Formation Of Organometallic Complexes Research Articles

Powdered Cogon Grass (Imperata cylindrica) as a Biosorbent for the Removal of Iron (II)

Powdered Cogon Grass (Imperata cylindrica) as a Biosorbent for the Removal of Iron (II)

Durability and micromechanical properties of biochar in biochar-cement composites under marine environment

Integrating biochar into traditional construction materials presents a promising avenue to reduce carbon emissions from the construction industry. While recent research has focused on the performance of biochar-cement materials, limited attention is given to the durability of biochar in cementitious materials. This study investigated the alterations in the structural, chemical, and mechanical properties of biochar in the cementitious system and marine environment. The results showed an increased pore size in the biochar and a potential collapse of its structure after long-term exposure of biochar to an alkaline cement environment. The decline of the aromaticity, 23.8% increase in matrix defectiveness, and formation of organometallic complexes between Ca2+ and oxygen-containing functional groups of biochar indicated that its interactions with hydrated cement would lead to the changes in its chemical properties. The exposure of biochar to the simulated cement solution reduced its Young’s modulus from 3.81 GPa to 1.55 GPa and hardness from 0.70 GPa to 0.13 GPa possibly due to the collapse of the pore structure. The saponification reaction might disrupt the cross-linking network structure constructed by COOC and C–O–C in the biochar and release the fulvic-acid organics, causing a decrease in the short- and long-term rebound ratios by 5.6–25.6% and 5–17%, respectively. Biochar exposed to the simulated harsh environment (seawater) exhibited an increase in Young’s modulus and hardness by ∼40% compared to virgin biochar. The long-term rebound ratio reached 96.6–99.2% due to brucite, NaCl, and KCl deposition and filling, implying the potential advantage of biochar-cement composites for long-term durability in the marine environment. These findings contribute new insights to the assessment of mechanical performance and durability of biochar-cement composites in diverse environmental conditions.

Can Soil Improvers (Biochar, Compost, Insect Frass, Lime, and Zeolite) Achieve Phytostabilization of Potentially Toxic Elements in Heavily Contaminated Soil with the Use of Purslane (Portulaca oleracea)?

In soil with extremely high contents of Cd (101.87), Pb (26,526.44), and Zn (17,652.63 mg kg−1), we aimed to test the phytostabilization capacity of purslane (Portulaca oleracea) with the use of various soil improvers, both organic (biochar, compost, insect frass) and inorganic (lime and zeolite). Thus, in a 60-day pot experiment, we amended this heavily contaminated soil with the five materials at two rates, 2% and 4%, resulting in 11 treatments (control plus five materials × two rates) replicated 10 times. We found that soil extractions of Cd with DTPA (diethylenetriaminepentaacetic acid) were not affected by any of the amendments, as there was no recorded significant reduction in soil Cd. In the case of Pb, there were even significant increases in its extractability with added biochar, and so was the case for compost at 4%. The reason may be the formation of organometallic complexes with organic substances of low molecular weight eluted by the organic amendments. Similarly, Zn extractability increased significantly compared to the control in the compost and frass treatments. As for purslane shoots, Cd decreased from 61 μg kg−1 fresh weight (FW) at control to 39 at biochar 4%, but the reduction was non-significant. As for Pb, it decreased with biochar but not significantly, while it exhibited a significant decrease in all other treatments. However, in all cases the content of Pb in purslane was well above the European regulation limit of 0.100 mg kg−1 FW (fresh weight) for vegetables and fresh herbs, while Cd fell below the regulation limit of 50 μg kg−1 FW at biochar 4%, compost 4%, and frass 2% and 4% (with control being 62.5 μg kg−1 FW). We conclude that in heavily contaminated soils, although biochar, along with compost and frass, was not entirely unsuccessful, the tested amendments did not reduce satisfactorily toxic elements to sufficiently low levels both in soil and in the test plant (here, purslane) in order to achieve phytostabilization. However, further research is necessary to identify exact mechanisms and to elucidate the role of different biochars.

