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Mangrove forests play an important role in biogeochemical cycles of metals, nutrients, and C in coastal ecosystems. However, these functions could be strongly affected by the mangrove soil degradation. In this study, we performed an intensive sampling characterizing mangrove soils under different types of environment (lagoon/gulf) and vegetation ( Rhizophora/ Avicennia/dead mangrove) in the Venezuelan coast. To better understand the spatial heterogeneity of the composition and characteristics of the soils, a wide range of the soil attributes were analyzed. In general, the soils were anoxic (Eh < 200 mV), with a neutral pH and low concentration in toxic metals; nevertheless, they varied widely in the soil and its quality-defining parameters (e.g., clay contents, total organic carbon, Fe, Al, toxic trace metals). It is noteworthy that the mangroves presented a low Fe content due to a limitation in the Fe oxyhydroxide contents, especially in soils with higher organic C content (TOC > 15%). Finally, the dead mangrove showed significantly lower amounts of TOC and fibers (in comparison to the well-preserved mangrove forest), which indicates that the C pools in mangrove soils are highly sensitive also to natural impact, such as ENSO. [ABSTRACT FROM AUTHOR]

Abstract: A 2month long column study was conducted to evaluate the mobility of heavy metals eluting from Technosols constituted from sewage sludges (aerobic or anaerobic) (as controls) or a mixture of different types of sewage sludges with green foundry sand (FS) or/and Linz–Donowitz slag (LD). The organic and inorganic wastes were mixed at a ratio of 56:44 (w/w). The mixtures and the controls were moistened to field capacity before adding them to the polypropylene columns (4.5cm wide and 14cm long). During the 8-week experimental period, the columns were watered, twice a week, with 100mL of deionised water. The concentrations of heavy metals (Cu, Zn, Ni, Pb, Cd, and Cr) in the leachates were determined periodically. The concentrations of all the heavy metals were generally higher in the leachates from the Technosols containing anaerobic sewage sludge as a component. The concentration of Cu was strongly dependent on pH and was significantly higher (P <0.05) in the most alkaline leachates (pH>10) than in the other leachates. More Zn was mobilized in the most acidic leachates (pH<6) than in other leachates. The concentration of Ni in 80% of the leachates exceeded the EU drinking water limit for Ni (0.02mgL−1). The concentrations of Pb were lower in the Technosols containing FS. The concentrations of Cd in the leachates from Technosols containing the conditioners were relatively high, while concentrations of Cr were higher in the controls. As far as the potential toxicity of heavy metals is concerned, the combination of aerobic sludge, inorganic conditioners able to buffer the pH to around neutrality, and reactive aluminosilicates, can be regarded as suitable choice for formulating Technosols from wastes. [Copyright &y& Elsevier]

The objective of this study was to determine to what extent the attenuation or loss of andic soil properties caused by land use change – from forest (FOR, average C content 118.2 ± 23.7 g kg−1) to agricultural land (AGR, average C content 55.7 ± 16.7 g kg−1) use – is reflected in soil organic matter (SOM) at the molecular level. For this, NaOH-extractable SOM of A horizons from 17 soils developed on amphibolitic parent material in NW Spain was studied by pyrolysis gas chromatography spectrometry (Py-GC/MS). We also included two buried andic A horizons (PAL, 2200 cal yr BP in age) on the same parent material, as a reference for the molecular composition of SOM from soils without recent litter additions. Organic matter of PAL soils had a composition largely different from that of superficial soils (FOR and AGR), with an important relative contribution of microbial polysaccharides and N-compounds, and an absence of compounds that characterize fresh plant litter (e.g. lignins). In the superficial soils, the relative contribution of lignin-derived compounds was greater in AGR than in FOR soils. Differences were also observed in the relative contribution of aliphatic compounds, FOR soils being enriched in this type of components compared with AGR soils. The results indicated that land use change from FOR to AGR, which was accompanied by a decrease in total SOM, resulted in an enrichment in primary SOM. The smaller relative abundance of primary SOM derivatives in andic FOR soils indicates that these compounds were quickly degraded in Andisols. [ABSTRACT FROM AUTHOR]

Pore-water and solid-phase analysis was undertaken to study the effects of different environmental conditions on redox processes in mangrove soils on the southern coast of Brazil. Three Rhizophora mangle (L.) mangrove forests were studied in different physiographic positions-riverine, fringe, and basin forest-and substrate compositions. Our results indicate different geochemical conditions in soils from different physiographic positions. In the fringe soils, the low acid-volatile sulfide and pyrite Fe contents, associated with high values of Fe2+ in pore water, indicate oxic and suboxic conditions in surface layers (0-10 cm). Below this depth, anoxic conditions prevail and sulfate reduction becomes the dominant process of organic matter decay, as indicated by higher concentrations of dissolved HS and pyrite Fe. In the basin forest, long periods of tidal flooding and low rates of litter export maintained anoxic conditions and high organic matter contents, necessary for anoxic respiration to take place, as shown by the low Fe2+ and HS- concentrations in pore water, along with high degree of Fe pyritization values and high concentrations of pyrite Fe. In the riverine soils, the lowest concentrations of pyrite Fe and the highest concentrations of HSin pore water were obtained in response to low availability of reactive Fe (0-10cm, 31.8 ± 8.0 mmol kg-1; 20-30 cm, 43.2 ± 32.3 mmol kg-1) due to its sandy texture, which limits pyrite synthesis. Our results indicate that the participation and intensity of each process may vary within different physiographic positions because of the effects on the frequency and duration of tidal flooding and soil composition. Our results also show that R. mangle is present on substrates with different geochemical conditions (oxic, suboxic, and anoxic). [ABSTRACT FROM AUTHOR]

