Horizon Depth Research Articles

Data-Driven Modeling of Dissolved Iron in the Global Ocean

The importance of dissolved Fe (dFe) in regulating ocean primary production and the carbon cycle is well established. However, the large-scale distribution and temporal dynamics of dFe remain poorly constrained in part due to incomplete observational coverage. In this study, we use a compilation of published dFe observations (n=32,344) with paired environmental predictors from contemporaneous satellite observations and reanalysis products to build a data-driven surface-to-seafloor dFe climatology with 1°×1° resolution using three machine-learning approaches (random forest, supper vector machine and artificial neural network). Among the three approaches, random forest achieves the highest accuracy with overall R2 and root mean standard error of 0.8 and 0.3 nmol L-1, respectively. Using this data-driven climatology, we explore the possible mechanisms governing the dFe distribution at various depth horizons using statistical metrics such as Pearson correlation coefficients and the rank of predictors importance in the model construction. Our results are consistent with the critical role of aeolian iron supply in enriching surface dFe in the low latitude regions and suggest a far-reaching impact of this source at depth. Away from the surface layer, the strong correlation between dFe and apparent oxygen utilization implies that a combination of regeneration, scavenging and large-scale ocean circulation are controlling the interior distribution of dFe, with hydrothermal inputs important in some regions. Finally, our data-driven dFe climatology can be used as an alternative reference to evaluate the performance of ocean biogeochemical models. Overall, the new global scale climatology of dFe achieved in our study is an important step toward improved representation of dFe in the contemporary ocean and may also be used to guide future sampling strategies.

Post-Fire Habitat Heterogeneity Leads to Black Spruce–Kalmia L. Shrub Savannah Alternate State

Many nutrient-poor coarse-textured Kalmia L.–black spruce forest sites in eastern Canada turn to ericaceous heath dominated by Kalmia angustifolia L. after clearcutting and fire. While the mechanisms of post-fire forest and heath formation have been well documented, the origin of shrub savanna vegetation has received limited attention. This study demonstrates the significance of post-fire island regeneration of black spruce in Kalmia heath to the origin of shrub savannah alternate state. The study was conducted in Three Brooks, 10 km west of Grand Falls-Windsor, Newfoundland (48°51′ N; 55°37′ E). Black spruce forest in the site was clearcut, then a wildfire burned the area, and the site was subsequently planted with black spruce. Plant species cover, black spruce growth (stem density, stem height, basal diameter, and yearly volume increment), and foliar nutrients of planted spruce and soil properties (pH, humus and Ae horizon depth, and nutrients) in tree islands were compared with adjacent Kalmia heath. Black spruce islands had significantly lower cover of Kalmia and higher stem density of black spruce compared to Kalmia heath (7100 stems/ha in islands vs. 1920 stems/ha in heath). Height, basal diameter, and yearly volume increment of black spruce were more than three times higher in spruce islands than in Kalmia heath. Foliar nutrients of black spruce growing in Kalmia heath had significantly lower N and Mg (33 and 38%, respectively) but had significantly higher Mn and Zn (46 and 33%, respectively) than in black spruce islands. Black spruce growth inhibition in Kalmia heath is attributed to soil nutrient imbalance due to Kalmia evidenced by reduced concentrations of N and Mg and increased concentrations of Al, Fe, and other inorganic ions in the foliage. These results suggest that post-fire black spruce islands in severely burned patches provide “safe sites” for spruce regeneration, whereas Kalmia heath developing in non-severe burn area inhibits spruce regeneration and creates shrub savannah community as an alternate vegetation state.

Spatial patterns in aragonite saturation horizon over the northern California shelf

Ocean acidification along the California Shelf is controlled by the upwelling of deep CO2-rich waters. This coastal upwelling is driven by along-shore winds, which vary seasonally. We report aragonite undersaturation based on proxy values derived from temperature, salinity, and dissolved oxygen data and show the relationship between the spatial extent of low aragonite saturation state values and upwelling-favorable along-shore winds. Our data were collected on seasonal hydrographic surveys off northern California that span several years. Transect data show a persistent spatial pattern with shoaling of the aragonite saturation horizon over the shelf (during May and July surveys, mean depth of horizon is less than 20 m within ∼20 km of the coast), and surfacing of the saturation horizon during times of strong upwelling events. Our model shows that a higher proportion of the water column is undersaturated in aragonite when northerly winds are stronger. In addition, we found that pteropod abundance was positively correlated with aragonite saturation state, with lower densities associated with lower saturation values. If upwelling-favorable winds increase with global warming, as anticipated, more shelf water habitat will become undersaturated in aragonite, negatively impacting populations of calcifying organisms like pteropods.

