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Consideration of natural formation of organochlorine compounds in soils is necessary in radioecology in order to understand chlorine radioisotope (Cl) cycling in various environments for safety assessment purposes, but also in ecotoxicology because certain chlorinated organics in soils are toxic compounds. On the other hand, occurrence of organic chlorine in soils is poorly documented, especially in non-forest ecosystems. We measured total and organic chlorine concentrations in 51 French surface soils sampled from grassland, arable and forest sites on a national scale (French soil quality monitoring network) in order to characterize the variability of organic chlorine concentrations for these different land uses. While previous studies reported that the chlorination of soil organic matter is responsible for chlorine retention in temperate forest ecosystems, this study shows that the non-extractable organohalogen pool accounts for the majority (>80 % on an average) of the total measurable chlorine in grassland and agricultural soils. This suggests that natural chlorination is a widespread phenomenon in all kinds of soils. A multiple linear regression analysis performed on the dataset indicated that retention of organochlorine in soils is related to the organic carbon content, Cl input and soil pH. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are widespread organic pollutants. Soils are a reservoir of PAHs because some soil constituents favour PAH accumulation. Therefore, soil is a key indicator of the degree of contamination. So far, studies mapping soil PAH levels over large territories are very rare. Here, we report the first nation-wide maps of soil PAHs in France. Results were obtained within the French National Soil Monitoring Network, which is the first European network monitoring systematically soil PAHs. We used advanced geostatistics to map PAH distribution over the whole French territory. Our results show clear trends of PAH levels at the nation scale. For instance, the highest PAH levels are found in Northern and Eastern France. This high contamination is explained by the intense industrial activity of these regions during the last century. High levels of PAH are also found near some coastlines. This observation could be explained by long-range atmospheric transportation. In addition, we found that light PAHs are rarely found in French topsoils. [ABSTRACT FROM AUTHOR]

Soil is a major carbon pool ruling the global C cycle and in climate change because soil carbon is a source and a sink of atmospheric CO. Soil organic carbon also controls many beneficial properties such as fertility, aggregate stability and degradation of groundwater pollutants. Therefore mapping soil carbon at landscape scale is needed to define appropriate management that will favour higher soil quality. Actual soil carbon maps of France have a too coarse resolution, i.e. 8 and 12 km, to define efficient land management practices. Therefore, here, we model soil organic carbon in France at a resolution of 250 m. We study the impact of land use, soil type, climate and agro-management on soil organic carbon. We found that the total soil carbon stock in France is about 3.7 ± 1.3 Pg. Results also show that the precipitation pattern dominates the overall spatial distribution of soil carbon. Land use is the most important factor controlling organic carbon changes at landscape scale. Our high resolution national map of soil organic C will be useful to define land management practices that will improve soil quality. [ABSTRACT FROM AUTHOR]

Microbial biogeography is the study of the distribution of microbial diversity on large scales of space and time. This science aims at understanding biodiversity regulation and its link with ecosystem biological functioning, goods and services such as maintenance of productivity, of soil and atmospheric quality, and of soil health. Although the initial concept dates from the early 20th century (Beijerinck (1913) De infusies en de ontdekking der backterien, in: Jaarboek van de Knoniklijke Akademie van Wetenschappen, Muller, Amsterdam), only recently have an increasing number of studies have investigated the biogeographical patterns of soil microbial diversity. A such delay is due to the constraints of the microbial models, the need to develop relevant molecular and bioinformatic tools to assess microbial diversity, and the non-availability of an adequate sampling strategy. Consequently, the conclusions from microbial ecology studies have rarely been generally applicable and even the fundamental power-laws differ because the taxa-area relationship and the influence of global and distal parameters on the spatial distribution of microbial communities have not been examined. In this article we define and discuss the scientific, technical and operational limits and outcomes resulting from soil microbial biogeography together with the technical and logistical feasibility. The main results are that microbial communities are not stochastically distributed on a wide scale and that biogeographical patterns are more influenced by local parameters such as soil type and land use than by distal ones, e.g. climate and geomorphology, contrary to plants and animals. We then present the European soil biological survey network, focusing on the French national initiative and the 'ECOMIC-RMQS' project. The objective of the ECOMIC-RMQS project is to characterise the density and diversity of bacterial communities in all soils in the RMQS library in order to assess, for the first time, not only microbial biogeography across the whole of France but also the impact of land use on soil biodiversity (Réseau de Mesures de la Qualité des Sols = French Soil Quality Monitoring Network, 2200 soils covering all the French territory with a systematic grid of sampling). The scientific, technical and logistical outputs are examined with a view to the future prospects needed to develop this scientific domain and its applications in sustainable land use. [ABSTRACT FROM AUTHOR]