Polygenic soils in the southern central Ecuadorian highlands as the result of long-lasting pedogenesis, geodynamic processes and climate change

In the high altitude (>3000 m asl) grasslands of northern Ecuador, the Páramo ecosystem, soils generally formed on recent volcanic ashes being <10,000 years old in the northern and central part of the cordilleras. With time these soils evolved in to non-allophanic Andisols with hydric properties such as evidenced in profiles from the Cajas massif located in the western central Cordillera. However soils at the Fierro Urcu massif and at the Oña plateau at the eastern Cordillera formed on a non pyroclastic indurated parent material. Compared to non-allophanic Andisols from the Cajas massif, they present similar morphological properties with a dark 50 cm thick carbon-rich (80–120 g kg−1) topsoil with a very low bulk density (<0.65 g cm−3) and high water retention. These top soils appear to have originated from fall-out, derived from close and still active volcanoes of Sangay and/or Tungurahua, both located in a distance of 200–250 km NNE of the Oña Massif, respectively. Geochemical determinations of trace and rare earth elements, however, confirm the lack of volcanic ash contribution in the Saraguro and Oña samples based on Eu/Eu* and Ce/Ce* anomalies relative to the lack of such anomalies in the Cajas samples. The Oña and Saraguro soils appear to be the result of a long-lasting double pedogenic process. The basement of the Saraguro soil is a Ferralsol with gibbsite and kaolinite and the Oña soil is a 5 m thick kaolinitic Ferralsol. The upper part of these profiles are the result of a major climatic change with increasing colder conditions, generating an increase in organic matter content and a very acidic environment leading to the instability of kaolinite and gibbsite, thereby liberating large amounts of free aluminium and iron oxides. The evolution of these very highly evolved Ferralsols into soils with Andic properties is proposed to be the result of rapid tectonic uplift calculated at a rate exceeding 0.6 mm/year in the region leading to a general decrease in temperature limiting carbon mineralization and favouring the formation of organo-metallic complexes. The soils studied here reveal compelling new evidence and information about the uplift of a part of the Ecuadorean Andes.

Electrochemical study and experimental simulation of the synergistic effect of a formulation based on Ficus pumila Linn. Leaves extract and zinc sulfate on the XC38 steel corrosion inhibition in NaCl solution

The inhibitive activity of a mixture of Ficus pumila Linn. leaves hydroalcoholic extracts (HEFP) and zinc ions against corrosion of XC38 steel in NaCl solution was investigated. Electrochemical measurements (potentiodynamic polarization and electrochemical impedance spectroscopy at and around the corrosion potential) and surface analysis (SEM/EDX) have shown that the presence of zinc ions considerably increases the inhibitive capacity of HEFP. However, appropriate concentrations of zinc ions (50 and 100 ppm) and of HEFP (200 ppm) are necessary to have an optimal inhibitive effect. The formation of organometallic complexes between zinc ions and some organic compounds of HEFP (polyphenols and carbohydrates) are the determining step of the synergistic inhibition. Since the main inhibitive agents in plant extracts are polyphenols, a simulation of this inhibitive character was electrochemically done with a mixture of flavonoid (quercetin), phenolic acid (gallic acid) and zinc ions in order to elucidate the inhibition mechanism. The obtained results showed that the electrochemical behavior of XC38 steel in the presence of this mixture is quite similar to that obtained in the presence of HEFP + Zn2+ formulation. The proposed inhibition mechanism, which explains the good inhibitive efficiency observed in presence of the HEFP + Zn2+ formulation, is based on concerted reactions between the steel oxidation products (Fe2+ and Fe3+), the zinc ions and the Iron(II) and Iron(III) complexing agents present in the extract.

Fe oxides and fulvic acids together promoted the migration of Cd(II) to the root surface of Phragmites australis

Dissolved organic matter (DOM) or iron/manganese (hydro)oxides were important factors in the migration of Cd in sediments of wetlands. DOM and Fe oxides simultaneously affect the longitudinal and transverse migration of Cd in wetlands sediments of plants was still unclear. In this study, a 14-day rhizobox experiment was conducted and the result showed that the rhizosphere effect of Cd migration was only limited to the upper layer of sediments (− 2 to − 4 cm). Fe with fulvic acid (FA) simultaneously existed can precipitate Cd(II) from supernatant to sediments downward. Fe oxides at sediment concentration could effectively prevent Cd(II) from migrating to root surface (0.21 vs 0.02 at%). While Fe oxides with FA together at sediment concentration could effectively promoted the migration of Cd(II) to root surface (0.07 vs 0.08 at%). The formation of organo-metallic complexes of Fe in the presence of FA profoundly proved this finding (increased by ~33.0%). And the polysaccharides and aromatics in organic matter were the chief functional groups participating in the incorporation of Cd and Fe oxides. The findings reveal the migration rules of Cd(II) in sediments by FA and Fe oxides and give an insight into the mechanisms of Cd(II) migration to the root surface around wetland plants.

