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The transport mechanisms of floating marine debris in coastal zones remain poorly understood due to complex geometries and the influence of coastal processes, posing difficulties in incorporating them into Lagrangian numerical models. The numerical model LOCATE overcomes these challenges by coupling Eulerian hydrodynamic data at varying resolutions within nested grids using Parcels, a Lagrangian particle solver, to accurately simulate the motion of plastic particles where a high spatial coverage and resolution are required to resolve coastal processes. Nested grids performed better than a coarse-resolution grid when analysing the model's dispersion skill by comparing drifter data and simulated trajectories. A sensitivity analysis of different beaching conditions comparing spatiotemporal beaching patterns demonstrated notable differences in the land–water boundary detection between nested hydrodynamic grids and high-resolution shoreline data. The latter formed the basis for a beaching module that parameterised beaching by calculating the particle distance to the shore during the simulation. A realistic debris discharge scenario comparison around the Barcelona coastline using the distance-based beaching module in conjunction with nested grids or a coarse-resolution grid revealed very high levels of particle beaching (>91.5 %) in each case, demonstrating the importance of appropriately parameterising beaching at coastal scales. In this scenario, high variability in particle residence times and beaching patterns was observed between simulations. These differences derived from how each option resolved the shoreline, with particle residence times being much higher in areas of intricate shoreline configurations when using nested grids, thus resolving complex structures that were undetectable using the coarse-resolution grid. LOCATE can effectively integrate high-resolution hydrodynamic data within nested grids to model the dispersion and deposition patterns of particles at coastal scales using high-resolution shoreline data for shoreline detection uniformity. [ABSTRACT FROM AUTHOR]

The transport mechanisms of floating marine debris in coastal zones remain poorly understood, primarily due to the complex geometry and influence of coastal processes which pose difficulties in incorporating them into Lagrangian numerical models at coastal scales. The numerical model presented in this study addresses these challenges using nested grids of varying hydrodynamic resolutions (2.5 km, 350 m, and 70 m). The model couples Eulerian hydrodynamic data with a Lagrangian particle solver to accurately simulate the motion of plastic particles in coastal regions. A Lagrangian validation of the model was conducted using drifter data to assess the model’s skill and confidence in simulation predictions. The results demonstrated high skill and stability in 72-hour forecast horizons and high skill score values close to the shoreline. Additionally, a beaching sensitivity analysis was performed to determine particle beaching parameterisations suitable for coastal zones. This analysis demonstrated that the real-time distance of particles to the shore during simulations was the most accurate method for detecting the land-water boundary at coastal scales, accurately representing residence times and spatiotemporal beaching patterns. Simulations were conducted using nested grids and a single coarse grid, both using the same plastic input from river outflows in a pilot test at the Barcelona coastline with a complex morphology due to coastal structures, two major river mouths, and a large harbour. The simulations revealed marked differences in beaching amounts and residence times. Both simulations exhibited high levels of beaching, with the nested grid simulation registering 91.5 % beaching and the low-resolution grid simulation showing 95.8 % beaching, surpassing other studies conducted at larger scales. Beaching amounts exhibited high levels of variability within demarcated areas between simulations, with the highest flux observed near the Llobregat River mouth release point. The inner port area showed that particles have 18 times longer residence times when using high-resolution data, demonstrating the model’s ability to solve complex coastal geometrical structures. By using nested grids, the model can resolve coastal processes with high-resolution hydrodynamic data and accurately simulate potential accumulation zones and litter hot-spots at coastal scales. [ABSTRACT FROM AUTHOR]

