20 research outputs found
ARPEGES, une méthode pour évaluer le potentiel de contamination des eaux de surface par les pesticides à l'échelle nationale
International audienceArpeges is an innovating and coherent method to assess the potential surface water's contamination by pesticides at the national scale. In France, it was implemented at Water Framework Directive water bodies' scale. The objectives are to identify of vulnerable zones and to determinate the main risk factors implied in pollution transfer according to the considered zones. Actually, this method allows a better understanding and a ranking of pollution's causes considering three essential aspects of the contamination: uses, environmental vulnerability to pesticides pollution and substances properties. The method is mostly based on transfer processes. In order to take into account the seasonal temporal variability, analyses are separately carried on winter and summer, and both acute and chronic approaches of the risk are considered. The segregation between these two risks is built on the different processes transfer times to reach surface waters. 18 relevant variables describing pesticides transfer are chosen (infiltration, pedology, drainage, climate, buffer zones...); they are aggregated according to up to date expert knowledge thanks to a Bayesian network to obtain pesticides contamination. This tool allows associating an uncertainty factor to each result and contributing to increase the adaptability of the method. Intermediary results as environmental vulnerabilities are relevant to identify the main causes of transfer
Effects of growth rate, size, and light availability on tree survival across life stages: a demographic analysis accounting for missing values and small sample sizes.
The data set supporting the results of this article is available in the Dryad repository, http://dx.doi.org/10.5061/dryad.6f4qs. Moustakas, A. and Evans, M. R. (2015) Effects of
growth rate, size, and light availability on tree survival across life stages: a demographic analysis accounting for missing values.Plant survival is a key factor in forest dynamics and survival probabilities often vary across life stages. Studies specifically aimed at assessing tree survival are unusual and so data initially designed for other purposes often need to be used; such data are more likely to contain errors than data collected for this specific purpose
Do fish go with the flow? The effects of periodic and episodic flow pulses on 0+ fish biomass in a constrained lowland river
The hydrological regime is a significant driver of fish population dynamics in rivers, but there is a dearth of information regarding the mechanisms behind its effects on temperate species, especially non-salmonids. This study investigated the effects of periodic and episodic flow pulses on 0+ fish biomass in a constrained lowland river. De-seasonalized cross-correlation analysis was used to examine time-lagged correlations in episodic signals, in isolation of seasonal periodicity, to identify the responses and response timings of 0+ fish production to abiotic variables, and whether apparent “pulse-depletions” in biomass occur instantaneously (e.g., due to fish displacement during high pulses) or after a time lag. As anticipated, 0+ fish biomass was highest during periods of low discharge and high temperatures in summer, but cross-correlation analysis revealed a negative impact of high pulses on 0+ fish biomass with a lag of 7 months. There was no evidence for an instantaneous pulse-depletion effect of discharge on 0+ fish biomass, suggesting that the indirect effects of high pulses, such as habitat or food-web modifications, are more influential
Guide d'installation et d'utilisation de l'interface informatique associée à la méthode ARPEGES
Ce rapport présente les résultats d'un travail de programmation informatique réalisé en 2017, visant à retranscrire le modèle ARPEGES (Analyse du Risque PEsticides pour la Gestion des Eaux de Surface), initialement développé sur le logiciel propriétaire Netica, dans un format libre de droit, afin de faciliter sa diffusion et son utilisation par les utilisateurs finaux, et de fournir une interface permettant l'utilisation du modèle dans un but de simulation sans devoir écrire des commandes en ligne de code. La plateforme retenue est le logiciel de statistiques R, libre de droit. Ce rapport reprend très brièvement les éléments descriptifs de la démarche ARPEGES, présente rapidement les données d'entrée, puis présente la structure et guide l'utilisateur dans la prise en main de l'interface et de son utilisation dans un but de simulation. La dernière partie de ce rapport est un guide d'installation de l'interface sous R. L'interface est disponible sous forme d'un fichier .zip nommé « Install_Arpeges » auprès de l'Agence Française de la Biodiversité. Les produit finaux des simulations sont des tableaux de résultats, exploitables dans des logiciels de type tableur et permettant le lien vers de nmbreux logiciels statistiques, ainsi que des couches de données de type shape, permettant la cartographie des résultats, à l'échelle des bassins versants des masses d'eau des cours d'eau métropolitains. L'interface est également dotée d'un éditeur de cartes. En complément de ce travail «de programmation », un travail thématique visant à aider les Agences de l'Eau à prendre en main du modèle et à interpréter les résultats a été réalisé en déroulant le modèle sur 15 substances actives prioritaires au regard de la DCE et rapporté dans un guide d'aide à l'interprétation (Adoir et al, 2017)
Projet Indeco-IBBHIS : Indicateurs de Biodiversité en Bayésien Hiérarchique Spatialisé
National audienceNous présentons les premiers résultats du projet IBBHIS. Ces premiers résultats concernent le lien entre volume de bois mort et biodiversité saproxylique. Nous comparons différentes plateformes statistiques pour estimer ces relations. Les différentes plateformes donnent des résultats proches. Les premiers résultats indiquent une relation qui varie dans l'espace, et des seuils de bois mort qui varient aussi d'un massif à l'autre