Silicon and aluminum in Bulgarian coals

The presence and distribution of Si and Al in 19 Bulgarian coal basins and deposits, belonging to 8 coal provinces, were studied. Coals are of different rank (lignite to anthracite) and age (Late Carboniferous to Pliocene). The presence of both studied major elements depends strongly on: i) their concentration within the basin’s provenance; ii) the extent of terrigenous supply; iii) environmental acidity during peat formation; and iv) the presence and composition of epigenetic mineralization within the coal seams. Because of the presumed abundant terrigenous supply, the concentrations of both Si and Al are higher than the world average for most of the studied coals. Exceptions are the Maritsa-West, Burgas, Staniantsi, Oranovo, Chukurovo and Pernik Basins, for which reduced terrigenous supply can be suggested. For most of the basins, both Si and Al demonstrate good positive correlation with the ash yields, thus arguing for predominant inorganic affinity. Relatively low Si/Al ratios (typically &lt;2) and good positive correlation between Si and Al (ro&gt;0.6) imply the predominant role of the clay mineral assemblages as the main source of the elements in coal. Quartz is presumed to have dominant role only in Maritsa-West Basin. Poorer or negative correlations with the ash yields in part of the studied basins (i.e. Svoge, Maritsa-West, Sofia, Burgas and Dobrudzha Basins) suggest either mixed or predominantly organic affinity of the elements. Release of Si and Al from the clay minerals during the peat formation/diagenesis and subsequent formation of organo-metallic complexes is considered to responsible for such affinity.

Silicon and aluminum in Bulgarian coals

The presence and distribution of Si and Al in 19 Bulgarian coal basins and deposits, belonging to 8 coal provinces, were studied. Coals are of different rank (lignite to anthracite) and age (Late Carboniferous to Pliocene). The presence of both studied major elements depends strongly on: i) their concentration within the basin’s provenance; ii) the extent of terrigenous supply; iii) environmental acidity during peat formation; and iv) the presence and composition of epigenetic mineralization within the coal seams. Because of the presumed abundant terrigenous supply, the concentrations of both Si and Al are higher than the world average for most of the studied coals. Exceptions are the Maritsa-West, Burgas, Staniantsi, Oranovo, Chukurovo and Pernik Basins, for which reduced terrigenous supply can be suggested. For most of the basins, both Si and Al demonstrate good positive correlation with the ash yields, thus arguing for predominant inorganic affinity. Relatively low Si/Al ratios (typically &lt;2) and good positive correlation between Si and Al (ro&gt;0.6) imply the predominant role of the clay mineral assemblages as the main source of the elements in coal. Quartz is presumed to have dominant role only in Maritsa-West Basin. Poorer or negative correlations with the ash yields in part of the studied basins (i.e. Svoge, Maritsa-West, Sofia, Burgas and Dobrudzha Basins) suggest either mixed or predominantly organic affinity of the elements. Release of Si and Al from the clay minerals during the peat formation/diagenesis and subsequent formation of organo-metallic complexes is considered to responsible for such affinity.

