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Temperature is a key factor that influences pesticide degradation. Extrapolating degradation half-lives (DT50) measured at a given temperature to different temperatures remains challenging, especially for tropical conditions with high temperatures. In this study, the use of the standard Arrhenius equation for correcting temperature effects on pesticide degradation in soils was evaluated and its performance was compared with that of alternative Arrhenius-based equations. To do so, a database of 509 DT50 values measured between 5 and 35 °C for 32 pesticides on tropical and temperate soils was compiled for the first time through an extensive literature search. The temperature correction models were fitted to the database using linear mixed regression approaches that included soil type and compound effects. No difference in the temperature dependence of DT50 between tropical and temperate soils was detected, regardless of the model. A comparison of the prediction performances of the models showed that constant activation energy (E

International audience; Recently, Comte et al. (2022) re-examined the natural degradation of chlordecone (CLD) in the soils of the French West Indies (FWI) by introducing an additional ‘dissipation parameter’ into the WISORCH model developed by Cabidoche et al. (2009). Recent data sets of CLD concentrations in FWI soils obtained by Comte et al. enabled them optimizing the model parameters, resulting in significantly shorter estimates of pollution persistence than in the original model. Their conclusions jeopardize the paradigm of a very limited degradation of CLD in FWI soils, which may lead to an entire revision of the management of CLD contamination. However, we believe that their study is questionable on several important aspects. This includes potential biases in the data sets and in the modeling approach. It results in an inconsistency between the estimated dissipation half-life time (DT50) of five years that the authors determined for CLD and the fate of CLD in soil from the application period 1972–1993 until nowadays. Most importantly, a rapid dissipation of CLD in the field as proposed by Comte et al. is not sufficiently supported by data and estimates. Hence, the paradigm of long-term persistence of CLD in FWI soils is still to be considered.

International audience; The current study aims to document evapotranspiration and associated surface energy fluxes for rainfed annual crops within a Mediterranean hilly agrosystem, in order to provide information on crop water use under such little-studied conditions. For this, an experimental study is conducted within the Tunisian study site of the OMERE observatory (French acronym for the Mediterranean Observatory of Water and the Rural Environment), located in the northeastern Cap Bon peninsula. It relies on eddy covariance (EC) measurements at the plot scale. We report that (1) observations are consistent with previous studies under Mediterranean or semi-arid contexts, with time series of energy fluxes that depict classical seasonal dynamics, (2) common flux ratios (i.e., Bowen Ratio, ratio of actual to reference evapotranspiration) may change according to upwinds and downwinds, which requires further investigations about possible changes in aerodynamic conditions, and (3) a reference evapotranspiration value of 4 mm day − 1 seems to be a threshold beyond which actual evapotranspiration decreases systematically and rapidly. In terms of agricultural water management, the current study suggests to look for early sowing species/varieties, in order to reduce the evaporation-based water loss in autumn. Overall, EC measurements seem promising over rainfed annual crops within semiarid hilly agrosystems, for long term observations, environmental modelling and operational purposes. Since the current study is conducted over few small fields within a specific hilly topography, the original results we report here need to be strengthened with complementary studies.

International audience

The use of pesticides in agriculture leads to widespread contamination of various environmental compartments. Surface water contamination represents a major environmental and health risk to manage. Models are a valuable tool for quantifying levels and temporal dynamics of contamination and for identifying and locating the physico-chemical processes involved in pesticide fate. The use of a model requires to know its performance for a given objective. Models simulating pesticide transfers to surface waters have generally been validated either in the laboratory or on a small scale (Gao et al., 2004, Joyce et al., 2010), or at field scale on mass export of discrete floods (Young and Fry, 2019), or at catchment scale on average concentrations or mass exports with minimum daily resolution (Wang et al., 2019). To our knowledge none have been evaluated on multi-year and field-scale databases. MHYDAS-Pesticide-1.0 is a continuous distributed mechanistic model used to simulate water and pesticide transfers from agricultural plots to the river system. The aim of this study is to evaluate at field scale the performance of this model to reproduce multi-year chronicles of runoff water contamination by a post-emergence herbicide intensively used in viticulture, glyphosate. The model was applied to a vineyard plot belonging to the Long-Term Observatory OMERE (Molénat et al., 2018), which outlet runoff discharge and glyphosate concentration have been monitored since 2001. The evaluation was conducted sequentially: the model was first evaluated on its performance in reproducing the runoff hydrographs observed at the plot outlet, then on its performance in simulating the temporal dynamics of glyphosate concentrations measured in runoff water. In both cases, the evaluation included a calibration and a validation step. The simulations were compared to data acquired between 2001 and 2017. The first three years were used for calibration and the following years for validation. To compare simulation results to observations, we considered variables of interest at flood event scale : the flood volume, the peak outflow and the mean glyphosate concentration. Goodness of fit was evaluated considering classical statistical performance indicators such as percent bias and Nash-Sutcliffe efficiency. These indicators were adapted to decrease the weight of the highest values relative to the lowest values. First calibration-validation results of saturated conductivity and height of surface detention enabled to identify a change of soil surface state during the assessment period that was corroborated by field observations. Taking this change into account by specific calibrations, the model reproduced very well runoff heights and peaks during the validation periods. The reproduction of concentration dynamics was also very satisfactory after calibration of glyphosate degradation kinetic and sorption coefficients and depth of the mixing layer between topsoil and surface runoff. This study demonstrates the ability of MHYDAS-Pesticide-1.0 to simulate multi-year time series of pesticide concentrations in surface water. It also provides a better understanding of the hierarchy of transfer processes occurring at the plot scale.

