A model for the estimation of water filtration and nutrient regeneration by exposed sandy beaches

Exposed sandy beaches filter huge volumes of sea water daily as a result of wave and tide action. A regression model is developed which predicts the volume of water filtered daily by a beach as a function of tide range, beach slope and sand particle size. From these parameters estimates are also made of intertidal distance, the degree of expansion of the intertidal above the still water tide range by wave action and the average path length through the sand interstices percolated by filtered sea water. An equation is derived relating the degree of mineralisation of organic matter in the filtered sea water to the distance filtered through the sand and the sand particle size. Employing all this information, a simple model is used to estimate the volumes of sea water filtered and the amounts of inorganic nitrogen regenerated by intertidal sandy beaches over a range of physical conditions. The implications of this nutrient generation for the inshore zone are discussed.     

Microzooplankton and mesozooplankton in an upwelling filament off Galicia: modelling and sensitivity analysis of the linkages and their impact on the carbon dynamics

This paper reports estimates of trophic flows of carbon off the Galician coast from a 1D ecological model, which are compared with field data from a two week Lagrangian drift experiment. The model consists of 9 biological components: nitrate, ammonium, >5μm phytoplankton, <5μm phytoplankton, heterotrophic nanoflagellates/dinoflagellates (5–20 μm), heterotrophic dinoflagellates (>20 μm), ciliates, fast sinking detritus and slow sinking detritus. Calculations were made for the fluxes of carbon between biological components within the upper 45m of the water column. The temporal development of primary production during the simulation period of two weeks was in good agreement with field estimates, which varied between 248 and 436mgC.m⁻².d⁻¹. Heterotrophic nanoflagellates had the greatest impact on carbon flux, with a grazing rate of 168mgC.m⁻².d⁻¹. Herbivorous grazing by microzooplankton amounted to 215mgC.m⁻².d⁻¹, whereas grazing by copepods on phytoplankton was 35mgC.m⁻² d⁻¹. Copepods grazing on microzooplankton was minor (0.47mgC.m⁻².d⁻¹) and the export flux from the upper 45m was 302mgC.m⁻².d⁻¹. Sensitivity analyses, in which the grazing parameters (i.e the functional relationship between ingestion and food concentration) were changed, were carried out on the heterotrophic dinoflagellate, ciliate and heterotrophic nanoflagellates/dinoflagellate components of the model. These changes did not alter the temporal development of heterotrophic nanoflagellates/dinoflagellates biomass significantly, but ciliates and heterotrophic dinoflagellates were more sensitive to variations in the grazing parameters. The overall conclusion from this modelling study is that the coupling between small phytoplankton and heterotrophic nanoflagellates was the quantitatively most important process controlling carbon flow in this region.     

RARE EARTH ELEMENT CONCENTRATIONS IN USGS AND CCRMP IGNEOUS ROCK STANDARDS DETERMINED BY HIGH PERFORMANCE ION CHROMATOGRAPHY

Eleven rare earth elements (REE) have been determined in ten USGS and two CCRMP igneous rock standards using high performance ion chromatography. Duplicate analyses of two or more separately prepared aliquots of each sample were undertaken; reproducibility was better than 5% for each of the REE. In most cases, the results compare closely with published REE values for those samples for which the REE are well characterised. Where the results for individual elements are in disagreement with published data, the more erratic patterns yielded by the earlier data when plotted on chondrite-normalised REE diagrams suggest that values determined in this study are of greater accuracy.     

Calcium isotope fractionation in modern scleractinian corals

The ⁴⁴Ca/⁴⁰Ca ratios of cultured (Acropora sp.) and open ocean (Pavona clavus, Porites sp.) tropical reef corals are positively correlated with growth temperature. The slope of the temperature-fractionation relation is similar to inorganic aragonite precipitates. However, δ^44/40Ca of the coral aragonite is offset from inorganic and sclerosponge aragonite by about +0.5‰. This offset can neither be explained by the very fast, biologically controlled calcification of scleractinian corals, nor as a consequence of calcification from a partly closed volume of fluid. As corals actively transport calcium through several cell layers to the site of calcification, the most likely explanation for the offset is a biologically induced fractionation. Our results indicate a limited use of Ca isotopes in scleractinian corals as temperature proxy.     

Spectroscopic characterisation and crystal field calculations of varicoloured kyanites from Loliondo, Tanzania

Orange, ochre-coloured, light green and dark blue varieties of kyanite, ideally Al₂SiO₅, from Loliondo, Tanzania, have been characterised by electron microprobe analysis and polarised infrared and optical absorption spectroscopy. All colour varieties show elevated Fe contents of 0.39 to 1.31 wt.% FeO, but Ti contents only in the range of the EMP detection limit. Orange and ochre-coloured crystals have Mn contents of 0.23 and 0.06 wt.% MnO, respectively, the dark blue kyanite contains 0.28 wt.% Cr₂O₃, while the light green sample is nearly free from transition metal cations other than Fe. Polarised infrared spectra reveal OH defect concentrations of 3 to 17 wt.ppm H₂O with structural OH defects partially replacing the O_B (O2) oxygen atoms. Polarised optical absorption spectra show that the colour of all four varieties is governed by crystal field d-d transitions of trivalent cations, i.e. Fe³⁺ (all samples), Mn³⁺ (orange and ochre) and Cr³⁺ (blue kyanite), replacing Al in sixfold coordinated triclinic sites of the kyanite structure. Intervalence charge transfer, the prevalent colour-inducing mechanism in ‘usual’ (Cr-poor) blue kyanites, seems to play a very minor, if any, role in the present samples. Crystal field calculations in both a ‘classic’ tetragonal and in the semiempirical Superposition Model approach, accompanied by distance- and angle-least-squares refinements, indicate that Fe³⁺ preferably occupies the Al4 site, Cr³⁺ prefers the Al1 and Al2 sites, and Mn³⁺ predominantly enters the Al1 site. In each case specific local relaxation effects were observed according to the crystal chemical preferences of these transition metal cations. Furthermore, the high values obtained in the calculations for the interelectronic repulsion parameter Racah B correspond to a high ionic contribution to Me³⁺–O bonding in the kyanite structure. In the particular case of the blue sample, band positions specifically related to the high Racah B value enable this ‘unusual’ type of blue colouration of kyanite solely due to Cr³⁺ cations.     