Geothermal Resources and ATES Potential of Mesozoic Reservoirs in the North German Basin

Mesozoic sandstone aquifers in the North German Basin offer significant potential to provide green and sustainable geothermal heat as well as large-scale storage of heat or chill. The determination of geothermal and subsurface heat storage potentials is still afflicted with obstacles due to sparse and partly uncertain subsurface data. Relevant data include the structural and depositional architecture of the underground and the detailed petrophysical properties of the constituting rocks; both are required for a detailed physics-based integrated modeling and a potential assessment of the subsurface. For the present study, we combine recently published basin-wide structural interpretations of depth horizons of the main stratigraphic formations, with temperature data from geological and geostatistical 3D models (i.e., CEBS, GeotIS). Based on available reservoir sandstone facies data, additional well-log-based reservoir lithology identification, and by providing technical boundary conditions, we calculated the geothermal heat in place and the heat storage potential for virtual well doublet systems in Mesozoic reservoirs. This analysis reveals a large potential for both geothermal heating and aquifer thermal energy storage in geologically favorable regions, and in many areas with a high population density or a high heat demand. Given the uncertainties in the input data, the applied methods and the combination of data from different sources are most powerful in identifying promising regions for economically feasible subsurface utilization, and will help decrease exploration risks when combined with detailed geological site analysis beforehand.

Uniform bathymetric zonation of marine benthos on a Pan-Arctic scale

While numerous regional studies of bathymetric zonation of benthic fauna globally have been done, few large-scale analyses exist, and no ocean-scale studies have focused on the Arctic Ocean to date. In the present work we, hence, examined bathymetric zonation of macro- and megabenthos over a depth range spanning from the shelf to the abyssal plain (14 – 5416 m) and regionally extending from the Fram Strait to the Beaufort Sea (as a whole hereafter called the Central Arctic). Based on 104 quantitative (box-corers and grabs) and 37 semi- quantitative (trawls) samples compiled from different studies we evaluated bathymetric zonation patterns in abundance, biomass and diversity, and also compared species composition among samples. Abundance and biomass decreased with depth from > 3000 ind. m−2 and > 40 g ww m−2 to ∼ 130 ind. m−2 and < 1 g ww m−2 corroborating previous studies. Diversity showed a parabolic pattern, peaking at ∼ 100–600 m. Cluster analysis revealed four (macrofauna) and five (megafauna) groups of benthic assemblages, including three that covered the upper and lower continental slope and the abyssal plains with relatively little overlap (named the Lower Shelf – Upper Slope 1, the Lower Slope and the Abyss). Substantial changes in benthic community composition were observed at depths 650–950 m (between the Lower Shelf – Upper Slope 1 and the Lower Slope) and 2600–3000 m (between the Lower Slope and the Abyss), so we interpreted these two depth horizons as major bathymetric boundaries. The first boundary (650–950 m) corresponds to the transition from sublittoral to bathyal fauna consistent with previous studies. The second boundary (2600–3000 m) reflects a decrease in benthic abundance, biomass and diversity within the Central Arctic abyssal plain. Bathymetric patterns and species overturn of benthos were relatively uniform throughout the entire Central Arctic continental slope and abyssal plain. For some regions of the Arctic Ocean, foremost for the area north from Greenland and Canadian Archipelago, benthic data are still unavailable and further research is needed.

