Net Transport Rate Research Articles

Observations of near-bed orbital velocities and small-scale bedforms on the Dutch lower shoreface

The lower shoreface, with water depths between about 8 and 20 m, forms the transition between the inner shelf and upper shoreface. Knowledge of the lower shoreface is essential, as it is – in many cases – the sediment source for the upper shoreface and beach. This paper presents new data of near-bed orbital velocities and small-scale bedforms at various depths and locations on the Dutch lower shoreface. Near-bed orbital velocities were beyond 1 m/s during high-energetic wave conditions. They increase with wave height and decrease with water depth, and can be reasonably well described by linear wave theory. Ripple heights range between 0.01−0.03 m and ripple lengths between 0.08−0.20 m. Ripple dimensions are controlled by wave mobility, with lower and shorter ripples for higher waves, and not so much by the currents. The Van Rijn (2007) formula generally overpredicts the ripple heights, and the variation with tidal currents in time. The measurements clearly indicate significant sediment mobility at the lower shoreface under higher wave events. It is yet unclear what this means for the net sand transport. This will depend on the subtle timing of sediment suspension, wave-mean currents and near-bed orbital velocities. It requires detailed modeling to determine lower shoreface net transport rates, and to unravel the controlling sand transport mechanisms.

Modelling of annual sand transports at the Dutch lower shoreface

Dutch coastal policy aims for a safe, economically strong and attractive coast. This is achieved by maintaining the part of the coast that support these functions; the coastal foundation. The coastal foundation is maintained by means of sand nourishments. Up to now, it has been assumed that net transports across the coastal foundation’s offshore boundary at the 20 m depth contour are negligibly small. In the framework of the Coastal Genesis 2.0 program we investigated sand transports across this boundary and across other depth contours at the lower shoreface.This paper presents a computationally efficient approach to compute the annual sand transport rates at the Dutch lower shoreface. It is based on the 3D Dutch Continental Shelf Model with Flexible Mesh (3D DCSM-FM), a wave transformation tool and a 1DV sand transport module. We validate the hydrodynamic input against field measurements and present flow, wave and sand transport computations for the years 2013–2017.Our computations show that the net annual sand transport rates along the Dutch coast are determined by peak tidal velocities (and asymmetry thereof), density driven residual flows, wind driven residual flows and waves.The annual mean alongshore transports vary along the continuous 20 m depth contour. The computed total cross-shore transports are onshore directed over the continuous 20 m, 18 m and 16 m depth contours and increase with decreasing water depth.The effect of density difference and wind on the 3D structure of the flow and on the sand transports cannot be neglected along the Dutch lower shoreface. Our computations show that excluding the effect of density results in a significant decrease of the onshore directed transports. Also switching off wind largely counteracts this effect.The net cross-shore transport is determined by a delicate balance between gross onshore and offshore transports, where wave conditions are important. We show an example for Scheveningen where the net cross-shore transport is onshore directed when including all wave conditions but would be offshore directed when excluding waves higher than 3.5 m. In contrast, at Callantsoog the highest waves contribute more to the offshore directed transports. These results suggest that storm conditions play an important role in the magnitude and direction of the net annual transport rates at the lower shoreface.

Effect of surface wave skewness on near-bed sediment transport velocity

The paper presents a two-dimensional model, based on the Lagrangian description of sand grain dynamics, for the estimation of mean velocities of sediment particles driven by the oscillatory motion of water generated by non-linear gravitational surface waves of the Stokes type. The model was verified against experimental results obtained in a wave flume, by comparing its predictions with the sediment velocities measured by applying a PIV (particle image velocimetry) technique. The model was used to calculate near-bed sediment transport velocities generated by surface waves of the parameters encountered in real sea conditions, with the purpose to investigate the effect of the wave velocity skewness on the near-bed sediment net transport rates. The results of numerical simulations, carried out for a range of wave parameters and sand grain sizes, showed that normalized sediment transport velocities vary approximately linearly with an index defining the wave skewness, and are practically independent of sediment grain diameters. Based on the laboratory measurements, also approximate formulae relating a bed ripple asymmetry index with the surface wave skewness index were derived.

