Bottom Flux Research Articles

Physically consistent temperature fields for geophysical inversion based on the parametrized location of an isotherm

PurposeThis paper aims to provide a method for obtaining physically sound temperature fields to be used in geophysical inversions in the presence of immersed essential conditions.Design/methodology/approachThe method produces a thermal field in agreement with a given location of the interface between the Lithosphere and Asthenosphere. It leverages the known location of the interface to enforce the location of a given isotherm while relaxing other constraints known with less precision. The method splits the domain: in the Lithosphere the solution is immediately obtained by standard procedures, while in the Asthenosphere a minimization problem is solved to fulfill continuity of temperatures (strongly imposed) and fluxes at the interface (weakly imposed).FindingsThe numerical methodology, based on the relaxation of the bottom fluxes, correctly recovers the thermal field in the complete domain. To obtain bottom fluxes following geophysical expected values, a constrained minimization strategy is required. The sensitivity of the method could be improved by relaxing other quantities such as lateral fluxes or mantle velocities.Originality/valueA statement of the energy balance problem in terms of a known immersed condition is presented. A novel numerical procedure based on a domain-splitting strategy allows the solution of the problem. The procedure is tailored to be used within geophysical inversions and provides physically sound solutions.

Stochastic analysis of plant available water estimates and soil water balance components simulated by a hydrological model

AbstractThe uncertainty in soil hydraulic parameters is often not taken into account in process‐based hydrological modeling. Performing runs with 104 stochastic parameter realizations, we evaluated the propagation of uncertainty in the Van Genuchten–Mualem (VGM) parameters into estimates of the threshold values of soil water content used to calculate the total and readily available water, and on the long‐term (30 years) simulations of evaporation, transpiration, bottom flux, and runoff by the SWAP hydrological model. The simulated scenarios included weather data from a location in southeast Brazil and seven soils from the same region cropped with maize, comprising a wide range of texture classes. The results showed that uncertainties in VGM parameters affect the estimates of total and readily available water. Water balance components obtained by a deterministic simulation with average VGM parameters did not always agree with the average or median of stochastic simulations, and stochastic simulations including parameter uncertainties should be preferred. Variations in yearly rainfall characteristics were more important for bottom flux and evaporation, while transpiration and runoff were more strongly influenced by the variations in soil hydraulic properties.

Spatial distribution of vertical carbon fluxes on the Agulhas Bank and its possible implication for the benthic nepheloid layer

Vertical particle fluxes of particulate organic carbon (POC), chlorophyll a (Chl a) and biogenic silica (bSi) were measured on the productive shelf of southern Africa, the Agulhas Bank (AB), in March 2019. Sinking particulate material in the form of aggregates is hypothesized to form the benthic nepheloid layer (BNL) which is a turbid layer found near the seabed. This layer is known to affect the spawning success of squid as it is linked to high turbidity which reduces visibility during mating. To determine the distribution of fluxes and particle composition in the AB, we collected water samples below the surface mixed layer (‘export’) and near the seabed (‘bottom’) using a Marine Snow Catcher. POC export fluxes were significantly higher inshore than offshore (mean ± SD: 944.6 ± 302.0 & 461.1 ± 162.1 mg POC m−2 d−1, respectively). There was no significant difference in the cross-shelf distribution of Chl a and bSi export fluxes, however the inshore fluxes of Chl a and bSi were higher than offshore, suggesting a link between export fluxes and sinking organic matter derived from the more productive inshore surface waters. All bottom fluxes were significantly higher inshore, suggesting the contribution of sinking organic particles and resuspended bottom sediments to inshore fluxes. POC export efficiency (ratio of exported POC flux relative to net primary production (NPP)) was higher on the AB (range: 0.58–9.56) compared to the global shelf seas ratio of 0.18 and not related to NPP, suggesting an export of standing stock of carbon biomass, likely produced before the cruise. Transfer efficiency (i.e., the amount of exported flux that reaches the bottom) was also high (max: 0.99, 1.0 and 33.04 for POC, Chl a and bSi, respectively) but did not show a clear spatial pattern. We observed a significant positive correlation between bottom turbidity (a proxy for BNL presence) and export POC flux, suggesting the possibility that sinking organic matter is contributing to BNL formation on the AB.

