Highly weathered mineral soils have highest transfer risk of radiocaesium contamination after a nuclear accident: A global soil-plant study.

Accidental release of radiocaesium (137Cs) from nuclear power plants may result in long-term contamination of environmental and food production systems. Assessment of food chain contamination with 137Cs relies on 137Cs soil-to-plant transfer data and models mainly available for regions affected by the Chornobyl and Fukushima accidents. Similar data and models are lacking for other regions. Such information is needed given the global expansion of nuclear energy. We collected 38 soils worldwide of contrasting parent materials and weathering stages. The soils were spiked with 137Cs and sown with ryegrass in greenhouse conditions. The 137Cs grass-soil concentration ratio varied four orders of magnitude among soils. It was highest in Ferralsols due to the low 137Cs interception potential of kaolinite clay and the low exchangeable potassium in these soils. Our results demonstrate, for the first time, the high plant uptake of 137Cs in tropical soils. The most recent 137Cs transfer model, mainly calibrated to temperate soils dominated by weathered micas, poorly predicts the underlying processes in tropical soils but, due to compensatory effect, still reasonably well predicts 137Cs bioavailability across all soils (R2 = 0.8 on a log-log scale).

Microtopography effects on pedogenesis in the mudstone-derived soils of the hilly mountainous regions.

Topography is a critical factor that determines the characteristics of regional soil formation. Small-scale topographic changes are referred to microtopographies. In hilly mountainous regions, the redistribution of water and soil materials caused by microtopography is the main factor affecting the spatial heterogeneity of soil and the utilization of land resources. In this study, the influence of microtopography on pedogenesis was investigated using soil samples formed from mudstones with lacustrine facies deposition in the middle of the Sichuan Basin. Soil profiles were sampled along the slopes at the summit, shoulder, backslope, footslope, and toeslope positions. The morphological, physicochemical, and geochemical attributes of profiles were analyzed. The results showed that from the summit to the toeslope, soil thickness increased significantly and profile configuration changed from A-C to A-B-C. The total contents of Ca and Na decreased at the summit, backslope, and footslope, while the total contents of Al, Fe and Mg showed an opposite trend. On the summit and shoulder of the hillslope, weathered materials were transported away by gravity and surface erosion, exposing new rocks. As a result, soil development in these areas was relatively weak. In flat areas such as the footslope and toeslope with sufficient water conditions, the addition of weathered components and the prolonged contact between water, soil, and sediment led to further chemical weathering, resulting in highly developed characteristics. Microtopography may influence physicochemical properties, chemical weathering, and redistribution of water and materials, causing variations in pedogenic characteristics at different slope positions.

Soil property and crop yield responses to variation in land use and topographic position: Case study from southern highland of Ethiopia.

Understanding soil property and crop yield responses to variations in land use and topographic gradient is vital for designing targeted soil and agronomic management practices. This study investigated the interrelationships between land use, topographic position, soil properties, and crop yield. Three replicates of three land use types - enset agroforestry, cropland (annual crop), and grazing land - were selected along a toposequence (upper, middle and lower) for the study. A total of 54 composite soil samples were collected and analyzed. Grain yield and above ground biomass were also gathered from the cropland and analyzed. Soil profile descriptions revealed notable variations in soil physical properties, including soil texture, bulk density, color, horizons, and depth among the pedons of the three topographic positions. Clay and silt fractions exhibited significant differences between land uses and topographic positions, while the sand fraction was influenced by topographic position alone. Crop and grazing lands displayed higher clay content compared to the enset field. A decreasing trend in clay fraction was observed from upper to lower topographic positions. The enset field had significantly higher soil pH, OC, TN, and K+ contents than crop field. A significantly higher available P of 16.61 mg kg-1 was measured from lower slope position followed by 14.08 mg kg-1 in middle slope. The upper slope position had the highest exchangeable acidity of 3.09 cmol(+) kg-1), followed by middle slope with 2.77 cmol(+) kg-1), 2.45 cmol(+) kg-1) in the lower slope position. Grain yield and above ground biomass decreased from lower slope to middle slope and upper slope positions. These observed variations in soil properties and crop yield among land uses and topographic positions underscore the necessity for tailored soil management strategies and agronomic practices specific to land use types and the specific localized topographic conditions to optimize agricultural productivity.

