Fine sediment deposits in gravel bed rivers: sensitivity analysis to particle properties using a 2D hydrodynamic and sediment model

Hydrodynamic

Data plane throughput vs control plane delay: Experimental study of BitTorrent performance

n/

Outcome and Predictors of Treatment Failure in Total Hip/Knee Prosthetic Joint Infections Due to Staphylococcus aureus

The results of the present study suggest that ASA score ≤ 2 and use of rifampin-combination therapy are two independent factors associated with favorable outcome of patients treated for total hip or knee prosthetic infections due to S. aureus

Carbon-nitrogen interactions in European forests and semi-natural vegetation - Part 2: Untangling climatic, edaphic, management and nitrogen deposition effects on carbon sequestration potentials

The effects of atmospheric nitrogen deposition (N$_{dep}$) on carbon (C) sequestration in forests have often been assessed by relating differences in productivity to spatial variations of N$_{dep}$ across a large geographic domain. These correlations generally suffer from covariation of other confounding variables related to climate and other growth-limiting factors, as well as large uncertainties in total (dry+wet) reactive nitrogen (N$_{r}$) deposition.We propose a methodology for untangling the effects of N$_{dep}$ from those of meteorological variables, soil water retention capacity and stand age, using a mechanistic forest growth model in combination with eddy covariance CO$_{2}$ exchange fluxes from a Europe-wide network of 22 forest flux towers. Total N$_{r}$ deposition rates were estimated from local measurements as far as possible. The forest data were compared with data from natural or semi-natural, non-woody vegetation sites. The response of forest net ecosystem productivity to nitrogen deposition (dNEP= dN$_{dep}$) was estimated after accounting for the effects on gross primary productivity (GPP) of the co-correlates by means of a meta-modelling standardization procedure, which resulted in a reduction by a factor of about 2 of the uncorrected, apparent dGPP/dN$_{dep}$ value. This model-enhanced analysis of the C and N$_{dep}$ flux observations at the scale of the European network suggests a mean overall dNEP/dN$_{dep}$ response of forest lifetime C sequestration to N$_{dep}$ of the order of 40–50 g C per g N, which is slightly larger but not significantly different from the range of estimates published in the most recent reviews. Importantly, patterns of gross primary and net ecosystem productivity versus N$_{dep}$ were non-linear, with no further growth responses at high N$_{dep}$ levels (N$_{dep}$ >2.5–3 gNm$^{-2}$ yr$^{-1}$) but accompanied by increasingly large ecosystem N losses by leaching and gaseous emissions. The reduced increase in productivity per unit N deposited at high N$_{dep}$ levels implies that the forecast increased N$_{r}$ emissions and increased Ndep levels in large areas of Asia may not positively impact the continent’s forest CO$_{2}$ sink. The large level of unexplained variability in observed carbon sequestration efficiency (CSE) across sites further adds to the uncertainty in the dC/dN response

Development and validation of a questionnaire assessing volitional competencies to enhance the performance of physical activities in chronic low back pain patients

BACKGROUND: Motivation has long been emphasized as the most important determinant of action. However, there is a substantial gap between people's goals and their attainment. Patients may be motivated and yet unable to take action if their volitional competencies are insufficient. One of the important tasks of volition is goal-maintenance. Research has stressed the importance of a volitional tool, the implementation intentions. Implementation intentions indicate where, when, and how the action leading to the goal will be performed. Forming implementation intentions favours the execution of goal-directed efforts, and reinforces the relationship between intentions and behaviours. Results from various studies clearly suggest that volitional competencies and implementation intentions could play a role in low back pain (LBP) patients. However, there is at present no questionnaire allowing assessing the capacity of implementation intentions of physical activities in LBP patients. METHODS/DESIGN: This study will develop such a questionnaire, using a 3-step approach. A first qualitative step to build categories and generate items; 30 patients suffering chronic LBP will be invited to participate in semi-structured interviews; verbatim and derived items will then be submitted to a panel of experts, using a Delphi method; a second quantitative step to examine the properties of items, and determine the factorial structure of the questionnaire; 100 patients suffering chronic LBP will be recruited to respond to this phase; and third, preliminary psychometric analyses (item-scale correlations, construct validity, reliability); 180 chronic LBP patients will be recruited for this phase of the study. The relationships between implementation intentions and variables affecting physical activity on chronic LBP patients, i.e. pain, physical capacities, fear-avoidance beliefs, kinesiophobia, work status, and level of physical activity will be considered. DISCUSSION: Developing a questionnaire to assess implementation intentions would allow investigating the role of these intentions in the transition from acute to chronic LBP. The results of this study should contribute to the understanding of the psychological processes at stake in the development of chronic LBP, and in particular to the identification of factors eventually favouring patients' participation in and adherence to active physical treatments

