Soil Parent Material Research Articles

Holocene dust dynamics archives in archaeological ruins in arid and semi-arid environments in the Southern Levant

Ruins of archaeological structures, mainly dating to the Bronze Age till Byzantine period, were investigated in a case study in the Petra region in southern Jordan and in the northern Negev desert in Israel. They are covered by post-abandonment debris sediments which provided the parent material of initial soils now developed on the ruins. Such debris sediments have so far rarely been studied although they likely contain a significant aeolian dust fraction because structures and wall remains may act as effective dust traps. We analyzed different types of archaeological structures: cult sites on hilltops, runoff-irrigated terraces on slopes, and cisterns including associated cleanout mounds. As well, we collected current aeolian sediments in nearby dry marble dust traps. It was expected that the various ruins and location types would matter for sediment properties, but substrate composition in all investigated structures was similar. This suggests that most of the fine fractions of the debris material were primarily supplied by wind whereas fluvial processes only re-distributed aeolian sediments. A major aeolian contribution from local weathered rocks could be observed in the Petra region, but not in the Negev, which seems connected with the geology. In situ pedogenesis in both investigation regions is negligible. The ruins seem to act as current dust collectors, but their sediments cannot directly be compared with the material collected in nearby dry marble dust traps. Analogies to different types of collectors for aeolian sediments can be made: depending on design, dust traps gather aeolian material differently. Standard dry marble dust collectors are characterized by similar size of settling dust samples as compared to average aeolian deposition in the ruins, but are of dissimilar substrate composition with regard to particle size distribution and contents of major and trace elements. Sediments in the archaeological structures in southern Jordan show finer textures and higher contents of most major and trace elements which may indicate preferential fixation of silt and clay against sand in the ruins, whereas sediments in dry marble dust collectors in Jordan are relatively depleted in silt and clay. This could be due to crusts and clast covers because the studied archaeological hilltop structures were found covered by surface crusts and pavements of stones and pottery sherds. These may mirror the effect of desert pavements. In addition, current dust samples suggest that precipitation during aeolian sedimentation, in particular in case of snow, is connected with enhanced deposition of (possibly clay-coated) silt. Sediments in the archaeological structures include material from remote and local sources as well as from “recycled” paleosols. Average hilltop dust accretion rates were calculated as ~ 0.14 mm/year, which is in good agreement with results from dry marble dust collectors. They exceed rates calculated for Pleistocene hilltop loess in the Negev. This seems due to enhanced dust fixation in the archaeological ruins as compared to natural Negev loess soils, underlining a so far rarely considered but important role of sediment fixation mechanisms.

Soil Related Factors Controlling Erosion And Landslides In Malaysia

The high temperature and rainfall in Malaysia results in intensive tropical weathering and depending on the parent material, the resultant soil can have deep or shallow soil profiles. Thus, a variety of soils can form with different textures (clay content), structure and porosity. With the high rainfall, soils in steep terrain are subjected to surface erosion when exposed or landslides if the rainwater percolates into the soil profile. Key soil-related factors controlling soil erosion and landslides include local climate, parent material of soils and depth of the weathered profile. Slope and geomorphology, vegetation and land use as well as land management practices also influence erosion and landslides. Measures used to control soil erosion and stabilize slopes require improved understanding of soil weathering, erosion, landslide and their linkages in steep terrain.

Digital mapping of soil carbon sequestration potential with enhanced vegetation cover over New South Wales, Australia

AbstractDigital soil maps of soil organic carbon (SOC) sequestration potential resulting from a hypothetical 10% relative increase in long‐term vegetation cover are presented at 100‐m resolution across the state of New South Wales (NSW) in southeast Australia. This land management outcome is considered realistically achievable for many land managers, using strategies such as revegetation, grazing management or crop residue management. A mean state‐wide potential increase of 5.4 Mg ha−1 over the 0‐ to 30‐cm depth interval was derived. Assuming a 20‐year period of re‐equilibration, this equates to an average SOC increase of 0.27 Mg ha−1 year−1. Sequestration potential is systematically influenced by a combination of climate, soil parent material and current vegetation cover, for example only 1.6 Mg ha−1 SOC under dry conditions in sandy, infertile soil material with sparse vegetation cover, compared with 15.9 Mg ha−1 under wet conditions in clay‐rich, fertile soil material with moderate–high vegetation cover. The outputs could be used to identify locations of highest sequestration potential and thereby help prioritize areas and inform decisions on sequestration programmes. Future application of the method at field scale with high levels of accuracy, together with strategic sampling, may provide statistically reliable estimates of carbon sequestration, for application in carbon trading schemes such as Australia's Emissions Reduction Fund. The modelling involved a conceptually transparent ‘space‐for‐time substitution’ process. Multiple linear regression (MLR) and random forest (RF) modelling techniques were applied, but only MLR gave consistently meaningful results. The apparent failing of RF in this application warrants further examination.