Integrative Geophysical Studies at the Novaya Kurya-1 Cemetery in the Kulunda Steppe

We outline the results of prospection studies at the Novaya Kurya-1 cemetery in the south of Western Siberia, using remote sensing methods such as aerial photography, ground-based magnetometry, high-precision aeromagnetic survey, electromagnetic profi ling, and electrotomography. Original techniques were used to construct relative relief maps, and an inversion of data from ground-based magnetic survey at various altitudes was carried out. The fi rst technique reduces the effect of natural relief, and highlights anthropogenic altitudinal anomalies, making the analysis of digital elevation models more effi cient. The second technique is helpful for assessing the thickness and depth of anomalous magnetic bodies or horizons, not only providing planigraphic information but enabling us to evaluate two- and threedimensional geometric properties of the detected objects. As a result of the analyses, at least 14 kurgans were identifi ed at the cemetery, six of which lack salient outward features. Structural details suggest that most of them date to the Early Scythian time (800–400 BC). On the basis of the interpretation of the results of highly effi cient prospection analyses using the UAV platform, offering the possibility of surveying a large area (about 25 ha), the boundaries of the site were determined. Several features were detected. To identify these, further studies are needed.

Agrogena evolucija humusno-podzolastog zemljišta - mogućnost ponovnog uključivanja u obradu ugara formiranog na trakastim glinama

Transformations of the soddy-podzolic gleyic clay soil in a long-term agricultural use (&gt; 200 years) was studied in Leningrad region, northwest Russia. This feasibility study investigated the possibility of re-cultivation of these soils after long term fallowing. Morphological structure, particle size distribution, content and ratio of ferrous and oxide forms of iron in the profile of virgin (indigenous forest) and arable drained soil were analysed. In addition, changes in the organogenic-profile were traced in the course of long-term agrogenesis (&gt; 200 years). In virgin forest soil, during its pedogenesis the loss of fractions &lt;0.01 mm from the eluvial layer was 877.4 kg m-2 , and the loss of &lt;0.0001mm was 287.5 kg m-2 , as compared with parent material not affected by the processes of pedogenesis. However, long-term agrogenesis (&gt;200 years) led to increased eluvial losses of fine earth particles. The loss of fraction &lt;0.01 mm from the arable horizons was 1244.8, and &lt; 0.0001 mm was 570 kg m-2 , respectively. This was due to multiple yearly tillage that increased the porosity of the soil and thus intensified lessivage, which led to increased leaching and eluvial losses. The total loss of colloids from the entire profile of virgin soil was 262.1 kg m-2 , and from the arable layer of drained soil - 290.1 kg m-2 . The humus enrichment of the colloids of the plough (P) horizon of the arable soil was two times lower than that of the surface (AY) horizon of the virgin soil. The relative share of the participation of colloids in the fixation of humus by the soil was the same (11.6 and 10.9%, respectively). In the subsurface horizons, the absolute content of humus in the colloids decreased, and the share of participation in the fixation of humus increased. When soddy-podzolic gleyic clay soil is brought to cultivation then the water-air regime is improved, content and composition of humus, depth of arable horizon is increased and the soil acidity decreased. At the same time the leaching of fine earth materials is accelerated. When this soil was withdrawn from crop production, the positive changes achieved as a result of cultivation were gradually lost. For the first time we could qualitatively calculate the losses of the fine earth fractions for the given soil from top soil. Taking into account the high costs of re-cultivation of the former land and a high cost of re-installation and maintenance of an optimal hydrological regime (drainage network) we concluded that repeated ploughing and involvement of arable soddy-podzolic gleyic clay soil into cultivation is economically unreasonable.

Guideline Values for the Content of Chemical Elements in Soils of Urban Functional Zones: A Review

—The Russian soil quality assessment system, where the guideline values for the content of heavy metals and metalloids derived for arable lands (mostly, in terms of the general sanitary indicator of harmfulness) are applied to soils of the residential area and the protected area of water supply sources, can be updated using international experience, e.g., substantiation of generic values for urban functional zones since, with a few exceptions, the Russian soil quality guidelines are the same for all soils of the country. In order to assess the applicability of foreign approaches to Russian realities, we have thoroughly analyzed the original and most developed legislation systems of the soil quality control in cities of Germany, Canada, and the United States, as well as the systems of Australia, New Zealand, Republic of South Africa, and the countries of the European Union, where the values are land use specific. In this paper, we summarize the principles of soil quality assessment for the contents of chemical elements, brief the methodology used in different countries and the consequences of exceeding the standards, and highlight some clues for improving the Russian soil quality assessment system. The Russian soil quality assessment system can be improved and updated by substantiating (i) the land use specific standards for cities with the focus on actual subjects of standardization (the health of ecosystems, children, or adults); (ii) the standards for different geochemical environments taking into account the specific features of migration of substances; and (iii) the standards for the soil materials used to construct lawns and roadside areas. In addition, we suggest (i) developing a comprehensive system of management decisions for the case when soil quality standards are exceeded; (ii) legitimizing the concept of historical pollution that existed before the commencement of business activities; and (iii) establishing the minimum volume of soil and the depth or set of soil horizons to be remediated or removed due to pollution.