Biogeochemical cycling of elements largely occurs in dissolved state, but many elements may also be bound to natural nanoparticles (NNP, 1-100 nm) and fine colloids (100-450 nm). We examined the hypothesis that the size and composition of stream water NNP and colloids vary systematically across Europe. To test this hypothesis, 96 stream water samples were simultaneously collected in 26 forested headwater catchments along two transects across Europe. Three size fractions (~1-20 nm, >20-60 nm, and >60 nm) of NNP and fine colloids were identified with Field Flow Fractionation coupled to inductively coupled plasma mass spectrometry and an organic carbon detector. The results showed that NNP and fine colloids constituted between 2 ± 5% (Si) and 53 ± 21% (Fe; mean ± SD) of total element concentrations, indicating a substantial contribution of particles to element transport in these European streams, especially for P and Fe. The particulate contents of Fe, Al, and organic C were correlated to their total element concentrations, but those of particulate Si, Mn, P, and Ca were not. The fine colloidal fractions >60 nm were dominated by clay minerals across all sites. The resulting element patterns of NNP

International audience

International audience; The 1:250,000 soil mapping program of France is nearly complete. Although mapping has been conducted using conventional methods, there is a discernible need to obtain more precise soil data using other methods, and this is attracting considerable attention. However, it is currently not possible to implement a conventional and systematic program throughout the French territory, as the cost of acquiring new data on a finer scale is too high. In light of this, the Ministry of Agriculture commissioned a national survey to determine the needs of soil mapping in France, which asked questions to soil data producers and end-users. The results presented here summarize the main needs expressed by end-users. The main topics covered by soil mapping applications are identified in addition to the main mismatches between topics currently covered using available soil maps and the needs of end-users. Certain priorities for producing new soil information are identified in relation to geographical environments and settings, soil attributes, the spatial resolution of maps and the use of uncertainty estimates. Digital Soil Mapping is identified as a method that can bridge economic, scientific and practical considerations, but it requires dedicated efforts in order to build capacity. Finally, there is discussion of how the consideration of user needs can be employed to enhance the contribution of a new Digital Soil Mapping era, and to launch an operational soil security paradigm in France.

International audience; Although ditches limit surface water contamination, groundwater recharge through ditches in Mediterranean catchments may result in groundwater contamination. We analysed the dynamics of pesticide percolation in ditches by conducting an original lab experiment that mimicked the successive percolation processes that occur during a flood season. Nine successive percolation events were operated on an undisturbed soil column collected from a ditch bed. The infiltrating water was doped with C-14-Diuron at concentrations that were chosen to decrease between the events so as to correspond to values observed during actual flood events. The water and solute fluxes were monitored during each event, and the final extractable and non-extractable Diuron residues in the column were determined. Two main observations were made. First, a high leaching potential was observed through the ditch bed over a succession of infiltrating flood events, with 58.9% of the infiltrated Diuron and its metabolites leaching. Second, compared with the contamination of surface water circulating in the ditches, the contamination of seepage water exhibited smaller peak values and persisted much longer because of the desorption of Diuron residues stored in the ditch bed. Thus, ditches serve as buffering zones between surface and groundwater. However, compared with field plots, ditches appear to be a preferential location for the percolation of pesticides into groundwater at the catchment scale.

International audience; Statistical calibration of flow and transport models in unsaturated porous media is often carried out with Markov Chain Monte Carlo (MCMC) methods. However, the practicality of these methods is limited by their computational requirement, particularly when large prior intervals are assigned to the model parameters. In this work, a new operational strategy is investigated to alleviate the computational burden of MCMC samplers using results from a preliminary calibration performed with the First-Order Approximation (FOA) method. With the new strategy, the posterior distribution is approximated using a high-order Polynomial Chaos Expansion (PCE) surrogate model constructed over reduced parameter ranges. The latter are obtained from the 99.9 FOA confidence intervals. Two challenging test cases are investigated to assess efficiency and accuracy of the new strategy. The first test case considers estimation of flow and pesticide transport parameters from a synthetic infiltration experiment. The second test case deals with the assessment of unsaturated hydraulic soil parameters from a real-word laboratory drainage experiment. The results of the proposed strategy are compared to those of FOA, of the standard MCMC method and of an improved MCMC method in which the sampler is preconditioned with draws from the FOA posterior distribution. For both test cases, the new strategy provides accurate mean estimated parameter values and uncertainty regions and is much more efficient than the other MCMC methods. It is up to 50 times more efficient than the standard MCMC method.