Management of crops sensitive to iron deficiency chlorosis (IDC) includes the use of effective methods to predict the incidence of this nutritional disorder. The objective of this work was to validate the use of hydroxylamine-extractable Fe ([Fe.sub.ha]) for predicting the incidence of IDC in olive (Olea europaea L.), grapevine (Vitis berlandieri Planch x Vitis rupestris Scheele), chickpea (Cicer arietinum L.), and sunflower (Helianthus annuus L.) typical of the Mediterranean climate of Spain. This test was compared with the 'active lime' test and oxalate, citrate-ascorbate, and diethylenetriaminepentaacetic acid extractions. Overall, [Fe.sub.ha] provided the best estimates of leaf chlorophyll concentration, accounting for 26 to 66% of the variance (linear-plateau regression) depending on the particular crop. The optimum extractant/soil ratio for accurately predicting the chlorophyll content was 100 for olive and 20 for grapevine, chickpea, and sunflower. The concentration of Fe in the hydroxylamine extracts was found to be related to that of poorly crystalline Fe oxides in the soil, which testifies to the ability of this test to accurately predict the incidence of IDC. Proposed critical levels of [Fe.sub.ha] below which IDC is likely to occur were 60 mg [kg.sup.-1] for olive, 11 mg [kg.sup.-1] for grapevine, and 10 mg [kg.sup.-1] for chickpea and sunflower. Abbreviations: ACCE, 'active' calcium carbonate equivalent; CCE, calcium carbonate equivalent; DTPA diethylenetriaminepentaacetic acid; IDC, iron deficiency chlorosis; [Fe.sub.ca], citrate-ascorbate-extractable iron; [Fe.sub.ha], hydroxylamine-extractable iron; [Fe.sub.ox], oxalate-extractable iron.

Variations in tile low-field magnetic susceptibility of the wind-blown Chinese Loess Plateau (CLP) loess-paleosol sequences reflect changes ill the global paleoclimate on different time scales. Magnetic enhancement in paleosols has been ascribed to the neoformation of finegrained maghemite; however, little is known about the pathway through which this mineral was formed in the CLP paleosols, its relationships with the other pedogenic Fe oxides (viz. hematite and goethite), and the pedoclimatic significance of such relationships. In this work, we characterized various magnetic, chemical, and mineralogical properties of the loess-paleosol units at depths from about 23 to 55 m in the Upper Luochuan section, central CLP. The concentration of pedogenic hematite ([DELTA]Hm) and the frequency-dependent magnetic susceptibility ([X.sub.FC])), which is used as a proxy for the concentration of fine-grained pedogenic maghemite, were found to be linearly correlated ([R.sup.2] = 0.825, P < 0.001). This supports the idea that these two minerals were formed concomitantly during pedogenesis, which is consistent with the results of previous in vitro experiments showing that the ferrihydrite [right arrow] maghemite [right arrow] hematite transformation takes place under aerobic conditions. By contrast, the concentration of pedogenic goethite ([DELTA]Gt) was only weakly correlated with either [X.sub.FD] or [DELTA]Hm, which suggests that goethite formed through an alternative pathway. The paleosols above 40 m (S4, S5, corresponding to marine isotope stages 9 and 11, respectively) exhibit a higher degree of weathering and higher [DELTA]Hm/([DELTA]Hm + [DELTA]Gt) ratio than those below such a depth (S6-S8). This was ascribed to differences in paleoclimatic conditions, which are moister and warmer in the former paleosols than in the latter, rather than to differences in pedogenesis duration. Abbreviations: CLP, Chinese Loess Plateau; [Fe.sub.d], citrate bicarbonate-dithionite-extractable iron; [Fe.sub.t], total iron; GSD, grain size distribution; Gt and Hm, goethite and hematite concentrations, respectively; PSD, pseudo-single domain; SD, single domain; SP, superparamagnetic; [DELTA]Gt and [DELTA]Hm, pedogenic goethite and hematite concentration, respectively; [X.sub.ARM] anhysteretic remanent magnetization susceptibility; [X.sub.FD], frequency-dependent mass magnetic susceptibility; [X.sub.HF], high-frequency magnetic susceptibility; [X.sub.LF] low-frequency magnetic susceptibility.