Features of vanadium geochemistry in oils from the oil and gas fields of eastern region of Ukraine

The results of long-term studies of the geochemical features of vanadium in the oil from 36 deposits of the Eastern oil and gas region of Ukraine. Based on the results of correlation and regression analyses, the nature and forms of the relationship between the vanadium content in oil and nickel, zinc, chromium, manganese, cobalt, iron, mercury, aluminum and the total content of these metals were determined; average capacity of the productive horizon; oil density value; oil viscosity value; resin content; the density of formation water from the productive horizon; sulfur content in oil; actual depth of the productive horizon; actual temperature of the productive horizon; actual pressure of the productive horizon; oil boiling point; paraffin content; the value of mineralization for formation water from the productive horizon; content of asphaltenes. Correlation coefficients, pairwise linear regression equations as well as curves that illustrate relationships between these parameters are obtained. Based on the results of the cluster analysis, a dendrogram of the results for clustering by means of the weighted centroid method of the considered fields by the content of vanadium in the oils was elaborated. Based on the results of clustering by means of the weighted centroid method, the first natural classification of oil and gas fields of eastern region of Ukraine according to the content of vanadium in oils was developed. It has been proven that heteroatomic low-molecular sulfur-containing components of the petroleum system are the main concentrators of vanadium in the oil for the studied deposits. It has been shown that, based on the results of the cluster analysis, sample average values of vanadium concentrations that vary significantly between individual deposits or groups of deposits for established ranges could be interpreted in terms of qualitative assessment as follows: abnormally low; low; below average; average; above average; high; abnormally high. The implementation of this kind of approach makes it possible to visually compare and interpret in terms of geology various scale and various indicators of oil deposits obtained by means of experimental study. Keywords: vanadium, oil deposits, cluster analysis, linear regression equations, geochemical oil parameters, correlation coefficient.

Распределение температурных показателей по профилю серогумусовой почвы, остров Западный Шпицберген

The air and profile of Umbrisols in the south-western part of Svalbard are characterized by negative average annual temperatures. The duration of the period with positive temperatures at the depth of the umbric horizon (8–10 cm) is 128 days; the sum of positive temperatures is about 500 оС. The distribution of average monthly temperatures in all horizons in the profile of 0–60 cm in the annual cycle reliably correlates with air temperature.

Reclaimed Mine Sites: Forests and Plant Diversity

The relationship between vegetation and selected soil characteristics in different monoculture forest types was investigated as part of a landscape restoration project after brown coal mining. Six forest types were selected: alder (Alnus sp.), spruce (Picea sp.), pine (Pinus sp.), larch (Larix sp.), long-term deciduous forest (Quercus robur, Tilia sp.), and forest created by spontaneous succession. These stands were classified into two age categories (younger and older). The soil attributes, C/N, TC, TN, pH, and A horizon depth were assessed. The observed species were categorized into functional groups by life history, life forms according to Raunkiær, and affinity to the forest environment. C/N ratio, humus thickness, and canopy cover were the main soil parameters affecting plant communities. The highest C/N values were recorded in Pinus and Larix stands, which were significantly different from deciduous and succession stands. The highest diversity index was noted in younger stands of Alnus and the lowest in younger stands of Picea. Intermediate values of the diversity index were achieved in successional stands at both age levels and in Larix and Alnus stands. The species belonging to a functional group was not an important factor in these habitat types. The species composition and vegetation change over time in the Alnus, long-life deciduous, and Larix stands show that these species are more suitable for forestry reclamation than spruce or pine. The study also emphasizes the great value of spontaneous succession areas as full-fledged alternatives to forestry reclamation.

