Soil Organic Layer Research Articles

Long-term deepened snow promotes tundra evergreen shrub growth and summertime ecosystem net CO2 gain but reduces soil carbon and nutrient pools.

Arctic climate warming will be primarily during winter, resulting in increased snowfall in many regions. Previous tundra research on the impacts of deepened snow has generally been of short duration. Here, we report relatively long-term (7-9years) effects of experimentally deepened snow on plant community structure, net ecosystem CO2 exchange (NEE), and soil biogeochemistry in Canadian Low Arctic mesic shrub tundra. The snowfence treatment enhanced snow depth from 0.3 to ~1m, increasing winter soil temperatures by ~3°C, but with no effect on summer soil temperature, moisture, or thaw depth. Nevertheless, shoot biomass of the evergreen shrub Rhododendron subarcticum was near-doubled by the snowfences, leading to a 52% increase in aboveground vascular plant biomass. Additionally, summertime NEE rates, measured in collars containing similar plant biomass across treatments, were consistently reduced ~30% in the snowfenced plots due to decreased ecosystem respiration rather than increased gross photosynthesis. Phosphate in the organic soil layer (0-10cm depth) and nitrate in the mineral soil layer (15-25cm depth) were substantially reduced within the snowfences (47-70 and 43%-73% reductions, respectively, across sampling times). Finally, the snowfences tended (p=.08) to reduce mineral soil layer C% by 40%, but with considerable within- and among plot variation due to cryoturbation across the landscape. These results indicate that enhanced snow accumulation is likely to further increase dominance of R.subarcticum in its favored locations, and reduce summertime respiration and soil biogeochemical pools. Since evergreens are relatively slow growing and of low stature, their increased dominance may constrain vegetation-related feedbacks to climate change. We found no evidence that deepened snow promoted deciduous shrub growth in mesic tundra, and conclude that the relatively strong R.subarcticum response to snow accumulation may explain the extensive spatial variability in observed circumpolar patterns of evergreen and deciduous shrub growth over the past 30years.

Vegetation Succession on Degraded Sites in the Pomacochas Basin (Amazonas, N Peru)—Ecological Options for Forest Restoration

The Andes of northern Peru are still widely covered with forests, but increasingly suffer from habitat fragmentation. Subsequent soil degradation often leads to the abandonment of overused forests and pastures. Ecological knowledge on the restoration potential, e.g., on dependencies of soil conditions and altitude, is scarce. Therefore, we compared soil and vegetation patterns along nine transects within the upper Pomacochas Basin, which is an important biodiversity corridor along the Andes, between remaining forests, succession sites and pastures. Anthropogenic successional and disturbance levels, geological substrate, and altitude have the most important ecological impacts on vegetation and tree species composition. Species responded to sandstone versus calcareous substrates, but also to depths of the organic soil layer, and light conditions. The absence of organic layers under pastures contrasted with the accumulation of thick organic layers under forest cover. Vegetation composition at succession sites revealed certain starting points (herbal stage, bush stage, or secondary forest) for restoration that will determine the length of regeneration paths. Pre-forest patches of Alchornea sp. and Parathesis sp. may act as habitat stepping stones for expeditiously restoring biocorridors for wildlife. The key findings can contribute to the sustainable use and conservation of biodiversity in a fragile ecoregion.

Pesticide fate modelling in conservation tillage: Simulating the effect of mulch and cover crop on S-metolachlor leaching

Conservation tillage practices mainly based on cover crops and no-tillage with accumulation of crop residues at the soil surface (mulch) modify the environmental fate of pesticides. However, only few pesticide fate models are able to consider mulch of crop residues as well as the effect of intermediate cover crops. Thus, the objective was to develop an approach to model the effects of crop residues left at the soil surface and cover crops on the fate of pesticides. This approach consisted in (1) considering the crop residues as a soil layer with specific physical, hydrodynamic and pesticide-reactivity properties close to that of a high organic content soil layer, and (2) introducing a correction factor of the potential evapotranspiration, estimated through a calibration step, to take into account the reduction of soil evaporation by the presence of a mulch. This approach was developed using MACRO as support pesticide model. To assess the model performances, we used the data from a field experiment designed in an irrigated maize monoculture under conservation tillage. Soil water content, water percolates, soil temperature and S-metolachlor herbicide concentrations in the leachate at 1m depth were measured during two years. The approach chosen to simulate the mulch effects allowed MACRO to make acceptable predictions of the observed water percolation, soil temperature and to a less extent herbicide leaching. However, it showed a poor performance to simulate the soil water content. Results are discussed in terms of further modelling options to better assess the environmental risks of pesticides under conservation tillage. This approach remains to be tested against various soils, crops, pesticides and types of mulch.

