Sols artificialisés

Considered as one of the main factors in erosion of the biodiversity, land take describes the global reduction in the proportion of land allocated to farming and forestry or to natural spaces. This work identifies the decisive economic and social factors in land take and its impact on the environment and agriculture. It suggests levers of action likely to limit its development and its negative effects

Sols artificialisés

Considered as one of the main factors in erosion of the biodiversity, land take describes the global reduction in the proportion of land allocated to farming and forestry or to natural spaces. This work identifies the decisive economic and social factors in land take and its impact on the environment and agriculture. It suggests levers of action likely to limit its development and its negative effects

The role of urban agriculture in food-energy-water nexus policies: Insights from Europe and the U.S

The growth of urban agriculture (UA) has raised the awareness of city officials and civil society organizations of its potential effects on food systems. This has led to various policies to regulate and support UA. This research characterizes existing food, energy and water (FEW nexus) policies based on policy data from five case study cities in Europe and the U.S. (Dortmund, Gorz´ow Wielkopolski, London, Nantes, and New York City) to analyze their relationships to UA, and to identify policy types that support resource-efficient UA. The paper presents the results of an analysis of 78 policy documents related to UA and the FEW nexus, and the results of a Q-sort ranking by UA policy experts on the effectiveness of 16 generalized UA policies in promoting resource-efficient UA. The number, type, and degree of support for nexus policies vary among the five case studies. The results show that the majority of policies (36) are implemented at the local scale, that few policies (19) incorporate all elements of the nexus, yet many nexus policies include UA indirectly. Regulations are more prevalent and are considered more effective at ensuring resource-efficient UA than incentives or awareness-raising policies. The study offers guidance to policy makers who want to improve resource use in future UA pointing at the increasing importance of local food policies

How to evaluate nature-based solutions performance for microclimate, water and soil management issues – Available tools and methods from Nature4Cities European project results

International audienceIn the context of climate change, Nature-Based Solutions (NBSs), a recently developed concept, are increasingly considered as part of the adaptation strategies of the cities. Studies using expert models and methods (EMM) receive a great deal of scientific attention. Considering EMM increasing use, this study aims to perform an analysis of the reported evaluation results, reflecting the capability of the EMM to accurately tackle urban challenges identified within the EU Nature4Cities project. Then, we propose a set of indicators and recommendations about sixteen EMM to be used by funders, researchers and practitioners when evaluating the performance of NBSs. The coupling of the different components (climate, water and soil) is not a simple matter. The analysis relies on the definition of the range of the reported metrics and on the investigation of the relationship between the various indices, applied for the EMM evaluation. Secondly, the study assesses the existing EMM, indicating the potential of NBSs: (i) to reduce urban heat island, (ii) to limit surface warming, (iii) to increase the thermal comfort of people, (iv) to limit the overheating and runoff of surfaces due to impervious areas, (v) to increase water retention during stormy episodes, (vi) to improve storm water quality at the outlet of the sustainable urban drainage systems, (vii) to promote the filtration and epuration of storm water runoff in soil and (viii) to be a support for vegetation. The analysis reveals that EMM can be considered as helpful tools for urban microclimate, urban soil and water management analysis, provided their limitations and characteristics are taken into account by the user when choosing tools and interpreting results (e.g. application scale). With regard to the performance of NBSs, the most commonly used indicators clearly depend on the scale of the project

Development and analysis of the Soil Water Infiltration Global database

In this paper, we present and analyze a novel global database of soil infiltration measurements, the Soil Water Infiltration Global (SWIG) database. In total, 5023 infiltration curves were collected across all continents in the SWIG database. These data were either provided and quality checked by the scientists who performed the experiments or they were digitized from published articles. Data from 54 different countries were included in the database with major contributions from Iran, China, and the USA. In addition to its extensive geographical coverage, the collected infiltration curves cover research from 1976 to late 2017. Basic information on measurement location and method, soil properties, and land use was gathered along with the infiltration data, making the database valuable for the development of pedotransfer functions (PTFs) for estimating soil hydraulic properties, for the evaluation of infiltration measurement methods, and for developing and validating infiltration models. Soil textural information (clay, silt, and sand content) is available for 3842 out of 5023 infiltration measurements ( ∼ 76%) covering nearly all soil USDA textural classes except for the sandy clay and silt classes. Information on land use is available for 76% of the experimental sites with agricultural land use as the dominant type ( ∼ 40%). We are convinced that the SWIG database will allow for a better parameterization of the infiltration process in land surface models and for testing infiltration models. All collected data and related soil characteristics are provided online in *.xlsx and *.csv formats for reference, and we add a disclaimer that the database is for public domain use only and can be copied freely by referencing it. Supplementary data are available at https://doi.org/10.1594/PANGAEA.885492 (Rahmati et al., 2018). Data quality assessment is strongly advised prior to any use of this database. Finally, we would like to encourage scientists to extend and update the SWIG database by uploading new data to it