Sustainable irrigation management in tropical lowland rice in Brazil

Drought events and water use conflicts drive the need for more efficient water management in rice-growing areas of the Brazilian Cerrado. Recent studies have shown the advantages of adopting water-saving irrigation in the region but a comprehensive assessment is needed. This study aims to model the performance of rice cultivation and water productivity in the tropical floodplains of the Cerrado biome of northern Brazil in response to irrigation management under contrasting seasonal rainfall levels. Twenty-seven scenarios of rice cultivation, resulting from the combination of three sites, three irrigation treatments, and three rainfall regimes, were simulated with the calibrated and validated hydrological model SWAP/WOFOST. The rainfall levels high (1501 mm), intermediate (952 mm), and low (510 mm) were relative to 120 days and obtained from weather stations located in the region. Two irrigation methods (flooding and water-saving irrigation) were compared against rainfed cultivation. Actual transpiration of the flooding and water-saving irrigation was 9 % and 4 % higher in the intermediate and high rainfall scenarios while it was 30 % and 20 % higher in the low rainfall scenario compared to the rainfed treatment. The largest deep percolation loss was 12700 mm per season for flood irrigation in the low rainfall scenario, whereas the lowest one was 349 mm for the rainfed treatment in the low rainfall scenario. Changing from flooding to water-saving irrigation increases water productivity by an average of 9 % and decreases relative grain yield by 5–12 %. Water productivity based on bottom flux increased on average by about five times (high rainfall scenario) to ten times (low rainfall scenario) when comparing flooding with water-saving irrigation. Results suggest that saving irrigation based on crop transpiration can reduce deep percolation losses and increase water productivity in the rice-growing areas of the Brazilian Cerrado.

Implications of Watershed Management Practices on Water Availability Using Hydrus-1D Model in the Aba Gerima Watershed, Upper Blue Nile Basin, Ethiopia

The main objective of this study was to examine the implications of watershed management (WSM) on hydrological parameters in the Aba Gerima watershed in the Upper Blue Nile Basin. The Hydrus 1D model simulations were conducted in control sites and sites under WSM to estimate various components of the hydrologic cycle, using different soil physical & hydrological data under each category of experimental sites. Results were calibrated with measured soil moisture data through inverse solutions. Thus, Hydrus 1D model was found to be effective in predicting results, with R2 values of 0.73 to 0.853 and RMSE values ranging from 0.015 to 0.04. The cumulative evaporation estimated for 365 days for control sites was 37.6% higher than that of sites under WSM. Surface and bottom fluxes in the sites under WSM were 4.6% and 12.5%, respectively, higher than the control sites. This could be attributed to the increased soil water availability resulting from the implemented WSM practices in Aba Gerima, and the results of this study can be used as empirical evidence of the positive implications of WSM on water availability. Finally, WSM should be strengthened by concerned bodies and development partners in all watersheds, especially where water availability is affected by severe land degradation.

A semi-analytical solution to organic contaminants transport through composite liners considering a single crack in CCL

Compacted clay liners (CCLs) are extensively used as engineering barriers for groundwater and soil pollution. The existence of cracks/fractures in CCL caused by thermally induced shrinkage is reported to importantly damage the performance of the CCL. An analytical model is developed to study the effects of the cracks/fractures on the migration of organic contaminants through a composite liner system. Laplace transformation and Laplace inversion using the Stehfest method are adopted to derive the analytical solution, which is validated by the experimental data. The existence of crack shows a significant impact on the breakthrough curve and bottom flux of organic contaminants. Increasing the crack width from 1 to 25 mm results in an enhancement of contaminant bottom concentration by a factor of 280. Increasing the adsorption factor and degradation rate of contaminants can effectively improve the performance of the composite liner with cracks. The effects of degradation of contaminants on the breakthrough curve are found to be more significant for the case with a larger retardation factor. This may be due to the fact that increasing the retardation factor can significantly slow down the transport of contaminants, which may indirectly create a longer period for the degradation of contaminants.