A Numerical Study of Sheet Flow Driven by Skewed-Asymmetric Shoaling Waves Using SedWaveFoam

SedWaveFoam, an OpenFOAM-based two-phase model that concurrently resolves the free surface wave field, and the bottom boundary layer is used to investigate sediment transport throughout the entire water column. The numerical model was validated with large-scale wave flume data for sheet flow driven by shoaling skewed-asymmetric waves with two different grain sizes. Newly obtained model results were combined with previous nonbreaking and near-breaking wave cases to develop parameterization methods for time-dependent bed shear stress and sediment transport rate under various sediment sizes and wave conditions. Gonzalez-Rodriguez and Madsen (GRM07) and quasi-steady approaches were compared for intra-wave bed shear stress. The results show that in strongly asymmetric flows, considering the separated boundary layer development processes at each half wave-cycle (i.e., GRM07) is essential to accurately estimating bed shear stress and highlights the impact of phase-lag effects on sediment transport rates. The quasi-steady approach underpredicts (∼60%) sediment transport rates, especially for fine grains under large velocity asymmetry. A modified phase-lag parameter, incorporating velocity asymmetry, sediment stirring, and settling processes is proposed to extend the Meyer-Peter and Mueller type power law formula. The extended formula accurately estimated the enhanced net onshore sediment transport rate observed under skewed-asymmetric wave conditions.

Silicon fertilization increases gas-exchange and biomass by silicophytolith deposition in the leaves of contrasting drought-tolerant sugarcane cultivars under well-watered conditions

PurposeSilicon (Si) fertilization provides benefits to sugarcane. However, information remain scarce about the relationship between Si fertilization, gas exchange responses, biomass and silicophytolith accumulation in contrasting drought tolerant sugarcane cultivars under well-watered conditionsMethodsSugarcane cultivars (drought-tolerant and drought-sensitive) were grown in pots containing soil with low available Si and were treated (at rates equivalent to 0, 250, 500, 750, and 1000 kg ha−1 Si) with Si as silicate. The silicophytolith contents, morphotype descriptions, Si concentrations and gas exchange were evaluated in the top visible dewlap leaves. Stalk length and stalk biomass were also evaluated.ResultsThe silicophytolith, Si contents, net CO2 assimilation rate (A), plant transpiration (E), stomatal conductance (gs) and electron transport rate (ETR) of leaves and fresh biomass and length of stalks increased linearly as functions of the Si application rate, independent of cultivar. RB86-7515 showed the highest stalk length, fresh stalk and green leaf biomass, relative water content, and water potential, while RB85-5536 showed superior values for A, E, gs, and ETR.ConclusionsSi fertilization improved photosynthesis, transpiration, stalk length, and stalk biomass production in sugarcane. The highest silicophytolith content was reflected in a diversity of silicified cells, which may favor a higher photosynthesis and biomass. The increase of silicification in stomata complexes and trichomes with Si may be associated to a higher Si availability and transpiration. Contrasting drought-tolerant cultivars showed similar silicification and gas exchange responses with Si. Considering these benefits, Si should be included in the fertilization program of sugarcane.

Interactive Effects of Nitrogen and Sulfur Nutrition on Growth, Development, and Physiology of Brassica carinata A. Braun and Brassica napus L.