Pollutant characteristics and size distribution of trace elements during stormwater runoff events

Priority trace elements As, Cu, Cr, Ni, Pb, and Zn are largely present in urban stormwaters and should be controlled due to their impact on water bodies. As it has been observed that there are numerous limitations in the purification performance of roadway stormwater runoff treatment systems, the particulate size distribution of trace elements was studied extensively to assess the colloidal fractions present in stormwater runoff of a high-traffic roadway site (100 000 vehicles/day). Besides the evaluation of the total Event Mean Concentrations (EMCs) and dissolved concentrations, a complete fractionation scheme of low settling phase of runoff water (<30 µm) was applied to a series of rain events, considering 8 µm and 5 kDa, as relevant cut-offs between particulate/colloidal elements, and colloidal/truly dissolved elements. The intra-event size distribution was also considered to assess the first-flush effect and the variation of the physical speciation. The high-level traffic associated with climatic conditions (rainfall depth) are responsible for very high EMCs for Zn and Cu, together with a significant exceedance of the European environmental water standards (<0.45 µm concentrations). Ni, Cr and Pb are mainly present as particulate and colloidal metals. Therefore, considering a more complete size distribution is relevant for these elements. For As, Cu and Zn, the conventional fractionation at 0.45 µm seems to be sufficient to evaluate the highly mobile fraction. The results also indicate that, while the main particulate load may be collected within the early volumes of the rainfall events (about 30%), the variability of rain intensity during long events induces changes in particulate and colloidal metals in the runoff. The treatment of runoff must then be considered as a whole in view of the variability of trace metal size distribution. This suggests that urban stormwater runoff treatment systems which employ only the settleable fraction are not sufficient to limit the chemical and ecological risks to receiving water bodies

Variabilité temporelle de la spéciation physique des éléments trace dans les eaux de ruissellement au cours des événements pluvieux

International audienceThe particulate size distribution of trace elements was studied to assess the colloidal form presence in stormwater runoff of a high-traffic roadway site (100 000 vehicle/day). A complete fractionation scheme was applied to a series of rain events, considering 8 µm and 5 kDa as relevant cut-offs between particulate/colloidal elements and colloidal/truly dissolved elements. The intra-event size distribution was also considered to assess the first-flush effect and the variation of the physical speciation. Ni, Cr and Pb are mainly present as particulate and colloidal metals. Therefore, considering a complete size distribution is relevant for these elements. For As, Cu and Zn, the conventional fractionation at 0.45 µm seems to be sufficient to evaluate the highly mobile fraction. Moreover, the results indicate that the variability of rain intensity during long events induces changes in particulate and colloidal metals in the runoff. The treatment of runoff must then be considered as a whole in view of the variability of trace metal size distribution. This suggests that urban stormwater runoff treatment based only on the removal of settleable fraction is not sufficient to limit the chemical and ecological risks to receiving water bodies.La spéciation physique des éléments trace a été étudiée afin d’évaluer leur présence sous forme colloïdale dans les eaux de ruissellement d'un site routier à fort trafic (100 000 véhicules/jour). Un schéma de fractionnement complet a été appliqué à une série d'événements pluvieux, en considérant 8 µm et 5 kDa comme des seuils pertinents entre forme particulaire - forme colloïdale et forme colloïdale - forme dissoute. La distribution intra-événement a également été prise en compte pour évaluer l'effet "first-flush" ainsi que la variation de la spéciation physique. Ni, Cr et Pb sont présents principalement sous forme particulaire et colloïdale. Il est donc pertinent de considérer une distribution en taille fine pour ces éléments. Pour As, Cu et Zn, la filtration conventionnelle à 0,45 µm semble être suffisante pour évaluer la fraction mobile. Par ailleurs, les résultats indiquent que la variabilité de l'intensité des pluies lors d'événements longs induit des changements de distribution entre forme particulaire et forme colloïdale des éléments trace dans les eaux de ruissellement. Le traitement du ruissellement doit alors être considéré dans son ensemble compte tenu de la variabilité de la distribution des éléments trace. Ceci suggère que le dimensionnement des ouvrages de gestion des eaux de ruissellement basé sur la fraction décantable devrait être revu pour limiter les risques chimiques et écologiques pour les masses d'eau réceptrices

La mémoire des sols : rôle des usages historiques sur la contamination par des éléments traces - exemples de jardins associatifs (Nantes, France)

