Bh Horizons Research Articles

Fire-excluded and frequently burned longleaf pine forests have contrasting soil microbial communities

Prescribed fires are common in forest management, yet we lack a clear picture of how different fire frequencies impact soil systems. Here, we present evidence of microbial community and soil chemistry shifts following sixty years of continuous prescribed fire interval manipulation at the Olustee Experimental Forest in Northeastern Florida. We investigated three fire interval treatments (1 year, 2 years, and 4 years) in addition to an unburned control treatment. We sampled three mineral soil horizons (A, E, and Bh) to elucidate prescribed fire impacts across the soil profile. Our results indicate that only the A horizon was affected by the fire interval manipulations, whereas the deeper E and Bh horizons were minimally impacted. Richness of both bacterial and fungal communities in recurring fire treatments was higher than, and their community composition different from, those in the unburned control in A horizon soils. Similar to the biotic soil attributes, fire interval treatments altered soil chemistry only in the top-most A horizon: the burned treatments had higher total nitrogen, total carbon, phosphorus, and NH4+ than the fire exclusion treatment; the soil chemistry of the deeper E and Bh horizons did not differ among the treatments. All soil chemistry properties correlated with bacterial community composition of the A horizon and nearly all properties correlated with fungal community composition of the A horizon as well, especially when comparing the more frequent burns to the fire exclusion treatment. Indicator taxon analyses identified fire-responsive bacteria and fungi, such as Ktedonobacteria sp. and an unclassified ascomycete that were abundant in the fire exclusion treatment and the ectomycorrhizal Russula spp. that were most abundant in the annual burn treatment. The different fire intervals also impacted fungal guilds, suggesting shifts in community function. The fire exclusion treatment was enriched with ectomycorrhizal, lichenized, and wood saprotrophic fungi, whereas the annual burn treatment was enriched with arbuscular mycorrhizal fungi compared to the other treatments. Our results indicate that long-term changes in the type and amount of detrital inputs and changes in the plant community associated with differing fire frequencies can induce shifts in the soil microbial community.

Thermodynamical analysis of charged rotating black hole surrounded by perfect fluid dark matter

This paper is devoted to studying thermodynamics and particle acceleration around charged rotating BHs surrounded by perfect fluid dark matter. In the beginning, we discuss BH horizons, ergosphere and inner stable circular orbits in the framework of perfect fluid dark matter. It is observed that perfect fluid dark matter effects Hawking's temperature, Gibbs free energy, and other physical quantities related to thermodynamics. Some different aspects of thermodynamics are discussed within the scope of different values of the involved parameters. Further, we discuss the thermal fluctuations of considered BH solutions, which refer to the random motion of particles around a BH due to temperature fluctuations. Specifically, thermal fluctuations are affecting the entropy and Hawking radiation of a BH, which are crucial for understanding the behavior of physical quantities. It is found that corrected thermodynamical quantities of charged rotating perfect fluid dark matter BHs are smaller than the charged rotating BH without perfect fluid dark matter. We emphasize that the assumptions made in the literature and the thermodynamics of the previous BH solutions are well consistent with our results.

Spodosol formation on sandy ruins in a semi-arid climate in the Catimbau National Park, Northeast Brazil

The Catimbau National Park (CNP) is found in the Caatinga biome under a semi-arid climate. The soils of certain humid areas have horizons with morphology typical of Spodosols, and their occurrence in the CNP seems to be in discord with their formation model. This study aimed to investigate the genesis of Spodosols in the semi-arid climate of the CNP, testing the hypothesis that these soils are the result of local tectonic conditions associated with a past climate. As such, a sandy soils toposequence over sandstone of the Tacaratu Formation, under Caatinga vegetation and a semi-arid climate in northeast Brazil was studied. Sampling was based on the structural model of the pedological coverage, whereby physical and chemical analyses, Fourier transform infrared spectroscopy, X-ray diffraction, and soil micromorphological analysis were carried out. The results indicate that paludization of the soils occurred in two more humid phases, being compounded by the occurrence of distended faults/fractures related to the geology of the CNP. Microbiological decomposition under hydromorphic conditions led to humification of the organic constituents, which acidified the environment and increased Al solubility, forming organometallic complexes with fulvic and humic acids. The FTIR spectra and the presence of charcoal confirm the condensed aromatic nature and the abundance of carboxylic groups in the soils, these being related to the pyrolysis of biotransformed plant residues. Podzolization occurred in pulses promoted by intense rains under a dry climate and Fe-poor parent material, which favored the translocation of organometallic compounds of Al. The dense packing of fine organomineral material in the Bh horizons and the open matrix in the adjacent horizons indicate that the narrowing of the porous environment may be an important factor for the immobilization of translocated material. With the return of the current drier conditions in Brazil’s semi-arid, the podzolization process remains incipient.