Brassica carinata (carinata) has emerged as a potential biofuel source due to its high erucic acid content, making it desirable for various industrial applications. Nitrogen (N) and sulfur (S) are required as primary sources of nutrition for growth and development in different oilseed crops and their utilization is interdependent. The purpose of the study was to analyze the interactive effect of N and S nutrition on the growth and other physiological activities of carinata and B. napus (napus). Four treatments, i.e., optimum NS (+N+S, 100% N and 100% S); N limited (−N+S, 0% N, 100% S); S limited (+N−S, 100% N, 0% S), and NS limited (−N−S, 0% N and 0% S) of N and S in full-strength Hoagland solution were imposed in the current study. Effect of different NS treatments was observed on vegetative traits such as number of primary and secondary branches, total leaf area, total biomass production and allocation, and physiological traits such as production of photosynthetic pigments, net photosynthesis, electron transport, and other aspects for both carinata and napus. The traits of stem elongation, number of nodes, node addition rate, internode length, number of primary and secondary branches were 60%, 36%, 50%, 35%, 56%, and 83% lower, respectively, in napus in comparison to carinata. Different NS treatments also positively influenced the production of photosynthetic pigments such as chlorophyll (Chl) a and b and carotenoids in carinata and napus. The concentration of Chla was 11% higher in napus in comparison to carinata. The rate of net photosynthesis, electron transport, and fluorescence was 12%, 8%, and 5% higher based on overall value, respectively, in napus compared to carinata. On the other hand, the overall value for stomatal conductance decreased by 5% in napus when compared to carinata. Different growth-related traits such as vegetative (plant height, node number, internode length, leaf area, number of primary and secondary branches), reproductive (pod number, pod length, seeds per pod), and photosynthetic capacity in oilseed brassicas are correlated with the final seed and oil yield and chemical composition which are of economic importance for the adoption of the crop. Thus, the analysis of these traits will help to determine the effect of NS interaction on crop productivity of carinata and napus.

Effect of wave climate change on longshore sediment transport in Southwestern Black Sea

As a result of long-term changes of the wave climate, changes in spatial and temporal scales occur in coastal regions and cause coastal morphology to change. This study investigates the effect of changes in wave climate (wave height, wave period, wave direction) on longshore sediment transport (LST) at Karasu coast, located on the southwestern coast of the Black Sea. European Center for Medium-Range Weather Forecasts (ECMWF) ERA-Interim wind data covering the period of 1979–2018 was used to obtain the wave climate of the Southwestern Black Sea coasts and to understand the dynamics of LST throughout the region. Net and gross sediment transport rates were calculated according to three different empirical and one numerical methods by using hourly significant wave heights, peak wave periods and incident wave angles. According to the 40-year wave climate data in the region, the average annual significant wave height is 0.92 m, the peak wave period is 5.53 s and the angle of wave incidence is between N-NNE sector. Waves are composed of two components; swell waves and wind waves and as a result of the study, it has been observed that swell waves have an order of magnitude larger contribution to the LST along the coast than wind waves for the respective research area, by an average factor of 12 and 17 for the net and gross LST rate, respectively. At the end of the 40-year period between 1979 and 2018, according to three different empirical and one numerical LST methods, the average net LST rate along the Karasu coast was 65,000 ± 5,000 m3/year, while the gross LST rate was 190,000 ± 20,000 m3/year. When the change of gross LST during the study period was examined, it was observed that an average decrease of 5.6% occurred. This reduction in the LST rate was observed to be associated with a 4.1% decrease in the height of the swell waves at the end of 40 years.

The role of NHE3 (Slc9a3) in oxalate and sodium transport by mouse intestine and regulation by cAMP.

Intestinal oxalate transport involves Cl−/HCO3 − exchangers but how this transport is regulated is not currently known. NHE3 (Slc9a3), an apical Na+/H+ exchanger, is an established target for regulation of electroneutral NaCl absorption working in concert with Cl−/HCO3 − exchangers. To test whether NHE3 could be involved in regulation of intestinal oxalate transport and renal oxalate handling we compared urinary oxalate excretion rates and intestinal transepithelial fluxes of 14C‐oxalate and 22Na+ between NHE3 KO and wild‐type (WT) mice. NHE3 KO kidneys had lower creatinine clearance suggesting reduced GFR, but urinary oxalate excretion rates (µmol/24 h) were similar compared to the WT but doubled when expressed as a ratio of creatinine. Intestinal transepithelial fluxes of 14C‐oxalate and 22Na+ were measured in the distal ileum, cecum, and distal colon. The absence of NHE3 did not affect basal net transport rates of oxalate or sodium across any intestinal section examined. Stimulation of intracellular cAMP with forskolin (FSK) and 3‐isobutyl‐1‐methylxanthine (IBMX) led to an increase in net oxalate secretion in the WT distal ileum and cecum and inhibition of sodium absorption in the cecum and distal colon. In NHE3 KO cecum, cAMP stimulation of oxalate secretion was impaired suggesting the possibility of a role for NHE3 in this process. Although, there is little evidence for a role of NHE3 in basal intestinal oxalate fluxes, NHE3 may be important for cAMP stimulation of oxalate in the cecum and for renal handling of oxalate.