International audienceUrban gardening practices are exploding around the world, especially in industrialized countries. The question of soil contamination nevertheless arises, insofar as the soil memorizes the impacts linked to various successive human activities. Urban soils are therefore likely to have high concentrations of contaminants, particularly trace elements. Research on the link between contaminants distribution and different types of land use appears to be limited. In this context, this paper aims to illustrate how former land use influences the current spatial distribution of trace element in urban soils, based on the example of urban allotment gardens located in Nantes (France).The 8 gardens studied are part of a large urban allotment garden (UAG) program in Nantes (France). Land use changes were determined using a historical analysis of the human activities for each site. Trace elements measurements in topsoils and soil profiles were carried out using a portable X-Ray fluorescence spectrometer, with additional laboratory analyses to calibrate the results. The origin of trace elements and their spatial distribution in soils were interpreted in light of land-use changes. Successive human activities such as industry, backfilling, agricultural crops… appear as key factors of the distribution of trace element in soils. However, it is not always sufficient to understand the source of trace elements. Therefore, it is essential to characterize soil geochemistry in the context of soil management and urban redevelopment to ensure that soil quality is compatible with current and further land use

Occurrence et caractérisation des nanoparticules dans les eaux de ruissellement urbaines - Application au bassin de rétention du pont de Cheviré (Nantes, France)

International audienc

Evaluation de la reproductibilité des réponses hydraulique et épuratoire de deux noues pilote

Evaluation of hydraulic and pollutant filtration response replicability of two pilot swales. Swales are popular stormwater source-control infrastructures put in place to mitigate the environmental impacts of urban or road runoff. Over the past 30 years, swale design has evolved with more emphasis on swale outflow quality, but still has a strong empirical basis. Therefore, there is a need to gain insight into the design aspects that could impinge on the treatment efficiency of a swale. To address these knowledge gaps, two pilot swales were specifically designed and built at the CSTB Nantes. Differences between the pilot swales derived from their soil materials in order to assess and compare the performances of a standard swale and a filtering swale. For this purpose, the pilot swales were equipped with a runoff simulator and various measuring devices (i.e. flowmeters and soil moisture sensors). Given the importance to generate high-quality data, the present paper details this measurement chain and examines its operation by simulating the same runoff event six times between November 2017 and April 2018. The reproducibility of the swale responses is discussed in light of the test procedure and the estimated measurement uncertainties. Overall, results emphasize the high reproducibility of the swale hydraulic responses and demonstrate that pollutant fluxes can be accurately monitored at the inlet and the outlet of each swale. Regarding hydraulic indicators, slight dispersion (variation coefficient cv &lt; 5%) of the ratios between outgoing and incoming water (S/E) and between infiltrated and runoff water (I) are likely due to non-similar initial conditions (e.g., natural rainfall preceding the runoff event). Regarding performance indicators of the stormwater treatment, the mass and concentration reduction efficiencies for zinc (Zn) and copper (Cu) are within the estimated replicability boundaries. Nevertheless, the high contamination level of Zn in incoming stormwater could explain the lower dispersion of its removal (cv &lt; 30%) with respect to the dispersion of Cu removal (185% cv 176%). Overall, the estimated uncertainties of both the monitoring devices and the analytical methods were identified as potential explanations for the observed variations.Deux noues végétalisées ont été mises en oeuvre au sein d&apos;un pilote au CSTB (Nantes), et ont été équipées d&apos;un simulateur de ruissellement et d&apos;une instrumentation dédiée afin d&apos;en étudier leurs réponses hydraulique et épuratoire. La fonctionnalité de la chaîne de mesure et la reproductibilité des réponses des noues ont été évaluées sur un même évènement de ruissellement (pluie d&apos;environ 11 mm), simulé à 6 reprises entre novembre 2017 et avril 2018. Le dispositif instrumental s&apos;est avéré apte à restituer intégralement la réponse hydraulique des deux noues, et sa capacité à suivre finement les flux de polluants en entrée et en sortie de noue a été validée. Les valeurs brutes des ratios flux d&apos;eau sortant/injecté (S/E) et flux d&apos;eau infiltré/ruisselé (I) sont faiblement dispersées (coefficients de variation (cv) &lt; 5 %). Les abattements en masse et en concentration des deux polluants analysés dans cette étude, le zinc (Zn) et le cuivre (Cu), sont compris dans les limites de reproductibilité calculées. En revanche, le niveau de contamination élevé de Zn dans les eaux injectées pourrait expliquer la plus faible dispersion de son abattement (cv &lt; 30 %) par rapport à Cu (185 % cv 176 %). Enfin, les incertitudes liées à la mesure et aux méthodes analytiques ont été identifiées comme des sources potentielles de variations des réponses. Ces résultats seraient à approfondir pour des conditions initiales plus contrastées (pluies extrêmes, sol sec ou proche de la saturation