密闭微波消解-等离子体发射光谱法测定钢铁样品中的硅

为了准确测定高等级钢铁中的Si,必须使用ＨＦ。用ICP-AES法测定Si会受到Co、Mo、Ni、Ta、V和W的严重干扰,仅仅使用外标或内标（标准加入）无法保证足够的准确性,必须使用基质匹配空白校正技术才能得到准确的Si的测定结果。利用Multiwave 3000 密闭式微波加压湿法消解技术结合ＩＣＰ－AＥＳ测定高等级钢铁中Si的方法,与常规重量法相比,可以极大地节省时间和减小试剂的消耗。     

Holocene and Pleistocene fringing reef growth and the role of accommodation space and exposure to waves and currents (Bora Bora,Society Islands,French Polynesia)

Holocene fringing reef development around Bora Bora is controlled by variations in accommodation space (as a function of sea‐level and antecedent topography) and exposure to waves and currents. Subsidence ranged from 0 to 0·11 m kyr^?1, and did not create significant accommodation space. A windward fringing reef started to grow 8·7 kyr bp , retrograded towards the coast over a Pleistocene fringing reef until ca 6·0 kyr bp , and then prograded towards the lagoon after sea‐level had reached its present level. The retrograding portion of the reef is dominated by corals, calcareous algae and microbialite frameworks; the prograding portion is largely detrital. The reef is up to 13·5 m thick and accreted vertically with an average rate of 3·12 m kyr^?1. Lateral growth amounts to 13·3 m kyr^?1. Reef corals are dominated by an inner Pocillopora assemblage and an outer Acropora assemblage. Both assemblages comprise thick crusts of coralline algae. Palaeobathymetry suggests deposition in 0 to 10 m depth. An underlying Pleistocene fringing reef formed during the sea‐level highstand of Marine Isotope Stage 5e, and is also characterized by the occurrence of corals, coralline algal crusts and microbialites. A previously investigated, leeward fringing reef started to form contemporaneously (8·78 kyr bp ), but is thicker (up to 20 m) and solely prograded throughout the Holocene. A shallow Pocillopora assemblage and a deeper water Montipora assemblage were identified, but detrital facies dominate. At the Holocene reef base, only basalt was recovered. The Holocene windward–leeward differences are a consequence of less accommodation space on the eastern island side that eventually led to a more complex reef architecture. As a result of higher rates of exposure and flushing, the reef framework on the windward island side is more abundant and experienced stronger cementation. In the Pleistocene, the environmental conditions on the leeward island side were presumably unfavourable for fringing reef growth.     

Single-crystal EPR study of three radiation-induced defects (Al–O2 3?, Ti3+ and W5+) in stishovite

Single-crystal electron paramagnetic resonance spectra of electron-irradiated stishovite, measured at temperatures from 3.5 to 294?K, reveal three S?=?1/2 radiation-induced defects: an aluminum-associated oxygen hole center and two nd ¹ centers (Ti³⁺ and W⁵⁺). The aluminum-associated oxygen hole center, characterized by an orthorhombic site symmetry, coaxial matrices of the electronic Zeeman g, nuclear hyperfine A(²⁷Al) and nuclear quadrupole P(²⁷Al), and the orientation of the g-minimum axis along an O–O direction and those of the unique A(²⁷Al) and P(²⁷Al) axes perpendicular to the O–O direction, is an Al–O₂ ^3? center, with the unpaired electron equally distributed on two equatorial oxygen atoms of a substitutional Al³⁺ ion at the octahedral Si site. Fully optimized Al-doped structure, theoretical ²⁷Al nuclear hyperfine and quadrupole coupling constants and directions, and 3D spin densities from periodic hybrid density functional theory calculations provide further support for this structural model. Spin Hamiltonian parameters of the Ti³⁺ and W⁵⁺ centers, which are confirmed by their diagnostic ⁴⁷Ti, ⁴⁹Ti and ¹⁸³W hyperfine structures, arise from electron trapping on substitutional Ti⁴⁺ and W⁶⁺ ions at the octahedral Si site.     

Design of sediment detention basins: Scaled model experiments and application

Sediment detention basins are implemented on mountain rivers to trap solid material that may aggravate the flooding of downstream settlements.However,retention structures built in the past may unnecessarily retain sediment during non-hazardous flood events,resulting in high maintenance costs and sediment deficit downstream.In addition,the so-called spontaneous self-flushing of previously retained sediment during floods has occasionally been observed.Recent research suggests to design sediment detention basins for controlling sediment passage with a guiding channel across the deposition area upstream of a hybrid barrier.Such barriers consist of a check dam with a slot orifice and an upstream bar screen with a bottom clearance in order to benefit from a combined mechanical-hydraulic retention control.The present paper enhances this pioneering research with the help of new experimental data,including a wide range of sediment mixtures and large wood,as well as variable barrier heights.Improved design criteria are provided regarding the bar screen and the basin storage capacity.The functionality of the enhanced concept for sediment detention is illustrated by a case study on a physical model:the protection of the Villard-Bonnot village(France)against torrential hazards.