Analytical solution for one‐dimensional steady‐state contaminant transport through a geomembrane layer (GMBL)/compacted clay layer (CCL)/attenuation layer (AL) composite liner considering consolidation

AbstractA composite liner system consisting of a geomembrane layer (GMBL), a compacted clay layer (CCL) and an attenuation layer (AL) is widely used in the modern landfills. The field and experimental observations highlight the potential detrimental effects on breakthrough of contaminants induced by consolidation of soil liner when a relatively high applied stress is caused by the waste placement. A one dimensional steady‐state model is developed to investigate the behaviour of contaminant transport in GMBL/CCL/AL composite liner system considering consolidation. Effects of the consolidation process on the transport of typical contaminants are investigated by the proposed analytical solution. The analytical results show that the magnitude of volume compressibility coefficient in the AL is important in controlling the overall magnitude of the consolidation induced effects. The process of consolidation shows a larger impact on the absorbable pollutants compared to the non‐absorbable pollutants. This may be due to the fact that the migration of solid particles induced by the consolidation may assist the transport of contaminant absorbed on them. The thickness of the AL shows large impacts on the bottom flux for the case with a high volume compressible coefficient. Increasing the thickness of AL from 1 to 3 m can results in a factor of 2.6 increase of the bottom flux. Increasing the thickness of the AL leads to a larger consolidation advection and a longer consolidation path, which may be the dominant mechanisms for contaminant transport compared to the diffusion process.

Estimation of potential recharge through direct seeded and transplanted rice fields in semi-arid regions of Punjab using HYDRUS-1D

The present study utilizes soil water balance and HYDRUS-1D for estimating and predicting potential recharge in groundwater declining region of central Punjab, respectively. A field experiment was conducted at Punjab Agricultural University, Ludhiana. Two treatments viz direct-seeded (DSR) and transplanted rice (TPR) with three replications, were sown/transplanted during kharif season of 2019. The amount of water applied through rainfall/irrigation was recorded and bottom flux was measured using frequency domain reflectometry (FDR) and then predicted using HYDRUS-1D in order to assess potential groundwater recharge which was further compared with deep percolation determined using soil water balance. The performance of the HYDRUS-1D was evaluated using RMSE, NSE, and R2 and found to be performing well. The paired t-test (t = 1.28 and t = 1.30 for TPR and DSR, respectively) was found to be non-significant at P = 0.05 which showed the correspondence between predicted and estimated parameters. The percentage change between estimated and predicted potential groundwater recharge was found to be 0.7% and 2.32% in TPR and DSR, respectively. The study revealed that there was 9% water saving and 14.6% more deep percolation (cumulative bottom flux) in DSR as compared to TPR that may potentially contribute to groundwater recharge.

Polynomial functions to predict flux-based field capacity from soil hydraulic parameters

We propose two new polynomials as pedotransfer function, PTF, to predict the flux-based Field Capacity water content, ΘFC. The inputs for the PTF are the bottom flux criterium, the profile depth, and the retention and conductivity parameters of the Van Genuchten – Mualem model, VGM. A first polynomial was developed including all VGM parameters and a second polynomial considers VGM parameter l equal to 0.5, the most commonly applied value. The polynomials were built using stepwise multiple linear regression and a generated dataset over a wide range of VGM model parameters. The “observed values” for the polynomial calibration were acquired from internal drainage simulations performed by the Richards equation-based model SWAP. The derived polynomials predicted the simulated ΘFC with high accuracy. The RMSD between observed and predicted ΘFC on tested datasets, for the complete version and the l = 0.5 polynomial version were, respectively, 0.01912 and 0.01362. The proposed polynomials may be combined with other PTFs providing the VGM parameters from texture and/or other basic data. Examples of predicted FC water content and pF are shown on texture triangles using the Rosetta PTF to predict VGM parameters from soil texture data. For stand-alone use, the polynomials allow predicting the flux-based ΘFC from VGM parameters without the need for numerical simulations.