Inter-laboratory comparison of cryogenic water extraction systems for stable isotope analysis of soil water

For more than two decades, research groups in hydrology, ecology, soil science, and biogeochemistry have performed cryogenic water extractions (CWEs) for the analysis of δ2H and δ18O of soil water. Recent studies have shown that extraction conditions (time, temperature, and vacuum) along with physicochemical soil properties may affect extracted soil water isotope composition. Here we present results from the first worldwide round robin laboratory intercomparison. We test the null hypothesis that, with identical soils, standards, extraction protocols, and isotope analyses, cryogenic extractions across all laboratories are identical. Two standard soils with different physicochemical characteristics along with deionized (DI) reference water of known isotopic composition were shipped to 16 participating laboratories. Participants oven-dried and rewetted the soils to 8 and 20 % gravimetric water content (WC), using the deionized reference water. One batch of soil samples was extracted via predefined extraction conditions (time, temperature, and vacuum) identical to all laboratories; the second batch was extracted via conditions considered routine in the respective laboratory. All extracted water samples were analyzed for δ18O and δ2H by the lead laboratory (Global Institute for Water Security, GIWS, Saskatoon, Canada) using both a laser and an isotope ratio mass spectrometer (OA-ICOS and IRMS, respectively). We rejected the null hypothesis. Our results showed large differences in retrieved isotopic signatures among participating laboratories linked to soil type and soil water content with mean differences compared to the reference water ranging from +18.1 to −108.4 ‰ for δ2H and +11.8 to −14.9 ‰ for δ18O across all laboratories. In addition, differences were observed between OA-ICOS and IRMS isotope data. These were related to spectral interferences during OA-ICOS analysis that are especially problematic for the clayey loam soils used. While the types of cryogenic extraction lab construction varied from manifold systems to single chambers, no clear trends between system construction, applied extraction conditions, and extraction results were found. Rather, observed differences in the isotope data were influenced by interactions between multiple factors (soil type and properties, soil water content, system setup, extraction efficiency, extraction system leaks, and each lab's internal accuracy). Our results question the usefulness of cryogenic extraction as a standard for water extraction since results are not comparable across laboratories. This suggests that defining any sort of standard extraction procedure applicable across laboratories is challenging. Laboratories might have to establish calibration functions for their specific extraction system for each natural soil type, individually.</p

Carbon-nitrogen interactions in European forests and semi-natural vegetation - Part 1: Fluxes and budgets of carbon, nitrogen and greenhouse gases from ecosystem monitoring and modelling