Contribution of Tamarix aphylla to soil organic matter evolution in a natural semi-desert area in Tunisia

A soil, classified as Arenosol (Eutri-Aridic Arenosol (Calcaric)), located in Neffatia (Tunisia) and populated by the shrub tamarisk (Tamarix aphylla), was studied to assess how the litter deriving from tamarisk can affect its characteristics. Several parameters were considered: particle size distributions (PSD), pH, cation exchange capacity (CEC), total CaCO3 content, total nitrogen (TKN), phosphorus and total organic carbon (TOC). Down the soil profile the pH increased from 7.83 to 8.32 as a probable consequence of salts accumulation deriving from the mineralization of the organic matter and the limited leaching due to low rainfall. As expected, TOC and TKN decreased, from the top downwards, and the two parameters were well correlated (TOC vs TKN: R2 = 0.98; p < 0.05; n = 3). CEC assumed progressively lower values reflecting the decreasing organic matter content (CEC vs TOC: R2 = 0.93; p < 0.05; n = 3). PSD showed that the presence of roots influenced the quantity of fine particles down the profile and the PSD cumulative curves were indicative of an aeolian origin for the soil parent material, confirming the hypothesis that tamarisk interacts with the environment, trapping sediment and forming the so-called phytogenic dunes. By chemical and spectroscopic analyses, it was possible to assess that tamarisk plant residues directly contributed to the soil organic matter (SOM) accumulation and characteristics. Stable SOM (ligno-humic fraction) closely resembles that of the plant (leaves and stems) and is chemically lacking in the more easily degradable organic components such as fats, hemicellulose, cellulose and proteins. 13C CPMAS NMR spectroscopy showed that the so-called soil ligno-humic fraction consists of aromatic molecules such as tannins, and aliphatic carbon (i.e. cutins and suberins) already present in the plant and preserved by mineralization processes because they are the most resistant to biological degradation.

Heterotrophic soil respiration and carbon cycling in geochemically distinct African tropical forest soils

Abstract. Heterotrophic soil respiration is an important component of the global terrestrial carbon (C) cycle, driven by environmental factors acting from local to continental scales. For tropical Africa, these factors and their interactions remain largely unknown. Here, using samples collected along topographic and geochemical gradients in the East African Rift Valley, we study how soil chemistry and fertility drive soil respiration of soils developed from different parent materials even after many millennia of weathering. To address the drivers of soil respiration, we incubated soils from three regions with contrasting geochemistry (mafic, felsic and mixed sediment) sampled along slope gradients. For three soil depths, we measured the potential maximum heterotrophic respiration under stable environmental conditions and the radiocarbon content (Δ14C) of the bulk soil and respired CO2. Our study shows that soil fertility conditions are the main determinant of C stability in tropical forest soils. We found that soil microorganisms were able to mineralize soil C from a variety of sources and with variable C quality under laboratory conditions representative of tropical topsoil. However, in the presence of organic carbon sources of poor quality or the presence of strong mineral-related C stabilization, microorganisms tend to discriminate against these energy sources in favour of more accessible forms of soil organic matter, resulting in a slower rate of C cycling. Furthermore, despite similarities in climate and vegetation, soil respiration showed distinct patterns with soil depth and parent material geochemistry. The topographic origin of our samples was not a main determinant of the observed respiration rates and Δ14C. In situ, however, soil hydrological conditions likely influence soil C stability by inhibiting decomposition in valley subsoils. Our results demonstrate that, even in deeply weathered tropical soils, parent material has a long-lasting effect on soil chemistry that can influence and control microbial activity, the size of subsoil C stocks and the turnover of C in soil. Soil parent material and its control on soil chemistry need to be taken into account to understand and predict C stabilization and rates of C cycling in tropical forest soils.

