A conceptual framework for landscape-based environmental risk assessment (ERA) of pesticides

While pesticide use is subject to strict regulatory oversight worldwide, it remains a main concern for environmental protection, including biodiversity conservation. This is partly due to the current regulatory approach that relies on separate assessments for each single pesticide, crop use, and non-target organism group at local scales. Such assessments tend to overlook the combined effects of overall pesticide usage at larger spatial scales. Integrative landscape-based approaches are emerging, enabling the consideration of agricultural management, the environmental characteristics, and the combined effects of pesticides applied in a same or in different crops within an area. These developments offer the opportunity to deliver informative risk predictions relevant for different decision contexts including their connection to larger spatial scales and to combine environmental risks of pesticides, with those from other environmental stressors. We discuss the needs, challenges, opportunities and available tools for implementing landscape-based approaches for prospective and retrospective pesticide Environmental Risk Assessments (ERA). A set of “building blocks” that emerged from the discussions have been integrated into a conceptual framework. The framework includes elements to facilitate its implementation, in particular: flexibility to address the needs of relevant users and stakeholders; means to address the inherent complexity of environmental systems; connections to make use of and integrate data derived from monitoring programs; and options for validation and approaches to facilitate future use in a regulatory context. The conceptual model can be applied to existing ERA methodologies, facilitating its comparability, and highlighting interoperability drivers at landscape level. The benefits of landscape-based pesticide ERA extend beyond regulation. Linking and validating risk predictions with relevant environmental impacts under a solid science-based approach will support the setting of protection goals and the formulation of sustainable agricultural strategies. Moreover, landscape ERA offers a communication tool on realistic pesticide impacts in a multistressors environment for stakeholders and citizens

Prédiction de la sorption du glyphosate et du diuron sur les sols et évaluation de la spécificité des sols de fond de fossés

National audienc

Using fluorescent dyes as proxies to study herbicide removal by sorption in buffer zones

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

Analysis of coupling errors in a physically-based integrated surface water-groundwater model

International audienceAbstract: Several physically-based models that couple 1D or 2D surface and 3D subsurface flow have recently been developed, but few studies have evaluated the errors directly associated with the different coupling schemes. In this paper we analyze the causes of mass balance error for a conventional and a modified sequential coupling scheme in worst-case scenario simulations of Hortonian runoff generation on a sloping plane catchment. The conventional scheme is noniterative, whereas for the modified scheme the surface-subsurface exchange fluxes are determined via a boundary condition switching procedure that is performed iteratively during resolution of the nonlinear subsurface flow equation. It is shown that the modified scheme generates much lower coupling mass balance errors than the conventional sequential scheme. While both coupling schemes are sensitive to time discretization, the iterative control of infiltration in the modified scheme greatly limits its sensitivity to temporal resolution. Little sensitivity to spatial discretization is observed for both schemes. For the modified scheme the different factors contributing to coupling error are isolated, and the error is observed to be highly correlated to the flood recession duration. More testing, under broader hydrologic contexts and including other coupling schemes, is recommended so that the findings from this first analysis of coupling errors can be extended to other surface water-groundwater models

Glyphosate sorption to soils and sediments predicted by pedotransfer functions

International audienceGlyphosate 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

Parameterization and evaluation of a three-dimensional modelling approach to water table recharge from seepage losses in a ditch