The impact of atmospheric reactive nitrogen (N$_{r}$) deposition on carbon (C) sequestration in soils and biomass of unfertilized, natural, semi-natural and forest ecosystems has been much debated. Many previous results of this dC/dN response were based on changes in carbon stocks from periodical soil and ecosystem inventories, associated with estimates of N$_{r}$ deposition obtained from large-scale chemical transport models. This study and a companion paper (Flechard et al., 2020) strive to reduce uncertainties of N effects on C sequestration by linking multi-annual gross and net ecosystem productivity estimates from 40 eddy covariance flux towers across Europe to local measurement-based estimates of dry and wet N$_{r}$ deposition from a dedicated collocated monitoring network. To identify possible ecological drivers and processes affecting the interplay between C and N$_{r}$ inputs and losses, these data were also combined with in situ flux measurements of NO, N$_{2}$O and CH$_{4}$ fluxes; soil NO$_{3}$̅ leaching sampling; and results of soil incubation experiments for N and greenhouse gas (GHG) emissions, as well as surveys of available data from online databases and from the literature, together with forest ecosystem (BASFOR) modelling. Multi-year averages of net ecosystem productivity (NEP) in forests ranged from -70 to 826 gCm$^{-2}$ yr$^{-1}$ at total wet+dry inorganic N$_{r}$ deposition rates (N$_{dep}$) of 0.3 to 4.3 gNm$^{-2}$ yr$^{-1}$ and from -4 to 361 g Cm$^{-2}$ yr$^{-1}$ at N$_{dep}$ rates of 0.1 to 3.1 gNm$^{-2}$ yr$^{-1}$ in short semi-natural vegetation (moorlands, wetlands and unfertilized extensively managed grasslands). The GHG budgets of the forests were strongly dominated by CO$_{2}$ exchange, while CH$_{4}$ and N$_{2}$O exchange comprised a larger proportion of the GHG balance in short semi-natural vegetation. Uncertainties in elemental budgets were much larger for nitrogen than carbon, especially at sites with elevated N$_{dep}$ where N$_{r}$ leaching losses were also very large, and compounded by the lack of reliable data on organic nitrogen and N$_{2}$ losses by denitrification. Nitrogen losses in the form of NO, N$_{2}$O and especially NO$_{3}$̅ were on average 27%(range 6 %–54 %) of N$_{dep}$ at sites with N$_{dep}$ 3 gNm$^{-2}$ yr$^{-1}$. Such large levels of N$_{r}$ loss likely indicate that different stages of N saturation occurred at a number of sites. The joint analysis of the C and N budgets provided further hints that N saturation could be detected in altered patterns of forest growth. Net ecosystem productivity increased with N$_{r}$ deposition up to 2–2.5 gNm$^{-2}$ yr$^{-1}$, with large scatter associated with a wide range in carbon sequestration efficiency (CSE, defined as the NEP = GPP ratio). At elevated N$_{dep}$ levels (> 2.5 gNm$^{-2}$ yr$^{-1}$), where inorganic N$_{r}$ losses were also increasingly large, NEP levelled off and then decreased. The apparent increase in NEP at low to intermediate N$_{dep}$ levels was partly the result of geographical cross-correlations between N$_{dep}$ and climate, indicating that the actual mean dC/dN response at individual sites was significantly lower than would be suggested by a simple, straightforward regression of NEP vs. N$_{dep}$

Etude des mécanismes hydrologiques et biogéochimiques de la recharge des nappes à surface libre

Ce travail vise à étudier les mécanismes hydrologiques et biogéochimiques de la recharge des nappes à surface libre. La recharge des nappes à surface libre est un maillon essentiel dans le cycle hydrochimique des bassins versants sur socle. Avant d'être transférés de la nappe vers le réseau hydrographique, les solutés transitent dans la zone non saturée constituée de sol et d'altérite. Nous nous intéressons aux solutés anioniques et plus particulièrement aux nitrates compte tenu des enjeux environnementaux que revêt la pollution diffuse azotée. Les mécanismes hydrologiques et biogéochimiques de la recharge des nappes ont été caractérisés et étudiés en conditions naturelles sur le bassin versant de Kerbernez sur l'ensemble du continuum zone non saturé / zone de fluctuation de nappe / zone saturée en permanence, par modélisation numérique sur un versant théorique et par traçage sur une colonne d'arène granitique. L'activité bactérienne dans la zone non saturée profonde a été quantifiée par expérimentations en batch.Les observations faites dans la nappe à Kerbernez montrent que si les concentrations sont très stables en profondeur, elles présentent de fortes variations en surface à l'échelle de l'année hydrologique, particulièrement dans la zone de fluctuation de nappe. La zone de fluctuation de nappe est une zone active de mélange entre des eaux d'origine et d'âge différents, et où des transferts latéraux rapides peuvent avoir lieu. L'inaptitude des modèles classiques de transfert (Convection-Dispersion et Mobile-Immobile) à reproduire les traits caractéristiques des variations chimiques dans la zone de fluctuation de nappe a été montrée, confirmant la nécessité de prendre en compte l'hétérogénéité des écoulements.Ainsi, nous proposons une représentation du milieu sous forme de deux compartiments de porosité mobile, un lent et un rapide, expliquant l'origine des fortes variations chimiques intra-annuelles dans la zone de fluctuation de nappe. Les courbes d'élution en sortie de colonne au laboratoire montrent que la dispersion des solutés augmente en régime de fluctuation de nappe par rapport aux régimes d'écoulement stationnaire. Ces fortes dispersions seraient le résultat de l'activation alternée de chacun des deux compartiments de porosité mobile, activation contrôlée par le degré de saturation du milieu. Les variations inter-annuelles des concentrations en conditions naturelles dans la zone non saturée nous ont conduit à définir un troisième compartiment de porosité immobile échangeant par diffusion avec les autres compartiments de porosité. Nous avons par ailleurs montré à partir de l'analyse des concentrations mesurées sur le terrain et dans les incubations au laboratoire que de la dénitrification hétérotrophe se produisait dans la zone non saturée profonde. Le compartiment immobile de la porosité serait le lieu de cette dénitrification.Soo