Analytical model for coupled consolidation and diffusion of organic contaminant transport in triple landfill liners

A triple-layer composite liner consisting of a geomembrane liner (GMB), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) is commonly used at the landfill bottom liner system to isolate the contaminated leachates. In this paper, one-dimensional quasi-steady-state small deformation model (SDSS) was developed to investigate the behavior of organic chemicals transport in landfill composite liner system considering coupled effect of consolidation, diffusion and degradation. The first and second type bottom boundary conditions are used to derive the analytical solutions. The generalized integral transform technique (GITT) is adopted to derive the analytical solutions. The effect of consolidation on the performance of GMB/GCL/CCL with intact or leaking GMB is investigated. The triple liner under double drainage boundary condition (DDBC) has better performance compared to the case under single drainage boundary condition (SDBC). This is because the velocity induced by consolidation under DDBC is lower than that under SDBC. The effect of GCL consolidation shows an opposite trend compared to CCL consolidation. Considering GCL consolidation can increase the breakthrough time. The effective diffusion coefficient of GCL can be two magnitude orders smaller after consolidation, which provides a better diffusion barrier for the chemical transport. The effects of adsorption and degradation have been analyzed as well. Increasing the adsorption capacity of a deforming composite liner can increase the steady-state bottom flux, which shows the opposite tendency compared to the case without considering consolidation. This is due to the fact that for the case of a deforming composite liner, the advection induced by consolidation includes a new term due to the solid velocity. This velocity will result in the increase the mass of chemical migration through the composite liner.

Sequential Lid Removal in a Triple-decker Chain of CME-producing Solar Eruptions

Abstract We investigate the onsets of three consecutive coronal mass ejection (CME) eruptions in 12 hr from a large bipolar active region (AR) observed by the Solar Dynamics Observatory (SDO), the Solar Terrestrial Relations Observatory (STEREO), the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and the Geostationary Operational Environmental Satellite (GOES). Evidently, the AR initially had a “triple-decker” configuration: three flux ropes in a vertical stack above the polarity inversion line (PIL). Upon being bumped by a confined eruption of the middle flux rope, the top flux rope erupts to make the first CME and its accompanying AR-spanning flare arcade rooted in a far apart pair of flare ribbons. The second CME is made by eruption of the previously arrested middle flux rope, which blows open the flare arcade of the first CME and produces a flare arcade rooted in a pair of flare ribbons closer to the PIL than those of the first CME. The third CME is made by blowout eruption of the bottom flux rope, which blows open the second flare arcade and makes its own flare arcade and pair of flare ribbons. Flux cancellation observed at the PIL likely triggers the initial confined eruption of the middle flux rope. That confined eruption evidently triggers the first CME eruption. The lid-removal mechanism instigated by the first CME eruption plausibly triggers the second CME eruption. Further lid removal by the second CME eruption plausibly triggers the final CME eruption.

Modeling Unsaturated Zone Water Movement in the Floodplain Wetlands of the Volta Basin

The unsaturated zone of floodplain wetlands in the White Volta River basin provides an inextricable link between basin hydrology and the sustenance of plant growth. The HYDRUS-1D model was used to derive water budgets and to estimate fluxes to understand the hydrological complexities of these wetland systems. The model result indicates Spatio-temporal variation in the volume of vertical fluxes. In 2005, the estimate for average simulated flux was 0.29 cm/month in June and 1.23 cm/month in July. Consequently, the hydraulic head increased from 138.94 m to 139.30 m for the period from June to July 2005. For all sample sites, the increase in hydraulic head occurs within July and October, coinciding with high surface water fluxes. From the calculated water balance, the average monthly estimate of bottom flux was 0.01 cm/month for 2004 and 1.1 cm/month for 2005. The flow through the unsaturated zone and discharging into the subsurface water system has a high dependency on both the soil structure and the volume of water infiltrating through the surface; the highest discharge is within the period of highest water input.