Widespread elevated iridium in Upper Triassic\u2013Lower Jurassic strata of the Newark Supergroup: implications for use as an extinction marker

Anomalous levels of iridium in sedimentary strata are associated with mass extinction events caused by impact events. In the case of the end-Triassic extinction event, the anomalies as well as the extinctions are linked to the eruption of the Central Atlantic Magmatic Province (CAMP) flood basalts. We report new data on concentrations of iridium in continental strata of the Fundy, Deerfield, Hartford and Newark basins, both above and below the oldest CAMP flows in these basins, that demonstrate that these anomalies are more common than previously known. We conclude that the enrichments were at least in some instances likely derived locally by concentration due to leaching directly from the lavas into sediments proximal to the CAMP flows due to post-eruptive hydrothermal activity. In other instances, the enrichments likely record the global fallout of aerosols and/or ash particles during the eruptions of the CAMP basalts. The common association of the highest levels of enrichment with organic matter suggests either redox control or stabilization by formation of organometallic complexes following post-eruptive redistribution. These findings demonstrate the importance of considering the distribution and magnitude of iridium anomalies in considering the source of the iridium and possible extinction mechanisms.

Relationship of soil water retention characteristics and soil properties: a case study from the Colombian Andes

Differences in soil water retention (SWR) characteristics between soil types and the factors driving those differences provide important information for land management, particularly in regions such as the Colombian Andes, which have limited water-storage infrastructure and where soils provide plant-available water and other ecosystem services. The objective of this study was to explore relationships between SWR and physical, chemical, and mineralogical properties of Andisols and Inceptisols through a case study of two watersheds in the Colombian Andes. This study identified a complex relationship between total carbon (TC), short-range order (SRO) minerals, and SWR. Both soil types had high SWR, with volumetric water content at permanent wilting point between 39% and 53%. Principal component analysis showed association of SWR with TC, SRO minerals, and % clay in both soil types. The Andisols of this study were coarse textured, allophanic (rich in allophane and imogolite — up to 17% in the B horizon), and with up to 15% TC in the A horizon. In contrast, the Inceptisols were fine textured (&gt;30% clay) and higher in ferrihydrite than the Andisols. The formation of organo-metallic complexes was observed in A horizons; however, TC was lower under pasture than forest in both soil types. The addition of organic matter to soils with SRO minerals, such as the soils of this study, may foster the formation of organo-metallic complexes, stabilize soil C, and enhance SWR. Consequently, both study sites may benefit from management practices that increase soil organic matter.

Processes that influence dissolved organic matter in the soil: a review

ABSTRACT: In tropical regions, climate conditions favor fast decomposition of soil organic matter (SOM), releasing into the soil organic composts in solid, liquid, and gaseous forms with variable compositions. Dissolved organic matter (DOM), a complex mixture of thousands of organic compounds, is only a small fraction of the decomposition products; however, it is highly mobile and reactive to the soil. Therefore, DOM play a key role in soil aggregation (formation of organometallic complexes), energy source for microorganisms, as well as C storage, cycling, and provision of plant-available nutrients. DOM multifunctionality to sustain soil functions and important ecosystem services have raised global scientific interest in studies on DOM fractions. However, previous studies were conducted predominantly under temperate soil conditions in natural ecosystems. Therefore, there is paucity of information on tropical soil conditions under agricultural systems, where DOM turnover is intensified by management practices. This review synthesized information in the literature to identify and discuss the main sources, transformations, and future of DOM in soils. We also discussed the importance of this fraction in C cycling and other soil properties and processes, emphasizing agricultural systems in tropical soils. Gaps and opportunities were identified to guide future studies on DOM in tropical soils.

Raman spectroscopy along with Principal Component Analysis for the confirmation of Silver(I)-N-heterocyclic carbene complex formation.

In this study Raman spectroscopy is employed for the characterization of two different ligands called as S1 and S2 and their respective co-ordinate complexes called C1 and C2. Specific Raman spectral signatures are observed for each of these Silver(I)-N-heterocyclic carbene complexes Ag(I)-(NHCs), which can be associated with the imidazolium ring, part of both of the ligands, indicating the formation of new coordinate covalent bond. For the detailed analysis, Raman spectral data of these ligands and complexes is analyzed by multivariate data analysis technique, Principal Component Analysis (PCA) which is found very helpful to differentiate two ligands and complexes from each other. The significant Raman peaks with higher intensities in the complexes as compared to the respective ligands are associated with imidazole ring which can be attributed to the enhanced polarizability of this ring on complex formation. Moreover, the spectral features associated with (AgC) bond are observed with higher intensity at 360 in (C1) and 383 in (C2). This study indicates the potential of Raman spectroscopy for the characterization and confirmation of formation of organometallic complexes and other chemical products.