Mineralization of soil organic matter from equatorial giant podzols submitted to drier pedoclimate: A drainage topochronosequence study

Podzol soils are an important carbon pool in the Amazon, due to the high organic matter (OM) content in their topsoil horizons and deep Bh. To quantify the evolution of the stock and the lability of this carbon pool in the hypothesis of the onset of drier climates, we studied a soil toposequence at the end of which the incision of a river meander lowered the water table, as would result from a drier climate, allowing oxidation the Bh horizons. The soil OM was quantified and characterized (physical fractionation, humification indexes, 14C average age) and its lability under oxic conditions was estimated by measuring respiration during a 660-days experiment. Podzol genesis time was calculated by constraining the carbon fluxes using both C stock and 14C average age. The results confirmed that the studied podzols store large amounts of carbon (62.8 kgC m−2 on average). They resulted from a long genesis time, probably greater than 30–50 ky. Topsoil OM is very labile with a residence time of about 100 y; Bh OM is highly humified with a high C/N (62.7 on average) related to low respiration rates. The measured respiration rates were used to estimate the C emission that would result from drier climates at 55 gC m−2 y−1 on average during the first 100 y, which would correspond, by extrapolation, to 8.5 1012 gC y−1 for all Amazonian podzols.

Quantum oscillations in the black hole horizon

By applying Rosen's quantization approach to the historical Oppenheimer and Snyder gravitational collapse and by setting the constraints for the formation of the Schwarzschild black hole (SBH), in a previous paper [1] two of the Authors (CC and FF) found the gravitational potential, the Schrodinger equation, the solution for the energy levels, the area quantum and the quantum representation of the ground state at the Planck scale of the SBH. Such results are consistent with previous ones in the literature. It was also shown that the traditional classical singularity in the core of the SBH is replaced by a quantum oscillator describing a non-singular two-particle system where the two components, named the "nucleus" and the "electron", strongly interact with each other through a quantum gravitational interaction. In agreement with the de Broglie hypothesis, the "electron" is interpreted in terms of the quantum oscillations of the BH horizon. In other words, the SBH should be the gravitational analogous of the hydrogen atom. In this paper, it is shown that these results allow us to compute the SBH entropy as a function of the BH principal quantum number in terms of Bekenstein-Hawking entropy and three sub-leading corrections. In addition, the coefficient of the formula of Bekenstein-Hawking entropy is reduced to a quarter of the traditional value. Then, it is shown that, by performing a correct rescaling of the energy levels, the semi-classical Bohr-like approach to BH quantum physics, previously developed by one of the Authors (CC), is consistent with the obtained results for large values of the BH principal quantum number. After this, Hawking radiation will be analysed by discussing its connection with the BH quantum structure. Finally, it is shown that the time evolution of the above mentioned system solves the BH information paradox.