International audience

International audience; In the French West Indies, high pest pressure on cropping systems has triggered high inputs of pesticides, especially in banana cropping systems. These pesticides then disperse in soil, ground and surface water, threatening ecosystem and human health. Reducing the environmental impact of banana cropping systems in this area requires i) predicting environmental states according to cropping systems evolution, ii) identifying key factors triggering pollution, and iii) proposing measures to reduce impact. Since farmers apply pesticides at the field scale while environmental impacts spring up at the watershed scale, multi-scale environmental impact assessments of pesticide use are required. Therefore, our work focuses on the characterization of i) pollutant input (type of molecule, quantity applied, frequency), ii) pollutant transfers, through hydrological modelling, and iii) environmental state through water quality measurements. Studies carried out at field scale, sub-watershed scale and watershed scale will be presented. They were located in Perou river catchment in Guadeloupe and Galion river catchment in Martinique. Results provide a wide overview of the main hydrological processes involved in pesticides transfers towards rivers in tropical volcanic catchments. However, those studies focused either on chlordecone, an old organochlorine, or cadusafos, a nematicide used 10 years ago in banana cropping systems. Recent measurements performed at the watershed scale showed herbicides applied in sugarcane fields and banana post-harvest fungicides to be among the main pollutants in these rivers. Consequently, long-term and multi-residue monitoring is required to understand the fate of the different molecules applied in fields taking account of cropping systems evolution over time. This will be further performed thanks to the set-up of the Observatory of agricultural-source pollution in the French West Indies (OPALE).

Understanding the temporal and spatial variability of soil moisture is fundamentalfor improving the management of water and soil resources on rainfed agrosystems.The present study focused on the soil moisture (SM) patterns observed in a hillyrainfed agrosystem. We analyzed five datasets from measurement at 15 sites duringvarious crop growth cycles under the common cereals/legumes/pasture croppingsystems within the Kamech catchment in Tunisia. Results indicated a strongseasonality in the precipitation and evapotranspiration dynamics that stronglyinfluences soil moisture patterns, with a strong reduction in the water availabilityduring summer (average SM = 0.20 m3/m3) as compared to winter (average SM =0.40 m3/m3). The data of two consecutive years showed that the spatial variability,expressed through the coefficient of variation of soil moisture, was at its highestpoint during spring. The averaged soil moisture of the two years yielded areasonable significant linear relation (R²=0.67**), indicating temporal stability ofthe spatial pattern. Actual evapotranspiration was found to be the predominantfactor influencing the dynamics of soil moisture.

French Office for Water and Aquatic Bodies (ONEMA); French National Institute for Agricultural Research (INRA) [22-6-20]; International audience; Farm ditch networks, infrastructures designed to regulate excess water in cropped landscapes, constitute pesticide dispersal pathways or buffer zones, depending on their soil properties. Despite the key role that ditch soils play in the regulation of water and pesticide fate, their properties, especially in intermittently flooded ditches, remain poorly characterized. Therefore, our aim was to evaluate the specificity of ditch material properties to determine whether ditches require an approach that differs from that of field soils when studying water and pesticide fate in farmed landscapes. We thus analysed the variations in the pedological, herbicide sorption and flow properties of soil materials along a 2D cross-section of an intermittently flooded ditch in the Roujan catchment of southern France. We found that the upper part of the ditch bed soil profile is composed of 3 horizons that formed after the original creation of the ditch, most likely via the deposition of field-eroded particles and the accumulation of organic matter. These specific horizons have greater porosity, mostly due to their dense root systems, and contain up to 2 times more organic carbon than the neighbouring banks or field soils. Consequently, the hydraulic conductivity is greater, and the sorption of hydrophobic herbicides is up to 2 times greater in ditch bed materials than it is in soils located farther away from the ditch surface. Moreover, significant macroporal flow was evidenced in both profiles but with different contribution to the global flow. The contrasts in the hydrodynamic and sorption properties between both the ditch bed and banks materials likely results in significantly different water and pesticide infiltration patterns in ditches compared to crop fields. Given these differences, we recommend investigating the specific properties of ditch beds when studying and modelling water and pesticide fate in croplands.

International audience; Glyphosate is the most applied herbicide for weed control in agriculture worldwide. Excessive application of glyphosate induces water pollution. The transfer of glyphosate to freshwater and groundwater is largely controlled by glyphosate sorption to soils and sediments. Sorption coefficients are therefore the most sensitive parameters in models used for risk assessment. However, the variations in glyphosate sorption among soils and sediments are poorly understood. Here we review glyphosate sorption parameters and their variation with selected soils and sediment. We use this knowledge to build pedotransfer functions that allow predicting sorption parameters, Kd, Kf and n, for a wide range of soils and sediments. We gathered glyphosate sorption parameters, 101 Kf, n and equivalent Kd, and associated soil properties. These data were then used to perform stepwise multiple regression analyses to build the pedotransfer functions. The linear (Kd) and Freundlich (Kf, n) pedotransfer functions were benchmarked against experimental data. We found the following major points: (1) Under current environmental conditions, sorption is best predicted by the Kd pedotransfer function. (2) The pedotransfer function is Kd = 7.20*CEC - 1.31*Clay + 24.82 (Kd in L kg(-1), CEC in cmol kg(-1) and clay in %). (3) Cation exchange capacity (CEC) and clay content are the main drivers of Kd variability across soils and sediments. Freundlich parameters are additionally influenced by pH and organic carbon. This suggests that the formation of complexes between glyphosate phosphonate groups and soil-exchanged polyvalent cations dominates sorption across the range of analyzed soils.