Spatial distribution and main controlling factor of cadmium accumulation in agricultural soils in Guizhou, China

A large-scale investigation was conducted on the cadmium (Cd) content in the farmland soils of Guizhou to explore the spatial variation in soil Cd content, identify the main factors responsible for causing Cd pollution, and determine the zonation of Cd pollution. Multivariate statistical analysis, geographic information system (GIS) analysis, and decision tree methods were used to study the distribution, spatial variation, and pollution partitioning of Cd and the factors influencing the Cd accumulation in agricultural soils of the Guizhou province. Areas with high Cd content in agricultural soil were found to be concentrated in the high-altitude areas in the western region of Guizhou province. The results of the single factor pollution index showed that the proportion of sample sites with Cd class I (priority protection), II (security utilization), and III (strict control) in the agricultural soils of Guizhou province were 65.96%, 31.27%, and 2.77%, respectively. In high-altitude areas, the Cd content in the agricultural soils was mainly derived from the soil parent material. In contrast, mining activities and road traffic were the main factors Cd accumulation in agricultural soils in lower altitude areas.

Impact of ecosystem water balance and soil parent material on silicon dynamics: insights from three long-term chronosequences

Impact of ecosystem water balance and soil parent material on silicon dynamics: insights from three long-term chronosequences

Source analysis of heavy metal pollution in agricultural soil irrigated with sewage in Wuqing, Tianjin

In this study, the contents of heavy metals and Cd and Pb isotope ratios of agricultural soil and potential source samples collected from farmland receiving sewage irrigation in Wuqing District, Tianjin, China were determined. Multiple methods were used for source analysis, including positive matrix factorization (PMF), correlation analysis, principal component analysis (PCA), and the Cd and Pb isotope ratio method. The results showed that agricultural soil was slightly contaminated by heavy metals in the research area, with relatively higher Cd and Pb accumulation levels compared to those of other heavy metals. Four types of pollution sources, including the soil parent material sources, industrial emission sources, agricultural practice sources, and mixed sources of sewage irrigation and transportation were apportioned and quantified by PMF, combined with the results of PCA and correlation analysis. The contribution rates quantified by the Cd and Pb isotope ratio method were similar, suggesting that no single source dominates Pb and Cd pollution. The contribution rates of Pb analyzed by the isotope ratio method were almost identical to those of the PMF model, indicating the rationality of the PMF result. Our results suggested that correlation analysis and PCA should be utilized to provide information for obtaining reasonable results and defining source categories for PMF, whereas the isotope ratio method should be applied to verify the accuracy of source contributions analyzed by PMF.

Geochemical Anomaly Characteristics of Cd in Soils around Abandoned Lime Mines: Evidence from Multiple Technical Methods

Lime mines are a potential source of pollution, and the surrounding soil environment is generally at threat, especially in abandoned lime mines. This paper focuses on the study area in eastern Anhui, attempting to analyze whether Cd enrichment is related to abandoned mines. On the basis of geological investigation, this study systematically used XRD, XRF, GTS and universal Kriging interpolation to determine the distribution law of Cd in the study area, and evaluated the potential ecological risk of Cd. The results showed that the main mineral types of soil samples of red clastic rock soil parent material (RdcPm) and soil samples of carbonate soil parent material (CPm) were not completely the same. Correlation analysis showed that CaO, MgO and Cd were positively correlated with the CPm. Human activities led to the accumulation of Cd in the study area. High Cd was mainly concentrated in the northwest of the study area, which was correlated with abandoned mines and soil parent materials. The study area was dominated by slight potential risks, although some areas had medium potential risks and high potential risks. All potential high risks were in the CPm field. This study provides a scientific basis for the comprehensive utilization and development planning of soil in the study area.