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We selected a typical dolomite slope and set up three micro-plots (projection length was 2 m, width was 1.2 m) on the upper, middle, and lower slopes to analyze the variations of soil losses and the key influencing factors during two hydrological years (2020-2021). The results showed that soil losses at different slope positions on dolomite slopes followed an order of semi-alfisol in lower slopes (386 g·m-2·a-1) > inceptisol in middle slopes (77 g·m-2·a-1) > entisol in upper slopes (48 g·m-2·a-1). Downward along the slope, the positive correlation gradually increased between soil losses and surface soil water content, as well as rainfall, while it gradually decreased with the maximum 30 min rainfall intensity. The meteorological factors affecting soil erosion on the upper, middle and lower slopes were the maximum 30 min rainfall intensity, precipitation, average rainfall intensity and surface soil water content, respectively. Soil erosion processes on upper slopes were mainly driven by raindrop splash erosion and infiltration-excess runoff, while that on lower slopes were mainly driven by saturation-excess runoff. The volume ratio of fine soil in the soil profile was the key factor of soil losses on dolomite slopes, with an explanation rate of 93.7%. The lower slope was the key site of soil erosion in the dolomite slopes. Subsequent rock desertification management should be based on the erosion mechanism of different slope positions, while control measures should be arranged according to local conditions.

Black carbon flux in terrestrial and aquatic environments of Kodaikanal in the Western Ghats, South India: Estimation, source identification, and implication.

Evolving Anthropocene epoch wields significant influence in altering atmospheric carbon, which affects the carbon cycle, leading to climate change. Understanding the carbon stock, fate, and transport across ecosystems are essential in determining India's carbon budget, hitherto, unavailable. In this study, we have analysed the stock, source, distribution, flux, and the relationship between terrestrial and aquatic black carbon over a high-altitude mountainous area in the Western Ghats region using the data collected from September 2019 to February 2021. Soil Organic Carbon (SOC) and Black Carbon (BC) are the highest in the forest region (SOC:23 ± 3 g of C/kg (dry weight (dw)), BC:6 ± 3 g/kg) and are the lowest in the urban region (SOC: 13 ± 2 g of C/kg (dw), BC:2 ± 1 g/kg). SOC is labile, whereas BC is non-labile. The BC/SOC ratio represents soil carbon lability. Topsoil BC/SOC ratios vary by land use and land cover, with urban areas having greater labile carbon pools than the forests. Dissolved BC (DBC) concentrations were most strongly correlated with bulk Dissolved Organic Carbon (DOC) concentrations in midstream (R = 0.6, p < 0.05), headwater streams (R = 0.3, p < 0.05) and to the soil bulk DBC (R = 0.3, p < 0.05), indicating the presence of transfer mechanism of soil to streams. The molecular associations revealed the presence of biolabile autochthonous compounds suggesting the crucial role land use and land cover play on watersheds. A positive relationship between DOC with seasonal hydrology and gradient significantly influences the DBC flux across regional streams. Intercomparison of observed terrestrial and aquatic carbon stocks with globally modelled data indicates an overestimation of regional-scale stock. These new findings have repercussions to policy framework on regional climate change. Further, the results suggest that a consistent quantification of BC and integration of regional, and global source-to-sink process are needed in order to understand and better quantify biogeochemical process cycles and associated climatic impacts.