As agricultural hilly watersheds are widespread throughout the world, there is a strong need for reliable estimates of land surface fluxes, especially evapotranspiration, over crop fields on hilly slopes. In order to obtain reliable estimates from eddy covariance (EC) measurements in such conditions, the current study aimed at proposing adequate planar fit tilt corrections that account for the combined effects of topography, wind direction, and vegetation height on airflow inclinations. EC measurements were collected within an agricultural hilly watershed in northeastern Tunisia, throughout the growth cycles of cereals, legumes, and pasture. The wind had two dominant directions that induced upslope and downslope winds. For upslope winds, the airflows were parallel to the slopes and slightly came closer to the horizontal plane when vegetation grew. For downslope winds, over fields located in the lee of the rim top, the airflows were almost horizontal over bare soil and came closer to the topographical slope when vegetation grew. We therefore adjusted the planar fit tilt correction on EC measurements according to vegetation height and by discriminating between upslope and downslope winds. This adjusted tilt correction improved the energy balance closure in most cases, and the obtained energy balance closures were similar to that reported in the literature for flat conditions. We conclude that EC data collected within crop fields on hilly slopes can be used for monitoring land surface fluxes, provided planar fit tilt corrections are applied in an appropriate manner.

International audience

The performance of buffer zones for removing pesticides from runoff water varies greatly according to landscape settings, hydraulic regime, and system design. Evaluating the performance of buffers for a range of pesticides and environmental conditions can be very expensive. Recent studies suggested that the fluorescent dyes uranine and sulforhodamine B could be used as cost-effective surrogates of herbicides to evaluate buffer performance. However, while transformation mechanisms in buffers have been extensively documented, sorption processes of both dyes have rarely been investigated. In this study, we measured the adsorption, desorption, and kinetic sorption coefficients of uranine and sulforhodamine B for a diverse range of buffer zone materials (soils, litters, plants) and compared the adsorption coefficients (Kd) to those of selected herbicides. We also compared the global sorption capacity of 6 ditches, characterized by varying proportions of the aforementioned materials, between both dyes and a set of four herbicides using the sorption-induced pesticide retention indicator (SPRI). We found that both the individual Kd of uranine for the diverse buffer materials and the global sorption capacity of the ditches are equivalent to those of the herbicides diuron, isoproturon, and metolachlor. The Kd of sulforhodamine B on plants and soils are equivalent to those of glyphosate, and the global sorption capacities of the ditches are equivalent for both molecules. Hence, we demonstrate for the first time that uranine can be used as a proxy of moderately hydrophobic herbicides to evaluate the performance of buffer systems, whereas sulforhodamine B can serve as a proxy for more strongly sorbing herbicides.

International audience; Ditch networks were traditionally designed to protect fields from soil erosion or control waterlogging. They are still frequently managed by either mowing, chemical weeding, dredging or burning to ensure their optimal hydraulic capacity. Ditches were recently reported also to improve water quality and sustain biodiversity. These ditch functions are related to specific ditch properties. By contrastingly modifying ditch properties, maintenance operations were supposed to regulate these functions. There is, therefore, a need to re-examine the design and maintenance strategies of ditches to optimize the whole range of ecosystem services that they provide. In this study, we address the innovator question of how maintenance operations affect the yearly evolution of ditch properties, and in turn, the panel of functions that ditches support. During one year, we monitored the vegetation, litter, soil properties, and ash cover of five ditches that were being unmanaged, dredged, mowed, burned, and chemically weeded, respectively, with timing and frequency as generally operated by farmers in the study area. We then used indicators to evaluate the effect that the evolution of these properties has on the ditch water conveyance, herbicide retention and biodiversity conservation functions. We found that the evolution of these properties significantly contrasted among the 5 maintenance strategies. All the maintenance operations cleared the vegetation, which improves the hydraulic capacity by up to 3 times. The optimal hydraulic capacity is maintained longer after chemical weeding and dredging, but these operations have negative impacts on the herbicide retention and biodiversity conservation functions. The litter and ash layers generated by mowing and burning, respectively, improve the herbicide retention by up to 45%. Our results confirm that maintenance can be an efficient tool for optimizing ditch functions. The choice of maintenance operation and timing are key to successfully optimizing most of the functions that ditches can support.

International audience; Banana plantations in tropical humid regions require a high input of pesticides. Given the long history of this practice, a number of pesticides that are now banned have accumulated in these soils. Little is known about the sorption of two banned insecticides, chlordecone and cadusafos, which are known to cause adverse environmental and health effects. We studied the sorption-desorption characteristics (Freundlich sorption-desorption coefficient, K-f, and partition coefficient, K-d) of these two molecules in tropical volcanic soils with different soil properties. In particular, we observed the effect of the chemical nature of the soil organic carbon (SOC). The sorption of chlordecone (35.56< K-d < 144.96 L kg(-1)) and the desorption hysteresis (apparent hysteresis index, H

International audience; Chlordecone is a persistent organochlorine insecticide that, even decades after its ban, poses a threat to the environment and human health. Nevertheless, its environmental fate in soils has scarcely been investigated, and elementary data on its degradation and behaviour in soil are lacking. The mineralisation and sorption of chlordecone and the formation of possible metabolites were evaluated in a tropical agricultural andosol. Soil microcosms with two different soil horizons (S-A and S-B) were incubated for 215 days with C-14-chlordecone. At five different times (1, 33, 88, 150 and 215 days) the extractability of C-14-chlordecone was analysed. Mineralisation was monitored using (CO2)-C-14 traps of NaOH. The appearance of metabolites was studied using thin layer and gas chromatography techniques. At the end of the experiment, the water soluble C-14-activity was 2% of the remaining C-14-chlordecone for S-A and 8% for S-B. Only 12% of the remaining activity was non extractable and more than 80% remained extractable with organic solvents. For the first time to our knowledge, a significant mineralisation of chlordecone was measured in a microcosm under aerobic conditions (4.9% for S-A and 3.2% for S-B of the initial C-14-activity). The drastically lower emission of (CO2)-C-14 in sterilised microcosms indicated the biological origin of chlordecone mineralisation in the non-sterilised microcosms. No metabolites could be detected in the soil extracts. The mineralisation rate of chlordecone decreased by one order of magnitude throughout the incubation period. Thus, the chlordecone content in the soil remained large. This study confirms the existence of chlordecone degrading organisms in a tropical andosol. The reasons why their activity is restricted should be elucidated to allow the development of bioremediation approaches. Possible reasons are a heterogeneous distribution a chlordecone between sub-compartments with different microbial activities or a degradation of chlordecone by co-metabolic processes controlled by a limited supply of nutrients. (C) 2013 Elsevier B.V. All rights reserved.