A sensors-based profile heterogeneity index for soil characterization

The technological and computational development has raised new possibilities for soil scientists to describe and infer about soil-forming processes and functions. Thus, why not to insert the contrasts between soil layers in a profile revealed by proximal sensing? We proposed to study the soil profile heterogeneity by reflectance (Vis-NIR-SWIR), X-ray fluorescence and magnetic susceptibility aiming to quantify it with the proposed “Profile Heterogeneity Index” (PHI) through seven soil sequences in twenty-seven locations over different hillslope positions and parent materials. The study was conducted in a 165-ha farm, at Rio das Pedras municipality, São Paulo State, Brazil. The differences between two consecutive soil layers were calculated by subtracting the data to the bottom and the immediately above for each soil profile. The results are depicted as a depth function with proportional colors to highlight the heterogeneity in the soil profiles. This approach provided a new method to identify where the transitions of soil attributes occur exactly and improve the understanding about soil-formation factors and processes. In this study, greater PHI values were mainly related to erosion and redeposition process through the landscape, differences in soil parent materials and also soil-forming processes. The sensors can furnish important and complementary information to the characterization of soil profile heterogeneity.

Level, source, and risk assessment of toxic elements in traditional agricultural soils and coping strategies.

The level, source, and risk of toxic elements in traditional agricultural soils are particularly crucial for the sustainable development of agriculture. An important agricultural production base was selected, a total of 251 topsoil samples were collected, eight toxic elements (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) in soil were analyzed, and environmental and health risk assessments were conducted. Results showed that all concentrations of eight elements in soil samples were lower than the risk screening values with negligible pollution risk. Approximately 83.8% of Hg in soil was originated from atmospheric deposition related to industrial emissions, 53.2% of Cd was derived from direct industrial activities, and the other elements came from soil parent materials or agricultural activities. Accumulation risk of As in agricultural products, potential ecological risk from Cd, and As's ingestion risk and Cr's dermal contact risk should be paid more attention. More stricter monitoring and coping countermeasures and strategies should be established to ensure the sustainable development of agriculture.

Estimation of the accumulation rates and health risks of heavy metals in residential soils of three metropolitan cities in China

Heavy metal concentrations in urban soils are likely to increase over time because of continuous urbanization and heavy metal emissions. To estimate the accumulation rates of heavy metals in urban soils, we collected soil samples from residential areas with different building ages in the metropolitan cities of Shanghai, Shenzhen, and Beijing, China. Heavy metal concentrations in the soils varied among the cities and were primarily affected by soil parent material and the intensity of anthropogenic sources. Regression analyses revealed that the accumulation rates of Cd and Cu in the soils ranged from 0.0034 to 0.0039 mg/(kg•year) and 0.343 to 0.391 mg/(kg•year), respectively, and were similar across the three cities, while accumulation rates of Zn and Pb in Shanghai were higher than those in Shenzhen and Beijing. The higher accumulation rates of Zn and Pb in Shanghai can be explained by differences in city history and industrial structures among the cities. Residential soils with high health risks posed by the heavy metals were mostly collected from old towns of Shanghai because of high Pb content in the areas. Although recent urbanization resulted in elevated concentrations of Cd, Cu, Zn, and Pb in the residential soils, the effect on the total health risks of residents exposed to the soils was negligible.

The role of geochemistry in organic carbon stabilization against microbial decomposition in tropical rainforest soils

Abstract. Stabilization of soil organic carbon (SOC) against microbial decomposition depends on several soil properties, including the soil weathering stage and the mineralogy of parent material. As such, tropical SOC stabilization mechanisms likely differ from those in temperate soils due to contrasting soil development. To better understand these mechanisms, we investigated SOC dynamics at three soil depths under pristine tropical African mountain forest along a geochemical gradient from mafic to felsic and a topographic gradient covering plateau, slope and valley positions. To do so, we conducted a series of soil C fractionation experiments in combination with an analysis of the geochemical composition of soil and a sequential extraction of pedogenic oxides. Relationships between our target and predicting variables were investigated using a combination of regression analyses and dimension reduction. Here, we show that reactive secondary mineral phases drive SOC properties and stabilization mechanisms together with, and sometimes more strongly than, other mechanisms such as aggregation or C stabilization by clay content. Key mineral stabilization mechanisms for SOC were strongly related to soil geochemistry, differing across the study regions. These findings were independent of topography in the absence of detectable erosion processes. Instead, fluvial dynamics and changes in soil moisture conditions had a secondary control on SOC dynamics in valley positions, leading to higher SOC stocks there than at the non-valley positions. At several sites, we also detected fossil organic carbon (FOC), which is characterized by high C/N ratios and depletion of N. FOC constitutes up to 52.0 ± 13.2 % of total SOC stock in the C-depleted subsoil. Interestingly, total SOC stocks for these soils did not exceed those of sites without FOC. Additionally, FOC decreased strongly towards more shallow soil depths, indicating decomposability of FOC by microbial communities under more fertile conditions. Regression models, considering depth intervals of 0–10, 30–40 and 60–70 cm, showed that variables affiliated with soil weathering, parent material geochemistry and soil fertility, together with soil depth, explained up to 75 % of the variability of SOC stocks and Δ14C. Furthermore, the same variables explain 44 % of the variability in the relative abundance of C associated with microaggregates vs. free-silt- and-clay-associated C fractions. However, geochemical variables gained or retained importance for explaining SOC target variables when controlling for soil depth. We conclude that despite long-lasting weathering, geochemical properties of soil parent material leave a footprint in tropical soils that affects SOC stocks and mineral-related C stabilization mechanisms. While identified stabilization mechanisms and controls are similar to less weathered soils in other climate zones, their relative importance is markedly different in the tropical soils investigated.

