Title : UV­_Visible and Fluorescence Green Waste Composts Monitoring: Material Dependency

International audienceThe most frequent way to survey green waste composts is to monitor the temperature during the composting process. However, if the temperature is a good index for global biological processes, it is not for the chemical stability. In order to identify a reliable index, this work investigates water extraction coupled to spectroscopic indexes such as E 2 /E 3 , E 4 /E 6 and SUVA 254 ratios, and fluorescence indexes such as Kalbitz, Milori, CP/PARAFAC and Fluorescence Region Integration. The measurements of these indexes are carried out with six samples from different sites with different green waste material composition. The results show that most indexes depend on the green waste origin more than the composting time; some depend mostly on the material origin while others on compost age. A comparison of these results indicates that the biochemical process occurs more rapidly than expected by the compost producers. The combination of these indicators gives useful information on the processes that take place during composting

Gestion et valorisation énergétique des déchets de la biomasse : aide au choix des filières de traitement et de leur lieu d'implantation

International audienc

Effects of forest fires on water extractable organic matter and humic substances from Mediterranean soils: UV–vis and fluorescence spectroscopy approaches

International audienceHumic substances (HS) and water extractable organic matter (WEOM) represent an important part of soilorganic matter (SOM) which plays many roles in this ecosystem. Forest fires are known to have potentialimpacts on soil organic matter. We studied these impacts, first on global HS and the three relevant fractions(humic acids (HA), fulvic acids (FA) and non-humified fraction (NHF)) and secondly on WEOM and the threecorresponding fractions (hydrophilic (Hpi), transphilic (Tpi) and hydrophobic (Hpo)) fractionated by the useof XAD-8 and XAD-4 resins. Measurements of total organic carbon (TOC) and the use of both UV–vis andfluorescence spectroscopy gave us quantitative and qualitative results to evaluate the impacts of forest firesabundance and recurrence on the restoration process of the burned soils. As for the TOC-SOM, the quantitativeimpact of fires on TOC-WEOM is indirect and depends on the fire number. The fires have a direct impact onWEOM quality where, depending on the fraction properties, fires lead to the homogenization of the differentcompounds of the WEOM. Fires have a direct impact on HS quantity leading to a significant decrease of theamounts. The quality of HS is also affected by fires showing an increase in aromaticity of humified fractions forlong time spans (more than 16 years). On a short term the non-humified fractions appear less structured andcomplex. In general, the more structured the compounds in the fraction, the greater recovery time

Chapter 10 Leachates and organic extracts from solids

International audienceThis chapter presents some applications related with landfill leachates, contaminated soils, and solid waste composts. A complementary study concerning natural sediments is presented in the chapter. Landfill leachates are considered to be highly polluted media, containing various organic compounds refractory to biodegradation. Regarding leachate analysis, ultraviolet (UV) spectrophotometry can be useful for a fast characterization or the study of landfill evolution. Depending on the nature of organic components, aqueous solutions can limit the interest of the approach. In this case, an extraction step of the solid matrix with an organic solution can be necessary in order to have more specific information. The aim of solid wastes treatment is both to reduce their size and to stabilize their organic content. The characterization of natural soils and sediments with UV spectrophotometry applied after leaching tests is possible

