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941.
ABSTRACT National-scale analyses of land cover effects on water quality can aid in directing environmental policy. We compiled a coastal water quality database for New Zealand comprising 320 estuarine and coastal sites with records between 2013 and 2018. Previous literature had shown strong effects of agricultural and urban land cover on the quality of New Zealand’s rivers, so we examined their effects on estuaries, while controlling for marine dilution and freshwater flushing. Sites with greater freshwater influence had higher nutrient and faecal indicator bacteria concentrations, and turbidity, indicating that open coast and estuarine water quality is reduced predominantly via flows from the land. Nitrate, ammonium, total and dissolved reactive phosphorus, and water column chlorophyll-a concentrations were greater in estuaries with higher urban land cover and total phosphorus concentrations were greater with higher agricultural land cover. There was a marginally significant increase in turbidity as agricultural land cover increased. This is the first national-scale compilation and analysis of New Zealand coastal water quality data, and the first national analysis of land cover effects on water quality in New Zealand estuaries. 相似文献
942.
Moqin He Brain Veitch Neil Bose Bruce Colbourne Pengfei Liu 《Ocean Engineering》2007,34(8-9):1197-1210
Potential flow based vortex numerical methods have been widely used in aerodynamics and hydrodynamics. In these methods, vortices shed from lifting bodies are traced by using vortex filaments or dipole panels. When the wake elements encounter a downstream body, such as a rudder behind a propeller or a stator behind a rotor, a treatment is necessary to divert the wake elements to pass by the body. This treatment is vital to make wake simulations realistic and to satisfy the non-penetration condition during wake body interaction. It also helps to avoid pure numerical disturbances such as when a vortex filament or an edge of a dipole panel passes through the collection point of a body element; this is a singularity for induced velocity and it will introduce a large numerical disturbance. This necessary treatment for three-dimensional problems with geometrical complexity has not been found to date. In this study, a wake impingement model was developed to divert wake elements to slip over the body surface, model the vortex/body interaction, and predict forces on fluctuating components. The model was also tested on configurations of oscillating foils in tandem with an existing panel method code. Simulation results with the wake impingement model are shown to be in closer agreement with limited published experimental data than those without the model. With the established wake impingement model, force fluctuations on the after body due to the wake vortex impingement were investigated based on a series of simulations. The series varied several parameters including distance between two foils, oscillating frequency, span, rear foil pitch angle, swap angle and vertical position. 相似文献
943.
Emanuele Di Lorenzo Andrew M. Moore Hernan G. Arango Bruce D. Cornuelle Arthur J. Miller Brian Powell Boon S. Chua Andrew F. Bennett 《Ocean Modelling》2007,16(3-4):160-187
We describe the development and preliminary application of the inverse Regional Ocean Modeling System (ROMS), a four dimensional variational (4DVAR) data assimilation system for high-resolution basin-wide and coastal oceanic flows. Inverse ROMS makes use of the recently developed perturbation tangent linear (TL), representer tangent linear (RP) and adjoint (AD) models to implement an indirect representer-based generalized inverse modeling system. This modeling framework is modular. The TL, RP and AD models are used as stand-alone sub-models within the Inverse Ocean Modeling (IOM) system described in [Chua, B.S., Bennett, A.F., 2001. An inverse ocean modeling system. Ocean Modell. 3, 137–165.]. The system allows the assimilation of a wide range of observation types and uses an iterative algorithm to solve nonlinear assimilation problems. The assimilation is performed either under the perfect model assumption (strong constraint) or by also allowing for errors in the model dynamics (weak constraints). For the weak constraint case the TL and RP models are modified to include additional forcing terms on the right hand side of the model equations. These terms are needed to account for errors in the model dynamics.Inverse ROMS is tested in a realistic 3D baroclinic upwelling system with complex bottom topography, characterized by strong mesoscale eddy variability. We assimilate synthetic data for upper ocean (0–450 m) temperatures and currents over a period of 10 days using both a high resolution and a spatially and temporally aliased sampling array. During the assimilation period the flow field undergoes substantial changes from the initial state. This allows the inverse solution to extract the dynamically active information from the synthetic observations and improve the trajectory of the model state beyond the assimilation window. Both the strong and weak constraint assimilation experiments show forecast skill greater than persistence and climatology during the 10–20 days after the last observation is assimilated.Further investigation in the functional form of the model error covariance and in the use of the representer tangent linear model may lead to improvement in the forecast skill. 相似文献
944.
