Can Natural Attenuation be Considered as an Effective Solution for Soil Remediation?

Natural attenuation is described as a naturally occurring process, mostly in soils and also in groundwater, without human intervention, which transforms, reduces and destroys the organic and inorganic contaminants. As an eco-friendly, cost-effective and relatively simple technology, natural attenuation is widely used for the treatment of contaminated soils. However, the application of this technology must be carefully controlled and monitored not only for its efficiency and durability over time, but also for the migration of contaminants to ensure no risk to human health and ecosystems. Furthermore, the success of this technique requires a good knowledge of the type of contaminants, the physical and chemical characteristics of the soils, as well as the living actors, including plants, fauna, microorganisms and their interactions, that live in the soils to be treated and that will be involved in this process. The purpose of this chapter is to provide the most recent information regarding the principle of this technology, the role of the living actors and the interactions between plant, fauna and microorganisms, the advantages and disadvantages, and finally to discuss the efficiency of this technique in comparison with other techniques such as phytoremediation or bioremediation. In fine, we will discuss its social acceptability

Phytoremediation: An Ecological Solution for Decontamination of Polluted Urban Soils

Urbanization and industrialization are the main causes of increasing contaminated soils in cities all around the world. This leads to numerous abandoned lands, reduction in biodiversity, and thereby posing a serious health risk for urban inhabitants. The development of effective and ecological remediation approaches is necessary. Phytoremediation is well known as an ecological solution with good acceptation for remediation of contaminated soils. Since, urban soils are particularly characterized by their highly disturbed, heterogeneous and low fertility, the application of phytoremediation to rehabilitate contaminated soils in urban areas is until now very limited at the laboratory scale and even less at the field scale. In this context, we have to take into account all these parameters and precautions when it’s application. The main objective of this chapter is to discuss how to take phytoremediation approaches from a proven technology to an accepted practice in an urban context. An overview of urban soil types is provided following phytoremediation’s application for urban soils with the focus on inorganic and organic pollutants, to provide a frame of reference for the subsequent discussion on better utilization of phytoremediation. At last, we offer suggestion on how to gain greater acceptance for phytoremediation by urban inhabitants

Can natural attenuation be considered as an effective solution for soil remediation?

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Increased lead availability and enzyme activities in root-adhering soil of Lantana camara during phytoextraction in the presence of earthworms

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A climatic chamber experiment to test the short term effect of increasing temperature on branched GDGT distribution in Sphagnum peat

International audienceBranched glycerol dialkyl glycerol tetraethers (br GDGTs) are membrane lipids produced by unknown Bacteria and are being increasingly used as temperature proxies. Nevertheless, the direct effect of temperature on br GDGT distributions has been rarely evaluated. In this study, the impact of increasing temperature on br GDGT distributions and the speed of adaptation of br GDGT source microorganisms to temperature change were investigated by analysing br GDGTs in Sphagnum peat cores incubated under controlled conditions at two different temperatures - 12 and 15 C - for 1 yr. Br GDGTs present as intact polar lipids (IPLs, presumably derived from recently active microorganims) and core lipids (CLs, derived from dead biomass) were analysed. There were no significant differences in the relative abundances of the most abundant br GDGTs in the CL and IPL pools after 3 months' incubation. In contrast, the distribution of the br GDGT IPLs was significantly affected by temperature after 1 yr, whereas no change was observed in the CL fraction. This suggests that (i) the CL pool of br GDGTs has a turnover of at least 1 yr in peat and (ii) br GDGT source microorganisms rapidly adjust their membrane lipid composition (in > 3 months and < 1 yr, based on IPL analysis)

Increasing the ability of a green roof to provide ecosystem services by adding organic matter and earthworms

International audienceThe aim of this study was to increase the ecosystem services provided by a green roof by ameliorating the biological and chemical properties of a commercial green roof substrate through the addition of earthworms and compost. We conducted a mesocosm (120 × 80 × 33 cm) experiment with a plant community comprising Hylotelephium maximum,Centaurea jacea, Lotus corniculatus, Koeleria glauca, and Dianthus carthusianorum. Two substrates were compared (i) a low complexity commercial green roof substrate with no alterations and (ii) a high complexity substrate with a layer of locally produced vermicompost and earthworms (Lumbricus terrestris) placed on top of the commercial substrate. The mesocosms were placed on the roof of a 20 m high building and at ground level.Results show that the percent of vegetative cover on both substrates was lower in the roof mesocoms than on those placed at ground level. This is explained by climatic conditions, such as higher light intensity at roof level. The substrate with earthworms and vermicompost had significantly higher enzyme activity, microbial biomass, and metabolic activity. This resulted in more available nitrogen and phosphorus for plants, increased the plant biomass, floral nectar volume and sugar concentration which resulted in the flowers receiving more diverse and abundant insect pollinators. This is the first time that adding earthworms and compost to a green roof substrate has been shown to have a significant effect on plant growth and plant-pollinator interactions. These findings will help in designing green roof systems that are more efficient at preserving ecosystem services in urban areas

Variations in snow depth modify N-related soil microbial abundances and functioning during winter in subalpine grassland

International audienceIn alpine and arctic ecosystems, the snowpack has been shown to insulate soils from the winter climatic harshness. Ongoing climate change modifies snowpack quantity and quality, but the consequences of these changes on the soil functioning remain largely unknown. We benefited from a subalpine landscape of the French Alps where, 700 years ago, agricultural practices led to the formation of terraces. Subsequently , on each terrace, snow thickness patterns significantly differed between the bank and the front areas inducing strong divergence in their soil microclimatic conditions. Using this framework, we measured abundances and activities of nitrifiers and denitrifiers, together with a set of environmental variables, on three grassland terraces between December and May to test the following hypotheses: (i) soil N-related microbial abundances and activities are sensitive to soil microclimatic variations and differ along the terrace snow depth gradient during winter, (ii) a thicker snowpack favors higher abundances and activities, and (iii) the driving forces for nitrification and denitrification abundances and activities vary along the snow depth gradient. Our results showed significantly and changing N-related microbial activities and abundances during winter despite partly frozen soils, and suggested the selection and/or adaptation of psychrophilic microbial communities. Moreover, activities as well as abundances of ni-trifiers and denitrifiers were significantly higher under a weak or absent snowpack during winter, and mostly related to soil water content and soil surface temperature according to our models. We suggest that strongly variable soil abiotic conditions at the front stations enabled the release of nutrients from soil organic and inorganic compounds favoring psychrophilic bacterial abundances and activities. Contrastingly , a thicker and permanent snowpack maintained circum-zero soil temperatures during winter which limited the microbial community's turnover and release of organic and inorganic N. This created N-limited conditions and N-competition between microbial populations resulting in lower abundances and activities. Overall, changes in the snowpack depth strongly affect the soil microbial functioning of subalpine grasslands with potential consequences on nutrient dynamic and other trophic levels