КОНТРОЛЬ ПОТЕНЦИАЛЬНОЙ ПОПОЛНЯЕМОСТИ МИДИИ С УЧЕТОМ НЕКОТОРЫХ ПАРАМЕТРОВ СРЕДЫ В ЭСТУАРНОЙ ЗОНЕ СЕВАСТОПОЛЯ

In 2020-2021, potential recruitment of the mussel Mytilus galloprovincialis was measured in Sevastopol estuarine waters with regard to temperature, salinity, and pH in three depth horizons 1–3, 7, and 11 m. Compared to the previous annual period in 2021, spring mussel recruitment at all depth horizons in-creased by an order of magnitude. This increase was preceded by a mild winter. Also in 2021, a decrease in salinity and an increase in the vertical variability of the thermohaline structure of water were observed. The obtained data may indirectly indicate the improvement of environmental conditions for mussel productivity increase in 2021. The necessity of improving the method of the control for mussel recruit-ment related to possible vertical migrations of its post-larvae is shown.

METACRITICISM AS A LITERARY PROBLEM

The latest decades are associated with an active rethinking of the existing literary and philosophical achievements, which are reflected significantly in changes and refinements in contemporary literary terminology. Along with the already known concepts such as "literature", "postmodernism", "criticism", the concepts "metafiction", "metamodernism" and "metacriticism" exist and become popular. At the same time, one may notice that the widely used now prefix meta- lays claim to a greater depth and coverage of higher horizons. If criticism marks the analysis, comprehension, and interpretation of literary works, then metacriticism focuses on literary-critical, historical-literary, and methodological researches, thus showing "criticism of criticism". The article deals with a complex analysis of the concept of "metacriticism". On the one hand, both aesthetic and philosophical approaches to the understanding of the notion of criticism are taken into account – starting from the antique times to Karl Popper’s critical-rationalistic approach. On the other hand, it is found that metacriticism as a phenomenon dates back to the end of the XVIII century when the works of two famous German philosophers Johann Georg Hamann’s "Metacritique on Purism of Reason" and Johan Gottfried Herder’s "Metacriticism of Critique of Pure Reason" were published as a debate on Immanuel Kant’s ideas. Based on the available data, it is found that metacriticism is a rather convenient multilevel term that may qualitatively contain various interpretations, including the criticism of criticism, metascience concerning criticism, criticism of the highest level, short form of the term "metaphysical critique" as a critique of "metaphysical realism". At the same time, while taking into account the current trends of the digital age, metacriticism becomes a product of digital technology - popular platforms for writing reviews, making discussions, and even creating a virtual library, such as site Metacritic, the English-language portal Goodreads and its Russian equivalent Livelib. The article itself does not exhaust the problem of metacriticism as a multidimensional phenomenon, but it provides opportunities for further and deeper studies of the outlined issues, in particular within the context of theoretical and literary discourse.

Restoration objectives create surface carbon cycle trade‐offs in coastal habitats

Coastal habitats are important and imperiled. To mitigate climate change impacts, carbon (C) sequestration has joined established restoration objectives, including habitat diversity, public access, and native vegetation. Changing topography, maintaining trails, and removing invasive plants may influence coastal C production and retention in different ways depending on how each activity influences the stabilization of organic matter in surface sediments. We quantified variation in litter and surface soil dynamics within and between coastal parks that varied in age from prerestoration to nearly 20 years old in Manatee County, Florida. Older parks had deeper soil organic horizons with higher levels of soil moisture and respiration, indicating that restoration sequesters soil C despite increases in microbial efficiency. However, variation within parks indicated that detrital C dynamics change depending on local management objectives. Relative to unmanaged locations, restored wetlands, including mangroves, salt marshes, and freshwater ponds, had soil organic horizons nearly 20 cm deeper, with high litter stabilization rates despite less litter mass and shorter projected soil sample C mineralization. In contrast, public access features like trails and kayak launches were associated with increased surface CO2 efflux and marginally reduced soil organic horizon depth. Removing invasives had little impact on detrital carbon pools and fluxes. Incorporating detrital C dynamics improved a multivariate model for variation in C pool sizes across sites. Overall, our results suggest that management objectives influence the C production and retention capacity of restored coastal habitats with restored uplands and public access points storing less C than relatively inaccessible wetlands.