Ana M. Dreher Roberto P. Xavier Bruce E. Taylor Sérgio L. Martini 《Mineralium Deposita》2008,43(2):161-184
The Igarapé Bahia Cu–Au deposit in the Carajás Province, Brazil, is hosted by steeply dipping metavolcano-sedimentary rocks
of the Igarapé Bahia Group. This group consists of a low greenschist grade unit of the Archean (∼2,750 Ma) Itacaiúnas Supergroup,
in which other important Cu–Au and iron ore deposits of the Carajás region are also hosted. The orebody at Igarapé Bahia is
a fragmental rock unit situated between chloritized basalt, with associated hyaloclastite, banded iron formation (BIF), and
chert in the footwall and mainly coarse- to fine-grained turbidites in the hanging wall. The fragmental rock unit is a nearly
concordant, 2 km long and 30–250 m thick orebody made up of heterolithic, usually matrix-supported rocks composed mainly of
coarse basalt, BIF, and chert clasts derived from the footwall unit. Mineralization is confined to the fine-grained matrix
and comprises disseminated to massive chalcopyrite accompanied by magnetite, gold, U- and light rare earth element (LREE)-minerals,
and minor other sulfides like bornite, molybdenite, cobaltite, digenite, and pyrite. Gangue minerals include siderite, chlorite,
amphibole, tourmaline, quartz, stilpnomelane, epidote, and apatite. A less important mineralization style at Igarapé Bahia
is represented by late quartz–chalcopyrite–calcite veins that crosscut all rocks in the deposit area. Fluid inclusions trapped
in a quartz cavity in the ore unit indicate that saline aqueous fluids (5 to 45 wt% NaCl + CaCl2 equiv), together with carbonic (CO2 ± CH4) and low-salinity aqueous carbonic (6 wt% NaCl equiv) fluids, were involved in the mineralization process. Carbonates from
the fragmental layer have δ13C values from −6.7 to −13.4 per mil that indicate their origin from organic and possibly also from magmatic carbon. The δ34S values for chalcopyrite range from −1.1 to 5.6 per mil with an outlier at −10.8 per mil, implying that most sulfur is magmatic
or leached from magmatic rocks, whereas a limited contribution of reduced and oxydized sulfur is also evident. Oxygen isotopic
ratios in magnetite, quartz, and siderite yield calculated temperatures of ∼400°C and δ18O-enriched compositions (5 to 16.5 per mil) for the ore-forming fluids that suggest a magmatic input and/or an interaction
with 18O-rich, probably sedimentary rocks. The late veins of the Igarapé Bahia deposit area were formed from saline aqueous fluids
(2 to 60 wt% NaCl + CaCl2 equiv) with δ18Ofluid compositions around 0 per mil that indicate contribution from meteoric fluids. With respect to geological features, Igarapé
Bahia bears similarity with syngenetic, volcanic-hosted massive sulfide (VHMS)-type deposits, as indicated by the volcano-sedimentary
geological context, stratabound character, and association with submarine volcanic flows, hyaloclastite, and exhalative beds
such as BIF and chert. On the other hand, the highly saline ore fluids and the mineral assemblage, dominated by magnetite
and chalcopyrite, with associated gold, U- and LREE-minerals and scarce pyrite, indicate that Igarapé Bahia belongs to the
Fe oxide Cu–Au (IOCG) group of deposits. The available geochronologic data used to attest syngenetic or epigenetic origins
for the mineralization are either imprecise or may not represent the main mineralization episode but a later, superimposed
event. The C, S, and O isotopic results obtained in this study do not clearly discriminate between fluid sources. However,
recent B isotope data obtained on tourmaline from the matrix of the fragmental rock ore unit (Xavier, Wiedenbeck, Dreher,
Rhede, Monteiro, Araújo, Chemical and boron isotopic composition of tourmaline from Archean and Paleoproterozoic Cu–Au deposits in the Carajás Mineral
Province, 1° Simpósio Brasileiro de Metalogenia, Gramado, Brazil, extended abstracts, CD-ROM, 2005) provide strong evidence of the
involvement of a marine evaporitic source in the hydrothermal system of Igarapé Bahia. Evaporite-derived fluids may explain
the high salinities and the low reduced sulfur mineral paragenesis observed in the deposit. Evaporite-derived fluids also
exclude a significant participation of magmatic or mantle-derived fluids, reinforcing the role of nonmagmatic brines in the
genesis of Igarapé Bahia. Considering this aspect and the geological features, the possibility that the deposit was generated
by a hydrothermal submarine system whose elevated salinity was acquired by leaching of ancient evaporite beds should be evaluated. 相似文献
945.