International audience; Many farming-system studies have investigated the design and evaluation of crop-management practices with respect to economic performance and reduction in environmental impacts. In contrast, little research has been devoted to analysing these practices in terms of matching the recurrent context-dependent demand for resources (labour in particular) with those available on the farm. This paper presents Dhivine, a simulation model of operational management of grape production at the vineyard scale. Particular attention focuses on representing a flexible plan, which organises activities temporally, the resources available to the vineyard manager and the process of scheduling and executing the activities. The model relies on a generic production-system ontology used in several agricultural production domains. The types of investigations that the model supports are briefly illustrated. The enhanced realism of the production-management situations simulated makes it possible to examine and understand properties of resource-constrained work-organisation strategies and possibilities for improving them.

The aim of this study was to identify primary flow paths involved in the chlordecone (CLD) river contamination and quantify the CLD fluxes to assess CLD pollution levels and duration according to a typical catchment of the banana cropping area in the French Indies (Guadeloupe): the Perou Catchment (12 km(2)) characterized by heavy rainfall (5686 mm year(-1)). Three sub-catchments (SC1, SC2 and SC3) were studied during the hydrological year 2009-2010: a pedological survey combined with a spatialized hydrochemical approach was conducted. The average soil concentration is higher in the Perou Catchment (3400 mu g kg(-1)) than in the entire banana cropping area in Guadeloupe (2100 mu g kg(-1)). The results showed that CLD stocks in soils vary largely among soil types and farming systems: the weakest stocks are located upstream in SC1 (5 kg ha(-1)), where a majority of the area is non-cultivated; medium stocks are located in Nitisols downstream in SC3 (9 kg ha(-1)); and the greatest stocks are observed in SC2 on Andosols (12 kg ha(-1)) characterized by large farms. The annual water balance and the hydro-chemical analysis revealed that the three sub-catchments exhibited different behaviors. Perou River contamination was high during low flows, which highlighted that contamination primarily originated from groundwater contributions. The results showed that only a small part of the catchment (SC2), contributing little to the water flow, comprises a major CLD contribution, which is in agreement with the highly contaminated andosol soils observed there. Another significant result considers that at least 50 years would be required to export the totality of the actual CLD soil stocks retained in the topsoil layer. The actual time for soil remediation will however be much longer considering (i) the necessary time for the chlordecone to percolate and be stored in the shallow aquifers and (ii) its travel time to reach the river.rights reserved.

International audience; Pesticide sorption to ditch-bed materials can efficiently decrease pesticide concentrations in the flowing water. Pesticide sorption depends on flood characteristics and the nature and abundance of ditch-bed materials, such as soils, living and decaying vegetation and ash. However, the affinities of pesticides for various ditch-bed materials have rarely been investigated, and variations in the global sorption capacity of ditch beds resulting from their heterogeneous compositions and variable flood characteristics have not been determined. Thus, we studied the variability of sorption capacities of ditch-bed materials for glyphosate and diuron in three catchments in France and propose a method for calculating global sorption processes in heterogeneous ditch beds. The methodology consists in estimating a global sorption coefficient for the composite ditch-bed materials (Kd ditch ) and an indicator of the amount of pesticide potentially retained by sorption during a flood event (SPRI). Furthermore, we computed the Kd ditch and SPRI of glyphosate and diuron for 8 ditches subjected to 3 h flood events with water levels varying from 0.5 to 15 cm. Our results show that increasing the water level from 0.5 to 15 cm resulted in a 90% decrease in the sorption capacities of the ditch beds for both pesticides. At a medium water depth of 5 cm, SPRI varied from 25 to 51% and from 7 to 35% among the ditches for glyphosate and diuron, respectively. The variabilities of the glyphosate and diuron sorption capacities among the ditches were mainly driven by the nature and abundance of soil and ash. As the management of farm ditches, performed to maintain their hydraulic performance, modifies the abundances of various ditch-bed materials, it constitutes a potential lever of action for water quality improvement. Thus, Kd ditch and SPRI could serve as rapid and cost-effective tools for optimizing ditch network management strategies to improve water quality in cropped catchments.