Carbon and nitrogen pools in thermokarst-affected permafrost landscapes in Arctic Siberia

Abstract. Ice-rich yedoma-dominated landscapes store considerable amounts of organic carbon (C) and nitrogen (N) and are vulnerable to degradation under climate warming. We investigate the C and N pools in two thermokarst-affected yedoma landscapes – on Sobo-Sise Island and on Bykovsky Peninsula in the north of eastern Siberia. Soil cores up to 3 m depth were collected along geomorphic gradients and analysed for organic C and N contents. A high vertical sampling density in the profiles allowed the calculation of C and N stocks for short soil column intervals and enhanced understanding of within-core parameter variability. Profile-level C and N stocks were scaled to the landscape level based on landform classifications from 5 m resolution, multispectral RapidEye satellite imagery. Mean landscape C and N storage in the first metre of soil for Sobo-Sise Island is estimated to be 20.2 kg C m−2 and 1.8 kg N m−2 and for Bykovsky Peninsula 25.9 kg C m−2 and 2.2 kg N m−2. Radiocarbon dating demonstrates the Holocene age of thermokarst basin deposits but also suggests the presence of thick Holocene-age cover layers which can reach up to 2 m on top of intact yedoma landforms. Reconstructed sedimentation rates of 0.10–0.57 mm yr−1 suggest sustained mineral soil accumulation across all investigated landforms. Both yedoma and thermokarst landforms are characterized by limited accumulation of organic soil layers (peat). We further estimate that an active layer deepening of about 100 cm will increase organic C availability in a seasonally thawed state in the two study areas by ∼ 5.8 Tg (13.2 kg C m−2). Our study demonstrates the importance of increasing the number of C and N storage inventories in ice-rich yedoma and thermokarst environments in order to account for high variability of permafrost and thermokarst environments in pan-permafrost soil C and N pool estimates.

Influences of fine-scale disturbance on germinant success in a treeline ecotone

ABSTRACTFine-scale disturbance can increase seed access to suitable substrates, facilitating germinant emergence and survival, which are necessary elements for treeline advance. We conducted an experiment to test this hypothesis in a white spruce (Picea glauca) treeline ecotone in southwest Yukon, Canada. Sixty seed germination quadrats were established at two elevations (treeline and alpine tundra) and subjected to three levels of simulated disturbance. We sowed 125 seeds in half of the quadrats (30) and measured their emergence and survival over 3 years. Soil temperature, moisture, and organic depth were recorded in all treatments. Treeline quadrats had significantly greater seedling emergence and survival than alpine tundra quadrats. Mean soil temperature, moisture, and organic layer depth were all greater in treeline quadrats. Partially scarified quadrats had the highest germinant emergence compared to unscarified and completely scarified quadrats. Completely scarified quadrats had the highest temperature range and the lowest soil moisture. The results indicate that moderate levels of disturbance can positively influence seedling emergence, while more severe disturbance can lead to high temperature ranges and moisture loss that negate the benefits of lower interspecific competition. Collectively, our findings suggest that fine-scale disturbance can play a significant role in influencing seedling presence in treeline ecotones.