Avaliação da condutividade hidraulica do solo saturada utilizando dois métodos de laboratório numa topossequência com diferentes coberturas vegetais no Baixo Amazonas / Evaluation of the saturated hydraulic conductivity using two laboratory methods in a topossequence with different vegetation cover in the lower Amazon

O objetivo desse trabalho foi avaliar dois métodos de laboratório para a determinação da condutividade hidráulica do solo saturada (Ko) conhecidos como Permeâmetro de carga constante (PCC) e Permeâmetro de carga decrescente (PCD), com o intuito de verificar sua aplicabilidade e variabilidade em solos amazônicos. Coletaram-se 125 amostras de solo com estrutura indeformada, através de amostrador tipo Uhland, com anéis volumétricos, de 0,072 m de altura e 0,069 m de diâmetro, devido à variabilidade apresentada pelas determinações de tal parâmetro. Nos mesmos pontos de amostragens da Ko, procedeu-se coleta de anéis volumétricos para a determinação da porosidade do solo. Ainda nesses pontos foram coletadas amostras com estrutura deformada para análises físicas e químicas. Os resultados obtidos demonstram que o método do PCC foi o mais apropriado para a classe dos Latossolos estudados, apresentando os menores coeficientes de variação e desvio padrão ao longo da topossequência. Os valores de Ko estiveram distribuídos entre P1(2,65 à 3,34 cm dia-1), P2(2,85 à 3,38 cm dia-1), P3(2,86 à 3,63 cm dia-1), P4(2,75 à 3,49 cm dia-1), P5(2,38 à 3,83 cm dia-1) e P6 (2,47 à 3,52 cm dia-1); havendo uma tendência para maiores valores de Ko na superficie. A utilização de Ko como parâmetro de análise hídrica em solos porosos na superfície e muito argilosos em profundidade, como os amazônicos, necessita ser realizada com precaução, evitando a interrupção da continuidade dos poros e compactação da amostra. Mudanças na condutividade hidráulica saturada estiveram mais relacionadas a alterações nas propriedades físicas do solo e posição no relevo do que nas alterações das coberturas vegetais ao longo da topossequência.

The objective of this work was to evaluate two different laboratory methods for determining the saturated hydraulic conductivity (Ko), namely, the constant head permeameter method (PCC) and the falling decreasing head permeameter method (PCD) and their applicability and variability to Amazon soils. 125 undisturbed soil samples were collected with an Uhland soil sampler using volumetric rings of 0,072 m height and 0,069 m in diameter. Soil porosity was also estimated by volumetric ring samples collected at the same spots where Ko was evaluated. Disturbed soil samples were also collected for chemical and particle size analysis at the same spots. The results showed that the PCC method was more appropriate for the studied soils Oxisols, leading to the lowest coefficient of variation and standard deviation throughout the topographic sequence. The Ko values were distributed among P1(2,65 to 3,34 cm day-1), P2(2,85 to 3,38 cm day-1), P3(2,86 to 3,63 cm day-1), P4(2,75 to 3,49 cm day-1), P5(2,38 to 3,83 cm day-1) and P6 (2,47 to 3,52 cm day-1); having a tendency to show higher Ko values at soil surface. The use of Ko as a parameter for hydraulic analysis in soils with high porosity in the surface layer and high clay content in the subsoil, as is the case in the Amazon, must be undertaken with caution to avoid compacting the sample and porous discontinuities. Throughout the studied topographic sequence, changes of saturated hydraulic conductivity were more related to changes in soil physical properties than to changes in vegetation cover throughout the studied topographic sequence.

Avaliação da condutividade hidraulica do solo saturada utilizando dois métodos de laboratório numa topossequência com diferentes coberturas vegetais no Baixo Amazonas