Experimental Measurement of the Time-Based Development of Oil Film Thickness, Lubricating Film Extent and Lubricant Transport in Crosshead Engines

This paper describes the design of a test apparatus which simulates the lubrication of large, slow, two-stroke marine engines in which the ring pack is lubricated by means of injectors supplying lubricant above the piston. The equipment is able to control lubricant injection parameters (volume, frequency, etc.) and employs capacitance based lubricant film thickness transducers to allow instantaneous oil film thickness and film extent around the compression ring to be investigated on a stroke-by-stroke basis. It is demonstrated that the equipment can be used to study the development of lubricating films on successive strokes under differing injection strategies. Time varying changes in lubricating film thickness and film extent have been measured and the rate at which the lubricant spreads across the cylinder wall has also been investigated. It has been observed that increases in oil-film thickness are strongly linked to the transition from starved to fully-flooded inlet conditions and that net lubricant transport rates along different parts of the cylinder can be evaluated from measured data.

SIMULATION OF LONG-TERM SHORELINE CHANGE DRIVEN BY LONGSHORE AND CROSS-SHORE SEDIMENT TRANSPORT

Driven by wave and current, sediment transport alongshore and cross-shore induces shoreline changes in coasts. Estimated by breaking wave energy flux, longshore sediment transport in littoral zone has been studied for decades. Cross-shore sediment transport can be significant in a gentle-slope beach and a barred coast due to bar migration. Short-term beach profile evolution (typically for a few days or weeks) has been successfully simulated by reconstructing nonlinear wave shape in nearshore zone (e.g. Hsu et al 2006, Fernandez-Mora et al. 2015). However, it is still lack of knowledge on the relationship between cross-shore sediment transport and long-term shoreline evolution. Based on the methodology of beach profile evolution modeling, a semi-empirical closure model is developed for estimating phase-average net cross-shore sediment transport rate induced by waves, currents, and gravity. This model has been implemented into GenCade, the USACE shoreline evolution model.

Seasonal variation in longshore sediment transport rate and its impact on sediment budget along the wave-dominated Karnataka coast, India

The Karnataka coast is subjected to high wave activity during the southwest monsoon when most of the sandy beaches undergo erosion. Based on the littoral cell concept, the Karnataka coast is broadly divided into 14 major littoral cells and 26 stations are selected in the present study. WaveWatch III global wave model data at 0.5° interval were used to derive the nearshore wave characteristics from XBeach numerical model. The model results were validated with the measured wave rider buoy data of the Indian National Centre for Ocean Information Services. The beach orientation, nearshore slope, median sediment size, significant wave height, mean wave direction, and the peak wave period were used in the estimation of longshore sediment transport rate. The mean significant wave height along the Karnataka coast was about 0.86 m, wave direction was about 210° and peak wave period was about 13 sec. The wave height during southwest monsoon (June–September) was higher, post-monsoon (October–December) was moderate and pre-monsoon (January–May) was the calmest period. Direction of longshore sediment transport was southwards during pre- and post-monsoons when waves were from the south–southwest. Whereas, northwards during monsoon when the wave approach from west–southwest to west. The annual net longshore sediment transport rate estimated was about 0.65×106 m3 towards the south and the sediment budget investigation depicts the loss of 0.067×106 m3 during the study period.

