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11.
Dissolved and suspended concentrations of hexachlorocyclohexane isomers, α, γ and δ HCH, and Zn, Cu and Cd have been measured in the Napostá Grande stream, located in the Blance Bay area, Argentina, for the purpose of studying the behaviour of these compounds in the freshwater-seawater mixing zone. The aim was to establish the mobilization processes, according to their distribution over the dissolved and suspended forms, in order to obtain a better understanding of their impact on organochlorine and heavy metal levels in the marine environment. It is concluded that the compounds studied are removed from solution by suspended matter which is afterwards precipitated during the freshwater-seawater mixing process. Seawater and surface sediment concentrations of these pollutants for two sampling sites in Blanca Bay, Argentina, are also reported. 相似文献
12.
Adélie Delacour Marie-Christine Gerbe Jean-Claude Thouret Gerhard Wörner Perrine Paquereau-Lebti 《Bulletin of Volcanology》2007,69(6):581-608
Minor centres in the Central Volcanic Zone (CVZ) of the Andes occur in different places and are essential indicators of magmatic
processes leading to formation of composite volcano. The Andahua–Orcopampa and Huambo monogenetic fields are located in a
unique tectonic setting, in and along the margins of a deep valley. This valley, oblique to the NW–SE-trend of the CVZ, is
located between two composite volcanoes (Nevado Coropuna to the east and Nevado Sabancaya to the west). Structural analysis
of these volcanic fields, based on SPOT satellite images, indicates four main groups of faults. These faults may have controlled
magma ascent and the distribution of most centres in this deep valley shaped by en-echelon faulting. Morphometric criteria
and 14C age dating attest to four main periods of activity: Late Pleistocene, Early to Middle Holocene, Late Holocene and Historic.
The two most interesting features of the cones are the wide compositional range of their lavas (52.1 to 68.1 wt.% SiO2) and the unusual occurrence of mafic lavas (olivine-rich basaltic andesites and basaltic andesites). Occurrence of such minor
volcanic centres and mafic magmas in the CVZ may provide clues about the magma source in southern Peru. Such information is
otherwise difficult to obtain because lavas produced by composite volcanoes are affected by shallow processes that strongly
mask source signatures. Major, trace, and rare earth elements, as well as Sr-, Nd-, Pb- and O-isotope data obtained on high-K
calc-alkaline lavas of the Andahua–Orcopampa and Huambo volcanic province characterise their source and their evolution. These
lavas display a range comparable to those of the CVZ composite volcanoes for radiogenic and stable isotopes (87Sr/86Sr: 0.70591–0.70694, 143Nd/144Nd: 0.512317–0.512509, 206Pb/204Pb: 18.30–18.63, 207Pb/204Pb: 15.57–15.60, 208Pb/204Pb: 38.49–38.64, and δ
18O: 7.1–10.0‰ SMOW), attesting to involvement of a crustal component. Sediment is absent from the Peru–Chile trench, and hence
cannot be the source of such enrichment. Partial melts of the lowermost part of the thick Andean continental crust with a
granulitic garnet-bearing residue added to mantle-derived arc magmas in a high-pressure MASH [melting, assimilation, storage
and homogenisation] zone may play a major role in magma genesis. This may also explain the chemical characteristics of the
Andahua–Orcopampa and Huambo magmas. Fractional crystallisation processes are the main governors of magma evolution for the
Andahua–Orcopampa and Huambo volcanic province. An open-system evolution is, however, required to explain some O-isotopes
and some major and trace elements values. Modelling of AFC processes suggests the Charcani gneisses and the local Andahua–Orcopampa
and Huambo basement may be plausible contaminants. 相似文献
13.
Adão H. Matonse Donald C. Pierson Allan Frei Mark S. Zion Aavudai Anandhi Elliot Schneiderman Ben Wright 《Climatic change》2013,116(3-4):437-456
Future climate scenarios projected by three different General Circulation Models and a delta-change methodology are used as input to the Generalized Watershed Loading Functions – Variable Source Area (GWLF-VSA) watershed model to simulate future inflows to reservoirs that are part of the New York City water supply system (NYCWSS). These inflows are in turn used as part of the NYC OASIS model designed to simulate operations for the NYCWSS. In this study future demands and operation rules are assumed stationary and future climate variability is based on historical data to which change factors were applied in order to develop the future scenarios. Our results for the West of Hudson portion of the NYCWSS suggest that future climate change will impact regional hydrology on a seasonal basis. The combined effect of projected increases in winter air temperatures, increased winter rain, and earlier snowmelt results in more runoff occurring during winter and slightly less runoff in early spring, increased spring and summer evapotranspiration, and reduction in number of days the system is under drought conditions. At subsystem level reservoir storages, water releases and spills appear to be higher and less variable during the winter months and are slightly reduced during summer. Under the projected future climate and assumptions in this study the NYC reservoir system continues to show high resilience, high annual reliability and relatively low vulnerability. 相似文献
14.