Inferring changes in soil organic matter in post-wildfire soil burn severity levels in a temperate climate

Simple, rapid and reliable methods of assessing soil burn severity (SBS) are required in order to prioritize post-fire emergency stabilization actions. SBS proxies based on visual identification and changes in soil organic matter (SOM) content and quality can be related to other soil properties in order to determine the extent to which soil is perturbed following fire. This task is addressed in the present study by an approach involving the use of differential scanning calorimetry-thermogravimetric analysis (DSC-TGA) to determine changes in SOM generated in soils subjected to different levels of SBS.Intact topsoil monoliths comprising the organic horizons and the surface mineral soil (alumic-humic umbrisols) were collected from a representative P. pinaster stand in NW Spain. The monoliths were experimentally burned in a combustion wind tunnel to simulate different fire conditions (fuel bed comprising forest pine litter and wood; air flow, 0.6 m s−1). Changes in OM properties in the soil organic layer and mineral soils samples (0–2 cm) at the different temperatures and SBS levels were identified.For both duff and mineral soil, the data revealed a temperature-induced increase in aromatic compounds and a concomitant decrease of carbohydrates and alkyl products. However, for a given temperature, the degree of carbonization/aromatization was lower in the mineral soil than in the duff, possibly due to the different composition of the OM and to the different combustion conditions. The low degree of aromatization of the organic matter suggests that this soil component could undergo subsequent biological degradation. SOM content and thermal recalcitrance (measured as T50) discriminated the SBS levels. Use of visual identification of SBS levels in combination with DSC-TGA enables rapid evaluation of the spatial variability of the effects of fire on SOM properties. This information is useful to predict soil degradation process and implement emergency soil stabilization techniques.

高山森林林窗对苔藓及土壤微量元素含量的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 高山森林林窗对苔藓及土壤微量元素含量的影响 DOI: 10.5846/stxb201703020342 作者: 作者单位: 四川农业大学,四川农业大学,四川农业大学,四川农业大学,四川农业大学,四川农业大学,四川农业大学,四川农业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31570445，31500509） Effects of forest gaps on microelement concentrations of mosses and soil in an alpine forest Author: Affiliation: Sichuan Agricultural University,Sichuan Agricultural University,Sichuan Agricultural University,Sichuan Agricultural University,Sichuan Agricultural University,Sichuan Agricultural University,Sichuan Agricultural University,Sichuan Agricultural University Fund Project: The National Natural Science Foundation of China (General Program, Key Program, Major Research Plan) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:苔藓植物和土壤在森林元素循环过程中具有重要作用，其元素含量特征可能受林窗和生长基质的影响，但有关不同林窗位置对苔藓和土壤微量元素含量影响的研究尚未见报道。为理解林窗更新对森林苔藓和土壤微量元素含量及分布特征的影响，于2016年10月，调查研究了在川西高山岷江冷杉（Abies faxoniana）原始林林下、林缘、林窗和旷地中地表苔藓和石生苔藓Na、Zn、Mg、Mn、Ca、Fe元素含量以及对应土壤有机层和矿质土壤层的元素含量。结果表明：川西高山森林地表苔藓与石生苔藓的Na、Zn、Mg、Fe、Ca含量差异不显著，地表苔藓的Mn元素含量显著高于石生苔藓；土壤有机层的Zn、Mg、Mn和Ca元素含量显著高于矿质土壤层，但Fe元素含量则相反，Na元素含量差异不显著。林窗位置对地表苔藓和石生苔藓Na、Zn、Ca和Fe元素含量具有相似的影响，均以林窗和旷地相对较高；石生苔藓与地表苔藓的Mn含量对林窗的响应存在差异，石生苔藓的Mn含量以林下最高，而地表苔藓则以林窗中心最高。但是，林窗对苔藓植物Mg元素含量的影响不显著。森林林窗位置对土壤有机层和矿质土壤层微量元素含量具有相似的影响。Na元素含量以旷地土壤最高，而Zn、Mn、Ca和Fe含量以林窗中心的土壤最高；除元素Na，所有微量元素均以林缘的土壤最低。此外，地表苔藓的Na、Zn、Mn和Ca含量显著高于土壤，而土壤中的Fe含量显著高于苔藓植物；苔藓中Ca和Mn元素含量与土壤的Ca和Mn元素含量呈显著正相关。