Holocene pedogenesis along a chronotoposequence of soils from the Altiplano to the Cordillera Real, Bolivian Andes

The high mountains of Central Andean represents one of the most diverse and heterogeneous landscape of South America, with very contrasting climates across an east-west gradient that remains poorly investigated in terms of Late Quaternary soil formation. Climatic forces within a diverse pedogeomorphological framework generates a complex geoenvironmental scenario, extremely susceptible to climatic changes. From the high aridic bolivian altiplano to moist periglacial regions at high mountain, and from these, to the tropical rainforest downslope, one finds soil chronosequences and different ecosystems. The objective of this work was to describe and interpret chronological, morphological, physical, chemical and mineralogical attributes of 18 profiles along a long and representative east-west transect through the Cordillera Real, at altitudes varying between 1800 and 5030 m a.s.l. The parent material is lithologically diverse, ranging from till, fluvio-glacial, talus and loess sediments. Most soils show a sequence of O, A, C and C/R with high organic carbon contents at surface and subsurface, forming Umbric horizons. Buried, polycyclic organic layers are common and the 14C dating reveals a sequence of processes as one moves away from the glaciated peaks, varying from 1500 to 6000 years (BP). The occurrence of paleo-peatlands and past and present-day hydromorphic areas (bofedales) result in widespread melanization trend, with histic horizons and histosols formation in the bottomlands. The relict, degraded state of bofedales indicates a reduction of waterlogging in the Altiplano in the late Holocene, resulting in increasing water shortage. Inceptisols occur at the high mountain sector, under periglacial conditions and high slope instability and solifluxion. In general soils are acid or high acid, with low base saturation and high Al saturation. High mountain Tundra soils at (5020 m) are exclusively developed on moraines of resistant granodiorite and have low clay content and less mineralogical diversity. Soils at the western slope were affected by the last glaciation and show more diverse mineralogy with cryogenic features under dry, open vegetation (Puna). On the other hand, soils at the eastern slope are associated with a greater climatic variation, varying mineralogical attributes, greater organic carbon mineralization and formation of organometallic complexes. Although most soils show influence of non-crystalline minerals, such as allophanes and amorphous Fe oxides, andic soil properties were apparently absent.

Soils in transition: saltwater intrusion alters soil chemistry in agricultural fields

As global sea-levels rise, low-lying coastal lands are subject to shallow coastal flooding and saltwater intrusion, affecting the productivity of farmlands worldwide. Soil biogeochemistry can be dramatically altered as saltwater intrudes agricultural fields. We selected three farm fields in Somerset Co., Maryland affected by saltwater intrusion and established transects from the ditch bank to the center of the cropped field and collected soils (to ~ 140 cm) at five points along this transect. The three fields in this study have different soil types, are located along different tributaries in the county, and receive different fertilizer rates, yet they all showed similar biogeochemical responses to saltwater intrusion. We found an increase in electrical conductivity and concentrations of chloride, sulfate, and forms of phosphorus (P) from the center of the field (low) to the ditch banks (high). As inundation increased, the structure of iron (Fe) changed from crystalline to non-crystalline forms, possibly due to dissolution under saturated conditions. Near the edges of the fields, the formation of organometallic complexes was positively associated with increases in soil carbon and organic soil P concentrations. Compared to areas of the fields where crops were actively growing, soil P concentrations are 2–3 higher on field edges, suggesting that saltwater intrusion may be transporting P to the edges of agricultural fields. These field edges are frequently saturated, thus reduction of Fe could lead to P release into solution potentially harming water quality. As climate change pushes saltwater further inland, it is important to understand the biogeochemical consequences for ecosystems up- and downstream. Understanding the how fractions of P move and change across fields affected by saltwater intrusion will be crucial for planning current and future management of coastal agricultural lands.