The spillage of sphalerite-containing pyrite sludge in April 1998 contaminated 45 [km.sup.2] of Xerofluvents, Haploxerepts, and Calcixerepts in the Guadiamar valley, an area with a Mediterranean climate in southwestern Spain. The strung impact of sulfide oxidation on soil quality and phytotoxicity risks made it compulsory to investigate the products and rate of weathering of pyrite and sphalerite remaining in the soils alter most of the sludge was mechanically removed and lime plowed in the autumn of 1998. To this end, 31 soil samples were collected in November 2000 and 32 in June 2001 (i.e., two and three rainy seasons, respectively, after the spillage). Based on concentrations of various extractable forms of S, Fe, and Zn, the soils contained up to 109 and 3.5 g [kg.sup.-1] of residual pyrite and sphalerite, respectively, immediately alter remediation. About 51 and 69% of this pyrite had weathered by November 2000 and June 2001, respectively, the higher degree of weathering on the latter dale being associated with an increased proportion of the resulting Fe oxides in poorly crystalline forms. Sphalerite had weathered roughly to the same degree as pyrite and a significant proportion of Zn released was occluded in Fe oxides. There was thus no evidence for preferential sphalerite weathering through galvanic effects as observed in other pyrite--sphalerite mixtures. An in vitro experiment with aerated soil--water suspensions revealed limited oxidative weathering of the pyrite and sphalerite in the samples, probably because only the coarse less reactive particles remained after the sludge weathered in the field.

The hydrothermal transformation of 2-line ferrihydrite into hematite proceeds slowly if a sufficient quantity of some strongly adsorbing ligand, such as phosphate or citrate, is sorbed on the starting product. In this work, we studied such transformation at temperatures ranging from 125 to 200[degrees]C, a molar P/Fe ratio of 0-6%, and a molar citrate/Fe ratio of 3%. The products were characterized by X-ray diffraction (XRD), infrared spectroscopy, Mossbauer spectroscopy (MS) at various temperatures and in an applied field of 60 kOe, magnetic and thermal analysis, and transmission electron microscopy (TEM). At 150[degrees]C, pure 2-line ferrihydrite transformed rapidly into hematite. The products of transformation of 2-line ferrihydrite with P/Fe = 2.75% or citrate/Fe = 3% had a magnetic susceptibility of >240 X [10.sup.-6] [m.sup.3]/kg and were, according to XRD and MS data, mixtures of hematite with structural P, 6-line ferrihydrite, and a magnetic phase. This phase exhibited most of the characteristic reflections and MS features of maghemite, and occurred as 7-30 nm subrounded particles with lattice fringes corresponding to the maghemite (310) and (220) planes. It was designated 'hydromaghemite' because it lost >3% water between 110 and ~350[degrees]C. At 150[degrees]C, complete transformation into hematite occurred in < 120 days.

Differences in crystallinity may explain why total Fe (hydr)oxide content has a variable effect on aggregate stability. Therefore, surface soil samples with a range of poorly crystalline Fe (hydr)oxide contents were characterized for water-stable aggregates >0.25 mm (WSA), mean-weighted diameter (MWD), soil organic C (OC), particle-size distribution, pH, exchangeable cations, citrate/bicarbonate/dithionite (subscript d), and acid ammonium oxalate (subscript o) extractable Fe, Al, and Si. The WSA and MWD range from 23 to 95%, and 0.3 to 5.1 mm, respectively. The effects of [Fe.sub.o] (1.1-6.8 g [kg.sup.-1), [Fe.sub.d] (3.2-19.6 g [kg.sup.-1]), OC (2.4-24.0 g [kg.sup.-1]) and clay (141-467 g [kg.sup.-1]) contents on WSA and MWD of both A and B horizons of these soils was studied using linear regression. The poorly crystalline Fe (hydr)oxide ([Fe.sub.o]) and OC contents are significantly correlated with WSA in the A horizons ([r.sup.2] = 0.95, n = 6, p = 0.001, and [r.sup.2] = 0.93, n = 6, p = 0.002, respectively) and in the B horizons ([r.sup.2] = 0.73, n = 6, p = 0.029, and [r.sup.2] = 0.76, n = 6, p = 0.024, respectively). When regressed against MWD, [Fe.sub.o] has an [r.sup.2] of 0.89 (n = 6, p = 0.004) in the A, and 0.97 (n = 6, p = 0.000) in the B horizons. The coefficient of determination of MWD vs. OC contents is 0.98 (n = 6, p = 0.000) in the A and 0.79 (n = 6, p = 0.018) in the B horizons. Clay and Fed contents are not significantly correlated to WSA or MWD. Apparently, the [Fe.sub.o] component (poorly crystalline) is more effective than Fed at stabilizing soil aggregates, even though it is present in lower concentrations. The [Fe.sub.o] component appears more important than OC in terms of WSA and MWD for soils with relatively low soil organic matter contents.