Cross-shelf exchanges in the northern Bay of Biscay

Abstract The spatio-temporal distribution of cross-shelf exchanges in the northern Bay of Biscay from 2007 to 2010 were investigated using a high-resolution three-dimensional model as well as sea-surface temperature and chlorophyll-a concentration satellite observations. Our results show that the net yearly mean transport was upslope each year, with 2010 showing the highest value (0.93 Sv upslope). Bottom fluxes showed peak values near Chapel Bank, with mean values of 0.1 m3 s−1 m−2 and maximum values of 0.2 m3 s−1 m−2. Our model demonstrated that cross-shelf exchanges can be divided into three vertical layers. At the surface, cross-shelf transports are driven by wind forcing (Ekman transport accounts for about 60% of the total cross-shelf transport) and mesoscale activity (eddy advection accounts for about 30% of transport). In the absence of mesoscale activity, Ekman transport at the surface is typically balanced out by a downslope flux at the bottom boundary layer. Exchanges at mid-depths are regulated by mesoscale activity and tides. A ubiquitous feature appeared at the bottom boundary with a cross-shelf flow in the downslope direction. Numerical simulations suggest bottom fluxes of 0.1 m3 s−1 m−2, in agreement with previous in situ observations. We discuss the impact of winds, tides and mesoscale eddies on cross-shelf exchanges using different examples. The eddy census was obtained using an eddy-tracking algorithm. The shelf break was shown to be an important area of eddy presence due to slope current instabilities. The impact of eddies on surface and mid-depth transport is illustrated with a shelf-break eddy as an example, from its generation to dissipation and its contribution to cross-shelf exchanges. Results suggest that the largest magnitudes of downslope transports occur in the presence of both strong winds and intense eddy activity. Our detailed and quantitative exploration of cross-shelf transports in the northern Bay of Biscay highlights the relative contribution of intermittent processes (e.g. wind-driven events, eddies, frictional bottom layer) and confirms the complex links between the coastal and open ocean over shelf breaks.

Long-term hydraulic behaviour and soil ripening processes in a dike constructed from dredged material

PurposeClimate change necessitates heightening and strengthening of dikes, requiring large volumes of suitable soil. This study investigated soil ripening and long-term development of hydraulic behaviour of a dike constructed from slightly contaminated, partially dewatered dredged material from the Port of Hamburg under realistic conditions of construction and operation.Materials and methodsTwo test fields of 126 m2 each were constructed in 2004 for long-term analysis of hydraulic behaviour in combination with the possible mobilisation of contaminants. In test field 1 (MS), the 1-m-thick cover above the sand core consisted of traditionally used alluvial marsh sediment (reference), while in test field 2, the lower 0.7 m of the cover was substituted with dredged material (DM + MS). An HDPE tray below each field served the collection of bottom fluxes and hence the quantification of discharges and analysis of their chemical composition. In 2012, an excavation was carried out to inspect the development of the soil structure.Results and discussionThe discharge pattern revealed three distinct phases related to the post-construction structure development and therefore physical ripening of the soils. Within a single year, bottom fluxes typically started in mid-winter and ended in late spring. The dike cover containing DM had a high water retention capacity; however, the vertically continuous primary shrinkage cracks led to higher total bottom fluxes compared to the dike constructed from MS only. System hydraulic conductivities increased by up to six orders of magnitude compared to the as-built condition before soil ripening and structuring. The dredged material maintained a reduced geochemical status for about two years after construction. After first shrinkage and intrusion of oxygen, the material changed to an oxidised state, earmarking the onset of the chemical ripening process. Oxidising conditions were sustained in the long term, seen from the absence of previously elevated ammonium concentrations in the dike seepage.ConclusionsSystem hydraulics of the test field with dredged material were mainly determined by the covering layer of marsh sediment. After construction, the dredged material underwent physical, chemical and biological soil ripening processes, coupled to a respective change in discharge patterns, which, however, did not impair dike stability. It is recommended that soil ripening processes are induced and completed as part of the material’s pre-treatment, precluding the formation of irreversible shrinkage cracks and changeover of redox conditions after construction. The findings contribute to assessing the feasibility of the beneficial use of dredged material.