Armoring and exposure effects on the wave-driven sediment transport

Coastal sediment transport of graded spherical particles with the material properties of sand was simulated and compared to transport of the uniform-sized spherical particles using a two-phase Eulerian-Lagrangian model. The fluid phase solver was based on SedFoam developed in OpenFOAM and the open-source discrete element method solver LIGGGHTS was used for the particle phase. We validated the model for sheet flow of well-sorted medium sand (d50 = 0.28 mm) and mixed sand with bimodal size distribution in velocity-skewed oscillatory flows as well as well-sorted coarse sand (d50 = 0.51 mm) in velocity-skewed and acceleration-skewed oscillatory flows. Simulation results of graded particles showed the formation of inverse grading (upward coarsening) in sediment bed under oscillatory flows, suggesting that the effects of armoring and exposure were important in the resulting transport rate. Examining different particle size distributions under onshore velocity-skewed flows, it was found that the largest increase of the net onshore sediment transport rate due to size gradation corresponded to the moderately sorted particle size distribution (d90/d10 = 3.41), where the coarse fraction (d > d50) had the maximum contribution to the transport. By analyzing intra-wave sediment transport quantities, the response of size gradation to the flow skewness and asymmetry and velocity intensity was investigated. Model results revealed that the armoring effect (reduction of sediment flux due to inverse grading) was dominant when flow velocity magnitude was lower (wave trough) or the fluid acceleration was higher. On the other hand, when flow velocity magnitude was larger (wave crest), the armoring effect was reduced or the exposure effect (enhancement of sediment flux due to inverse grading) may become more pronounced. Overall, we found that onshore net sediment transport was enhanced up to 30% due to particle size gradation under onshore velocity-skewed oscillatory flows. Conversely, the size gradation reduced the net onshore transport rate up to 35% under onshore acceleration-skewed oscillatory flows. Model results also suggested that the thickness of the active layer (surface layer affected by vertical sorting) in sheet flows can be quantified by the peak erosion depth. The simulation results presented here provide insights into the role of sediment size gradation (armoring and exposure effects) in wave-driven onshore transport which is important for predicting morphological evolution.

General velocity formula of boundary layer above mobile sediment bed induced by asymmetric waves

Sediment movement in the wave boundary layer above a mobile sediment bed is complex. A velocity formula for the boundary layer is proposed for sheet flow induced by asymmetric waves above a mobile sediment bed. The formula consists of a free stream velocity and a defect function which contains a phase-lead, boundary layer thickness and mobile sediment bed. Phase-lag of sediment movement is considered in the formula for the mobile sediment bed. The formula needs six dependent variables about asymmetric wave and sediment characteristics. Asymmetry effects on parameters (orbital amplitude, roughness height, bed shear stress, and boundary layer thickness) are properly considered such that the formula can yield velocity differences among onshore, offshore, acceleration, and deceleration stages. The formula estimates the net boundary layer velocity resulting from the mobile sediment bed and asymmetric boundary layer thickness. In addition, a non-constant phase-lead also contributes to the net boundary layer velocity in asymmetric oscillatory sheet flow. Results of the formula are as good as that of a two-phase numerical model. Sheet flow transport induced by asymmetric waves, and the offshore net sediment transport rate with a large phase-lag under velocity-skewed waves, can be adequately estimated by the formula with a power sediment concentration function.

Sediment Transport with Mixed Sand in Nonlinear Regular Waves

Ferreira, C.C.; Abreu, T.; Silva, P.A.; Bernabeu, A.; Romao, S., and Staudt, F., 2020. Sediment transport with mixed sand in nonlinear regular waves. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 408–411. Coconut Creek (Florida), ISSN 0749-0208.This work presents the results of an experiment carried out in the Large Wave Flume (Groser Wellenkanal, GWK) in Hannover, which enables full-scale wave experiments to be conducted above sand beds. The experiment consisted of a set of regular waves propagating over a 30 m long horizontal bed composed of a bimodal mixture of fine (F) and coarse (C) sands. Wave gauges placed along the test section and an ADV (Acoustic Doppler Velocimeter) placed above the wave bottom boundary layer allow characterizing the wave nonlinearity parameters (skewness and asymmetry). Fluorescent sand was inserted at the beginning of each experiment and subsequent bed samples allowed tracking its movement, differentiating between the coarse and fine sand fractions.This study presents the results obtained with a particular sediment mixture (75%F+25%C) for two regular trochoidal wave conditions with the same wave period, 7 s, but different wave heights, 1.0 and 1.5 m. The total net transport rates estimated from a practical sediment transport formula, which includes both effects of wave asymmetry and skewness, are comparable with those obtained with the fluorescent tracer.