International audience; Grass buffer strips limit the transfer of pesticides from cultivated fields to rivers. These solutions are generally efficient at reducing polluted surface flows, mainly by infiltration of the soil, raising the question of the fate of the infiltrated pollutants. An environmental evaluation was conducted on the efficiency of a grass strip receiving diuron-contaminated water from an uphill vineyard in France. During two runoff events, the following measurements were taken: surface inflow and outflow with Venturi flumes, vertical percolated flow below the root layer (0-50 cm), and variations in water and solute content of the root layer. One runoff event occurred under natural rainfall conditions, while the other runoff event was artificially provoked with water doped by diuron and bromide. For the natural runoff event, representative of medium intensity events, 94% of the diuron was retained in the root layer, whereas 2% left the grass strip by surface runoff and 4% left the grass strip in the water percolating under the root zone. For the artificial event, representative of intense runoff events, more than half of the incoming diuron was retained by the grass strip, whereas 24% and 18% of it were transferred by surface runoff and percolation, respectively. These results showed that the capacity of the root layer to retain diuron was highly significant despite a large percolation flux. However, for large runoff events, surface and subsurface losses can still be considerable, up to 40% of the pesticide load entering the strip.

The principal challenge in the parameterization of storm flow models for agricultural catchments with an artificial drainage network and fields with different degrees of tillage lies in the parsimonious definition of distributed model parameters in a way that reduces the number of calibration parameters to a justifiable minimum. This paper presents a comprehensive case study for the parameter estimation of a distributed storm flow model applied to an agricultural catchment (0.91 km2) in the Mediterranean region. Model parameterization was combined with procedures for multi-criteria, multi-storm calibration, where we automatically calibrated three parameters related to flow velocity and infiltration, and compared single and multi-storm criteria that are based on discharge volume, peak flow, and the Nash–Sutcliffe coefficient. Multi-storm calibration yielded a set of parameter values for the simulation batch with best multi-storm overall performance, which are close to the median values in the pre-calibration of individual storms. Our results suggest that flow velocities and proportionality of the channel infiltration rate do not vary significantly over the course of 11 years. Copyright © 2012 John Wiley & Sons, Ltd.

Summary The difference between the cumulative infiltration occurring during three-dimensional axisymmetric and one-dimensional vertical flow is a linear function of time. The slope of this line is a function of the source radius, initial and final volumetric soil water contents and the soil sorptivity. This allows the determination of the sorptivity and saturated conductivity of the soil from data of axisymmetric flow in a single ring of small diameter under negligible head of water. The method is based on the optimization of the sorptivity and saturated conductivity on the one-dimensional vertical cumulative infiltration inferred from axisymmetric flow data. To examine the reliability of the method to determine these parameters, numerical three- and one-dimensional data are generated on soils with known hydrologic properties from the literature. The linearity versus time of the difference of the two types of flow is verified. Several physically based expressions for the vertical cumulative infiltration as a function of time are considered. The optimized values of the sorptivity and saturated conductivity are compared to the their real known values. Despite the large errors on the optimized parameters, namely the saturated conductivity, the error on the vertical predicted cumulative infiltration is limited to 10%. This makes possible the application of this method on a large scale for hydrological modelling purposes.

International audience; AbstractAgriculture must now feed the planet with the lowest environmental impact. Landscape management is a means to protect natural resources from the adverse impacts. In particular, the adequate management of ditches could improve crop quality. Here, we review ditch design and maintenance. We found the following major points: (1) ditch networks have been primarily designed for waterlogging control and erosion prevention. Nonetheless, when properly managed, farm ditches provide other important ecosystem services, namely groundwater recharge, flood attenuation, water purification, or biodiversity conservation. (2) All ditch ecosystem services depend on many geochemical, geophysical, and biological processes, whose occurrence and intensity vary largely with ditch characteristics. (3) The major ruling characteristics are vegetative cover; ditch morphology; slope orientation; reach connections such as piped sections and weirs, soil, sediment and litter properties, biota, and biofilms; and network topology. (4) Ditch maintenance is an efficient engineering tool to optimize ecosystem services because several ditch characteristics change widely with ditch maintenance. For instance, maintenance operations, dredging, chemical weeding, and burning improve waterlogging and soil erosion control, but they are negative for biodiversity conservation. Mowing has low adverse effects on biodiversity conservation and water purification when mowing is performed at an adequate season. The effects of burning have been poorly investigated.

Correspondance: chahinia@ensam.inra.fr; International audience; Soil surface crusts are widely reported to favour Hortonian runoff, but are not explicitly represented in most rainfall-runoff models. The aim of this paper is to assess the impact of soil surface crusts on infiltration and runoff modelling at two spatial scales, i.e. the local scale and the plot scale. At the local scale, two separate single ring infiltration experiments are undertaken. The first is performed on the undisturbed soil, whereas the second is done after removal of the soil surface crust. The HYDRUS 2D two-dimensional vertical infiltration model is then used in an inverse modelling approach, first to estimate the soil hydraulic properties of the crust and the subsoil, and then the effective hydraulic properties of the soil represented as a single uniform layer. The results show that the crust hydraulic conductivity is 10 times lower than that of the subsoil, thus illustrating the limiting role the crust has on infiltration. Moving up to the plot scale, a rainfall-runoff model coupling the Richards equation to a transfer function is used to simulate Hortonian overland flow hydrographs. The previously calculated hydraulic properties are used, and a comparison is undertaken between a single-layer and a double-layer representation of the crusted soil. The results of the rainfall-runoff model show that the soil hydraulic properties calculated at the local scale give acceptable results when used to model runoff at the plot scale directly, without any numerical calibration. Also, at the plot scale, no clear improvement of the results can be seen when using a double-layer representation of the soil in comparison with a single homogeneous layer. This is due to the hydrological characteristics of Hortonian runoff, which is triggered by a rainfall intensity exceeding the saturated hydraulic conductivity of the soil surface. Consequently, the rainfall-runoff model is more sensitive to rainfall than to the subsoil's hydrodynamic properties. Therefore, the use of a double-layer soil model to represent runoff on a crusted soil does not seem necessary, as the increase of precision in the soil discretization is not justified by a better performance of the model.