Depth profile of colloidal iron in the pore water of an Albic Podzol

AbstractIron (Fe) colloids dominate the soil solution Fe and these colloids potentially act as vectors for nutrients and contaminants in soil. The question remains which factors, that is, gradients in soil chemical characteristics with depth or physical processes, cause vertical mobilisation and immobilisation of Fe colloids in soils. This question was addressed by characterising the change in concentration, size and composition of Fe colloids in a podzol profile and by relating these changes to soil properties along the profile. Pore waters were analysed with Flow Field Flow Fractionation (FlFFF‐UV‐ICP‐MS) to overcome the artefacts typically obtained when using filtration for fractionation. Pore water was obtained by centrifugation of field moist samples taken from an Albic Podzol. The samples were taken within a depth of 110 cm, at eight depths corresponding to different horizons. The pore water Fe concentration increased with depth and peaked at 66 μM in the E horizon just above the Bh horizon, beyond which, it sharply decreased to only 9 μM. The pore water Fe concentration correlated strongly with dissolved organic carbon (DOC). The high‐resolution size fractionation analysis with FlFFF suggested that the Fe colloids (<100 nm) in the pore water not only consisted of Fe‐organic carbon (OC) complexes, but also of mineral Fe colloids associated with organic matter (OM), as indicated by the colloid size (>5 nm) and by the relatively large Fe/OC ratio that exceeds the complexation capacity of natural OM. The smallest mineral Fe colloids dominated in the Ah1 horizon, while the larger mineral colloids increased with increasing depth, explaining the rise in total Fe towards the Bh horizon. This suggests that Fe complexation with OM and stabilisation of mineral Fe colloids with OM explain colloidal Fe in the pore water. The adsorption of the OM at the top of the Bs horizons is likely the primary mechanism of DOC retention in the Bh horizon. Below this depth, the concentration of DOC was very low, resulting in low Fe concentration in the pore water. The colloids (<100 nm) are considerably smaller than the soil pore size distribution and increase in size with depth, which suggests that straining was not a significant mechanism for colloid retention. This study demonstrates that OM plays a key role in the transport of Fe colloids in acid sandy soil.Highlights Depth profile of pore water Fe in a podzol is studied to investigate colloid migration processes Pore water colloids are characterised by Flow Field Flow Fractionation Fe colloids consist of complexes with OM and mainly larger mineral colloids Natural OM plays a key role in the transport of Fe colloids in acid sandy soil

Jet collision with accreting tori around SMBHs GRHD and light surface constraints in aggregates of misaligned tori

Abstract We explore the possibility of jet collisions with accreting tori orbiting around super-massive black holes. The analysis provides constraints on the formation and the observational evidence of the host configurations. We use a General Relativistic Hydrodynamic model, investigating the light surface contraints in aggregates of misaligned tori orbiting a central static Schwarzschild black hole. Each (toroidal) configuration of the agglomeration is a geometrically thick, pressure-supported, perfect fluid torus. Aggregates include proto-jets, the open cusped solutions associated with the geometrically thick tori. Collision emergence and the stability properties of the aggregates are considered at different inclination angles relative to a fixed distant observer. We relate the constraints to the relevant frequencies of the configurations and fluid specific angular momentum, separating the constraints related to the fluid hydrodynamics and those related to the geometric backgrounds. We analyze the existence of accreting tori supporting jet-emission. We discuss the existence of orbit-replicas that could host shadowing effects in replicas of the emissions in two regions; close to and far from the BH (horizon replicas in jet shells). Our investigation clarifies the role of the pressure gradients of the orbiting matter and the essential role of the radial gradient of the pressure in the determination of the disk verticality. Finally, we analyze the possibility that a toroidal magnetic field could be related to the collimation of proto-jets.

Revisiting the subalpine Mesolithic site Ullafelsen in the Fotsch Valley, Stubai Alps, Austria – new insights into pedogenesis and landscape evolution from leaf-wax-derived <i>n</i>-alkanes, black carbon and radiocarbon dating

