Controls of soil spatial variability in a dry tropical forest

We examined the roles of lithology, topography, vegetation and fire in generating local-scale (= 1 cm diameter at breast height (DBH), and spatial variation in fire frequency (times burnt during the 17 years preceding soil sampling) in a permanent 50-ha plot. Unlike classic catenas, lower elevation soils had lesser moisture, plant-available Ca, Cu, Mn, Mg, Zn, B, clay and total C. The distribution of plant-available Ca, Cu, Mn and Mg appeared to largely be determined by the whole-rock chemical composition differences between amphibolites and hornblende-biotite gneisses. Amphibolites were associated with summit positions, while gneisses dominated lower elevations, an observation that concurs with other studies in the region which suggest that hillslope-scale topography has been shaped by differential weathering of lithologies. Neither NO3--N nor NH4+-N was explained by the basal area of trees belonging to Fabaceae, a family associated with N-fixing species, and no long-term effects of fire on soil parameters were detected. Local-scale lithological variation is an important first-order control over soil variability at the hillslope scale in this SDTF, by both direct influence on nutrient stocks and indirect influence via control of local relief

Tailor-made biochar systems: Interdisciplinary evaluations of ecosystem services and farmer livelihoods in tropical agro-ecosystems

Organic matter management is key to sustain ecosystem services provided by soils. However, it is rarely considered in a holistic view, considering local resources, agro-environmental effects and harmonization with farmers’ needs. Organic inputs, like compost and biochar, could represent a sustainable solution to massive current challenges associated to the intensification of agriculture, in particular for tropical regions. Here we assess the potential of agricultural residues as a resource for farmer communities in southwestern India to reduce their dependency on external inputs and sustain ecosystem services. We propose a novel joint evaluation of farmers’ aspirations together with agro-environmental effects of organic inputs on soils. Our soil quality evaluation showed that biochar alone or with compost did not improve unilaterally soils in the tropics (Anthroposol, Ferralsol and Vertisol). Many organic inputs led to an initial decrease in water-holding capacities of control soils (-27.3%: coconut shell biochar with compost on Anthroposol). Responses to organic matter inputs for carbon were strongest for Ferralsols (+33.4% with rice husk biochar), and mostly positive for Anthroposols and Vertisols (+12.5% to +13.8% respectively). Soil pH responses were surprisingly negative for Ferralsols and only positive if biochar was applied alone (between -5.6% to +1.9%). For Anthroposols and Vertisols, highest increases were achieved with rice husk biochar + vermicomposts (+7.2% and +5.2% respectively). Our socio-economic evaluation showed that farmers with a stronger economical position showed greater interest towards technology like biochar (factor 1.3 to 1.6 higher for farmers cultivating Anthroposols and/or Vertisols compared to Ferralsols), while poorer farmers more skepticism, which may lead to an increased economical gap within rural communities if technologies are not implemented with long-term guidance. These results advocate for an interdisciplinary evaluation of agricultural technology prior to its implementation as a development tool in the field

Karstification in the Cuddapah Sedimentary Basin, Southern India: Implications for Groundwater Resources

The Cuddapah sedimentary basin extends over a significant part of the southern part of Andhra Pradesh State, Southern India. Proterozoic carbonate rocks in the basin are constituted by as three main units- the Vempalle dolomite, the Narji and Koilkuntla limestones. These carbonate rocks are of strategic importance for local communities as they provide the main water source for irrigation and domestic use and they are also intensively quarried for cement production and building stones. It is therefore, of primary importance to assess to which extent these carbonate units are karstified so as to provide recommendations for appropriate land and water resource management. The field investigations carried out indicate that these carbonate units are significantly karstified and karstification has been an ongoing process with several phases under variable climatic conditions. As a result, a significant part of aquifer recharge occurs as point-recharge through swallow-holes and groundwater flow is channelized by conduit networks which emerge at karst springs. Karst development was possibly more active during past humid conditions; however karstification is still an ongoing process under the present semi-arid climate especially in the favorable case where karst drains the runoff issued from upstream quartzitic hills. The karstic nature of these carbonate units need to be integrated in future research and development programmes to avoid practices that may lead to unexpected collapses, reservoir leaks, inaccurate groundwater budgeting, etc

Australian Sphingidae – DNA Barcodes Challenge Current Species Boundaries and Distributions

© 2014 Rougerie et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article

Etude du déséquilibre 234U-238U dans les eaux de rivière (cas du Strengbach, du mont Cameroun et de l'Himalaya)

STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Study of exchangeable metal on colloidal humic acids and particulate matter by coupling ultrafiltration and isotopic tracers: Application to natural waters

A new method is proposed to characterize the complexation properties of colloids and metal-colloid interactions in natural waters. Based on the association of ultrafiltration with isotopic tracing, this method could quantify the pool of elements in an exchangeable position and also address the kinetic aspects of these exchanges. Basically, it consists of the comparison of isotopic compositions between the bulk sample and a succession of filtrates through time. Exchanges between colloidal humic acids (HA) and metals were first characterized, before applying such manipulations on natural waters. A few elements, representative of a wide range of complexation properties, were chosen: Cu, Zn, Cd, Pb, Sr, Nd, Ni, Th and U. In the case of humic acids, very small (less than 10% of isotopes), but significant isotopic shifts were observed compared to the isotopic equilibrium. It means that more than 90% of the isotopes were exchanged just after addition of isotopic tracers. Experiments on natural organic-rich waters (Mengong and Nyong streams) indicate isotopic composition variations close to those of humic acids. On the contrary, ultrafiltration performed on the total Sanaga River water (including suspended matter "SM") shows an important isotopic shift between the filtered and unfiltered solutions. It means that in the case of the Sanaga River, a significant part of the chemical elements did not exchange

