Evidence for organic complexation of iron in seawater   总被引：1，自引：0，他引：1  

Constant M. G. van den Berg 《Marine Chemistry》1995,50(1-4)

Iron occurs at very low concentrations in seawater of oceanic origin and its low abundance is thought to limit primary production in offshore waters (Martin and Fitzwater, 1988). A new electrochemical method, cathodic stripping voltammetry (CSV), is used here to determine the speciation of iron in seawater originating from the Western Mediterranean taking advantage of ligand competition of an added electroactive ligand with the natural organic complexing matter to evaluate whether iron is organically complexed. The measurements indicate that iron occurs 99% (or 99.9% depending on which value is selected for α_Fe′) complexed by organic complexing ligands throughout the water column of the Western Mediterranean and by analogy probably also in other oceanic waters. The composition of the organic complexing ligands is as yet unknown, but the data indicate a major source from microorganisms (bacteria or phytoplankton) in and immediately below the fluorescence maximum in the upper water column. The organic complexes are apparently reversible releasing iron when the competing ligand is added and binding more iron when its concentration is increased. The organic complexing ligands occur at concentrations well above those of iron ensuring full complexation of this biologically essential element, and buffer the free iron concentration at a very low level against fluctuations as a result of removal by primary producers or inputs from atmospheric sources. The new data indicate that a re-evaluation of the concept of the bioavailable fraction of iron is required.  相似文献   

Experiments on the resuspension of estuarine sediments containing benthic diatoms     

V. N. de Jonge  J. van den Bergs 《Estuarine, Coastal and Shelf Science》1987,24(6)

A laboratory system was used to test the effect of water flow on the resuspension of mud and sand sediments and, specifically, benthic diatoms from the Ems estuary, The Netherlands. Current velocities generated by two rotating cylinders in a cylindrical tank were determined by a small float and a laser Doppler velocimeter. At low angular velocities, the amount of suspended matter increased linearly with angular velocity and the float current velocity. However, at higher angular velocities, the increase in current velocity was less because of the strong turbulence: concomitantly, the current velocity boundary layer (δ) became thinner and the suspended matter concentration increased rapidly. The dominant diatom species from the sandy sediment were suspended in two distinct groups, one of which consisted of the species Navicula aequorea, Navicula salinicola, Ophephora martyi and Opephora pacifica, and was more exclusively bound to sand grains than the other. The benthic diatom species inhabiting the silty sediment did not show this difference. The most important shortcoming in the experiments was the inability to determine the radial and vertical velocity components. This precluded reliable calculations of the shear stress. The data presented emphasize the importance of finding a method to determine the shear stress under experiments and field conditions so that direct comparisons can be made. Despite this it is assumed that, just as under the experimental conditions discussed, under natural conditions in shallow waters resuspension starts at current velocities as low as ca. 10 cm s⁻¹.  相似文献   

Getting your money's worth: Testing the value of data for hydrological model calibration     

Jan Seibert  Franziska M. Clerc-Schwarzenbach  H. J. van Meerveld 《水文研究》2024,38(2):e15094

Despite the big data era, observational data continue to be a limiting factor in the environmental sciences. To collect the most informative field data, studies on the value of data are essential. This article describes a model-based approach to assess the value of data. While we discuss the approach for hydrological model calibration, the approach is applicable across the environmental sciences. The overall goal is to provide guidance on optimal data collection strategies, that is, what to measure, where, and when.  相似文献   

Model calibration using hydropedological insights to improve the simulation of internal hydrological processes using SWAT+     

Edward Smit  George van Zijl  Edward Riddell  Johan van Tol 《水文研究》2024,38(5):e15158

Soils affect the distribution of hydrological processes by partitioning precipitation into different components of the water balance. Therefore, understanding soil-water dynamics at a catchment scale remains imperative to future water resource management. In this study, the value of hydropedological insights was examined to calibrate a processes-based model. Soil morphology was used as soft data to assist in the calibration of the Soil Water Assessment Tool (SWAT+) model at five different catchment scales (48, 56, 174, 674, and 2421 km²) in the Sabie River catchment, South Africa. The aim of this study was to calibrate the SWAT+ model to accurately simulate long-term monthly streamflow predictions as well as to reflect internal soil hydrological processes using a procedure focusing on hydropedology as a calibration tool in a multigauge system. Results indicated that calibration improved streamflow predictions where R² improved by 2%–8%. Nash-Sutcliffe Efficiency (NSE) improved from negative correlations to values exceeding 0.5 at four of the five catchment scales compared to the uncalibrated model. Results confirm that soil mapping units can be calibrated individually within SWAT+ to improve the representation of hydrological processes. Particularly, the spatial linkage between hydropedology and hydrological processes, which is captured within the soil map of the catchment, can be adequately reflected within the model simulations after calibration. This research will lead to an improved understanding of hydropedology as soft data to improve hydrological modelling accuracy.  相似文献   

Disaggregating and mapping crop statistics using hypertemporal remote sensing     

M.R. Khan  C.A.J.M. de Bie  H. van Keulen  E.M.A. Smaling  R. Real 《International Journal of Applied Earth Observation and Geoinformation》2010