Abstract. Archaeological research in high mountain regions has gotten a lot more attention since the discovery of the copper age mummy called “Ötzi” in the Ötztaler Alps in 1991. In the Tyrolean Stubai Alps, the Mesolithic site Ullafelsen at 1869 m a.s.l. (above sea level) close to the recent upper timberline in the Fotsch Valley represents, on the one hand, a very important archaeological reference site and offers, on the other hand, intriguing research questions related to, amongst others, pedogenesis. Given that no biomarkers and stable isotopes have been hitherto investigated, we aimed at contributing with respective analyses and additional radiocarbon dating to a better understanding of the landscape evolution and pedogenesis on and around the Ullafelsen. Our results for modern vegetation suggest that leaf-wax-derived n-alkanes allow us to chemotaxonomically distinguish between subalpine deciduous trees (nC27 predominance) versus (sub)alpine grasses, herbs and dwarf shrubs (nC29, nC31 and/or nC33 predominance). Except for Juniperus, conifers produce no or extremely low n-alkane contents. Although no clear vegetation changes could be inferred from the n-alkane patterns of the investigated soil profiles, the total n-alkane content (TAC) was developed for the first time as an unambiguous proxy for distinguishing between buried (= fossil) topsoils (2Ahb horizons) and humus-enriched subsoils such as Bh horizons of podzols. Based on this leaf wax proxy, we can rule out that the 2Ahb?/Bh? horizons under question on the Ullafelsen are buried topsoils as suggested previously. Dating of the H2O2-pretreated soil samples yielded 14C ages for the podzol Bh horizons ranging from 6.7 to 5.4 cal kyr BP. This is clearly younger than the overlying Mesolithic living floor (LL) (10.9 to 9.5 cal kyr BP) but pre-dates the assumed intensification of alpine pasturing from the Bronze Age onwards. Both the LL and the directly overlying OAh3 horizon yielded black carbon maxima and benzene polycarboxylic acid patterns reflecting fire-induced human impact during the Mesolithic. The discrepancy between the Mesolithic charcoal 14C ages (ages of ≥ 9.5 cal kyr BP) versus the 14C ages obtained for bulk n-alkanes ranging from 8.2 to 4.9 cal kyr BP suggests that non-alkane-producing conifers predominated the vegetation on and around the Ullafelsen after the Mesolithic occupation. Only with the anthropo-zoological lowering of the timberline associated with alpine pasturing since the Neolithic and especially the Bronze Age has an n-alkane-producing vegetation cover (grasses, herbs or dwarf shrubs) started to predominate.

Substantial changes in podzol morphology after tree‐roots modify soil porosity and hydrology in a tropical coastal rainforest

We investigated morphological variations in podzols caused by changes in soil porosity and permeability upon the growth of large tree-roots in a tropical barrier island (Ilha Comprida, Brazil). Soil morphology was described in a continuous lateral sequence of podzols on a 35 m-long cliff. A soil thin section was used to characterize organic matter (OM) accumulation and to estimate soil porosity, permeability, and saturated hydraulic conductivity (Ksat). Soil texture and the contents of organic carbon, Al, and Fe were determined for each pedogenic horizon containing large tree-roots. The evolution of podzol morphology was interpreted in the context of age determinations by optically stimulated luminescence and 14C. Taproots of cashew trees (Anacardium occidentale) penetrated the cemented Bhm horizon and the massive-clayey 2Cgj horizon. Aligned with the taproot, we found a vertical OM-band with lower porosity, permeability, and Ksat than the adjacent Bh and E horizons. Irregular or broken boundaries between the E and Bh horizons were caused by large tree-roots. While the maximum age of these podzols is 3390 ± 530 years, significant and rapid changes in the Bh-horizon morphology occurred within the lifetime of the cashew trees (~ 50 years). The interplay between reduction in flow adjacent to large taproots and the enhanced vertical infiltration at depth has resulted into the development of irregular and broken boundaries between the E and Bh horizons. Because tree-roots alter both local soil porosity and water flow paths, they simultaneously cause the formation and degradation of podzol Bh-horizon.

Soil properties influencing Hg vertical pattern in temperate forest podzols

Mercury content of twelve podzols from NW Spain was studied to elucidate the main soil properties involved in the Hg accumulation of these soils. The highest average Hg concentrations (HgT) were found in the Bh and Bs horizons (64 and 105 μg kg−1), whereas the lowest occurred in the E horizons (15 μg kg−1). Moderate values of HgT were obtained for the A and C horizons (38 and 52 μg kg−1). The Hg enrichment factors revealed that the predominant origin of Hg in these soils is the atmosphere instead of the parent material. As it was shown by the PCA performed (which explained 82% of the variance of the data), the main soil characteristics involved in the pedogenetic processes of the studied podzols are organic matter and Al and Fe compounds. The stepwise linear regressions made described between 54% and 84% of the predicted Hg depending on the soil horizon. Besides a complex ensemble of biogeochemical reactions involved in the balance between input and outputs of Hg, the most influencing variable in the A horizons was organic C, moderate stability Al-humus complexes in the E horizons, Fe-humus complexes and pHw in the Bh horizons, Al-humus compounds in the Bs horizons and crystalline Al and Fe compounds in the C horizons. Therefore, Hg is mobilized from the A and E horizons bound to dissolved organic matter and precipitated in the illuvial horizons due to the saturation of the organic matter with metals. The immobilization of Hg in the subsuperficial horizons of podzols leads to different environmental benefits derived from the removal of Hg from the A horizons, more exposed to climate-induced and land use/cover changes that could potentially modify the dynamics of Hg in those superficial horizons.