Multi-anvil and piston cylinder experiments were performed to determine the effect of both pressure and temperature on the diffusivities of several siderophile elements in a Fe90Ni10 core-analog alloy. Activation energies were calculated to be between 244 and 257 kJ/mol for Re, Pd, and Au at 10 GPa, and 264 kJ/mol for P at 1 GPa. It was found that pressure has a marked negative effect on the diffusivities of Au, Re, and Pd, and activation volumes for these elements were calculated to be between 3 and 6 cm3/mol at 10 GPa. The effect of both temperature and pressure on P diffusion is noticeably less, and the absolute diffusivity of phosphorus is consistently higher than that of the other elements. It is inferred that the reason for this difference is because P is diffusing via an interstitial mechanism as opposed to Re, Pd, and Au which occupy regular lattice sites in the crystal. The effect of pressure and temperature together with depth in the Earth suggests that these elements may continue to exhibit different behavior at more extreme conditions. The significance of these new results lies in the ability to place constraints on many time-dependent processes that pertain to the formation and evolution of planetary cores, as well as the formation and cooling histories of other metal-rich bodies in the solar system, such as meteorites. 相似文献
946.
Hydrogeological and hydrochemical characterization of the Voltaian Basin: the Afram Plains area,Ghana 总被引:1,自引:0,他引:1
In the Afram Plains area, groundwater is the main source of water supply for most uses. The area is underlain by aquifers
of the southern Voltaian sedimentary basin, which are predominantly sandstones, mudstones, conglomerates and shale. Ordinary
least squares regression analysis using 41 well-test data from aquifers in the Afram Plains portion of the Voltaian system
reveals that transmissivity, T, exists in a non-linear relationship with specific capacity, Sc. The analysis reveals that T = 0.769Sc1.075 with R
2 = 0.83 for aquifers in the area. The mudstone/conglomerate aquifer in the area appears to be the most variable in terms of
both specific capacity and transmissivity with transmissivity ranging from 0.18 to 197.7 m2/day and 0.5 and 148.5 m3/day/m, respectively. Horizontal fractures and joints resulting from secondary fracturing appear to be the main determinants
of both transmissivity and specific capacity in the area. PHREEQC modeling and mineral stability diagrams indicate that groundwater
quality in the Afram Plains area is controlled by the incongruent weathering of silicate minerals in the aquifers. These processes
concentrate calcium, sodium, magnesium, potassium, bicarbonate ion and quartz, leading to calcite, dolomite and aragonite
supersaturation at most locations. Hierarchical cluster analysis performed on the raw chemical data reveals two main water
types or facies: the calcium–sodium–chloride–bicarbonate facies, and the magnesium–potassium–sulfate–nitrate facies for the
southern and northern sections of the Afram Plains area, respectively. 相似文献
947.
Groundwater availability in the shallow aquifers of the southern voltaian system: a simulation and chemical analysis 总被引:1,自引:0,他引:1
A steady state groundwater flow simulation model was developed using available well data and general hydrogeological and geological
information, for the Afram Plains area, Ghana. The hydrochemistry of groundwater from wells in the area was then evaluated
to determine its suitability for irrigation and domestic uses. The assessment of the irrigation quality of groundwater from
this area was based on salinity (EC) and sodium adsorption ratios (SAR), residual sodium carbonate (RSC), and permeability
indices (PI). The simulation model reveals that groundwater in the Afram Plains area generally flows from the midsections
in the neighborhood of Tease and surrounding areas, where significant recharge takes place, to the outer regions and discharges
into the Volta Lake in the southern and eastern sections of the area. Flow magnitude and piezometric maps suggest that there
is probably of less potential for groundwater extraction for sustainable irrigation in the central regions of the area, when
compared to the other discharge areas. This study reveals that more than 70% of the samples analyzed fall within the C2–S1
category, referring to the medium level salinity and low sodium. Medium salinity waters may be used for irrigation on coarse
textured soils with good permeability. About 15% of the data fall within the C3–S2 category, referring to water of high salinity
and medium sodicity. High salinity, medium sodicity irrigation water cannot be used on fine-grained soils where drainage is
restricted. This is because restricted flow is likely to result in the accumulation of salts in the root zones of crops, leading
to salinity and soil clogging crisis. About 3% falls within the C3–S3 (high salinity, high sodicity) category. This category
requires special soil management including improved drainage, heavy leaching and the use of chemical amendments on the water.
Only one point plots within the extreme salinity–sodicity range. Concentrations of fluoride, arsenic and other natural elements
in the area generally fall well within the world health standards for domestic water. 相似文献
948.
949.