the distribution of nutrients in the different layers and the instabilities and meandering pattern of the PC was an important mechanism of fertilisation offshore.  相似文献   

High speed ship structural dynamics, practical application to design     

Julio G. Giannotti 《Ocean Engineering》1978,5(4):243-267

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Carbonate xenoliths in La Palma: Carbonatite or alteration product?     

Attila Demény  Ramón Casillas  Julio de La Nuez  Géza Nagy 《Chemie der Erde / Geochemistry》2008,68(4):369-381

Carbonate xenoliths containing olivine and rimmed by kaersutitic amphibole were collected in basaltic rocks of the Basal Complex of La Palma. The mineralogical composition and microscopic appearance may suggest a relationship with carbonatites in general, thus a major element, trace element and stable isotope study was conducted to investigate the origin of the carbonate formation. Based on electron microprobe analyses, the carbonate is calcite with up to 6.3 wt% MgO and 7.2 wt% SiO₂. The elevated SiO₂ content may suggest a melt origin for the carbonate. However, the C and O isotope compositions of the carbonate xenoliths (δ¹³C and δ¹⁸O around −1‰ and 13‰, respectively) are similar to those of calcite veins and amygdales in basaltic rocks of the Basal Complexes of La Palma and Fuerteventura and are interpreted as produced by fluid degassing and metasomatism by CO₂-H₂O fluid derived from mobilization of sedimentary material. Trace element contents determined by laser-ablation ICP-MS analyses support the assumed origin, thus, the relationship with carbonatitic melts can be excluded. Based on trace element compositions, the amphibole surrounding the xenoliths is not related genetically to the carbonate. The elevated SiO₂ content of the calcite can be attributed to submicron relics of pyroxene, thus, the use of this feature as an evidence for melt origin is questionable.  相似文献   

Variability of labile metals in estuarine sediments in areas under the influence of antifouling paints,southern Brazil     

Luiza Dy Fonseca Costa  Nicolai Mirlean  Julio Cesar Wasserman  Mônica Wallner-Kersanach 《Environmental Earth Sciences》2016,75(7):580

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The impact of stream-groundwater exchange on seasonal nitrate loads in an urban stream     

Julio Beltran  Laura K. Lautz  John R. Slosson 《水文研究》2021,35(8):e14324

Urbanization negatively impacts water quality in streams by reducing stream-groundwater interactions, which can reduce a stream's capacity to naturally attenuate nitrate. Meadowbrook Creek, a first order urban stream in Syracuse, New York, has an inverse urbanization gradient, with heavily urbanized headwaters that are disconnected from the floodplain and downstream reaches that have intact riparian floodplains and connection to riparian aquifers. This system allows assessment of how stream-groundwater interactions in urban streams impact the net sources and sinks of nitrate at the reach scale. We used continuous (15-min) streamflow measurements and weekly grab samples at three gauging stations positioned longitudinally along the creek to develop continuous nitrate load estimates at the inlet and outlet of two contrasting reaches. Nitrate load estimates were determined using a USGS linear regression model, RLOADEST, and differences between loads at the inlet and outlet of contrasting reaches were used to quantify nitrate sink and source behaviour year-round. We observed a nitrate load of 1.4 × 10⁴ kg NO₃⁻ per water year, on average, at the outlet of the urbanized reach while the nitrate load at the outlet of the downstream, connected reach was 1.0 × 10⁴ kg NO₃⁻ per water year, on average. We found the more heavily urbanized, hydrologically-disconnected reach was a net source of nitrate regardless of season. In contrast, stream-groundwater exchange caused the hydrologically connected reach to be both a source and sink for nitrate, depending on time of year. Both reaches alter nitrate source and sink behaviour at various spatiotemporal scales. Groundwater connection in the downstream, connected reach reduces annual nitrate loads and provides more opportunities for sources and sinks of nitrate year-round than the hydrologically disconnected stream reach. Mechanisms include groundwater discharge into the stream with variable nitrate concentrations, surface-water groundwater interactions that foster denitrification, and stream load loss to surrounding near-stream aquifers. This study emphasizes how loads are important in understanding how stream-groundwater interactions impact reach scale nitrate export in urban streams.  相似文献   

On the influence of etch pits in the overall dissolution rate of apatite basal sections     

Igor Alencar  Sandro Guedes  Rosane Palissari  Julio C. Hadler 《Physics and Chemistry of Minerals》2015,42(8):629-640

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