The organic matter (OM) of soils with andic properties has long been considered highly stable because of the presence of Al–humus complexes and sorption of organic ligands onto amorphous compounds. In this study, we characterized soils under different land use regimes located within an amphibolitic massif close to Santiago de Compostela (Spain), where soils with andic properties are present. Slash and burn agriculture was a common practice in the area until the second half of the 20th century. Thereafter, modern agriculture was progressively introduced into the area (AGR soils), and the rest of the land was either reforested or abandoned (FOR soils). We found that the mean organic C content of AGR soils (48.7 g kg−1) was∼ 50% that of FOR soils (94.2 g kg−1). Mean soil pH was significantly greater (P < 0.05) in the AGR than in the FOR soils (4.95 compared with 4.63), which is attributed to liming and Ca-phosphate fertilization of the former. Mean concentrations of the Al forms studied (extractable with CuCl2, sodium pyrophosphate, ammonium oxalate, or NaOH) were significantly smaller (P < 0.01) in AGR (1.4, 4.9, 9.3, 11.0 g kg−1, respectively) than in FOR soils (3.9, 10.2, 16.5, 17.9 g kg−1, respectively). The results show the vulnerability of the OM and Al–humus complexes in these soils to modern agricultural practices, which has led to the attenuation– and in some cases even the disappearance– of andic soil properties in a relatively short time (< 30 years) following changes in land use/management. We propose the inclusion of the formative element‘andic’ in the criteria for the definition of Umbrisol subunits; this would avoid the abrupt discontinuity observed in the current World Reference Base classification. [ABSTRACT FROM AUTHOR]

Highlights: [•] We determined total concentration and fractionation of metals in an old Pb/Zn-mining area. [•] We evaluated metal accumulation by native plants growing on mine-soils. [•] Mine-soils showed neutral pH and a high concentration of Cd, Hg, Pb and Zn. [•] Plants were pseudometallophytes with potential application in phytoremediation. [Copyright &y& Elsevier]

Abstract: Concentrations of the isomers of the organochlorine pesticide hexachlorocyclohexane (HCH) were determined in 252 surface soil samples collected within a sampling network covering agricultural areas in Galicia (NW Spain). The concentration of total HCH (sum of α+β+γ+δ) ranged between 4 and 2305ngg−¹ (dry weight), with the α-HCH and γ-HCH isomers predominating (<1–1404ngg−¹ and <1–569ngg−¹, respectively). The distribution of the pesticide residues was very heterogeneous, with the largest concentrations present in one of the studied areas (the province of A Coruña). The distribution of HCH was not found to be related to any soil property (organic matter, pH, clays, and metals). Multivariate statistical analysis of the data revealed that three populations of samples with a defined composition of HCH, can be related to the source of HCH: technical HCH (α/γ>3), lindane (99% γ-HCH), or both. The existence of a third population consisting almost exclusively of α-HCH suggests that background contamination of anthropogenic origin dates from several decades ago. The detailed analysis of these populations enabled the possible temporal scale of the application of these pesticides to be deduced. [Copyright &y& Elsevier]

Abstract: Five zones along a transect of 180 m were selected for study on the Island of Pai Matos (Sao Paulo, Brazil). Four of the zones are colonised by vascular plants (Spartina SP, Laguncularia LG, Avicennia AV and Rhizophora RH) and were denominated soils, and the other zone, which lacks vegetation, was denominated sediment (SD). The geochemical conditions differed significantly in soils and sediment and also at different depths. The soils were oxic (Eh>350 mV) or suboxic (Eh: 350–100 mV) at the surface and anoxic (Eh<100 mV) at depth, whereas in the sediment anoxic conditions prevailed at all depths, but with a lower concentration of sulphides in the pore water and pyrite in the solid fraction. Under these geochemical conditions Fe is retained in the soils, while the Mn tends to be mobilized and lost. The most abundant form of iron oxyhydroxide was lepidocrocite (mean concentration for all sites and depths, 45±19 µmol g−1), followed by goethite (30±19 µmol g−1) and ferrihydrite (19±11 µmol g−1), with significant differences among the mean concentrations. There was a significant decrease with depth in all the types of Fe oxyhydroxides measured, particularly the poorly crystalline forms. The pyrite fraction was an important component of the free Fe pool (non-silicate Fe) in all soils as well as in the sediment, especially below 20 cm depth (mean concentration for all sites and depths, 60±54 µmol g−1). Furthermore, the mean concentration of Fe-pyrite for all sites and depths was higher than that obtained for any of the three Fe oxyhydroxides measured. The Fe-AVS was a minor fraction, indicating that the high concentrations of dissolved Fe in the soils in the upper area of the transect result from the oxidation of Fe sulphides during low tide. Mössbauer spectroscopy also revealed that most of the Fe(III) was associated with silicates, in this case nontronite. The presence of crystals of pyrite associated with phyllosilicates in samples from the upper layer of the soils may indicate that pyritization of this form of Fe(III) is more rapid than usually reported for ocean bed sediments. The sequential extraction of Mn did not reveal any clearly dominant fraction, with the Mn-carbonate fraction being the most prevalent, followed by exchangeable Mn and oxides of Mn, whereas pyrite-Mn and Mn associated with crystalline Fe-oxides were present at significantly lower concentrations. The high concentration of dissolved Mn found in the soils in the lower part of the transect is consistent with the fact that the solubility is determined by the carbonate fraction. Unlike for Fe, in the soils in the higher zone, which are subject to intense drainage during low tide, there was loss of Mn, as reflected by the concentration of total Mn. [Copyright &y& Elsevier]