Lead isotope ratios in Podzol profiles as a tracer of pollution source in the subalpine zone of the Karkonosze National Park, Sudety Mts (south-western Poland)

The Karkonosze National Park (south-western Poland) represent central European medium-elevation mountains. At the end of the twentieth century, an ecological disaster was observed in this nature reserve, resulting in the defoliation of large areas of spruce forest. One of the considered reasons for this phenomenon was contamination with heavy metals. The aim of this study was to determine the origin of lead (lithogenic versus several specific anthropogenic sources) occurring in the soils of the highest located parts of the Karkonosze Mts. Lead concentrations and its isotope ratios were investigated in nine Podzol profiles located in the subalpine zone (1200–1400 m a.s.L.) of the Karkonosze Mts. Concentrations of total lead and its isotopes were measured in particular genetic horizons; then lead isotope ratios were calculated. On the basis of lead isotope signatures known from literature data, different anthropogenic sources of this element have been assessed (emissions from coal combustion, mining, metallurgy, and fuel combustion). The results obtained revealed the highest Pb concentrations (121.0–353.0 mg kg−1) in the surface horizons. The podzolization process, differentiating soil profiles into eluvial (Es) and illuvial (Bh and Bs) horizons, has contributed to different concentration of lead through the profile. The concentrations of this element in eluvial, illuvial Bh, and parent material horizons were 15.5–28.4 mg kg−1, 25.8–55.6 mg kg−1, and 8.7–29.6 mg kg−1, respectively. The Pb isotope composition determined in the ectohumus horizons and eluvial horizons showed that about 86–95% of lead existing in these surface horizons originated from emissions resulting from the burning of coal exploited in Poland and the Czech Republic. The Pb isotope signatures of lead present in the illuvial horizon (Bs) and parent material (C) pointed to the lithogenic origin of this element. The results obtained indicated that higher-elevation areas of the Karkonosze National Park have been contaminated with lead from long distance emissions. Pollution with lead has been limited only to ectohumus and eluvial horizons, although the soil-forming process contributed to translocation of lithogenic lead down the soil profile to the illuvial Bh horizon.

Morphologic and hydrologic distinctions between shallow and deep podzolized carbon in the southeastern United States Coastal Plain

Podzolization imparts soils and landforms of the southeastern United States Coastal Plain with two distinct pools of organic carbon (C), referred to as shallow podzolized C (SPC) and deep podzolized C (DPC). We evaluate podzolization across two catenas, and across the state of Florida, to establish that SPC and DPC are morphologically and hydrologically distinct. We demonstrate that SPC lightens downward (i.e. a Bh horizon with a darker top than bottom) and accumulates below low chroma material, while DPC darkens downward and accumulates below higher chroma material. We interpret these distinct morphologies to be manifestations of separate podzolization processes that are controlled by unique components of soil hydrology. Our analyses support existing notions that SPC is a product of vadose zone hydrology; formed within a pronounced eluvial-illuvial system where C, metals (predominately aluminum), and clay-sized particles are mobilized and immobilized together when near surface saturation thresholds are met. Our work however also identifies DPC to be a product of phreatic zone hydrology; part of an eluvial-illuvial system where C is translocated without metals or clays and immobilized when subsoil saturation thresholds are met. Recognizing the morphologic and hydrologic differences between SPC and DPC not only provides insights into interactions between soil hydrology and terrestrial C cycling in low-relief landforms, but also by incorporating these differences into field-based assessments soil scientists can improve their interpretations and communication of the hydropedology and podzolization.