可见，高山森林林窗更新过程在不同程度上影响了森林地表苔藓和土壤对微量元素的吸存特征，为进一步了解林窗和苔藓植物在高山森林生态系统物质循环中的作用提供了新的角度。 Abstract:Moss is an essential component in most forest ecosystems, and plays critical roles in material cycling and water retention. It is also an indicator of environmental change. An increasing numbers of studies have demonstrated that the growth and reproduction of mosses can be determined by light regime, substrate, and hydro-thermal dynamics. Theoretically, a forest gap might improve the growth and element uptakes by mosses on different growth substrates by altering the light regimes and the temperature and moisture dynamics on the forest floor through the redistribution of light and precipitation. As yet, the effects of forest gap position on microelement uptakes by mosses on different growth substrates remain unclear. To understand the effect of gap regeneration on microelement uptakes by mosses, the concentrations of sodium (Na), zinc (Zn), magnesium (Mg), manganese (Mn), calcium (Ca), and iron (Fe) in epilithic and epigeic mosses, and in the soil organic and mineral soil layers were investigated in open areas, the gap center, the gap edge, and the closed canopy in an alpine fir (Abies faxoniana) forest in western Sichuan during October 2016. No significant differences for the concentrations Na, Zn, Mg, Fe, and Ca were recorded between epilithic mosses and epigeic mosses, while the Mn concentration in epigeic mosses were significantly higher than those in epilithic mosses. The Zn, Mg, Mn, and Ca concentrations in the soil organic layer were significantly higher than the mineral soil layer, but the Fe concentrations in the mineral soil layer were significantly higher than the soil organic layer. However, no significant difference was observed in Na concentrations between the soil organic layer and the mineral soil layer. Gap positions had similar effects on the concentrations of Na, Zn, Ca, and Fe in epilithic mosses and epigeic mosses, and the mosses in the gap center and open areas had higher Na, Zn, Ca, and Fe concentrations. In contrast, different responses to gap positions were found in Mn concentrations between epilithic and epigeic mosses. Higher Mn concentrations in epilithic moss were found in the microenvironment under the closed canopy, whereas higher Mn concentrations in epigeic moss were observed in the gap center microenvironment. However, gap positions had only slight effects on Mg concentrations in moss plants. Forest gap positions had similar effects on microelement concentrations in the soil organic layer and mineral soil layer. Higher Na concentrations in the soil organic and mineral soil layers were found in the open area, while higher Zn, Mn, Ca, and Fe concentrations in the soils were found at the gap center. The lowest concentrations of the measured microelements in the soil organic and the mineral soil layers were found at the gap edge. In addition, the Na, Zn, Mn, and Ca concentrations in epigeic mosses were significantly higher than those in the corresponding soils, while the Fe concentrations showed an opposite trend. Furthermore, the Ca and Mn concentrations in moss plants correlated positively and significantly with the Ca and Mn concentrations in the corresponding soils. In conclusion, gap regeneration affects microelement sequestration by mosses and soils in an alpine forest, which provides new insights into the roles of forest gap regeneration and mosses on bioelement cycles in the alpine forest ecosystem. 参考文献 相似文献 引证文献