We used X-ray diffraction (XRD), scanning force microscopy (SFM), transmission electron microscopy (TEM), and color to investigate the effect of phosphate on the crystallization rate, nature, and morphology of iron oxides prepared from ferrihydrite in the laboratory. Synthesis was performed at two temperatures (323 and 373 K) and two pH values (9 and 12) from ferric nitrate, for P/Fe atomic ratios ranging from 0 to 2.5%. The presence of phosphate retarded crystallization, tended to favor hematite over goethite, and markedly influenced the morphology of the goethite crystals formed at high pH. Application of SFM in the deflection mode was useful to investigate the morphology of the small goethite crystals, with careful attention paid to operating conditions; in particular, sharp silicon probes were found to produce fewer artifacts than coarser silicon nitride ones. At low P/Fe ratios (1.5%), star-shaped, twinned crystals were produced. All the theoretical shapes, derived from the assumption that star-shaped crystals result from the epitaxial growth of goethite on a hematite core, were observed by SFM and TEM. The presence of such hematite nuclei was supported by XRD, selected-area electron diffraction, color, and preferential dissolution of the samples in HCl, because it is known that hematite dissolves faster than goethite in acid. With increasing P/Fe ratio, the arms of the star-shaped crystals became shorter. This was likely due to the higher density of P-adsorbing pairs of singly coodinated OH groups on terminal {021} faces relative to prismatic {110} arm faces.

Phosphorus desorption from fertilized soils is significant for agriculture and the environment. This study was aimed at characterizing the forms in which P occurs in calcareous and limed acid soils and their influence on P desorption patterns. The P forms of two limed acid and three calcareous soils of Europe were characterized by chemical extraction, isotopic exchange, and sequential fractionation. Phosphate Desorption was studied using resins and goethite as ion sinks. Total P ranged from 705 to 1400 mg [kg.sup.-1]. Isotopic exchange revealed more surface-adsorbed P in the limed acid than in the calcareous soils. Calcium phosphates predominated in the calcareous and Al and Fe phosphates in the limed acid soils; one limed acid soil contained significant amounts of Ca phosphates. The mixed cation and anion exchange resins (ACER) were more effective in desorbing P than the anion exchange resin (AER) and goethite. The desorption curves indicated significant differences in the degree of homogeneity of the P desorption reactions, the greatest and lowest degree of homogeneity corresponding with calcareous soils. The proportion of ACER-extractable P that was plant-available P was [is greater than] 50% for the limed acid and [is less than] 20% for the calcareous soils. The proportion of ACER-extractable P that was released to 0.002 M Ca[Cl.sub.2] was [is greater than] 60% for the limed acid and [is less than] 40% for the calcareous soils. Plant P availability was thus poorer in the calcareous soils than in the limed acid soils.

The soil phosphorus (P) test in Portugal is based on extraction with ammonium lactate (AL) at acidic pH. Because this test is rarely used in other countries, it is desirable to see whether the AL-P values correlate with the more commonly used P tests. In this work, we compared AL-P with bicarbonate-extractable P (Olsen's method) for a group of 48 samples from Portuguese acidic soils differing widely in P status. Despite their contrasting composition, both reagents extracted phosphate from the same sources, albeit in different proportions. Both Olsen P and AL-P were strongly correlated with resin-extractable and dilute electrolyte-desorbable P, which are respectively related to the soil contents in phytoavailable P and P that can be released to runoff or drainage water. Olsen P and AL-P were strongly correlated (R2 = 0.870), the correlation became stronger when three overfertilized soils were excluded (Olsen P = 2.35 + 0.45 AL-P; R2 = 0.908; P ≤ 0.001, n = 45). No correlation was observed for a group of soils recently fertilized with Gafsa phosphate probably because the acidic AL reagent dissolved residual calcium phosphate, thus overestimating the soil content in desorbable P. On the basis of the present results and the AL-P-based fertility classes used for fertilizer recommendation purposes, Olsen P-based fertility classes were tentatively proposed for Portuguese acidic soils. [ABSTRACT FROM AUTHOR]