Multi-level methods to quantify risk assessment, source apportionment and identifying key risk areas of soil toxic elements in Ashi River watershed, China

With the advancement of small watershed governance in agricultural production process, soil toxic element pollution issue in watersheds constitutes a recent research hot spot. The Ashi River watershed is an agriculture-dominated small watershed which is exposed to toxic element sources, posing high risk of toxic element pollution to the planting areas. In this study, collection of soil samples was carried out along the periphery of the river network, and the soil physicochemical parameters and toxic elements (As, Cd, Cr, Cu, Pb, and Zn) were analyzed. The results showed that: (1) The geo-accumulation index (Igeo) and potential ecological risk index were used to evaluate the pollution degree, and the contents of As, Cd, and Zn in some sampling sites exceeded risk screening values. Moreover, soils closer to mining sources were found to be more polluted; (2) Redundancy analysis confirmed the contribution rate relationship between environmental factors and toxic elements. C/N ratio, total carbon (C), and total potassium (K) exhibited significant relationships with toxic elements (P < 0.01 or P < 0.05), respectively. Moreover, geographic locations (longitude, latitude, and elevation) showed significant impacts on toxic element contents (except for Cu); (3) The apportionment of toxic element pollution sources by using principal component analysis showed that Pb, Zn, Cu, and Cd were mainly related to mining activities, while As was closely related to insecticide and herbicide, and Cr was mainly related to soil parent material and electroplating factory; (4) Through the integrated resistance base surface and toxic element sources combined with minimum cumulative resistance model, the toxic element risk areas were identified. The middle reaches corresponded to the extremely high risk zone, which undeniably requires the strengthening of the environmental management.

Accumulation and relationship of metals in different soil aggregate fractions along soil profiles

Different aggregates vary in their ability to retain or adsorb metals in soil. Five soil profiles were sampled from different soil horizons and grouped, and the concentrations of Al, Mg, Ca, Fe, Mn, Cd, Cu and Pb were determined in six sizes of aggregates (> 2, 2-1, 1-0.6, 0.6-0.25, 0.25-0.053, < 0.053 mm). Significantly high (p < 0.05) structural stability indexes (SSI) and aggregate stability indexes (ASI) were recorded in the topsoil horizon, which may be attributed to the high soil organic matter (SOM) content in aggregates from topsoil. In addition, ASI and SSI were positively correlated (r = 0.569, p < 0.05) with each other, which indicated that the stability of soil aggregates could contribute to the structural stability of bulk soil. Moreover, accumulation factors (AF), principal component analysis (PCA) and Pearson's correlation coefficients were used for metal element assessment. The results indicated that SOM was not a key factor affecting the accumulation of Ca, Mg, Al, Fe, Mn, Pb, Cd and Cu in soil aggregates. In general, AF values for metal elements in microaggregates (< 0.25 mm) were high, which showed that metals preferred to accumulate in fine soil aggregates. The PCA and Pearson's correlation coefficients indicated that soil parent materials primarily controlled the distribution of Al, Ca, Fe, Mg and Mn, while materials derived from technogenic sources have important impacts on the distribution of Cd, Cu and Pb in soil aggregates along the soil profile.