The objective of this work was to evaluate two different laboratory methods for determining the saturated hydraulic conductivity (Ko), namely, the constant head permeameter method (PCC) and the falling decreasing head permeameter method (PCD) and their applicability and variability to Amazon soils. 125 undisturbed soil samples were collected with an Uhland soil sampler using volumetric rings of 0,072 m height and 0,069 m in diameter. Soil porosity was also estimated by volumetric ring samples collected at the same spots where Ko was evaluated. Disturbed soil samples were also collected for chemical and particle size analysis at the same spots. The results showed that the PCC method was more appropriate for the studied soils Oxisols, leading to the lowest coefficient of variation and standard deviation throughout the topographic sequence. The Ko values were distributed among P1(2,65 to 3,34 cm day-1), P2(2,85 to 3,38 cm day-1), P3(2,86 to 3,63 cm day-1), P4(2,75 to 3,49 cm day-1), P5(2,38 to 3,83 cm day-1) and P6 (2,47 to 3,52 cm day-1); having a tendency to show higher Ko values at soil surface. The use of Ko as a parameter for hydraulic analysis in soils with high porosity in the surface layer and high clay content in the subsoil, as is the case in the Amazon, must be undertaken with caution to avoid compacting the sample and porous discontinuities. Throughout the studied topographic sequence, changes of saturated hydraulic conductivity were more related to changes in soil physical properties than to changes in vegetation cover throughout the studied topographic sequence.

O objetivo desse trabalho foi avaliar dois métodos de laboratório para a determinação da condutividade hidráulica do solo saturada (Ko) conhecidos como Permeâmetro de carga constante (PCC) e Permeâmetro de carga decrescente (PCD), com o intuito de verificar sua aplicabilidade e variabilidade em solos amazônicos. Coletaram-se 125 amostras de solo com estrutura indeformada, através de amostrador tipo Uhland, com anéis volumétricos, de 0,072 m de altura e 0,069 m de diâmetro, devido à variabilidade apresentada pelas determinações de tal parâmetro. Nos mesmos pontos de amostragens da Ko, procedeu-se coleta de anéis volumétricos para a determinação da porosidade do solo. Ainda nesses pontos foram coletadas amostras com estrutura deformada para análises físicas e químicas. Os resultados obtidos demonstram que o método do PCC foi o mais apropriado para a classe dos Latossolos estudados, apresentando os menores coeficientes de variação e desvio padrão ao longo da topossequência. Os valores de Ko estiveram distribuídos entre P1(2,65 à 3,34 cm dia-1), P2(2,85 à 3,38 cm dia-1), P3(2,86 à 3,63 cm dia-1), P4(2,75 à 3,49 cm dia-1), P5(2,38 à 3,83 cm dia-1) e P6 (2,47 à 3,52 cm dia-1); havendo uma tendência para maiores valores de Ko na superficie. A utilização de Ko como parâmetro de análise hídrica em solos porosos na superfície e muito argilosos em profundidade, como os amazônicos, necessita ser realizada com precaução, evitando a interrupção da continuidade dos poros e compactação da amostra. Mudanças na condutividade hidráulica saturada estiveram mais relacionadas a alterações nas propriedades físicas do solo e posição no relevo do que nas alterações das coberturas vegetais ao longo da topossequência.

Phosphorus and nitrogen status in soils and vegetation along a toposequence of dystrophic rainforests on the upper Rio Negro.

Amazon forests along a toposequence at San Carlos de Rio Negro (Venezuela) show distinct nutrient limitations depending on slope position. Soils were collected by genetic horizons and analysed to provide information on the relationships between soil P and N status and the nutrition of natural forest at three locations along the toposequence. The upper-slope tierra firme sites had total P concentrations between 100 and 200 µg g-1 in the mineral soil fines and between 700 and 1100 µg g-1 in lateritic nodules. Hyphae were seen to explore lateritic nodules and may contribute to P nutrition. Total P in the mineral soil of the lower slope ranged from only 3 to 130 µg g-1. In both the organic mats of the tierra firme and the humic horizon at the lower-slope tall Amazon caatinga site, 50-60% of the P was in inorganic forms, which, in the absence of P-fixing mineral soil, maintain high levels of plant-available P. As a result, the litter mats and humic horizon accounted for over 70% of the total available P in these soils. The proportion of available P increased, and P sorption decreased, downslope, supporting ecological studies which found that tall Amazon caatinga was least P-limited. Soil N and C levels show a maximum at the mid-slope and a minimum at the lower slope. Distributions of biomass C, N and P closely follow those of soil C, N and available (but not total) P along the slope.