Obstructions towards a generalization of no-hair theorems: Scalar clouds around Kerr black holes

We show that the integral method used to prove the no-hair theorem for black holes (BH's) in spherically symmetric and static spacetimes within the framework of general relativity with matter composed by a complex-valued scalar-field does not lead to a straightforward conclusion about the absence of hair in the stationary and rotating (axisymmetric) scenario. We argue that such a failure can be used to justify in a simple and heuristic way the existence of nontrivial boson clouds or hair found numerically by Herdeiro and Radu [Phys. Rev. Lett. 112, 221101 (2014); Classical Quantum Gravity 32, 144001 (2015)] and analytically by Hod in the test field limit [Phys. Rev. D 86, 104026 (2012); Phys. Rev. D 86, 129902(E) (2012); Eur. Phys. J. C 73, 2378 (2013); J. High Energy Phys. 01 (2017) 030]. This is due to the presence of a contribution that is negative when rotation exists which allows for an integral to vanish even when a nontrivial boson hair is present. The presence of such a negative contribution that depends on the rotation properties of the BH is perfectly correlated with the eigenvalue problem associated with the boson-field equation. Conversely, when the rotation is absent the integral turns to be composed only by non negative (i.e., positive semidefinite) terms and thus the only way it can vanish is when the hair is completely absent. This analysis poses serious challenges and obstructions towards the elaboration of no-hair theorems for more general spacetimes endowed with a BH region even when including matter fields that obey the energy conditions. Thus rotating boson stars, if collapsed, may lead indeed to a new type of rotating BH, like the ones found in [Phys. Rev. Lett. 112, 221101 (2014); Classical Quantum Gravity 32, 144001 (2015)]. In order to achieve this analysis we solve numerically the eigenvalue problem for the boson field in the Kerr-BH background by imposing rigorous regularity conditions at the BH horizon for the non-extremal case ($0<a<M$) which include the near extremal one in the limit $M\ensuremath{\rightarrow}a$, as well as the small BH limit $M\ensuremath{\rightarrow}a\ensuremath{\rightarrow}0$.

Mineral colloids mediate organic carbon accumulation in a temperate forest Spodosol: depth-wise changes in pore water chemistry

Mobile submicron mineral phases within soil pore waters are presumed to play a major role in the transport and availability of organic carbon (OC) in subsurface horizons. This work reports on the composition of the 95% of the total Fe and Al in SF-S are complexed with OC in all Spodosol horizons. In contrast with the SF-S, the SF-L had much greater OC concentrations and even lower M/C (< 0.01), except in the Bh horizon (M/C = 0.05). In Bh, major accumulation of organic matter occurred above the lesser-accumulating Bhs, the latter having higher pH, but much lower OC in all forms (soil, colloidal). Infrared spectroscopy indicates the SF-L fraction of soil pore waters contains both organic and inorganic constituents, including amorphous silica, the second-most abundant component after OC. Mineral-organic associations such as mineral crystallites embedded in OC are observed in the SF-L fraction by transmission electron microscopy (TEM). Transmission electron microscopy also reveal carbon-rich amorphous structures containing traces of Fe, Al and Si, and small (~ 100 nm) spherical amorphous SiO2 particles. These observations provide support for the main mechanism of OC accumulation in Spodosols being the downward movement of colloids (organic, OC-sorbed mineral and organo-mineral), followed by colloid immobilization due to a combination of increases in pH and M/C ratio. The occurrence of these three types of colloidal structures in pore waters seems to depend on the pH and the relative supply of OC and Fe + Al to pore waters. Similar colloidal structures might also contribute to the transport and availability of OC in subsurface horizons of soils that range in the accumulation of organic and organo-metallic compounds, that is, in the expression of spodic properties.

The quantum cat map on the modular discretization of extremal black hole horizons

Based on our recent work on the discretization of the radial hbox {AdS}_2 geometry of extremal BH horizons, we present a toy model for the chaotic unitary evolution of infalling single-particle wave packets. We construct explicitly the eigenstates and eigenvalues for the single-particle dynamics for an observer falling into the BH horizon, with as time evolution operator the quantum Arnol’d cat map (QACM). Using these results we investigate the validity of the eigenstate thermalization hypothesis (ETH), as well as that of the fast scrambling time bound (STB). We find that the QACM, while possessing a linear spectrum, has eigenstates, which are random and satisfy the assumptions of the ETH. We also find that the thermalization of infalling wave packets in this particular model is exponentially fast, thereby saturating the STB, under the constraint that the finite dimension of the single-particle Hilbert space takes values in the set of Fibonacci integers.