Utilisation des isotopes stables de Cd, Zn, Cu, Ni et Pb pour quantifier le compartiment échangeable des éléments trace métalliques et de delta66Zn pour tracer les pollutions polymétalliques

Une technique de " spikage ", ou dilution d'isotopes stables multi-élémentaire, a été est développée afin de quantifier et caractériser simultanément les compartiments échangeables de Cd, Zn, Cu, Ni et Pb dans des sols contaminés. Cette technique a étéest ici validée par comparaison avec les résultats de spikage d'isotopes radioactifs de Cd, ainsi que ceux d'extractions chimiques. Par ailleurs, une étude intégrée des signatures isotopiques du Zn (d66Zn) dans plusieurs compartiments d'écosystèmes contaminés (sites métallurgiques de Viviez-Decazeville, S.-O. France et de Kempen, N.-E. Belgique) permet de proposer un schéma cohérent des différents fractionnements isotopiques de Zn liés à son traitement métallurgique. L'existence de différents d66Zn pour le zinc " enrichi " et " résiduel " s'avère donc un outil puissant de localisation de sources de contamination métallurgique. Ces résultats démontrent l'efficacité des isotopes stables comme traceurs en matière de traçage de processus et de source de contaminationA multi-elementary spiking method has been is developpeddeveloped in order to simultaneously quantify and caracterizecharacterize simultaneously the labile pools fraction of Cd, Zn, Ni, Cu and Pb in contaminated soils. This method is has been validated by comparison with 1) radioactive Cd spiking data,g Cd and of2) chemical extractions results. In additionFurthermore, an integrated study of Zn isotopic signatures (d66Zn) in various compartments pools of two contaminated ecosystems (zinc smelting sites of Viviez-Decazeville, S.-W. of France and of Kempen, N.-E of Belgium) has been performed allowing the identification of various allows to assume a coherent scheme of Zn isotopic fractionations during associated to the metallurgical processes. The differents d66Zn ratio observed in between "enriched" and "residual" zinc would be a powerfull tool to identify the metallurgical contaminations origins. These results demonstrate the efficiency of stable isotopes as tracers for contamination processes and sourcescontaminations tracersTOULOUSE3-BU Sciences (315552104) / SudocTOULOUSE-Observ. Midi Pyréné (315552299) / SudocSudocFranceF

Bioremediation of hexavalent and trivalent chromium using Citrobacter freundii : a mechanistic study

The mechanisms involved in the bioremediation of hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) by a Gram negative bacterium, Citrobacter freundii were independently investigated. The biosorption isotherms of Cr(VI) and Cr(III) for C. freundii exhibited a typical Langmuirian behaviour. The Gibbs free energy (ΔG) was determined to be -25.5 and −27.2 kJ mol−1, respectively for Cr(VI) and Cr(III), suggestive of chemisorption between the functional groups of bacterial surface and Cr. The relatively lesser amount of desorption of Cr(VI) or Cr(III) from the bacterial cells attested to the irreversible nature of biosorption. FTIR studies revealed the involvement of carboxyl, amino and hydroxyl groups in the biosorption of Cr(VI) and Cr(III). X-ray photoelectron spectroscopic studies provided evidence in support of the bioreduction from Cr(VI) to Cr(III). Electrokinetic studies revealed that the bacterial cells become less electronegative after interaction with Cr species. The mechanisms of bioremediation have been delineated to involve both biosorption and bioreduction processes for Cr(VI), while for Cr(III), biosorption is the governing process of remediation

Soil organic carbon stocks and quality in small-scale tropical, sub-humid and semi-arid watersheds under shrubland and dry deciduous forest in southwestern India

Soil organic carbon is regulated by a dynamic interaction of vegetation inputs, organic matter degradation and stabilization processes in soils, and its redistribution in the landscape. Tropical ecosystems are highly important in terms of carbon stored in vegetation and soil, but many processes of the soil carbon cycle in the tropics are yet to be fully understood. Here, we studied soil organic carbon stocks and quality in small-scale tropical, sub-humid and semi-arid watersheds along a climate gradient in southwestern India with varying vegetation and geology to identify major drivers of soil organic carbon dynamics in three prevalent soil types (Lixisol, Vertisol and Ferralsol) under shrubland and dry deciduous forest. We used a combination of organic carbon analysis (total organic carbon content, 13C, C:N), mid-infrared spectroscopy and soil property information (bulk density, texture, oxides, pH, cation-exchange capacity). Soil organic carbon stocks in these watersheds showed a substantial range from 58.2 to 169.4 Mg C ha− 1 in the first 60 cm, and the differences depended on local- to watershed-scale variations in vegetation type and history, geology, soil physio-chemical (clay, oxides) and biological (bioturbation) properties. Considerable parts of the organic carbon stored in these soils was found below 30 cm (up to 40 %), stressing the importance of tropical subsoils. From our analysis of the soil organic carbon quality and literature data on paleoclimate and vegetation, we could identify land-use changes in these watersheds, from tropical moist evergreen forests, forest-savannah transitions and plantations to secondary regrowth forest over time. Our study provides new data and insights into the local-scale drivers of soil organic carbon quantity and quality of tropical, sub-humid and semi-arid watersheds under shrubland and dry deciduous forest with varying geology and soil types