This paper shows that geostatistical modelling can be extended to spatial supports such as directed trees and applied to variables spatially structured along a river network. Specific assumptions were necessary and main methods were redefined introducing modifications on metrics, proper variogram estimates and ad hoc drift models. We also proposed a model-based simulation procedure to generate random functions on directed trees. A case study on fluvisol delineation for the Herault river (South of France) was analyzed. Clear spatial structures were observed and modelled using variogram based on upstream–downstream distance along a hydrographic network. A drift was also modelled as a multiplicative term affecting the fluvisol width versus the cumulated length of the upstream network. The significance of the drift was then assessed conditionally to the former spatial variogram using Monte-Carlo simulations of the spatial observed process on the river network.

[Departement_IRSTEA]RE [TR1_IRSTEA]RIE / TRANSFEAU; International audience; Grassed buffer strips are one way to reduce pesticide transfer by surface runoff from farmed fields to streams. Numerous experimental studies have demonstrated that this type of development is very effective in various conditions. The results are nevertheless very variable. This variability is partially explained by the multiplicity of processes and contributive factors and by the fact that the latter are dynamic in nature and site-specific. Several results also show that the intercepted products are not systematically immobilized within the strip but can move in the subsurface, thus affecting the overall effectiveness of the system. As a consequence of this complexity, the present guidelines for the sizing and siting of grassed strips are still only qualitative or are the result of empirical approaches. The present review analyses the available results and defines needs for further research. This concern several basic processes determining the pesticide interception by grassed strip and numerical models necessary to integrate the complexity of interacting processes and formulate reliable managing guidelines.

Soil water status and its effect on plant water status are commonly evaluated for water stress diagnosis in annual crops. We investigated the application of this method to vineyards, using the fraction of transpirable soil water (FTSW) to characterise the soil water deficit experienced by the plant. The stability of the relationship between FTSW and predawn leaf water potential (Ψp) was analysed over two years (2000–2001), in two contrasted soils in vineyards in south eastern France, both planted with the cultivar Syrah, but grafted on different rootstocks (SO4 and 140Ru). FTSW was determined from soil moisture measurements performed with a neutron probe down to 2.5 m, under the rows and between the rows (3 replicates in each case). Vertical and horizontal variations in soil water content were analysed and the upper and lower limits of total vine’s transpirable soil water (TTSW) were calculated for each soil. The lower limit was also compared with the value of soil moisture content determined at −1.5 MPa in the laboratory. FTSW could be calculated for the soil depth analysed, without distinguishing horizontal position (row or inter-row). The lower limit of TTSW for vine was higher than the soil water content at −1.5 MPa, except in the upper horizons (0–0.2 m) which are prone to soil evaporation. A single relationship between Ψp and FTSW was obtained for the two vineyards and for the two years of measurement. This relationship was similar to that established by Lebon et al. (2003) on Gewurztraminer/SO4 in a vineyard in northern France. FTSW can therefore be used as an indicator of the water deficit experienced in vineyards, provided that TTSW is correctly estimated.

An experimental study was conducted in a 91.4-ha Mediterranean vineyard catchment in southern France to characterize the fate and transport of oryzalin in runoff water and thus to assess the risk of contamination of surface waters. Oryzalin concentrations in soil were monitored on two fields, one no-till and one tilled from March 1998 to March 2000. Concentrations in solution and on solid phase of runoff water were measured at the outlets of both fields and the catchment. The droughts in the two summer periods reduced the dissipation of oryzalin and increased its field half-life up to 35 days. Consequently, oryzalin was detected throughout the year in runoff water, with maximum dissolved concentrations > 600 microg l(-1) at the field scale. Oryzalin transport essentially occurred in solution. At the no-till field, seasonal losses were 2.29% and 1.89% of the applied amount in 1998 and 1999, respectively. The corresponding values at the tilled field were 1.56% and 0.29%, since tillage reduced total losses by reducing surface runoff. At the catchment scale, oryzalin concentrations were smaller than those at the field scale, due to dilution effects and staggering of application. Large part of the overland flow from the fields reinfiltrated in the ditches before reaching the outlet of the catchment. As a result, seasonal oryzalin losses were

The contamination of soil and runoff water by two herbicides, diuron [N'-(3,4-dichlorphenyl)-N,N-dimethylurea] and simazine (6-chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine), were monitored on two fields, one no-till and one tilled. Experiments were carried out in a 91.4-ha watershed in southern France during the 1997 growing season in order to understand the patterns of pesticide transport from field to watershed. The persistence of the herbicides in soil was prolonged due to the climatic conditions. At the field scale, annual herbicide loads were due to overland flow and amounted to 65.6 and 6.3 g ha(-1) of diuron for the no-till and tilled field, respectively, and to 29.6 and 1.83 g ha(-1) of simazine. Maximum herbicide concentrations exceeded 580 microg L(-1) during the first storm event after application and decreased thereafter but remained for 8 mo above 0.1 microg L(-1). At the watershed outlet, estimated annual loads amounted to 4.12 g ha(-1) of diuron and 0.56 g ha(-1) of simazine. Among them, 96% of the losses in diuron and 83% of those in simazine were caused by the fast transmission through the network of ditches of the overland flow exiting the fields. For diuron, which was sprayed over most of the vineyards, its in-stream concentrations during storm flow were close to those at the outlet of the fields. The herbicide loads in baseflow were smaller than 0.2 g ha(-1). The patterns of the loads at the field and watershed scales suggested that a major part of the herbicides leaving the fields reinfiltrated to the ground water by seepage through the ditches, and was there degraded or adsorbed.