Bioénergie

Rapport remis à la Région PAC

Quantitative and mid-infrared changes of humic substances from burned soils

International audienceThe humic substances are an abundant and important part of soil organic matter which plays manyroles in ecosystems. On the other hand, forest fires are known to have a potential impact on the soilorganic matter. Consequently, we chose to study the impact of forest fires on humic substances and thethree relevant fractions, e.g. humic acids (HA), fulvic acids (FA) and non-humified fraction (NHF), NHFbeing the fulvic acids not adsorbed on XAD-8 resins. The studied site is a Mediterranean forest called‘‘Maures Mountains’’, in France, where 30 sites were sampled in two layers: 0–5 and 5 to 15 cm. Inorder to validate the method, the 2 horizons from 5 sites randomly chosen were analyzed in triplicates.The extraction and fractionation procedures were achieved using alkali- and acid-solutions. Themeasurement of total organic carbon (TOC) using the TOC-meter and the use of Fourier transform infrared (FTIR) spectroscopy gave us quantitative and qualitative results to evaluate the impact of forest firesand the role of their repetition. The results show that the fires led to significant decreases (Student test,P¼0.05) of humic substances (HS), HA and of the fulvic fractions (FF¼FA+NHF) in surface layers,corresponding to 40%, 34% and 35%, respectively. Moreover, the significant HA/FF ratio increases(Student test, P¼0.05), as a result of the fire, indicate that NHF was probably transformed in FA-likecompounds. About the qualitative impact, the results showed a significant decrease of alkyl andhydroxyl groups (OH), carboxylic acids and carbohydrates in HA after a wildfire, whereas the decreasewas significant only for alkyl groups and carboxylic acids in FA. Lastly, the design of this work (controland burned sites, number of samples, time elapsed after fires, etc.) enables one to show the recovery ofthe Mediterranean forest ecosystem. FA quality and OH groups in HA are recovered between 3 and16 years after the fire whereas alkyl groups, carboxylic acids and carbohydrates in HA as well as HScontents are not returned to the control state 16 years after the last fire

Sécheresses et incendies répétés accroissent mutuellement leur impact sur l'écosystème

International audienceIn a recent research project performed in South-Eastern France on the impact of repeated fires on many components of forest environment (vegetation, fauna, microbiology, soil physics, chemical properties, organic matter, nutrients) we showed a strong interaction between repeated droughts and repeated fires. Each disturbance significantly increases the impact of the other one. Repeated droughts can stop and even reverse the recovery process after fire, and delay this recovery when they occurred before fire. Repeated fires lessen the resistance and resilience of the ecosystem to drought. Forest regeneration processes are threatened even in usually fire-prone environments usually resilient. Soil biological activity is severely affected, and particularly some key groups as earthworms and bacteria contributing to nitrogen cycle. Soil physics and chemical properties appear to be degraded as a habitat, and indirectly the reduction of biological activity limits their recovery, including a negative carbon balance. Four successive years appear to be the critical threshold for drought and four times in 50 years the critical threshold for fires. As climate change may lead to higher drought frequency and fire occurrence is tied to drought, the drought/fire interaction may degrade forest ecosystems more rapidly than expected from separate assessment of drought and fire impacts

La répétition des feux et des sécheresses menace la biodiversité fonctionnelle des écosystèmes méditerranéens

International audienceBetween 2005 and 2008, a group of 10 research teams studied vegetation, litter, earthworms, microfauna, bacteria, soil physics, nutriments, organic matter (quality and quantity) and toxic compounds in a multidisciplinary research program dealing with the impact of repeated forest fires on biodiversity and the soil in mediterranean forests. Plots were laid in old growth forests and in sites burned between 1 and 4 times in the last 50 years. For each fire regime, fires dating 1, 3, 5, 15 and 25 years were chosen. The goals were: (1) to look for biodiversity indicators for the assessment of the ecosystem status and functioning, (2) to understand interactions between biotic and abiotic factors in ecosystem resistance and resilience, (3) to look for critical fire frequency thresholds. Taking advantage of the exceptional drought which occurred during the experiment, we studied the interaction between fire and drought. Two thresholds appeared in fire frequency (1 and 4 fires in 50 years) leading to deep changes in the ecosystem biodiversity and functioning. Few differences were observed 3 and 15 years after fire between plots burned 1, 2 or 3 times, the ecosystem being used for millenniums to such fire frequencies. Earthworms and bacteria diversity and activity appeared critical for ecosystem functioning and recovery after fire. Due to drought, this activity was severely reduced and strong interactions were found between fire and drought, each of these disturbances amplifying the impact of the other. High disturbance frequency by fire or drought reduced biological diversity, increasing the resistance but reducing the resilience of communities. Some obligate seeders tree species disappeared when fire occurred at less than 15 to 20 years interval, changing the ecosystem structure. Trees mortality due to drought was far higher in recently burned areas, degrading vegetation from forest to matorals. The quantitative resilience of several physical and chemical parameters is achieved within 15 to 25 years after fire, but 50 years are necessary to fully recover the qualitative values and balance for these parameters as well as for most of the biological factors. Most of the critical biological, physical and chemical processes were concentrated in the topsoil (0-5 cm), deeper horizons being impoverished by a long fire history, except in old growth forests. These ecosystems are fragile and their dynamics may shift to desertification with increasing drought due to climate change

Étude de l'impact d'incendies de forêt répétés sur la biodiversité et sur les sols. Recherche d'indicateurs. Rapport final détaillé.