Influence of different fertilization and chemical recruitment systems on the phosphorus regime of gray forest soil

Phosphorus is extremely important in agriculture. This is due to the fact that without its participation in the plant body does not undergo any biochemical reaction, because it is part of the ATP molecule, which provides energy. It is an essential element of nucleic acids, phospholipids and the others is actively involved in the regulation of enzymatic reactions. It is part of human, animal, plant and bacterial cells. The research was conducted on the basis of a stationary experiment conducted in 1992 on gray forest coarsegrained light loam soil, studied the effect of long-term chemical reclamation and various fertilization systems (mineral, organic, organic-mineral) on the transformation of Optimal phosphorus nutrition promotes the development of the root system, which improves the supply of plants with moisture and nutrients, increases the share of marketable products in the organic crop, increases the starch content in potatoes, sugar in roots, vegetables and fruits, oilseeds, oilseeds the output of a long fiber, its strength increases. That is why the management of phosphorus nutrition of plants is one of the key issues. Changes in various forms of phosphorus (gross, mobile, water-soluble) under the influence of the above factors are analyzed. For a more objective assessment of these factors on the phosphate regime of the soil on the variant results of the analysis were compared not only with absolute control, but also tied to baseline (age of fallow 28 years), located next to the experimental field. It was found that the content of gross phosphorus, which characterizes the genetic characteristics of the soil, depends almost entirely on the total humus reserves and clearly repeats the parameters of the profile accumulation of carbon, taking into account the depth and thickness of humus horizons. The particle size distribution is of great importance in the processes of gross phosphorus accumulation, as defects are quite easily adsorbed on the surface of soil structures. Evaluation of the results of the analysis shows a large gap in the gross forms of phosphorus and low concentration of its mobile forms, the content of which is 4.7% of the total. According to our data, water-soluble salts of phosphoric acid in gray forest soil are generally found in very small quantities (0.62 mg / kg in the horizon NOT with a gradual decline down the profile), which often becomes a limiting factor in phosphorus nutrition of crops. Lime, by reducing the activity of one and a half oxides, weakens the adsorption bonds of phosphorus and increases the relative amounts of calcium phosphates. The application of mineral fertilizers replenished the pool of gross phosphorus (by 0.08% of the control dock), but mobile forms of phosphorus (according to Kirsanov) increased by only 23 mg/kg, which was second only to liming. In general, the effect of liming significantly increases the use of soil phosphates and fertilizers.

Potentialities and limitations of Planosols with distinct depths of diagnostic horizon

There is a variation in the depth of subsurface horizon of Planosols in semi-arid region, which may influence the agricultural potential and affect food production. The general aim of this study was to identify potentialities and limitations of two Planosols as a function of subsurface horizon depth. The adjacent profiles P1 and P2 were studied in Pentecoste (Ceará, Brazil). Morphological, physical, and chemical analyses were done aiming at soil characterization. Soil bulk density (BD), porosity, and penetration resistance (PR) were analyzed in a completely randomized split-plot design with four replicates to compare P1 and P2 and the horizons Ap and Btf. Btf was found at 62cm depth in P1 and at 18 cm depth in P2. Indicatives of water saturation were more evident in P2. The profile P1 showed lower hardness and higher friability, as well as higher acidity in subsurface (pHH2O from 4.4 to 4.7) and higher aluminum content (1.2cmolc kg-1). Both profiles were eutrophic and showed low contents of organic carbon (1.5 to 8.5g kg-1) and phosphorus (0.9 to 3.9mg kg-1). The sodium percentage in CEC was 9.1% in P1 and 5.5% in P2. Water retention increases in Btf compared with Ap was 7.3% in P2 and 2.7% in P1. Both profiles showed increase in BD in Btf, reaching 1.7g cm-3, while PR was higher in P2 (1.5 MPa). There are potentialities and limitations common to both soil profiles, but P1 has more physical potentialities and more chemical limitations than P2.

Modelling the transition from grain-boundary sliding to power-law creep in dry snow densification

AbstractThis paper presents a physics-based macroscale model for the densification of dry snow which provides for a smooth transition between densification by grain-boundary sliding (stage 1) and densification by power-law creep (stage 2). The model uses established values of the stage 1 and 2 densification rates away from the transition zone and two transition parameters with a simple physical basis: the transition density and the half-width of the transition zone. It has been calibrated using density profiles from the SUMup database and physically based expressions for the transition parameters have been derived. The transition model produces better predictions of the depth of the nominal bubble close-off horizon than the Herron and Langway model, both in its classical form and in a recent version with re-optimised densification rates.