The aim of this paper is to present to the community of ecologists concerned with predictive modelling by feedforward neural network, a new statistical approach to select the best neural network architecture (number of layers, number of neurons per layer and connectivity) in a set of several candidate networks. The interest of this approach is demonstrated on a soil hydrology problem.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; In the French West Indies, chlordecone (CLD), an organochlorine pesticide, was applied in banana plantations from 1972 to 1993. Our study was aimed at identifying the factors that determine soil CLD contamination and that thus can describe the spatial distribution of this contamination. For each of the 1045 plots analyzed for CLD, we collected spatial information on the physical environment and agricultural activities. Then, we searched for determinants of soil contamination and used a multiple regression model to predict the spatial distribution of CLD. First, the results showed that the soil type had a strong impact. Andosols, with a high organic carbon content (up to 100 g kg−1) and a high sorption capacity (Koc 20 000 L kg−1), had the highest CLD concentrations and stocks. Nitisols had 10-fold lower sorption capacities. Second, the results showed a "farm effect" on soil contamination, due to the more or less intensive application of inputs by farmers and to the shorter or longer application times, depending on the banana land-use frequency. However, despite these effects and given the weak accuracy of the usually available information on agricultural activities, it remained difficult to predict the spatial distribution of CLD contamination by a multiple regression model. In conclusion, this study highlighted the multifactorial nature of pollution. The main perspectives are related to better assessments of agricultural activities using remote sensing strategies and designing agricultural practices observatories focusing on pesticide use.

International audience; The current current study addressed the consistency of eddy covariance (EC) measurements collected in sloping conditions within a hilly agricultural catchment. In the context of operational monitoring and modelling devoted to decision support, it is important to increase the knowledge of surface fluxes under conditions of hilly topography. The two-metre-high EC measurements were collected at the field scale within the two opposite rims of a V-shaped catchment located in northeastern Tunisia on the southern shore of the Mediterranean Basin. Measurements were collected under bare soil conditions to enhance the effects of the slopes. The data pre-processing and quality control measures were conducted using standard procedures. In assessing the consistency of the EC measurements we first compared the airflow inclinations captured by the EC measurements against the topographical slopes captured by a Digital Elevation Model; we then assessed the energy balance closure. The analysis of the micrometeorological data indicated specific regimes: externally driven winds; forced convection; and stability conditions close to neutrality or low instability. The two dominant wind directions induced upward and downward flows on the two opposite rims. For the upward flows, the airflow inclinations followed the topographical slopes on both fields. For the downward flows, the flows followed the topographical slopes on the southern rim and were almost horizontal on the other rim. In all cases, and especially for the upward flows, the energy balance closure was similar to that reported in the literature. Overall, the behaviour observed for upward flows was close to that reported in the literature for flat conditions, whereas the downward flows exhibited different trends. The different trends we observed for the downward flows were ascribed to the bubble separation zone that implies streamline dilatation, turbulence and reverse flows. Future investigations should address the vegetation conditions. The expected outcomes are of importance for revisiting the operational methods devoted to the estimation of evapotranspiration.

Summary Conventional soil survey stratifies a region into mapping classes and characterizes each by a representative soil profile within it. The efficacy of the procedure for predicting particle-size fractions, bulk density, water retention, and available water capacity (AWC) of the soil at previously unvisited sites on the Plain of Languedoc in southern France is evaluated for three scales of survey (1/10 000, 1/25 000 and 1/100 000) and is compared to that of prediction from stratified random and simple random samples. Data from 85 soil profiles on a random transect were used for evaluation. Classification partitioned the variation of the measured properties, except for AWC, well at the 1/10 000 and 1/25 000 scales, whereas classification at the 1/100 000 scale was less effective. At the 1/10 000 and 1/25 000 scales both classification and stratified random sampling were better for prediction than simple random sampling for the same total sample. On average the representative profiles proved substantially better predictors than the stratified random samples, but in most situations where soil stratification performed well efficiencies of the two predictors were similar. In essence, the more successful the classification was the more difficult it was to improve prediction by selecting representatives instead of sampling randomly within classes. These results confirmed statistically that the soil surveyor can exercise intuition and judgement to classify and select representatives.

Methods for interpolating soil moisture curves at unrecorded sites from measurements of soil water content at fixed pressure heads at sample points are investigated. A spatial prediction procedure was devised with two steps: interpolation of the retention data followed by fitting the Van Genuchten function to the interpolated values. For the interpolation, four different methods were considered. Two are based on a tessellation into areas of equal values, namely the nearest neighbour and the soil classification. The other two were autokriging and cokriging. The performance of these methods were compared in an area of 92 ha of alluvial soil where soil changes were gradual. Mean deviations and mean square deviations between predicted and observed retention data at validation sites were compared for two sampling densities. Kriging performed best in both cases. Cokriging was only slightly better than autokriging, and the latter is recommended for use. The performance of the nearest neighbour method diminished markedly with decreasing sampling density. Conversely, the performance of soil classification diminished only slightly, and this technique appeared as a reasonable alternative to kriging for sparse samples.