Preferential flow and slow convective chloride transport through the soil of a forested landscape (Fougères, France)

International audiencehis study aims to assess the water flow and non-reactive solute transfers occurring in a glossic acidic soil under a beech forest in Brittany (Fougères, France). The specific objectives were to study the water and chloride transfers in this soil, to understand the spatial and temporal variability of these transfers and to produce a data set in this forest site for future modelling. For this, we carried out a field tracer experiment and sprinkled chloride enriched solution over two areas of soil (2 × 66 m2) in March, 2006. Subsequently, we monitored the composition of the soil solutions collected by zero tension plate lysimeters and ceramic cup lysimeters installed at depths between 0 and 240 cm, over a period of 18 months. We prove that preferential flow through rapid-mobile porosity and slow transfers by convective flux though slow-mobile porosity coexist in the soils of the experimental plot, and that the time scales brought into play ranged from a few days to a yearly scale. The transfer velocities ranged between 2.38 mm day− 1 for the slowest convective flux and 600 mm day− 1 for the fastest preferential flows. We also prove that the rapid-mobile porosity represents only a small proportion of the soil volume (the mean of all depths, except 10 cm, was about 11%) but the quantity of solute transferred, which by-passes a large part of the rooting zone, may be important (around 17% of the tracer mass applied). The rapid transfer is mainly governed by the soil moisture combined with precipitation intensities and the slow transfer mainly by the cumulative percolation flux. Both transfers are also characterised by wide spatial and temporal variability. The wide transfer variability may be explained by the hydrodynamic dispersion related to the heterogeneity of the slow and rapid porosities, combined with the impact of the 2006 growing season, which slowed down the tracer displacement. Lastly, the experiment proves that the zero tension plate lysimeters mainly collect rapid drainage water, as preferential flows, while the ceramic cup lysimeters mainly collect slow-mobile water mixed with rapid drainage water

The flocculation characteristics of freshly eroded aggregates

In Europe, 260,000 km2 of soils already suffer erosion by water. This worrying level of land degradation is expected to increase in the context of climate change, with situations particularly critical in mountainous environments. As any multi-use resources, there is also a growing human pressure on mountainous rivers. Data is required to obtain a better understanding of the cycles of deposition and erosion and of the respective contributions of natural and human-induced processes to fine, cohesive sediment fluxes. When placed in suspension in rivers, cohesive materials are principally transported as flocs. The quantity of suspended solids exported downstream depends mainly of their morphometric properties, including: size, shape and effective density. Once eroded on hillslopes, the conveyance of fine sediment particles on continental surfaces requires the maintenance of particles in suspension by nearbed turbulence and its advection downstream by the mean flow. Traditional Rouse profile relationships do not readily hold for highly concentrated riverine suspensions (~10 g/l), where processes such as flocculation, hindered settling and stratification interplay. This study aims at improving sediment transport parameterisation, by examining the kinetics of fine soil aggregates (size, settling velocity, density), once immersed in a turbulent flow. Particle properties of three Mediterranean materials (clay loam soil, black marl and molasse, all sampled in Badlands environments) were tested in the grid stirred experiment following the protocol previously used by Gratiot and Manning (2004). Hydrodynamic properties were monitored with ADV and turbidity sensors. For each soil, three sediment loads (1.5; 5; 10 g.l-1) representative of flood conditions were tested. Aggregate properties were obtained after sampling at four depths above the grid, using the LabSFLOC – Laboratory Spectral Flocculation Characteristics – technique (Manning, 2006) and laser techniques. These acquisition heights are associated with the corresponding turbulence dissipation rates G of 1.5, 3, 7 and 19 s-1. Flocculation rates and dynamics are reported and discussed