Modelling trace metal background to evaluate anthropogenic contamination in arable soils of south-western France

The trace metal (TM) content in arable soils has been monitored across a region of France characterised by a large proportion of calcareous soils. Within this particular geological context, the objectives were to first determine the natural levels of trace metals in the soils and secondly, to assess which sites were significantly contaminated. Because no universal contamination assessment method is currently available, four different methods were applied and compared in order to facilitate the best diagnosis of contamination. First, the TM geochemical background was determined by using basic descriptive statistics and linear regression models calculated with semi-conservative major elements as predictors. The natural concentrations of trace metals varied greatly due to the high soil heterogeneity encountered on the regional scale and were more-or-less accurately modelled according to the considered TM. Second, the basic descriptive statistics and the linear regression methods were then compared with the enrichment factor (EF) method and multivariate analysis (PCA), in order to evaluate whether the concentrations measured in soils were abnormally high or not. The advantages and disadvantages of each method were discussed and their results used to identify the most probable contamination cases, the influence of the soils characteristics, as well as the agricultural land cover. The basic descriptive method was good as a first and easy approach to describe the TM ambient concentrations, but may misinterpret the natural anomalies as contaminations. Based on geochemical associations, the linear regression method provided more realistic results even if the relationships between major and trace metals were not significant for the most mobile TM. The EF method was useful to identify high point source contaminations, but it was not suitable when considering a large dataset of low TM concentrations. Finally, the PCA method was a good preliminary tool for the description of the global TM concentrations in a studied area, but it could only give indication on the highest contaminated points. By comparing the results of the different methods in the studied region, we estimated that 24% of the arable soils were contaminated by at least one trace metal, mainly Cu in vineyards/orchards and Cd, Pb and/or Zn in grazing lands. In addition, the calcareous soils exhibited globally higher natural and anthropogenic TM concentrations than non-calcareous soils, probably because of the lower TM mobility at alkaline pH

X-ray absorption spectroscopy to elucidate the behavior of heavy metal in organic waste agricultural recycling

In the past century, waste production has risen tenfold, and by 2025 it will double again to reach 6 million tonnes per day1. Solutions have then to be found to this waste problem. Organic waste (e.g. pig slurry, sewage sludge etc.) represent a significant part of the world waste production and can be valorized following two routes. The first one is agricultural recycling. Organic wastes (OW) have fertilizing properties and can be used as an alternative to chemical fertilizers2. The second one is an energetic valorization. OW can be digested to produce biogas used to generate electricity and heat. Besides, this digestion produces a byproduct than can also be recycled in agriculture3. However, OW can have high pollutant concentration among which heavy metal (HM) is particularly concerning. Indeed, soils that have been amended with OW can present HM accumulation at their surface layers4. This accumulation could induce phytotoxicity and groundwater quality degradation. Consequently, the fate of HM in the cultivated soil system after OW amendment is a key issue, and it can better be predict by determining their speciation in the OW. Studies that investigate heavy metal speciation in OW with X-ray absorption spectroscopy (XAS) are presented. In the first study, pig slurry spreading on a tropical soil is used as an example (agricultural recycling valorization). Pig slurry present high concentration of Cu and Zn. Field experiment showed Cu and Zn accumulation in soil at different layers4. XAS permitted to elucidate the Cu and Zn speciation in pig slurry5 and explain their behavior on the field. The second study deals with anaerobic digestion of OW (energetic valorization). The anaerobic digestion of the studied OW permitted the production of methane, but increased the Cu and Zn concentration in the by-product. XAS was used to compare the Cu and Zn speciation in the OW (before digestion) and in the by-product (after digestion). Results shows that the anaerobic digestion tends to modify the Cu and Zn speciation. (Résumé d'auteur

Sewage sludge application for spontaneous plant restoration of a New Caledonian Ferralsol

