On the visual detection of non-natural records in streamflow time series: challenges and impacts

Large datasets of long-term streamflow measurements are widely used to infer and model hydrological processes. However, streamflow measurements may suffer from what users can consider anomalies, i.e. non-natural records that may be erroneous streamflow values or anthropogenic influences that can lead to misinterpretation of actual hydrological processes. Since identifying anomalies is time consuming for humans, no study has investigated their proportion, temporal distribution, and influence on hydrological indicators over large datasets. This study summarizes the results of a large visual inspection campaign of 674 streamflow time series in France made by 43 evaluators, who were asked to identify anomalies falling under five categories, namely, linear interpolation, drops, noise, point anomalies, and other. We examined the evaluators' individual behaviour in terms of severity and agreement with other evaluators, as well as the temporal distributions of the anomalies and their influence on commonly used hydrological indicators. We found that inter-evaluator agreement was surprisingly low, with an average of 12 % of overlapping periods reported as anomalies. These anomalies were mostly identified as linear interpolation and noise, and they were more frequently reported during the low-flow periods in summer. The impact of cleaning data from the identified anomaly values was higher on low-flow indicators than on high-flow indicators, with change rates lower than 5 % most of the time. We conclude that the identification of anomalies in streamflow time series is highly dependent on the aims and skills of each evaluator, which raises questions about the best practices to adopt for data cleaning.</p

Etalonnage du Chemcatcher pour des pesticides

Le Chemcatcher apolaire a été étalonné et largement étudié pour des composés tels que les HAP et PCB. Il existe en revanche très peu de données de calibration pour des pesticides hydrophobes. Les modèles cinétiques existants, basés sur des PRC du type HAP et la seule considération du log Kow des substances ne permettent pas d’estimer convenablement les taux d’échantillonnage de la plupart de composés considérés durant cette étude. Ainsi, des résultats acquis expérimentalement (constantes cinétiques et de distribution) sont présentés et des limites pressenties du Chemcatcher apolaire vis-à-vis des pesticides d’intérêt sont discutées

Spéciation et flux des métaux-trace dans une station d'épuration importante : impact des traitements successifs

International audienceSeven metals (Cd, Co, Cr, Cu, Fe, Ni and Pb) were monitored at the Seine-Aval wastewater treatment plant during 6 sampling campaigns in April 2004. Particulate and dissolved metals have been measured in 24 h composite samples at each treatment stage (primary settling, secondary activated sludge and tertiary flocculation by FeCl3). In addition, the diffusive gradient in thin film technique (DGT) was used to determine the dissolved inert and labile metal fraction. Although all treatment stages were able to decrease particulate metals concentrations in wastewater, most dissolved metals concentrations were mainly affected during primary settling. This unexpected result was attributed to tertiary sludge filtrate recirculation. Metals added via the FeCl3 reagent at the tertiary treatment were shown to lower the overall Cr removal from wastewater and to enrich Ni in effluents. The plant operating conditions (recirculation and reagent addition) appear therefore as important as treatment processes for the metals removal. Total metal fluxes were highly decreased by the whole treatment plant for Cd, Cr, Cu and Pb and to a lesser extend for Co and Ni. However, the labile metal fluxes were poorly decreased for Cu (18%), not significantly decreased for Ni and increased for Fe. The labile fraction of Cd, Co and Cr was not detectable at any stage of the plant. Discharged labile fluxes, at least for Ni, were potentially significant compared to the labile metal fluxes in the river measured downstream the plant. Treated urban wastewater discharges should be carefully considered as a possible source of bioavailable trace metals

Les métaux échantillonnés par la DGT sont-ils représentatifs de la fraction biodisponible ?

International audienceBioavailability of trace metals for aquatic organisms in the dissolved compartment of water is usually interpreted with the Free Ion Activity Model (FIAM) and its extension, the Biotic Ligand Model (BLM). Under fame generally hypothesis, the FIAM states that the biological response to a metal exposure is proportional to the activity of the free-ion {Mz+} in solution. The BLM generalizes this concept and includes competition between metal and major cations (Ca2+, Mg2+, Na+, K+ and H+) on specific binding sites at the surface of the biological membrane. As a speciation device, DGT samples labile metal concentration: free ion plus a fraction of organic metal complexes. It is claimed to estimate bioavailable fractions of metals. The aim of this communication is to synthesize the results of some recent work comparing biological response and labile fraction sampled by DGT in order to evaluate the ability of DGT to assess bioavailability. We investigated two types of biological responses: acute toxicity and bioaccumulation. In the first part, DGT were used to measure metals inducing lethality on daphnia magna during acute toxicity tests. Various media were studied: synthetic organic ligands, humic acids, and natural organic matter (algae and river extracts, wastewater), with two types of gels (classical open pores and restrictive pores). Copper and cadmium were studied. Measurements by DGT equipped with restricted gels appear to be in good agreement with inorganic fraction of metal, even if labile fraction could overestimate bioavailable fraction. In the second part, the accumulation of copper by aquatic mosses at environmentally relevant concentrations (1-5 µg.L-1) and with various organic ligands is compared to DGT-labile restricted gels measurements. In this case, DGT tends to underestimate the bioavailable fraction. This suggests that not only inorganic copper but also some weak organic complexes are available for aquatic mosses at realistic metal concentrations. Finally, we discuss the role of major cations in the bioavailability of copper, in the cases of acute toxicity and bioaccumulation at realistic environmental concentrations. Ca2+ and Mg2+ compete indeed with copper and play a protective role, which would not be highlighted by the sampling with DGT