Total mercury distribution among soil aggregate size fractions in a temperate forest podzol

This study determined the distribution of total Hg (Hg&lt;sub&gt;T&lt;/sub&gt;) among aggregate size fractions in the A, E, Bh and Bs horizons of a representative temperate forest podzol. The aggregate distribution was dominated by the coarse sand size fraction (average of 55%) followed by fine sand (29%), fine silt (10%), coarse silt (4%) and clay (2%). In general, Hg&lt;sub&gt;T&lt;/sub&gt; mean values increased as the aggregate size become smaller: clay (170 ng g&lt;sup&gt;-1&lt;/sup&gt;) &amp;gt; fine silt (130 ng g&lt;sup&gt;-1&lt;/sup&gt;) &amp;gt; coarse silt (80 ng g&lt;sup&gt;-1&lt;/sup&gt;) &amp;gt; fine sand (32 ng g&lt;sup&gt;-1&lt;/sup&gt;) &amp;gt; coarse sand (14 ng g&lt;sup&gt;-1&lt;/sup&gt;). Total Hg enrichment in clay-sized aggregates ranged from 2 to 11 times higher than the values shown by the bulk soil (&amp;lt; 2 mm). The accumulation of Hg&lt;sub&gt;T&lt;/sub&gt; in the finer size aggregates was closely related to total organic C, Na-pyrophosphate extracted C, metal (Al, Fe)-humus complexes and Al and Fe oxyhydroxides. Indeed, these parameters varied significantly (&lt;em&gt;p &lt;/em&gt;&amp;lt; 0.05) with the aggregate size and their highest values were found in the finer fractions. This suggested the role of these soil compounds in the increase of the specific surface area per mass unit and negative charges in the smallest aggregates, favouring Hg retention. Mercury accumulation factor (Hg&lt;sub&gt;AF&lt;/sub&gt;) values reached up to 10.8 in the clay size aggregates, being close to 1 in sand size fractions. Regarding Hg enrichment factors (Hg&lt;sub&gt;EF&lt;/sub&gt;), they were &amp;lt; 4 (“moderate pollution” category) in most of the horizons and aggregate sizes. Grain size mass loading (GSF&lt;sub&gt;Hg&lt;/sub&gt;) revealed that finer fractions had a higher Hg loading than their mass fractions, with a notable contribution of fine silt which made up &amp;gt; 50% of Hg&lt;sub&gt;T&lt;/sub&gt; in Bh and Bs horizons. The potential ecological risk index (PERI&lt;sub&gt;Hg&lt;/sub&gt;) increased as the aggregate size decreased, with the highest values in the illuvial horizons (45-903) and lowest in the E horizon (3-363). Heterogeneous distribution of Hg in the soil aggregate size fractions must be considered for Hg determination for purposes such as critical loads, background values or environmental risk indices. In addition, Hg accumulation in finer aggregates could be of concern due to its potential mobility in forest soils, either transferred by leaching to groundwater and freshwaters or mobilized by runoff in surface horizons.

Effect of Water Table Depth on Nutrient Concentrations Below the Water Table in a Spodosol

Water table depth manipulations as implemented in sugarcane fields of Southwestern Florida, USA, were hypothesized to influence the nutrient concentrations below the water table. Concentrations of phosphorus (P), potassium (K), nitrogen (N), and bromide (Br−) were monitored above and below the water table using a column leaching experiment. Three columns were packed with Immokalee soil (A, E, and Bh horizons) classified as a spodosol and fertilizers (NPK) were applied on the soil surface as solids using rates of 11 kg P ha−1, 166 kg K ha−1, and 200 kg N ha−1. A fourth column where fertilizer mixture and bromide were not added acted as a blank. Potassium was also applied as KBr with bromide used as tracer for water movement. Water table was maintained at 30 cm for 6 weeks and lowered to 50 cm deep for another 6 weeks. Samplers were placed in A, E, and Bh horizons and outlets were placed at 30 and 50 cm deep to obtain solutions for monitoring nutrients and tracer. Solution samplers placed in E and Bh horizons were located below the water table. Slightly elevated P, N, and K concentrations in E horizon for a 50-cm water table depth treatment were observed. For both water table treatments, minimal loss of applied N, P, and K below the water table was observed. The results of the study have shown that movement of nutrients below the water table is slow, and depends on the type of nutrients applied and the water table depth.