Andosolization of ferrallitic soils in the Bambouto Mountains, West Cameroon

Soils along a toposequence (1500–2260 m) on the southern slope of the volcanic Bambouto Mountains in western Cameroon were investigated to elucidate the occurrence and development of andic properties at high altitude (>1800 m) in the study area. The surface layer that has these properties has in the past been interpreted as a weathered volcanic ash layer, overlying ferrallitic soils that developed from lava flow deposits and derived pediments. Physico-chemical and mineralogical data demonstrate that the andic properties of the high-altitude pedons result from SOM accumulation, favoured by climate and vegetation. The ‘andosolization’ process affecting these profiles involves the formation of organo-metallic complexes, which is mediated by organic ligands and controlled by the dissolution of gibbsite and iron oxides. Increasing andosolization with increasing altitude, due to SOM accumulation, is well reflected by soil classification names, especially by the humic qualifier for the soils below 1800 m a.s.l. and the protoandic subqualifier for the soils at higher altitude. All analysed properties show features that are incompatible with derivation of the upper part of the high-altitude pedons from volcanic ash. In studies of soils from similar settings, care should be taken to avoid misinterpretation of surface horizons marked by environmentally conditioned development of organo-metallic complexes as ash-derived layers.

Pb2+ adsorption by a compost obtained from the treatment of tobacco from smuggled cigarettes and industrial sewage sludge.

The adsorption of Pb2+ by a compost obtained from the treatment of tobacco from smuggled cigarettes (SCT) and industrial sewage sludge (ISS) was investigated. The Pb2+ adsorption process was evaluated as function of different concentrations of adsorbent and adsorbate, pH variations, and contact time. Fourier transformed infrared spectroscopy (FTIR) and energy dispersive X-ray spectrometry (EDX) were adopted to obtain information regarding structural changes and a better understanding of the adsorption mechanism. The adsorbent maximum adsorption capacity for Pb2+, calculated using the Sips equation, was 21.454mg/g with 3g/L adsorbent at pH 5. The adsorption kinetics best adjustment was obtained using the pseudo-second-order model with a time of 240min to reach the adsorption equilibrium. FTIR and EDX results suggest that Pb2+ might have bonded to phenolic, carboxylic, hydroxyl, and amine groups; they also show formation of organometallic complexes and cationic exchange between the compost and the solution. The study confirmed that the compost evaluated can be used as a potential adsorbent in environments contaminated with Pb2+.

Impact of microbial activity on the mobility of metallic elements (Fe, Al and Hg) in tropical soils

Dissolved organic carbon (DOC), especially low molecular mass organic acids (LMMOAs) derives principally from biota degradation process in which soil microorganisms are the main actors and from roots exudates. The presence of LMMOAs led to an increase of availability and mobility of metallic elements through the formation of organo-metallic complex. In tropical soils, very few information about LMMOAs quantification and their role in the biogeochemical process related to trace metals cycling was available. Quantification of LMMOAs is limited due to their low concentration and rapid degradation. Until now, the role of microbial activity as well as LMMOAs in the biogeochemical cycle of metallic elements in tropical soils has not been investigated. The present study was conducted to evaluate the effect of microbial activity and biomass on the availability and mobility of metallic elements (Fe, Al and Hg) in two tropical soils, Ferralsol and Acrisol. We also quantified LMMOAs contents in soil solutions and addressed to their role in the mobilization of metals.Utilization of Diffuse Gradient in Thin film (DGT) method permits to analyze bioavailable metal in both fractions: organically complexed and free metals. The results show that the quantity of Fe, Al and Hg labile were higher in Ferralsol than Acrisol soils. This was more accentuated for the 50 cm-depth of soils where the microbial activities and the organic carbon content were important. Concentration of LMMOAs of Ferralsol and Acrisol were lower in compare to coniferous and deciduous forest soils. Proportions of LMMOAs in DOC were very small at 10.5% and 6.85% in the Ferralsol and Acrisol soils, respectively. The mobilization of Fe, Al and Hg in Ferralsol and Acrisol soils appeared to vary depending on the soil physico-chemical characteristics (sorption capacities and metals content) and also on the microbial biomass and activity. Soil pH influences the acidity of the functional groups in organic molecules and consequently their speciation. In addition, low pH increase proton competition within acidic functional groups involved in coordinate bond. The content of CEC in Ferralsol is higher than Acrisol that is related to the high contents of clay and organic carbon. Low CEC content can result in a decrease of retain of the cationic trace metals. Low CEC content led to a decrease of the capacity of retaining of metallic elements in tropical soils in compare to temperate soils.