ABSTRACTThe objective of this paper is to understand how the natural dynamics of a time-varying catchment, i.e. the rainfall pattern, transforms the random component of rainfall and how this transformation influences the river discharge. To this end, this paper develops a rainfall–runoff modelling approach that aims to capture the multiple sources and types of uncertainty in a single framework. The main assumption is that hydrological systems are nonlinear dynamical systems which can be described by stochastic differential equations (SDE). The dynamics of the system is based on the least action principle (LAP) as derived from Noether’s theorem. The inflow process is considered as a sum of deterministic and random components. Using data from the Ouémé River basin (Benin, West Africa), the basic properties for the random component are considered and the triple relationship between the structure of the inflowing rainfall, the corresponding SDE that describes the river basin and the associated Fokker-Planck equations (FPE) is analysed.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR D. Gerten 相似文献
15.
Simulations from a numerical model address the impact of nearshore morphology on surf zone retention on, open coast, rip-channelled beaches exposed to shore-normal waves. In the model, rip channels are regularly spaced alongshore with a given spacing λ. For a given reference case bathymetry (λ= 200 m), rip current circulations retain floating material at a hourly rate R of about 80 % which is in line with most existing field and laboratory studies in similar settings. The influence of a surf zone rip-channel morphology on surf zone retention is evaluated by a number of morphologic parameters. Results show that rip spacing is important. The ratio of the surf zone width X s to rip spacing λ controls surf zone retention with R rapidly increasing with increasing X s /λ up to a threshold of about 1 above which R levels off to become asymptotic to 100 %. The impact of the presence of a rip head bar is profound but nonlinear. The onset of wave breaking across the rip head bar drives a weak seaward located circulation providing major pathways for surface water exiting the surf zone compartment. Additional simulations suggest that alongshore variations in the offshore bathymetry are important. Patterns in the wave field enforced by wave refraction and potentially wave breaking across offshore bathymetric anomalies can provide a conduit for transporting floating material out of the surf zone and into the inner shelf region. This has major implications for surf zone flushing by inner-bar rips on multiple-barred beaches and on beaches facing bathymetric anomalies on the inner shelf. 相似文献
16.
Results of 2DH morphodynamic computations are presented to quantify the temporal evolution of the crescentic patterns emerging in a double nearshore bar system in response to constant wave boundary forcing. Sixteen different conditions varying both offshore wave height and angle of wave incidence were applied. The mean length scales of the emerging irregular crescentic patterns are linearly proportional to the local longshore velocity over the inner and outer bars. For similar longshore velocities, the length scales of the outer bar are larger than of the inner bar. This is explained by accounting for the difference in water depth above the bar crest. The variable morphological response times can be explained by including additional bathymetrical parameters. The active volume of the bar, defined by the breaker index, plays an important role in this response time. With larger active volumes the bar responds more rapidly to identical boundary conditions. Also, bars with a smaller total volume respond more quickly. This faster response is due to the steeper active volume of the bars. Different initial perturbations resulted in different locations of the emerging features, showing that their location is sensitive to the initial bathymetry. However, the range in length scales and response times due to the different perturbations was significantly smaller than those obtained for the different hydrodynamic conditions. Based on the present findings we hypothesize that morphological length scales in the field are rarely in equilibrium with the concurrent offshore wave height and angle of incidence owing to the slow response of the sandbars under constant conditions relative to the stochastic nature of natural wave forcing. 相似文献
17.
Marta Susana Orozco Storni Rubén José Lara Adán Edgardo Pucci 《Estuarine, Coastal and Shelf Science》1984,19(4):485-491
Oxygen, alkalinity, nutrients, pH, temperature and salinity were measured through tidal cycles in two points of Blanca Bay. A clear dependence of nutrients, oxygen and alkalinity with salinity and tide conditions was observed in the inner point, being attenuated in the outer one. 相似文献
18.