Ammonium and nitrate transport during saturated and unsaturated water flow through sandy soils

AbstractCitrus production in Florida accounts for ≈ 60% of national production in USA. The sandy soil characteristic (&gt; 95% sand) makes water and nutrient management extremely difficult, raising concerns about environmental sustainability as a result of nutrient inputs in citrus producing regions where sandy soils dominate. Thus, laboratory column and field experiments were conducted to better understand the leaching patterns of and ions in Florida's sandy soils. The soil columns were first saturated from the bottom with two pore volumes of simulated Florida rain followed by pumping a pulse of fertilizer mixture at a steady Darcy flux of 14 cm h−1. Nitrate and Cl− appeared earlier in the effluent than in the A and Bh horizons, due to cation exchange of . Essentially identical breakthrough curves (BTCs) for and were observed in the E‐horizon, due to very low sorption of . The convective and dispersive equilibrium (CDE) model simulations were in good agreement with measured breakthrough curves (BTCs) for , , and Cl−. However, the sorption coefficient (KD) values used in the CDE model to simulate the BTCs for were about 10 times less than the batch isotherm KD values. This was attributed to differences in pH, cation composition, and ionic strength between batch (static) and dynamic (leaching) systems. The field experiment showed that under unsaturated flow, improved short‐pulse fertigation systems (drip and microsprinkler) limited and transport beyond the root zone (top 30 cm), which might have promoted nutrient and water uptake in citrus. The column study revealed that under extreme weather events such as hurricanes or storm surge in Florida, saturated soil conditions can trigger N mobility below the root zone to surficial or groundwater aquifers. In the field experiment, the use of judicious, minimal and split applications and accurate placement of N‐fertilizers reduced leaching of N especially during heavy storms in the summer rainy months of Florida. The field experiment demonstrated that it is possible to manage inorganic N forms for optimal residence time for uptake and minimal leaching concerns.

Soil morphology related to hydrology and degradation in tropical coastal podzols (SE Brazil)

Morphology of podzol profiles can be used to improve our understanding of soil formation and degradation processes. The morphology of a podzol chronosequence was studied for a 1800m long cliff perpendicular to the coastline at the southern coast of the Island Ilha Comprida (São Paulo, Brazil). The large variation in hydrological conditions with time (surfaces with ages from 6000 to 300yrs BP) and space (topography) allowed studying the relation between podzol morphology and drainage conditions, both during soil formation and degradation. On the oldest two surfaces, the podzols formed under poorly drained circumstances. Uplift during their formation resulted in (1) very deep Bh horizons and (2) degradation of the upper B horizon as a result of improved drainage. On the younger surface most podzols were poorly drained, but well-drained podzols and transitions occurred in beach ridges. In the cliffs on the southern coast of the island, improved drainage of the poorly drained podzols resulted in degradation of the B horizon. This degradation exhibits various forms, including (1) complete removal of the B horizon down to an underlying clay layer, (2) degradation of the B horizon along root channels with preferential vertical water transport, (3) degradation of the upper B horizon resulting in a diffuse EB transition, and (4) areas of organic matter (OM) depletion related to microbial activity, sometimes combined with burrowing. Type (2) degradation may result in a convoluted EB transition, the formation of islands of B horizon in the deepening E horizon, and formation of E horizon tongues into the Bh. Recent (post degradation) OM bands were found in E and B horizons. A thorough study of podzol morphology can be used to reconstruct several stages of their formation and degradation in relation to drainage conditions.

Hydro-physical characterization of soils under the Restinga Forest

Knowledge of the hydraulic properties of the soil is of crucial importance to an understanding of the interactions between vegetation, soil and water. There is little information available about the hydraulic properties of Podzol soils found in tropical regions. The aim of this study was to present the soil morphology and hydraulic properties of a toposequence situated in a permanent plot at the Ilha do Cardoso State Park (Cananéia, SP, Brazil). Ultradetailed soil maps were used to define a toposequence inside the permanent plot. Five profiles, representing the main types of soil, were opened along the toposequence, in which Podzols are dominant. The levels of bulk density, sand content, porosity and permeability in these soils were all high. Consequently, these soils have a high level of hydraulic conductivity with low water retention. This behavior undergoes an alteration in the Bh and Bs horizons due to the accumulation of organic and metallic compounds and a changing structure that modifies the pore distribution. Furthermore, the characterization of the hydro-physical functioning of soils in natural environments is an important source of encouragement to further investigative study of soil water dynamics and its relationship to the native vegetation.