Soils from New Caledonia typically present poor nutrient content and large quantities of heavy metals such as nickel, chromium and cobalt, resulting in slow plant development. We evaluated the impact of sewage sludge application (0–30 t dry weight (DW) ha–1) on the passive revegetation of a former pine plantation. The spontaneously regenerated plant cover was mainly represented by the dominant Pinus caribaea, a shrub (Sannantha leratii), and a grass (Costularia comosa). The density of pine seedlings was significantly higher in the moderately amended zone (1.2 and 0.2 pines m–2 for 0.5 and 30 t DW ha–1 respectively). The same tendency was observed for S. leratii, but for C. comosa, no net change was observed. With no amendment, after 5 years many species were present, although aboveground biomass (0.3 kg m–2) was low, whereas, with sludge amendment, aboveground biomass was high (5 kg m–2) but diversity low. Amendment increased pine tree heights from 0.15 to 3.92 m with increased amendment from 0 to 30 t DW ha–1. The uptake of nitrogen (N) by pine trees was also improved with sludge supply, as was the uptake of phosphorus (P). Regarding S. leratii, N and P levels were highest at the sludge dosage of 2 t DW ha–1. Carbon storage in P. caribaea biomass increased from 0.40 to 180 kg m–2 with increased amendment applied. Five years after spreading at the highest amendment levels, available soil P remained enhanced. For heavy metal uptake by pine trees, no significant effect of sewage sludge was observed. The optimal dosage to stimulate biodiversity was 0.5–2 t DW ha–1 but maximal biomass was reached at 8–30 t DW ha–1.</jats:p

Indice de multifonctionnalité potentielle des sols de la région Occitanie

Laboratoire Écologie Fonctionnelle et Environnement, LISAH. Financements Région Occitanie, FEDER, Ministère de l’Agriculture et de l’AlimentationDans le cadre du projet ARTISOLS, le Laboratoire Écologie Fonctionnelle et Environnement et le LISAH ont développé une méthode permettant d’aider à répondre à la question suivante : quels sont les sols à protéger de l’artificialisation pour assurer la sécurité alimentaire de la région Occitanie dans 100 ans, tout en minimisant l’impact des activités agricoles sur l’environnement ? Un indice de multifonctionnalité potentielle des sols a ainsi été développé.L’évaluation s’appuie ici sur trois services écosystémiques, sélectionnés comme trois préoccupations agronomiques et environnementales actuelles des aménageurs et pouvant être traitées à l’échelle régionale. Il s’agit de (1) la production d’aliments, de biomasse et de fibres, (2) la régulation des crues et de la qualité des eaux de surface et souterraines et (3) la régulation du climat.Ces services écosystémiques sont caractérisés dans l’indice de multifonctionnalité potentielle des sols par l’agrégation de fonctions du sol pour un usage donné. Les fonctions à privilégier dépendent des services écosystémiques ciblés et donc des usages du sol d’intérêt. Dans le cadre d’ARTISOLS, les quatre fonctions du sol étudiées sont la fonction d’habitat physique pour la croissance végétale, la fonction d’habitat chimique pour la croissance végétale, la fonction de rétention et transferts d’eau et de polluants et enfin, la fonction de séquestration du carbone. Les usages agricoles du sol pris en compte dans l’évaluation sont les cultures annuelles et les prairies temporaires, les cultures pérennes et les prairies permanentes.L’indice de multifonctionnalité potentielle des sols utilise les données du Référentiel Régional Pédologique harmonisé de la région Occitanie, à l’échelle 1/250 000. Deux types de couches cartographiques ont été produites (format shapefile). La première est une carte de zonage des sols à fort indice de multifonctionnalité potentielle. La deuxième correspond à la carte intermédiaire du service de production d’aliments, de biomasse et de fibres

La méthanisation : une technologie productrice d’énergie renouvelable et d’amendement organique

International audienc

Multivariate digital soil mapping to support soil quality index mapping in southern France

International audiencePedometricians have spent a lot of effort on mapping soil types and basic soil properties. However, end-users typically need a more elaborate soil quality index (SQI) for land management. Soil quality indices are typically derived from multiple individual soil properties, by evaluating whether specific criteria are met. If this is based on individually mapped soil properties then an important problem is that cross-correlations between soil properties are ignored. This makes it impossible to quantify the uncertainties associated with the mapped indices.Our objective was to map a soil quality index over a 12 125 km2 study region located along the French Mediterranean coast to help urban planners preserve soils of highest quality. The index considered the ability of soils to fulfill four functions: 1) production of a physical habitat for plant growth; 2) production of a chemical habitat for plant growth; 3) retention and transfer of water and pollutants, and 4) carbon sequestration, under five land use scenarios: 1) annual crop; 2) perennial crop; 3) pastures; 4) forest; and 5) shrubland. Each soil function fulfillment for a given scenario was represented by a categorical map defined from a set of conditions involving basic soil properties (CEC, organic carbon, clay, silt, sand, pH, soil depth, and coarse fragments), and was represented by a 0/1 value. The final soil quality index was the sum of these values.A regression co-kriging model was developed that, first, mapped separately the basic soil properties from legacy soil data and spatial soil covariates using a Random Forest algorithm and, then, interpolated the residuals using cokriging and the linear model of coregionalization (LMC). Both correlations between different soil properties and between the same soil property for different depth layers were accounted for. The mapping uncertainties of soil properties were propagated by calculating the soil quality index over 300 stochastic simulations of soil properties derived from the LMCs. The final soil quality index and its associated uncertainty were estimated respectively by the mean and standard deviation across the 300 simulations. All resulting maps were at 25 m spatial resolution. For validation we used a cross-validation approach repeated 20 times.Although the final map was pedologically meaningful, its performance in terms of amount of variance explained (AVE) was low. The simulations were able to reproduce the width of the observed distribution, although the shapes of the distributions differed considerably. However, we envisage some ways for improvement, such as changing soil property thresholds that are hard to predict, creating probability maps instead of the mean from simulations, and changing the prediction support from point to area