Goals: This project aimed at assessing the impact of forest fire repetition on vegetation and the soil, in terms of biodiversity, carbon balance and the global ecosystem potential. The study area is the Maures massif (Mediterranean area in the South-East of France), an ecosystem developed on crystalline rocks. Because of the persistent drought during the project, we studied the interaction between fire recurrence and drought recurrence. Protocols: The sampling design includes 3 fire regimes during the last 50 years (many fires = 3-5, medium = 1-2 fires, control = no fire) and 3 time spans since the last fire (very recent = 9-12 months, recent = 3-5 years, old = 15-25 years). Control plots did not burn since either 50 years, or 200 years. 31 plots were laid out, five by treatment except for the old growth control forest (1 plot). The follow-up of the same plots during 3 years allowed furthermore studying the short-term dynamics of the environment after fire. We studied the functional relations between various aerial and soil compartments of the ecosystem at several spatial and temporal scales, combining physical, chemical and biologic factors, to identify key processes and species controlling the resilience of the environment or its resistance to disturbances. Results: Globally, the time since the last fire, thus the ecosystem resilience dynamics, were more influent on most of the measured parameters than the number or the frequency of fires. However, these last ones often play a functionally significant role, their relative importance increasing with the number of fires. The absence of fires for 150 - 200 years allowed a dramatic recovery of the fertility and biological activity. The repletion of the carbon stock in the superficial soil horizons (0 15 cm) and important modifications in flora structure and composition were particularly significant. With a mean fire frequency of one fire every 25 to 50 years, a good global resilience of the ecosystem, its flora and its functioning was observed, but at a low level of potential and at the shrinkage limit: most of the organic matter was limited to the first centimetres of the topsoil (0-5cm) where the biologic activity concentrated at fire's mercy. Most of the parameters which are modified by the fire recovered quantitatively in 15 to 25 years. But 50 years were generally necessary for the resilience of qualitative aspects, notably for the organic matter, biogeochemical cycles, microbiologic functioning of the soil and plant diversity.With higher fire frequencies (4 fires or more in 50 years, or fires occurring at less than 10 years interval), many parameters are durably altered, showing a global degradation of the ecosystem potential: it was particularly true for vegetation composition and structure, soil fauna and the loss of organic matter and its qualitative transformation. This last change led to drop in the activity, the resistance and the resilience of microbial communities. The nitrogen cycle was particularly disturbed. With one to 3 fires in 50 years, these forests do not store nor lose significantly carbon in the superficial soil horizons nor in the living biomass; a higher frequency led the forest to be a carbon source. With no fires over 50 years, and particularly after more than 150 years, these forests become a good carbon sink. The conjunction of numerous fires and repeated droughts led to a collapse of the biological functioning of the ecosystem. Fire and drought amplified mutually their deleterious impact. The persistent drought from 2003 to 2007 stopped the normally fast recovery dynamics in the first year after the fire of year 2003, and even made some biologic parameters decline. Plots with the higher fire frequency up to 2003 were the most impacted by drought. The preliminary effect of drought also dramatically increased the impact of the fires of year 2007. A threshold of 4 successive years of severe drought seems to be a critical threshold for the ecosystem, as well as 4 fires would be a critical threshold for the number of fires in 50 years. A set of indicators of the health status and dynamics of the ecosystem was selected among biological, physical and chemical parameters.Objectifs : Ce projet avait pour objectif d'évaluer l'impact de la répétition des feux de forêt sur le sol et la végétation en termes de biodiversité, de bilan de carbone et de dégradation générale des potentialités de l'écosystème. La zone d'étude se situe dans le massif des Maures (zone méditerranéenne au Sud-Est de la