Optical features of linear Fresnel collectors with different secondary reflector technologies

This paper is devoted to the analysis of different secondary reflector designs for linear Fresnel collectors. A number of authors have proposed alternative shapes of secondary reflectors in order to enhance the efficiency and the flux intensity at the absorber tube. In this work the primary mirrors layout has been maintained constant for all designs. Thus, only secondary concentrators that do not require a change in the primary mirrors field have been studied. In order to carry out the study a validated Monte Carlo ray trace code has been used, where three optical properties are considered: annual optical efficiency, mean flux intensity and circumferential flux intensity homogeneity. The maximum efficiency reached by each technology, for given optical flux specifications, is obtained. Finally, the optical performance of linear Fresnel collectors with secondary reflector is compared with that of state-of-the-art parabolic trough collectors. It is concluded that the efficiency of Fresnel collectors is around 23% than that of parabolic troughs, although with mean flux intensities around 46% higher and circumferential flux intensities notably more homogeneous (top to bottom flux intensity ratios five times higher).

Parametric soil water retention models: a critical evaluation of expressions for the full moisture range

Abstract. Few parametric expressions for the soil water retention curve are suitable for dry conditions. Furthermore, expressions for the soil hydraulic conductivity curves associated with parametric retention functions can behave unrealistically near saturation. We developed a general criterion for water retention parameterizations that ensures physically plausible conductivity curves. Only 3 of the 18 tested parameterizations met this criterion without restrictions on the parameters of a popular conductivity curve parameterization. A fourth required one parameter to be fixed. We estimated parameters by shuffled complex evolution (SCE) with the objective function tailored to various observation methods used to obtain retention curve data. We fitted the four parameterizations with physically plausible conductivities as well as the most widely used parameterization. The performance of the resulting 12 combinations of retention and conductivity curves was assessed in a numerical study with 751 days of semiarid atmospheric forcing applied to unvegetated, uniform, 1 m freely draining columns for four textures. Choosing different parameterizations had a minor effect on evaporation, but cumulative bottom fluxes varied by up to an order of magnitude between them. This highlights the need for a careful selection of the soil hydraulic parameterization that ideally does not only rely on goodness of fit to static soil water retention data but also on hydraulic conductivity measurements. Parameter fits for 21 soils showed that extrapolations into the dry range of the retention curve often became physically more realistic when the parameterization had a logarithmic dry branch, particularly in fine-textured soils where high residual water contents would otherwise be fitted.

The influence of stony soil properties on water dynamics modeled by the HYDRUS model

Abstract Stony soils are composed of two fractions (rock fragments and fine soil) with different hydrophysical characteristics. Although stony soils are abundant in many catchments, their properties are still not well understood. This manuscript presents an application of the simple methodology for deriving water retention properties of stony soils, taking into account a correction for the soil stoniness. Variations in the water retention of the fine soil fraction and its impact on both the soil water storage and the bottom boundary fluxes are studied as well. The deterministic water flow model HYDRUS-1D is used in the study. The results indicate that the presence of rock fragments in a moderate-to-high stony soil can decrease the soil water storage by 23% or more and affect the soil water dynamics. Simulated bottom fluxes increased or decreased faster, and their maxima during the wet period were larger in the stony soil compared to the non-stony one.