Effets directs et indirects des stresseurs multiples sur la faune des cours d'eau à travers les échelles bassin versant, tronçon et site
International audienceThe purpose of our approach was to take account of the nested scales of stream functioning on the links between pressures and ecological status by building and analysing a hierarchical model. The development of this model aimed at answering the following questions: Does the indirect links between pressures and ecological status modify the impact hierarchy of pressures? Do the different nested scales play a different role in the pressures-ecological status relationship? To achieve that goal, we used the PLS path modelling method for developing a structural model linking the latent variables of (i) land use, and hydromorphological alterations at watershed scale, (ii) hydromorphological alterations at reach scale, (ii) nutrients-organic matter contamination levels, and (iv) substrate samples to explain macroinvertebrate based index I2M2 score variation. As a first important result, we have highlighted the importance of land use effect exerted on both hydromorphology and physico-chemistry and their translation as an indirect effect on biological condition of streams. We have also demonstrated that hydromorphological alterations had an effect on substrates structure and nutrients and organic matter concentrations. This result implies that hydromorphology has a major indirect effect on macroinvertebrates
Exemple de difficulté d'estimation de modèle hiérarchique et de solution : cas d'un modèle non-linéaire hiérarchique
National audienceNous présentons le cas d'un modèle non-linéaire hiérarchique ayant posé des problèmes d'estimation. Une étude des raisons de ces problèmes d'estimation et une reparamétrisation du modèle passant par les distributions a priori (incorporation de dépendances entre paramètres) améliore grandement l'estimation (voire résout les problèmes)
Introduction du concept d'échelles emboitées dans les modèles multi-stress : vers une meilleure évaluation des impacts anthropiques sur l'écosystème rivière
International audienceWe investigated the relationships between the ecological status of wadeable rivers and the intensity of various stressors related with hydromorphological alterations, nutrient and organic matter contaminations. The French invertebrate-based multimetric index (I2M2), which efficiently responds to the effects of both physical and chemical and hydromorphological stressors, was used as descriptor of river reach ecological status. We developed a model focusing on the effects of hydromorphological and physical and chemical stressor gradients on the I2M2 in different physiographic contexts. The potential confounding effects of natural geographic conditions and watershed scale pressure gradients were taken into account and neutralized by gathering watersheds into homogeneous clusters integrated as an interaction factor in the model. Whatever effects were considered (general or within-spatial clusters), the I2M2 was impaired similarly by the same stressor types, being negatively influenced by an increase in BOD5, ammonium, nitrite, nitrate and total phosphorus concentrations. The I2M2 was also negatively influenced by variables describing hydromorphology at the reach scale, especially by the 'loss of sinuosity', 'increasing rates of bank erosion', 'flow reductions' and 'alteration of pool/riffle succession'. The I2M2 was generally more strongly impaired by physical and chemical pressures than by hydromorphological alterations
Difficultés avec les Modèles statistiques Hiérarchiques en écologie (DMH) : propositions pour le groupe de travail du GDR Ecostat
National audienceNous présentons ici les principales difficultés numériques rencontrées dans l'utilisation des modèles statistiques hiérarchiques en écologie et proposons l'organisation d'un groupe de travail sur le sujet
Des indicateurs multi-substances basés sur la bioaccumulation lors d'encagement de gammares révèlent l'influence de la contamination chimique sur l'abondance des macroinvertébrés des cours d'eau en France
International audienceMost anthropogenic stressors affecting freshwater systems are qualitatively known. However, the quantitative assessment of contaminant exposure and effects to aquatic communities is still difficult, limiting the understanding of consequences on aquatic ecosystem functioning and the implementation of effective management plans. Here, multisubstance indicators based on caged gammarid bioaccumulated contamination data are proposed (for metals and persistent organic pollutants, POPs) to map the bioavailable contamination level of freshwater ecosystems at a large spatial scale. We assessed the ability of these indicators to highlight the relationships between chemical exposure gradients and alteration in the abundance of macroinvertebrate populations on a data set of 218 watercourses distributed throughout France. We identified spatial regional heterogeneities in the levels of bioavailable contamination of metals (18 compounds) and POPs (43 compounds). Besides this, a degradation of Gammaridae, Ephemeridae, and Hydrobiidae densities with increasing levels of metal contamination are identified relative to Baetidae, Chironomidae, and Hydropsychidae. We show here that active biomonitoring allows the establishment of multisubstance indicators of bioavailable contamination, which reliably quantify chemical exposure gradients in freshwater ecosystems. Our ability to identify species-specific responses to chemical exposure gradients demonstrates the promising possibility to further decipher the effects of chemical contamination on macroinvertebrate assemblages through this type of indicator