Etude de la contamination en pesticides et en éléments traces métalliques des bassins versants du Trec et de l’Auvézère : application de l’échantillonnage intégratif passif : Rapport final synthèse campagnes 2012-2014

Pesticides have become a major component of modern agriculture and are largely use in many urban and domestic activities. These substances are found today in all compartments of the environment, particularly in aquatic environments. The emission and dispersion of active substances and their residues in the aquatic environment is potentially harmful to ecosystems, and their monitoring is then compulsory. The implementation of the Water Framework Directive (WFD) requires sampling and analysis, combining high sensitivity, accuracy and reliability, and must be easily implemented. Currently, the methodology consists of spot sampling (once a month, usually) of water bodies followed by laboratory analysis. This approach suffers from a lack of time representativeness, coupled to unsatisfactory analytical sensitivity for some substances. Passive sampling techniques developed over the last 20 years could be included in the regulatory monitoring networks in order to overcome these issues, but some questions still remain as to their applicability. This work aimed to develop and apply passive samplers like POCIS and DGT into two watersheds located in Adour-Garonne basin, in order to assess the contribution of these techniques over conventional spot sampling. Especially, a higher knowledge on the type of pressure (e.g. detection frequencies , main substances found in water) and a better understanding of the consequences of the establishment of agri-environmental measures (trend monitoring) are expected. This work has also provided information on the robustness of the data integrated over the time and the fraction sampled by these tools (e.g. labile complex for heavy metals). Finally, we examined the applicability of these tools in the context of the WFD, after setting a confidence interval associated with the time-weighted average concentrations estimates, and then we proposed a decision scheme for the comparison with environmental quality standards.Les pesticides sont devenus une composante majeure de l’agriculture moderne et se sont imposés dans de nombreuses activités urbaines et domestiques. Ces substances se retrouvent aujourd’hui dans tous les compartiments de l’environnement notamment dans les milieux aquatiques. Le suivi resserré des substances actives et de leurs résidus, présents dans l’environnement à des concentrations potentiellement dommageables pour les écosystèmes, apparaît aujourd’hui comme une nécessité. L’application de la Directive cadre sur l’eau requiert des techniques d’échantillonnage et d’analyse performantes, alliant haute sensibilité, facilité de mise ½uvre, coûts abordables, et surtout précision et fiabilité. Actuellement, la méthodologie employée consiste en des prélèvements ponctuels d’eau (une fois par mois en général) suivi de l’analyse en laboratoire. Cette approche souffre d’un manque de représentativité temporelle, couplée à une sensibilité analytique parfois peu satisfaisante. Les techniques d’échantillonnage passif développées au cours des 20 dernières années pourraient être intégrées dans les réseaux de surveillance réglementaire afin de pallier ces manques, mais des questions subsistent encore quant à leur opérationnalité. Ces travaux ont visé à développer puis tester des échantillonneurs passifs du type POCIS et DGT au niveau de deux bassin versants, situés en Adour-Garonne, afin de juger de l’apport de ces techniques, par rapport aux prélèvements ponctuels classiques, dans le but de fournir davantage de connaissance sur le type de pression (e.g. fréquences de détections, substances phytosanitaires majoritairement retrouvées dans les eaux) et mieux appréhender les conséquences de la mise en place de mesures agro-environnementales (suivi de tendance). Ces travaux ont également fourni des renseignements sur la robustesse de la donnée intégrée dans le temps et la fraction échantillonnée par ces outils (e.g. complexes labiles pour les éléments trace métalliques). Enfin, nous nous sommes intéressés à l’applicabilité de ces outils dans le cadre de la DCE, après avoir défini un intervalle de confiance associé aux concentrations moyennes estimées dans le temps, puis proposé un schéma décisionnel en lien avec le rapportage et la comparaison avec les normes de qualité environnementales

L'é́chantillonnage passif pour le suivi réglementaire de la contamination en pesticides des eaux de surface: intérêt et limites

National audiencePesticides have been used in agriculture and urban activities since the 1950s because they are cheap, easy to use and very efficient. But this intensive use has led to diffuse contamination of environmental compartments (air, soil, water). The presence of these molecules can lead to toxic effects for biota or affect human use of water. The implementation of the Water Framework Directive (WFD) requires the use of an efficient monitoring network, based on reliable sampling and analytical techniques. Nowadays, grab sampling followed by extraction of analytes and chromatographic analysis is the most widespread strategy because of its simplicity of implementation but it also has numerous drawbacks. The crux of the issue lies in the lack of temporal representativeness and the low analytical sensitivity. An alternative strategy to overcome some of these problems could be the use of passive samplers. This contribution aims at discussing the possible application of passive samplers in regulatory monitoring programs. After a brief review of the regulatory aspects of the WFD and the main characteristics of passive samplers, two examples of the implementation of a passive sampler (Polar organic chemical integrative sampler or Pocis) in the field are detailed. These field studies showed that Pocis can be adapted to the two components of the WFD, namely surveillance control and operational control, although some regulatory or technical adjustments are still needed. Passive sampling could therefore be used in addition to current practices fora better monitoring of surface water quality. © 2018 Assoc. Generale des Hygienistes et Techniciens Municipaux. All rights reserved

Dissolved and bioavailable contaminants in the Seine river basin

International audienc