Corresponding author. fax: +33 0 4 67 63 26 14. E-mail address: [email protected] (C. Dages).International audienceIt is essential to be able to model the surface–subsurface flow processes that occur within and at the vicinity of channels and ditches because of their major role in groundwater recharge in arid regions. The main aim of this study was to evaluate a three-dimensional Richards’ equation-based modelling approach for simulating groundwater recharge. Another aim was to evaluate various strategies for estimating the hydraulic properties of the soil–aquifer system near the ditch. The case study consists of two infiltration experiments on a ditch in a catchment located in South-France. One experiment was used for calibrating the soil hydraulic properties by inverse modelling and the other for validation. The simulations were performed with the SWMS_3D simulation code, which computes three-dimensional saturated–unsaturated water flow and solute transport. For calibration and validation, two criteria were considered: piezometric heads at different distances from the ditch and hydraulic head profiles. Four scenarios of hydraulic parameter distribution were tested: an ‘‘a priori’’ scenario with observed values obtained by classical measurement techniques and three calibration scenarios. These are ‘‘homogeneous isotropic’’, ‘‘heterogeneous isotropic’’ and ‘‘heterogeneous anisotropic’’ scenarios. The results obtained show that a threedimensional Richards’ equation-based approach could satisfactorily simulate groundwater recharge by seepage losses from ditches in case of induced surface ponding experiment. Although a multi-criteria calibration was performed, three sets of soil hydraulic properties of various complexity that could reproduce satisfactorily the flow experiments were found. Finally, the results obtained also showed that representing the variability of soil properties in greater detail did not necessarily improve water flow simulation. The Akaike information criteria was used in order to discriminate between the well-calibrated scenarios. The ‘‘homogeneous isotropic’’ scenario represents the best compromise between goodness of fit and parsimony. The study also indicates that hydraulic heads are not necessarily sufficient for the thorough evaluation of groundwater flow model

Can small reservoirs be used to gauge stream runoff?

International audienceUnderstanding stream runoff generation processes requires distributed stream runoff estimates; however the acquisition of such estimates remains challenging in hydrology, especially in remote areas. In regions with a high spatial density of small reservoirs, those reservoirs could be employed to gauge stream runoff (Liebe et al., 2009). Using a water balance approach, the stream runoff flowing into a reservoir from a drainage catchment could be estimated. Accordingly, this work aims to address the following two questions: i) what is the error in the estimated stream runoff and ii) what are the main estimation uncertainty factors? Based on a case study of the Kamech catchment, Tunisia, stream runoff was estimated at different temporal resolutions (1–32 days), and a global sensitivity analysis was performed to estimate the contributions of the reservoir water balance terms (evaporation, rainfall, percolation, reservoir water level and level-area-volume relations) to the estimated stream runoff uncertainty.The results reveal that stream runoff can be reliably estimated based on small reservoirs using a mass balance approach. The error and global stream runoff estimation uncertainties decrease as the temporal resolution increases. The bathymetric relationships (level-area and level-volume relations) constitute a strong factor of uncertainty for all temporal resolutions, and even the dominant factor for temporal resolutions ranging from 4 to 23 days. The estimation uncertainty for the shortest temporal resolutions (1–8 days) mainly originates from reservoir level uncertainty. As the temporal resolution increases, the contribution of percolation uncertainty increases. The general (not site-specific) conclusions of this study are that stream runoff gauging based on small reservoirs requires the determination of the bathymetric relations and that small reservoirs could be used as reliable stream runoff gauges at short temporal resolutions if the reservoir level is measured with limited uncertainty and at long temporal resolutions as long as the percolation rate from the reservoir is known with limited uncertaint

Numerical exploration of the dynamics of infiltration in hill reservoir

International audienc

A water balance approach for quantifying subsurface exchange fluxes and associated errors in hill reservoirs in semiarid regions

International audienceHill reservoirs are rain water-harvesting structures that have been increasingly adopted in arid and semi-arid regions, such as North Africa, to capture and conserve runoff water and for use as alternative water resources in agricultural development. Currently, process-based information on reservoir hydrology is needed to improve reservoir management practices. The study aims to develop an approach to estimate the reservoir-subsurface exchange flux and its associated error at the annual, monthly, and intra-monthly time scales to better understand the hydrological functioning and dynamics of hill reservoirs. This approach is based on a hydrological water balance of the hill reservoir by considering all water input and output fluxes and their associated errors. The results demonstrate the ability and relevance of the approach in estimating the net reservoir-subsurface exchange flux and its error estimations at various time scales. Its application on the Kamech catchment (Northern Tunisia) for the 2009-2012 period demonstrates that the net reservoir-subsurface exchange flux is positive, i.e. the infiltration from the hill reservoir to the aquifer dominates over the discharge from the aquifer to the reservoir. Moreover, reservoir-subsurface exchange constitutes the main output component in the water balance