An idealized model of tidal dynamics in the North Sea: resonance properties and response to large-scale changes 总被引:3,自引:1,他引:2
Pieter C. Roos Jorick J. Velema Suzanne J. M. H. Hulscher Ad Stolk 《Ocean Dynamics》2011,61(12):2019-2035
An idealized process-based model is developed to investigate tidal dynamics in the North Sea. The model geometry consists
of a sequence of different rectangular compartments of uniform depth, thus, accounting for width and depth variations in a
stepwise manner. This schematization allows for a quick and transparent solution procedure. The solution, forced by incoming
Kelvin waves at the open boundaries and satisfying the linear shallow water equations on the f plane with bottom friction, is in each compartment written as a superposition of eigenmodes, i.e. Kelvin and Poincaré waves.
A collocation method is employed to satisfy boundary and matching conditions. First, the general resonance properties of a
strongly simplified geometry with two compartments, representing the Northern North Sea and Southern Bight, are studied. Varying
the forcing frequency while neglecting bottom friction reveals Kelvin and Poincaré resonance. These resonances continue to
exist (but with lower amplification and a modified spatial structure) when adding the Dover Strait as a third compartment
and separating the solutions due to forcing from either the north or the south only. Including bottom friction dampens the
peaks. Next, comparison with tide observations along the North Sea coast shows remarkable agreement for both semi-diurnal
and diurnal tides. This result is achieved with a more detailed geometry consisting of 12 compartments fitted to the coastline
of the North Sea. Further simulations emphasize the importance of Dover Strait and bottom friction. Finally, it is found that
a sea level rise of 1 m, uniformly applied to the entire North Sea, amplifies the M2-elevation amplitudes almost everywhere
along the coast, with an increase of up to 8 cm in Dover Strait. Bed level changes of ±1 m, uniformly applied to the Southern
Bight only, imply weaker changes, with changes in coastal M2-elevation amplitudes below 5 cm. 相似文献
19.
Lavrushin V. Yu. Aliev Ad. A. Pokrovsky B. G. Kozmenko O. A. Kikvadze O. E. Sokol E. V. 《Lithology and Mineral Resources》2019,54(3):200-220
Lithology and Mineral Resources - This paper is devoted to the vein and dispersed carbonates from ejecta of mud volcanoes of Azerbaijan. The vein calcites are morphologically diverse and related to... 相似文献
20.
Alan L. Shanks Steven G. Morgan Jamie MacMahan Ad J.H.M. Reniers Marley Jarvis Jenna Brown Atsushi Fujimura Lisa Ziccarelli Chris Griesemer 《Estuaries and Coasts》2018,41(1):158-176
Surf zones, regions of breaking waves, are at the interface between the shore and coastal ocean. Surf zone hydrodynamics may affect delivery of phytoplankton subsidies to the intertidal zone. Over a month of daily sampling at an intermediate surf zone with bathymetric rip currents and a reflective surf zone, we measured surf zone hydrodynamics and compared concentrations of coastal phytoplankton taxa in the surf zones to concentrations offshore. At the intermediate surf zone, ~80% of the variability in the concentration of coastal phytoplankton taxa within the surf zone was explained by their variation offshore; however, concentrations were much higher and lower than those offshore in samples from a bathymetric rip current and over the adjacent shoal, respectively. Hydrodynamics at this intermediate surf zone did not hinder the delivery of coastal phytoplankton to the surf zone, but the bathymetric rip current system appeared to redistribute phytoplankton concentrating them within eddies. At the reflective shore, we sampled surf zones at a beach and two adjacent rocky intertidal sites. Concentrations of typical coastal phytoplankton taxa were usually an order of magnitude or more lower than those offshore, even when offshore samples were collected just 20 m beyond the breakers. The phytoplankton assemblages inside and outside the surf zone often appeared to be disconnected. Surf zone hydrodynamics at the steep, reflective shore coupled with low phytoplankton concentrations in near-surface water appeared to limit delivery of phytoplankton subsidies to the surf zone. Surf zone hydrodynamics may be a key factor in the alongshore variation in phytoplankton subsidies to coastal communities. 相似文献