Governments compile their agricultural statistics in tabular form by administrative area, which gives no clue to the exact locations where specific crops are actually grown. Such data are poorly suited for early warning and assessment of crop production. 10-Daily satellite image time series of Andalucia, Spain, acquired since 1998 by the SPOT Vegetation Instrument in combination with reported crop area statistics were used to produce the required crop maps. Firstly, the 10-daily (1998–2006) 1-km resolution SPOT-Vegetation NDVI-images were used to stratify the study area in 45 map units through an iterative unsupervised classification process. Each unit represents an NDVI-profile showing changes in vegetation greenness over time which is assumed to relate to the types of land cover and land use present. Secondly, the areas of NDVI-units and the reported cropped areas by municipality were used to disaggregate the crop statistics. Adjusted R-squares were 98.8% for rainfed wheat, 97.5% for rainfed sunflower, and 76.5% for barley. Relating statistical data on areas cropped by municipality with the NDVI-based unit map showed that the selected crops were significantly related to specific NDVI-based map units. Other NDVI-profiles did not relate to the studied crops and represented other types of land use or land cover. The results were validated by using primary field data. These data were collected by the Spanish government from 2001 to 2005 through grid sampling within agricultural areas; each grid (block) contains three 700 m × 700 m segments. The validation showed 68%, 31% and 23% variability explained (adjusted R-squares) between the three produced maps and the thousands of segment data. Mainly variability within the delineated NDVI-units caused relatively low values; the units are internally heterogeneous. Variability between units is properly captured. The maps must accordingly be considered “small scale maps”. These maps can be used to monitor crop performance of specific cropped areas because of using hypertemporal images. Early warning thus becomes more location and crop specific because of using hypertemporal remote sensing.  相似文献   

Organotin accumulation in an estuarine food chain: comparing field measurements with model estimations     

Veltman K  Huijbregts MA  van den Heuvel-Greve MJ  Vethaak AD  Hendriks AJ 《Marine environmental research》2006,61(5):511-530

The bioaccumulation model OMEGA (optimal modelling for ecotoxicological applications) is used to explore accumulation of organotins in the Western Scheldt food chain, consisting of herbi-detritivores, primary and secondary carnivorous fish and a piscivorous bird. Organotins studied are tributyltin (TBT) and triphenyltin (TPT) and the respective di- and mono-organotin metabolites. Empirical elimination rate constants are compared to model predictions for organic substances and metals. It is found that field bioaccumulation ratios are higher than predicted based on elimination kinetics relevant for organic compounds. The results indicate that uptake of organotins mainly occurs via hydrophobic mechanisms, whereas elimination may occur via metal-like kinetics. This results in very low elimination rates, which are comparable to model predictions for metals.  相似文献   

Infall and SiO emission in V838 Mon     

M. T. Rushton  T. R. Geballe  A. Evans  B. Smalley  J. Th. van Loon  S. P. S. Eyres 《Monthly notices of the Royal Astronomical Society》2005,359(2):624-628

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Magnetic hydrogen atmosphere models and the neutron star RX J1856.5–3754     

Wynn C. G. Ho †  David L. Kaplan ‡  Philip Chang  Matthew van Adelsberg  Alexander Y. Potekhin 《Monthly notices of the Royal Astronomical Society》2007,375(3):821-830

RX J1856.5−3754 is one of the brightest nearby isolated neutron stars (INSs), and considerable observational resources have been devoted to it. However, current models are unable to satisfactorily explain the data. We show that our latest models of a thin, magnetic, partially ionized hydrogen atmosphere on top of a condensed surface can fit the entire spectrum, from X-rays to optical, of RX J1856.5−3754, within the uncertainties. In our simplest model, the best-fitting parameters are an interstellar column density   N _H≈ 1 × 10²⁰ cm⁻²  and an emitting area with   R ^∞≈ 17 km  (assuming a distance to RX J1856.5−3754 of 140 pc), temperature   T ^∞≈ 4.3 × 10⁵ K  , gravitational redshift   z _g ∼ 0.22  , atmospheric hydrogen column   y _H≈ 1 g cm⁻²  , and magnetic field   B ≈ (3–4) × 10¹² G  ; the values for the temperature and magnetic field indicate an effective average over the surface. We also calculate a more realistic model, which accounts for magnetic field and temperature variations over the NS surface as well as general relativistic effects, to determine pulsations; we find that there exist viewing geometries that produce pulsations near the currently observed limits. The origin of the thin atmospheres required to fit the data is an important question, and we briefly discuss mechanisms for producing these atmospheres. Our model thus represents the most self-consistent picture to date for explaining all the observations of RX J1856.5−3754.  相似文献   

Spectral evolution of V838 Monocerotis in the optical and near-infrared in early 2002     

M. T. Rushton  T. R. Geballe  A. V. Filippenko  R. Chornock  W. Li  D. C. Leonard †  R. J. Foley  A. Evans  B. Smalley  J. Th. van Loon  S. P. S. Eyres 《Monthly notices of the Royal Astronomical Society》2005,360(4):1281-1289

We report optical and near-infrared spectroscopy, and optical spectropolarimetry, of the peculiar variable V838 Mon during the multiple outburst phase in early 2002. The spectral evolution is exceptional. Our earliest spectra (2002 January) are noteworthy for their strong absorption lines of barium and strontium in the optical, and bands of CO and circumstellar H₂O in the near-infrared. All but the CO weaken or are absent in later spectra. The behaviour of the CO band during this phase is extraordinary: initially in absorption, it was observed two months later in optically thick emission. The excitation of the CO is probably the result of the propagation of a shock wave at the third maximum. The two spectropolarimetric epochs were taken 6 and 27 d after the second outburst on 2002 February 8. The polarization at both times was measured to be   p_V ≈ 2.7  per cent. Nearly all of the measured polarization is believed to be due to interstellar dust, a conclusion that is consistent with previous studies. At both epochs, however, a weak and variable intrinsic component is thought to be present. Between January and March of 2002 the luminosity of V838 Mon increased by a factor of 15 and the apparent diameter increased fourfold.  相似文献   

Delaunay Tessellation Field Estimator analysis of the PSCz local Universe: density field and cosmic flow     

Emilio Romano-Díaz  Rien van de Weygaert 《Monthly notices of the Royal Astronomical Society》2007,382(1):2-28

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