Future wave-climate driven longshore sediment transport along the Indian coast

Longshore sediment transport is an important nearshore process that governs coastal erosion/accretion and in turn defines the orientation of coastlines. In this study, we assess the changes in longshore transport rates along the Indian coast due to the potential changes in wave parameters under the RCP4.5 climate scenario. The projected wave climate for two time slices, ‘near-term/present’ (2011–2040) and ‘mid-term/future’ (2041–2070) were used to investigate changes in the corresponding sediment transport rates. An empirical model accounting for major wave parameters, longshore current, resulting sediment transport and shoreline evolution was used. It was found that most of the Indian coast exhibited the same drift direction in both time slices, although changes in transport magnitude were present. To give a broad-brush characterisation of the coastline, the shoreline elements were classified as erosive, accretive or stable based on the comparative longshore transport rates of neighbouring elements. Similar characterisations, carried out for both time slices, showed that about 35% of the total coastline would remain unaffected due to the changing wave climate in the future (i.e. there is little to no change); about 20% is expected to ‘worsen’ (i.e. expected to undergo higher magnitudes of erosion wrt present rate) and 45% to ‘improve’ (i.e. expected to accrete/reach stability). It was also observed that the net annual transport rates pertaining to the future period are not expected to change significantly with respect to the current scenario. This indicates that the change in longshore transport rates arising from future changes in wave climate as represented by the RCP4.5 climate change scenario will have a broadly neutral effect.

Manganese Repairs the Oxygen-Evolving Complex (OEC) in Maize (Zea mays L.) Damage During Seawater Vulnerability

This study was aimed to investigate how exogenous manganese (Mn) would limit damage in the oxygen-evolving complex (OEC) and photosynthetic apparatus of maize seedlings caused during seawater vulnerability. In this study, seawater was applied in 2-week-old maize (Zea mays L.) seedling, and the degree of damage of photosynthetic pigment pool, the OEC, and net electron transport rate were observed. Mn supplement was also added in maize seedlings to limit the damage of the OEC and photosynthetic apparatus caused during salinity. Leaf relative water content (RWC), fresh weight (FW), and photosynthetic pigment pool (chlorophyll a, chlorophyll b, and carotenoids) sharply declined after 7 days of treatment; however, Mn supplement increased these values. Chlorophyll fluorescence induction (OJIP) transients showed low Fv/Fo, an additional K step, enhanced variable fluorescence (VK) and degree of damage to the OEC (WK) during salinity, and indicates damage of OEC at electron donor side of photosystem II (PSII). The OEC intact within PSII was a primary damage center during salinity which inhibited electron transport process that resulted in a huge loss of maximum quantum yield of PSII (Fv/Fm), but a significant recovery in photosynthetic apparatus was observed after exogenous application of manganese. Structural and functional integrity of the photosynthetic apparatus was recovered up to a certain extent after exogenous application of Mn. Findings from this study should help to understand the basic knowledge of photosynthetic apparatus efficiency in response to damage caused by exposure to seawater. Outcomes of this study will be used to mitigate salinity problem with Mn supplement for growth and development of crops.

A Numerical Model for Offshore Mound Evolution

A numerical model was developed to simulate the evolution of a mound placed in the offshore (i.e., outside the zone of wave breaking), exposed to varying non-breaking waves and water levels. The net sediment transport rate is assumed to be mainly dominated by bed load transport, where wave asymmetry plays an important role. The net transport over a wave cycle is expressed with reference to an equilibrium profile, which ensures model reliability and robustness. In order to validate the model, data collected at two field sites, Cocoa Beach and Perdido Key Beach in Florida, USA, were employed. The numerical results show good agreement with the measured data from the two sites in terms of the profile evolution. It demonstrates that the model has the capability to simulate the evolution of mounds placed in the offshore. In addition, several scenarios with different mound volume and location designs were investigated to indicate potential uses for the model. The results illustrate how the mound evolution is influenced by the volume and location of the mound placement.