France, écosystème développés sur roches cristallines. Nous avons simultanément étudié l'interaction entre récurrence des feux et récurrence des sécheresses. Protocoles : Le plan d'échantillonnage comprend 3 régimes d'incendies au cours des 50 dernières années (nombreux = 3-5 feux, peu nombreux = 1-2 feux, témoin) et 3 modalités de date du dernier feu (très récent = 9 mois -1 an, récent =3 ans, ancien = 15-25 ans), les témoins n'ayant pas brûlé depuis soit 50 ans, soit 200 ans ou plus. Il y a 5 placettes par modalité sauf témoin très ancien, soit au total 31 placettes. Le suivi sur plusieurs années des mêmes placettes a permis de plus d'étudier la dynamique à court terme du milieu après le feu. Nous avons étudié les relations fonctionnelles entre différents compartiments aériens et souterrains à plusieurs niveaux des échelles spatiale et temporelle de l'écosystème, en combinant des facteurs physiques, chimiques et biologiques, afin d'identifier des processus et espèces clefs de la résilience du milieu ou de sa résistance aux perturbations. Résultats : Globalement, le temps depuis le dernier feu, donc la dynamique de reconstitution de l'écosystème, influence plus les paramètres mesurés que le nombre ou la fréquence des feux, mais ces derniers jouent cependant un rôle souvent significatif et fonctionnellement important, plus rarement dominant. L'absence de feux durant 150 à 200 ans permet une spectaculaire remontée biologique et du potentiel de l'écosystème, marquée par la reconstitution d'un stock significatif de carbone dans les horizons superficiels du sol (0 à 15 cm) et une modification importante de la structure et composition floristique. Une fréquence moyenne d'incendie de l'ordre d'un feu tous les 25 à 50 ans permet une bonne résilience globale de l'écosystème, de sa flore et de son fonctionnement, mais à un niveau faible de potentialités et en limite de la rupture. L'essentiel du stock de matière organique est limité aux premiers centimètres du sol (0-5cm) où se concentre l'activité biologique. La plupart des paramètres qui sont modifiés par le feu récupèrent quantitativement au bout de 15 à 25 ans. Mais il faut en général 50 ans pour les aspects qualitatifs, notamment au niveau de la matière organique, des cycles biogéochimiques, du fonctionnement microbiologique du sol et de la biodiversité végétale. Avec des fréquences plus élevées, aboutissant à 4 feux ou plus en 50 ans ou à quelques feux très rapprochés (5-10 ans), de nombreux paramètres chimiques et biologiques sont durablement altérés, et marquent une dégradation globale des potentialités du système. On note un changement durable de la composition et de la structure de la végétation et une perte significative de matière organique et sa transformation qualitative, responsables d'une baisse sensible de l'activité, de la résistance et de la résilience microbiologique. Le cycle de l'azote est particulièrement touché. Pour les fonctions de séquestration de carbone : dans un régime moyen d'incendie de l'ordre d'un feu tous les 25 à 50 ans, ces forêts ne stockent pas ni ne perdent significativement de carbone dans les horizons superficiels du sol et dans la biomasse vivante ; elles en perdent par contre en cas de feux répétés plus souvent. Elles possèdent un grand potentiel de stockage (effet puits de CO2) en cas ne non-brûlage sur des durées de 150 à 200 ans. La conjonction de nombreux feux et de sécheresses répétées conduit à un effondrement du fonctionnement biologique de l'écosystème dans ses parties aérienne comme souterraine. Chacune des perturbations (feu et sécheresse) amplifie les effets néfastes de l'autre. La sécheresse persistante a non seulement totalement arrêté la dynamique normalement rapide de l'écosystème entre la 3ème et la 5ème année après le feu, mais a fait largement régresser certains paramètres biologiques. Les placettes les plus impactées par le feu (incendies récents ou nombreux) ont été les plus touchées. L'effet préalable de la sécheresse a aussi considérablement aggravé l'impact d'un feu survenu en 2007. Un seuil de 4 années successives de sécheresse marquée semble constituer un seuil critique pour l'écosystème, de la même manière que 4 feux seraient un seuil critique pour le nombre de feux en 50 ans. Le changement climatique ne peut donc que le fragiliser d'avantage ces écosystèmes, en accentuant les effets néfastes des incendies et en les multipliant. Un jeu d'indicateurs de l'état et de l'évolution de l'écosystème a été retenu, basé sur des paramètres biologiques, physiques et chimiques