Développement et spatialisation d'un indice de multifonctionnalité des sols pour la caractérisation des espaces potentiellement perdus par l'artificialisation en région Occitanie

National audienceEntre 2006 et 2014, les sols artificialisés ont progressé en moyenne de 60 000 ha/an sur le territoire national. Cette artificialisation du sol s’est faite pour deux tiers aux dépens des terres agricoles (SSP – Agreste – Enquêtes Teruti-Lucas). Dans ce contexte, le projet ARTISOLS s’est donné pour objectif de fournir une information cartographique permettant d’apprécier le préjudice d’une perte en sol par artificialisation en région Occitanie. Une partie du projet s’attache ainsi à développer un indice de multifonctionnalité des sols (IMS) et à définir la méthode de spatialisation la plus adaptée à son utilisation par les acteurs de l’aménagement.Afin de discriminer la multifonctionnalité des sols de la région, la démarche conceptuelle du projet UQUALISOL-ZU (Robert et al., 2012) a été reprise. Elle a été adaptée en termes de services écosystémiques, de fonctions du sol et d’indicateurs à prendre en compte afin de correspondre aux problématiques et à l’échelle régionale de l’évaluation. Cette méthode permet de représenter la multifonctionnalité des sols à travers les concepts de services écosystémiques et de fonctions du sol. Les sols les plus multifonctionnels sont considérés comme les sols à préserver de l’artificialisation. L’évaluation s’appuie sur trois services écosystémiques, sélectionnés comme trois préoccupations agronomiques et environnementales actuelles des aménageurs et pouvant être traitées à l’échelle régionale du projet. Il s’agit (i) de la production d’aliments, de biomasse et de fibres, (ii) de la régulation des crues et de la qualité des eaux de surface et souterraines et (iii) de la régulation du climat.Deux approches ont été testées afin de spatialiser l’IMS. La première utilise les données surfaciques (i.e., les propriétés de sols et les polygones des unités cartographiques de sols) du Référentiel Régional Pédologique de la région Occitanie, récemment construit par l’harmonisation des bases de données des deux anciennes régions Midi-Pyrénées et Languedoc-Roussillon. La deuxième approche utilise la cartographie des sols par modélisation statistique sur les profils de sols contenus dans le Référentiel Régional Pédologique, afin de prédire les propriétés de sols nécessaires au calcul de l’IMS sur l’ensemble de la surface régionale ou pour prédire directement le résultat de l’IMS. La cartographie des sols par modélisation statistique permet de produire des cartes de l’IMS à une plus haute résolution spatiale et d’exprimer l’incertitude associée à la prédiction

Particle size and metal distributions in anaerobically digested pig slurry

International audienceParticle size distribution and trace element patterns were studied in a full-scale anaerobic digestion plant treating pig slurry. Mass balance was established for major (N, P, K, Ca, Fe, Mg and S) and minor (Al, Cu, Mn and Zn) elements. Most of the elements were conserved through the process but part of the P, Ca, Mg and Mn was deposited as crystals lining the digester. In the dry matter of the slurry, Cu and Zn occurred at between 170 and 2600 mg/kg due to pig diet supplements. Analyses of particle size distributions in raw and digested slurries showed a general shift in distribution towards larger sizes due to degradation of small and easily degradable particles as well as formation of large microbial filaments. Graded sieving of digested slurry showed metals to be mainly present on 3–25 um particles. Less than 2% Cu and Zn was removed by passage through a 250 um rotary screen