Updating the Coupling Algorithm between HYDRUS and MODFLOW in the HYDRUS Package for MODFLOW

Core Ideas The coupling algorithm between HYDRUS‐1D and MODFLOW is updated. Pressure head profiles are updated based on the groundwater table and bottom flux after each time step. This eliminates sudden variations in inflow and outflow fluxes with groundwater table changes. The HYDRUS‐based flow package for MODFLOW (the HPM or the HYDRUS package) is an existing unsaturated zone flow package for MODFLOW. In MODFLOW with the HPM, the groundwater modeling domain is discretized into regular grids that can be combined into multiple zones based on similarities in soil hydrology, topographical characteristics, and the depth to the groundwater. Each of these zones is assigned one unsaturated soil profile (the HPM profile). In this model, after every MODFLOW time step, the flux at the bottom of the HPM profile is given as an input recharge flux to MODFLOW. MODFLOW simulates groundwater flow, and the water table depth at the end of the MODFLOW time step is assigned as the bottom boundary condition in the HPM profile. The current coupling algorithm assumes that the groundwater table in the HPM profile remains constant throughout the entire MODFLOW time step. This results in unrealistic sudden inflow and/or outflow fluxes at the bottom of the HPM profile after every time step. The objective of this study was to develop a methodology to eliminate the error in the determination of the recharge flux at the bottom of the HPM profile. This was achieved by updating or modifying the pressure head profile in the HPM profile after every MODFLOW time step. The effectiveness and the applicability of the new coupling algorithm were evaluated using different case studies. The new coupling algorithm is effective in eliminating unrealistic sudden variations in the bottom flux in the HPM profiles.

Field capacity, a valid upper limit of crop available water?

“Field capacity” (FC) is an agronomic measure with prime application in irrigation management, allowing the determination of irrigation gift without excessive leaching. FC can be determined by performing or simulating an internal drainage experiment until percolation reaches a “negligible” value. Alternatively, a static value of pressure head is often used to estimate FC, commonly −3.3m, −1m or −0.6m. FC is also used in definitions regarding soil water availability to crops and has been adopted in soil water balance models to define the maximum water storage. Nevertheless, crop water uptake may occur at water contents higher than FC. This uptake may represent a significant share of total uptake, and FC would then not be a true upper limit of available water. To investigate if FC can be considered an efficient soil physical quantity to characterize soil water availability we used information of unsaturated hydraulic properties (retention and hydraulic conductivity) of 8 soil profiles in Brazil. Using the hydrological model SWAP we estimated FC based on pressure head and bottom flux criteria and evaluated water uptake by pasture and maize from the soil drier than FC (hence: from the “available water” pool between FC and permanent wilting point) as well as from the water held at tensions between saturation and FC. Results show a considerable (10–50%) fraction of transpired water is taken up from the soil at water contents above FC, making FC a questionable quantity to truly estimate crop available water and casting doubt on the reliability of bucket-type soil water balance models.

Water loss and crust formation during bread baking, Part II: Technological insights from a sensitivity analysis of a numerical model of baking

ABSTRACTA 1D baking model was previously developed to improve the understanding of transport phenomena and bubble formation inside dough. Using this model, the present study focused on crust setting and its particular behavior. Simulation was used to study the influence of various parameters that govern crust setting and its characteristics such as thickness and porosity. On the basis of a literature review, the crust was defined as the “dry zone,” a region where the water content represents less than 0.60 kg/kg of dry matter. The mechanisms responsible for total water loss and crust setting were proposed in paper I and validated for multiple operating conditions: water loss is essentially driven by heat transport and to a lesser extent by the mechanism of water transport by evaporation–condensation–diffusion. In the present study, a sensitivity analysis of parameters of different driving mechanisms was undertaken through which it was possible to establish a hierarchy of the key parameters from a technological point of view. Overall heat transfer coefficient at the top of the loaf and thermal conductivity, or more generally the ratio between top and bottom heat fluxes, were ranked as the main parameters affecting crust setting and the water loss, thus suggesting a possible control of the process through the parameters evaluated.