Interaction effects of environmental factors on soil nitrogen fractions based on a novel sequential extraction method

AbstractSoil nitrogen (N) is controlled by several environmental factors. However, it is unclear how these factors and their interactions affect soil N fractions (SNFs) because of the lack of systematic N extraction methods. The Harbin–Dali belt, a transect more than 3,300 km long across China covering various climates, topographies, soil parent materials and vegetation types, was taken as the study area, and the interactive effects on SNFs in largely undisturbed woodlands and grasslands were explored using three SNFs: labile N, moderately stable N and stable N. The soil N fractions were obtained through a novel sequential extraction method that used distilled H2O, 0.5 M CaCl2, 1 M HCl, 6 M HCl, mixed acid (1 M HCl and 5 M HF; MA), concentrated HCl (cHCl) and concentrated H2SO4 as extractive agents to successively separate H2O‐, CaCl2‐, 1 M HCl‐, 6 M HCl‐, MA‐, cHCl‐ and RES‐N fractions. The results showed that increasing mean annual temperature (MAT) directly decreased the concentrations of H2O‐, CaCl2‐ and 1 M HCl‐N, suggesting that warming may reduce available N. The interactions between MAT, parent material, aspect and aridity index also contributed to the three SNFs. Vegetation and its interactions with parent material primarily controlled 6 M HCl‐, cHCl‐ and RES‐N, and climate and topography had indirect effects during these processes. Particularly, more cHCl‐ and RES‐N were accumulated in areas with warm humid climates and rich vegetation species than in other environments. Moreover, soil labile N (H2O‐, CaCl2‐ and 1 M HCl‐N) and cHCl‐N exhibited potential as sensitive indicators for reflecting the changes in MAT and vegetation, respectively. Therefore, the various interactions between climate and other environmental factors controlled the changes in most SNFs. This novel sequential extraction method thus offers a reliable analytical approach to measuring SNFs.Highlights Soil nitrogen fractions (SNFs) were fractionated via a novel sequential extraction method. Increasing MAT decreased the H2O‐, CaCl2‐ and 1 M HCl‐N concentrations. Interactions of climate, parent material and vegetation affected 6 M HCl‐, MA‐, cHCl‐ and RES‐N. H2O‐, CaCl2‐, 1 M HCl‐ and cHCl‐N are sensitive SNFs that reflect environmental changes.

Analysis of Spatial Distribution and Influencing Factors of Nitrogen and Phosphorus Fertilizer Application Intensity in Chengdu Plain

The spatial distribution of fertilization intensity and its influencing factors are significant for the accurate management of fertilization and pollution prevention and control. Previous studies are mostly limited to the discussion of human factors that influences the spatial distribution of fertilization intensity while ignoring natural geographical factors. Based on the chemical fertilizer survey data collected from 23492 sites in Chengdu Plain and combined with Geostatistics analysis and Geographic Information System (GIS) technology, the spatial distribution characteristics and influencing factors of average nitrogen and phosphorus fertilizer application intensity from 2010 to 2015 in this region were explored. The results show that:① the average annual application intensity of nitrogen and phosphorus fertilizer in the study area from 2010 to 2015 is generally in the low and medium risk intensity of 120-360 kg·hm-2 and 60-180 kg·hm-2. The high risk intensity is mainly distributed in the grain (fruit) and vegetable growing areas such as Pidu, Pengzhou, Shifang, Longquanyi and Jintang, while the relatively low value areas are mostly distributed in the south and northeast. ② the nugget coefficients of nitrogen and phosphorus fertilizer application intensities are 66.17% and 41.60%. Their spatial distribution is determined by structural and random factors, showing a moderate spatial autocorrelation. ③ both human and natural factors have significant effects on the application intensity of nitrogen and phosphorus fertilizer. The crop type (fine classification) can explain the spatial variation of nitrogen fertilizer and phosphorus fertilizer respectively by 12.90% and 25.10%, which is the main controlling factor affecting the spatial distribution of nitrogen and phosphorus application intensity; the importance of soil parent material is second only to the planting crop type, and the independent explanation ability of phosphorus application intensity is about 3.6 times higher than that of nitrogen application intensity. When the type of planting crop plays a decisive role, the soil parent material still deeply restricts and affects the spatial distribution of nitrogen and phosphorus fertilizer application intensity in the study area. Therefore, the comprehensive effects of planting crop types and soil parent materials should be considered in fertilization management and environmental risk analysis, and the effects of soil parent material should also be taken into account in the application of phosphate fertilizer.