Effect of soil erosion depth on crop yield based on topsoil removal method: a meta-analysis

A reliable correlation between crop yields and soil erosion is critical for the assessment of soil loss tolerance and loss of future food production in eroded farmlands. However, the heterogeneity between experiments in terms of soil properties, crop types, and farming management makes it difficult to compare and extrapolate results from different studies. This study is the first to compile data from 290 observations of crop yields from topsoil removal experiments worldwide, to conduct a hierarchical mixed-effects meta-analysis to quantify the relationship between erosion depth and crop yields, and to explore the influence of grain types and agricultural management measures. We found that crop yields did not decrease significantly when the remaining A horizon depth was greater than 25 cm or when the erosion depth was less than 5 cm. This provided evidence that a remaining A horizon depth of 25 cm may be a threshold for sustainable soil productivity in eroded soils and that the widely accepted linear equation does not describe the relationships of crop yield and soil erosion well. We also found that the sensitivity of crop yield to erosion varied with crop type, with decreasing sensitivity from soybean to maize and then to wheat. When the erosion depth was greater than 20 cm, crop yields cannot be restored to their pre-erosion levels, although conventional fertilization and irrigation increase crop yields on eroded soil. These findings are useful for better assessing soil erosion tolerance, selecting effective soil erosion control strategies, and quantitatively evaluating the impact of soil erosion on global food production.

The effects of tree-mycorrhizal type on soil organic matter properties from neighborhood to watershed scales

A large portion of terrestrial carbon (C) is stored as soil organic matter (SOM) so the balance between C inputs to SOM and soil C loss through respiration has important implications for global climate change. Tree-mycorrhizal association is a promising predictor of SOM dynamics, with the effect of ectomycorrhizal (ECM) trees and associated fungi scaling with the percent basal area of ECM-associated trees in a forest stand. However, uncertainty remains in the generality of ECM effects across the different spatial scales at which soil properties are known to vary. To determine the spatial variability of ECM effects on SOM pools within a forest stand, we used likelihood modelling techniques to compare non-spatial models, which average out ECM effects at the stand scale, against spatial models, which account for the size and spatial distribution of ECM-associated trees within a stand (i.e., the tree neighborhood). To investigate how watershed-scale variability in soil fertility and pH mediate ECM effects, we quantified forest floor leaf litter and soil properties in forest stands along mycorrhizal gradients within four adjacent watersheds that varied in parent material and rainfall. We found that ECM effects on SOM pools scaled with stand-level ECM dominance rather than varying based on individual trees at the neighborhood scale. Although forest floor leaf litter and mineral C:N ratios consistently increased with ECM dominance across watersheds, ECM effects on O horizon formation and the composition of SOM at depth differed among watersheds. Specifically, watersheds with lower soil pH and fertility exhibited greater changes along mycorrhizal gradients in O horizon depth, leaf litter δ15N and in the difference between δ15N of leaf litter and mineral soil fractions. Overall, this study shows the potential for intrinsic soil properties to mediate the effects of ECM trees and associated fungi on SOM formation and persistence in the tropics.

Organic substrate availability and enzyme activity affect microbial-controlled carbon dynamics in areas disturbed by a mining dam failure

We investigated key ecophysiological traits of microbial communities across different disturbance levels for two upper horizon depths (A1: 0–3 cm and A2: 10–13 cm) in areas disturbed by Fundão dam failure across Gualaxo do Norte river. We found that lower microbial growth (microbial biomass) and higher microbial-C losses (high qCO2) were linked to both decreases in organic substrate availability and enzyme activity suggesting important feedbacks on C dynamics in areas disturbed by Fundão dam failure. Basal respiration was not affected by organic substrate availability but increased with enzyme activity at A2 suggesting an enzymatic compensation in response to a lower plant-derived input. Lower degradative activity of extracellular enzymes (expressed as GMean index) was linked to lower organic matter content in mine tailings. Our results suggest that changes in organic substrate availability reflect changes in the microbial-controlled C dynamics in mine tailings. Thus, the design of restorative strategies based on microbial traits has the potential to accelerate the rehabilitation in areas disturbed by Fundão dam failure.