Erosion mechanism of the landward Oostgat tidal channel slope, The Netherlands

The Oostgat tidal channel, located in the mouth of the Scheldt estuary in The Netherlands, migrates in the landward direction by about 0.2 m/year as a result of erosion of the landward channel slope. This erosion threatens beach stability and the effectiveness of beach nourishments. The physical mechanisms controlling this channel slope erosion are yet unknown. We have studied this erosion problem with a high-resolution Delft3D coupled wave-flow-sand transport model, which we have validated against available hydrodynamic data. Initial sedimentation and erosion patterns were inferred from the computed net sand transport rates. The model results show that channel slope erosion is controlled by the tide; effects of waves and wind are relatively small. The net sand transport is mainly controlled by the interaction between the residual current and the tidal velocity variation. Previous studies attributed a prominent role to the sand ridge Bankje van Zoutelande offshore from the Oostgat channel. This has not been confirmed by our model results: erosion of the landward channel slope was still present if the ridge was removed, albeit smaller. Instead, the erosion seems to be related to a sharp channel bend just north of the erosional area. The bend drives cross-channel differences in tide-dominance resulting in an increasing ebb-directed/northward net sand transport away from the erosional area.

Importance of infragravity waves in a wave-dominated inlet under storm conditions

The processes associated with infragravity waves (IGW) and their role on the hydro-sedimentary dynamics of a wave-dominated inlet are investigated using field observations collected at the Albufeira Lagoon (Portugal) during storm Leslie in October 2018. During the storm, significant IGW heights reached up to 1.0 m in the surf zone and 0.4 m inside the lagoon. IGW frequencies were blocked by ebb currents at the flood-delta and this effect was stronger for higher IGW frequencies. Therefore, low-frequency IGW were able to propagate further into the inner lagoon. The application of a 1D energy balance equation suggests that depth-induced breaking and bottom friction contributed equally to dissipate IGW energy at the flood-delta and that this dissipation was stronger during the flood than during the ebb.Large horizontal velocities under IGW crests increased the instantaneous suspended sediment transport rate by up to two orders of magnitude during flood at the flood-delta. The net suspended sediment transport rate and its variability, associated with the wave motion, was positive (landward) during flood and negligible during ebb. These positive values were associated with large wave-induced orbital velocities, suggesting that waves were more effective than tidal currents in inducing suspended sediment transport. The oscillatory suspended sediment transport rate was directed towards the lagoon and dominated by IGW frequencies. The observed sediment accretion of the northern channel occurred during the most energetic IGW. The measurements presented in this study and their analyses demonstrate how IGW play a major role in the sedimentary dynamics of wave-dominated inlets during storm conditions.

Silicon nutrition mitigates the negative impacts of iron toxicity on rice photosynthesis and grain yield.

Excess iron (Fe) is commonly observed in wetland rice (Oryza sativa L.) plants, impairing crop growth and productivity. Some information suggests that silicon (Si) can reduce Fe content in leaves and roots of rice (vegetative phase), but nothing is known if Si could mitigate the effects of Fe toxicity on rice production and photosynthesis. Here, we assessed the role of Si in alleviating the well-known effects of Fe toxicity on nutritional imbalances, biomass accumulation, photosynthesis and grain yield using two rice cultivars having differential abilities to tolerate excess Fe. Plants were hydroponically grown under two Fe levels (25μM or 5mM) and the nutrient solutions were amended with Si (0 or 2mM). Under excess Fe were detected (i) nutritional deficiencies, especially of calcium and magnesium in leaves; (ii) negligible changes in grain nutritional composition, independently of Si application; (iii) decreases in net photosynthetic rates, stomatal conductance and electron transport rate, in parallel to decreased grain yield components (total grain biomass, 1000-grain mass, percentage of filled grains, number of grains per plant and harvest index), especially in the Fe-sensitive cultivar. These impairments were partially reversed by the application of Si. Results also suggest that Si alleviated the negative impacts of Fe on spikelet sterility. In summary, we conclude that the use of Si can be recommended as an effective management strategy to reduce the negative impacts of Fe toxicity on rice photosynthetic performance and crop yield.