Spatial Distribution Trends and Influencing Factors of Typical Heavy Metals in Subtropical Alpine Forest Soils: A Case Study from Ailao Mountain in Yunnan Province

In this study, we hypothesized that the distribution patterns of trace metal elements in montane regions would be controlled by the local climate, human activities, vegetation distribution and soil development. Hence, we selected nine forest sites among the elevation of 850 m to 2650 m on the windward (western slope) and leeward (eastern slope) slopes of Ailao Mountain in Yunnan Province of China to determine the typical heavy metal concentrations in forest surface soils, and their differences for distribution trends along with the increasing elevations, and the corresponding environmental factors. The results showed that surface soil Cd, Sb, As, Cr, and Pb had relatively higher concentrations and distinct enrichment factors both on eastern and western slopes. Specifically, the concentrations of Cd and Sb in surface soils of the eastern and western slopes and Pb on the western slope all had obvious altitude distribution trends, which showed their concentrations increased with the increasing elevation. In addition, we found the concentrations of Cd, Sb, As, and Cr in surface soils of the western slope were significantly higher than those of the eastern slope at the same altitude. The correlation analysis and principal component analysis further depicted that the elevation trends of Cd and Sb were mainly controlled by the strong combining effects from long-range atmospheric input and soil organic matter strong absorption, and there was an obvious "cold trapping" effect in high altitude areas. The distribution variations of As and Cr were mainly derived from the weathering difference of soil parent material, while the variations for Pb were controlled by the weathering of bedrock minerals. This study highlights the important role of combining effects from long-range atmospheric input, and from precipitation and vegetation (such as "cold trapping" effect, promoting canopy filtration, litterfall deposition and bedrock weathering) on the distribution trends of trace metals in remote alpine soils.

Vertical distribution characteristics of soil mercury and its formation mechanism in permafrost regions: A case study of the Qinghai-Tibetan Plateau

Continuing permafrost degradation is increasing the risk of mercury (Hg) exposure in the permafrost regions on the Qinghai-Tibetan Plateau (QTP), but related studies are still limited, especially the ones on the detailed Hg migration processes in permafrost. The vertical distribution characteristics of soil Hg were investigated in three ecosystems in the Beiluhe area on the QTP, and its influencing factors and formation mechanism were investigated. The results indicate that the total soil mercury (THg) concentration in the Beiluhe area remains at an extremely low level (6.33 ± 2.45 ng/g). In the vertical profile, the THg concentration of the shallow soil layer (0–50 cm) (5.96 ± 2.22 ng/g) is significantly lower than that of the deep layer (50–400 cm) (7.44 ± 2.71 ng/g) (p < 0.05). Within the upper 50 cm, the THg concentration decreases with soil depth, and the peak THg concentration occurs at 100–300 cm on the entire profile. Although the THg concentration is slightly affected by the organic matter in the shallow soil layer, in general, the soil parent material is the dominant factor affecting the THg concentration. Intense weathering results in a low THg concentration in the shallow soil layer because the soil Hg is carried downward with the soil moisture. To a certain depth, the impermeable frozen soil layer intercepts the flow of the soil Hg, and it forms a Hg enrichment layer. This paper presents the distinctive pattern of the soil Hg distribution in the permafrost regions of the QTP.

Nickel in forests – a short review on its distribution and fluxes

Abstract The distribution and cycling of nickel (Ni) in forests is greatly affected by their proximity to emission sources of the metal. The throughfall deposition is always richer in Ni than the bulk deposition. It can be inferred that some dry deposition enriches the throughfall. In remote forested areas, the hydrological fluxes of Ni do not differ a lot from those in litterfall. In addition, the current year needles in conifers have higher concentrations than the older needles, a sign of absorption and mobility of the metal. In contrast, near an industrial Ni source the older needles accumulate much more of the metal. The Ni content in bark tissue can be used to map the deposition distribution of the metal around an area (rural or urban). The concentrations of Ni in forest soils is also dependent on their distances from the Ni emission sources and the nature of the soil parent material. The Ni concentrations increase with soil depth due to the geogenic origin of the metal. Low pH greatly enhances the mobility of the metal in soils, much more than the leachability of organic matter.