Caracterización de un Andisol de la cuenca alta de la quebrada Santa Elena, Oriente Antioqueño, Colombia.

Se caracterizó detalladamente un Andisol derivado de ceniza volcánica de la cuenca alta de la quebrada Santa Elena, Oriente Antioqueño (Colombia), con el fin de realizar en él otros estudios más detallados de pedogénesis. El suelo estudiado presentó un bajo contenido de bases y de fósforo disponible y una alta acidez, lo que indica un bajo nivel de fertilidad natural. El alto contenido de materia orgánica superficial está en concordancia con el clima frío húmedo de la zona y con la formación de complejos organometálicos que la protegen de la mineralización. Los horizontes superficiales del perfil estudiado se clasificaron como no alofánicos mientras que los horizontes subsuperficiales se clasificaron como alofánicos. El suelo estudiado mostró evidencias de ser poligenético, así como de fenómenos de erosión asociados a cambios climáticos drásticos y fue clasificado como un Acrudoxic Fulvudand, medial, mezclado, isotérmico.

Hexavalent chromium availability and phytoremediation potential of Cichorium spinosum as affect by manure, zeolite and soil ageing

Cichorium spinosum (spiny chicory) is a wild edible vegetable, and a possible suitable species for Cr(VI)-phytoremediation. There are three approaches for altering Cr(VI) dynamics: reduction to Cr(III) by organic matter addition, soil ageing, and Cr(VI) retention by high binding capacity materials added to soil, e.g., zeolite. Our aim was to assess spiny chicory as a phytoremediation species in relation to these three methods of altering Cr(VI) soil dynamics. There were 5 treatments: control (C); soil with 100 mg kg−1 Cr(VI) (S); soil with zeolite plus 100 mg kg−1 Cr(VI) (Z); soil with manure plus 100 mg kg−1 Cr(VI) (M); and soil added with 100 mg kg−1 Cr(VI) one year before this experiment (AS, “aged soil”). In soil, Cr(VI) was higher at S, while Z, M and AS were lower. In plant, Cr(VI) at Z, S, and AS were similar and significantly higher than M. This indicates that added manure decrease Cr(VI) availability to chicory due to the formation of organometallic complexes. However, chicory uptake amounted to 0.26–0.40 kg Cr(VI) ha−1 for Z, S, and AS, while uptake at M was lower. In conclusion, manure addition was more successful in decreasing Cr(VI) bioavailability, but it also slowed Cr(VI)-phytoremediation process.

Pedogenesis across a climatic gradient in tropical high mountains, Cordillera Blanca — Peruvian Andes

Studies in alpine environments have shown that chemical weathering and clay mineral formation are mainly controlled by climate and vegetation. However, few studies have focused specifically on pedogenesis in tropical high mountains. We evaluated pedogenic processes and weathering intensity by physical, chemical and mineralogical properties of soils under different vegetation types across a climatic gradient (east/west) in the Northern Cordillera Blanca, Peru. We established 2 catenas and sampled 10 pedons - 6 at Llanganuco valley (east-dry) and 4 at Portachuelo valley (west-wet). Pedons from both catenas are formed on colluvial deposits, gravelly and weakly developed, showing a sequence of O, A, C and C/R horizons. Lithological discontinuities in all pedons revealed sequences of buried A horizons. They also shared the same soil forming processes related to organic matter accumulation, such as humification, melanization and formation of organometallic complexes. The uppermost horizons show high values of total organic carbon and are dark colored. In general, pedons are acidic to slightly acidic, have a low base saturation, a high Al saturation and low effective and potential cation exchange capacity. Seven pedons were classified as Umbrisols, one Fluvisol, one Leptosol and one Regosol. Their similarity is attributed to environmental instability, not allowing sufficient time to develop further. However, pedons at Portachuelo valley showed higher weathering intensity revealed by crystalline iron oxide formation and transformation of phyllosilicates minerals. Among them, pedon under Polylepis forest showed the highest weathering intensity, which favored transformation of chlorite to mixed-layered minerals, suggesting that combined climate and vegetation control chemical weathering and mineral transformation.