Soil organic layer combustion in boreal black spruce and jack pine stands of the Northwest Territories, Canada

Increased fire frequency, extent and severity are expected to strongly affect the structure and function of boreal forest ecosystems. In this study, we examined 213 plots in boreal forests dominated by black spruce (Picea mariana) or jack pine (Pinus banksiana) of the Northwest Territories, Canada, after an unprecedentedly large area burned in 2014. Large fire size is associated with high fire intensity and severity, which would manifest as areas with deep burning of the soil organic layer (SOL). Our primary objectives were to estimate burn depth in these fires and then to characterise landscapes vulnerable to deep burning throughout this region. Here we quantify burn depth in black spruce stands using the position of adventitious roots within the soil column, and in jack pine stands using measurements of burned and unburned SOL depths. Using these estimates, we then evaluate how burn depth and the proportion of SOL combusted varies among forest type, ecozone, plot-level moisture and stand density. Our results suggest that most of the SOL was combusted in jack pine stands regardless of plot moisture class, but that black spruce forests experience complete combustion of the SOL only in dry and moderately well-drained landscape positions. The models and calibrations we present in this study should allow future research to more accurately estimate burn depth in Canadian boreal forests.

ПРОСТРАНСТВЕННОЕ ВАРЬИРОВАНИЕ СОДЕРЖАНИЯ ВТОРИЧНЫХ МЕТАБОЛИТОВ, УГЛЕРОДА И АЗОТА В ПОДСТИЛКАХ СЕВЕРОТАЕЖНЫХ ЕЛЬНИКОВ*, "Лесоведение"

ПРОСТРАНСТВЕННОЕ ВАРЬИРОВАНИЕ СОДЕРЖАНИЯ ВТОРИЧНЫХ МЕТАБОЛИТОВ, УГЛЕРОДА И АЗОТА В ПОДСТИЛКАХ СЕВЕРОТАЕЖНЫХ ЕЛЬНИКОВ*, "Лесоведение"

Recovery of carbon pools a decade after wildfire in black spruce forests of interior Alaska: effects of soil texture and landscape position

We measured organic-layer (OL) recovery and carbon stocks in dead woody debris a decade after wildfire in black spruce (Picea mariana (Mill.) B.S.P.) forests of interior Alaska. Previous study at these research plots has shown the strong role that landscape position plays in governing the proportion of OL consumed during fire and revegetation after fire. Here, we show that landscape position likely influences fire dynamics in these stands through changes in mineral soil texture. The content of fine-textured materials in underlying mineral soils was positively related to OL depths measured 1 and 10 years after fire, and there was an interaction between soil texture and elevation in governing OL consumption and OL recovery a decade following fire. OL depths 10 years after fire were 2 cm greater than 1 year after fire, with a range of 19 cm of accumulation to 9 cm of subsidence. Subsidence was inversely related to the percentage of fine textures within the parent material. The most influential factor determining the accumulation of OL carbon stocks a decade following wildfire was the interaction between landscape position and the presence of fine-textured soil. As such, parent material texture interacted with biological processes to govern the recovery of soil organic layers.

Variability of undrained shear strength cu within one organic soli layer

For the purpose of this article a program of geotechnical laboratory tests was performed on organic soil (mud) samples from one geological layer. All undisturbed samples were taken within the same excavation in square grid with a side about 30 cm. Differences between specimen parameters were found both at basic test results and at shear strength tests results. Based on all performed tests authors suggest carefulness in assuming geotechnical parameters of organic soil layers because of theirs spatial variability even in very close vicinity.

Long-term effects of forest liming on mineral soil, organic layer and foliage chemistry: Insights from multiple beech experimental sites in Northern France

Abstract Most forest ecosystems grow on acid and nutrient poor soils. In many cases, a slow degradation of forest soil chemical fertility due to increasing external pressures (decreasing atmospheric inputs, intensification of biomass harvesting and silvicultural practices) has been observed and is a growing concern in the international forest community. When the pressure endured by low fertility forest ecosystems is too intense, nutrient losses and ecosystem function losses may occur, forest decline being the ultimate stage of this process. In such cases, forest liming with a carbonate product is a solution to restore soil fertility and reduce soil acidity, globally improve the ecosystem functioning and compensate for nutrient losses caused by biomass harvest and exportation. However, the effects of liming on ecosystem processes and the biogeochemical cycling of nutrients in forest ecosystems are still unclear. We studied the dynamics of magnesium and calcium originating from the dissolution of liming products in the different compartments (organic and mineral soil layers and, aboveground biomass) of five long-term (20 to 40 years) monitoring beech (Fagus sylvatica L.) plots located in Northern France from ecosystem magnesium and calcium budgets. Compared to the control plots, soil exchangeable pools of Mg and Ca in the 0–15 cm mineral soil layer increased during the first decade after liming but these differences rapidly decreased after 20–30 years. The effect of liming on foliar concentrations and tree growth was still observed after 40 years, most probably because the biological cycling of these elements was more dynamic in the limed plots. Liming increased the decomposition rate of the soil organic layer but the pools of Mg and Ca in this layer remained relatively stable over time, probably because Mg and Ca concentrations in foliage and litterfall increased after the liming. Liming effects varied between sites depending on the liming product and amount, and the initial chemical fertility level of the soil. Although liming operations may help improve forest soil fertility, they may also generate nutrient deficiencies and/or imbalances for nutrients that are poorly available in the soil. The planning of liming operations therefore necessitates a thorough soil chemical fertility diagnosis.

Phosphorus Availability Determines the Response of Tundra Ecosystem Carbon Stocks to Nitrogen Enrichment

Northern permafrost soils contain important carbon stocks. Here we report the long-term response of carbon stocks in high Arctic dwarf shrub tundra to short-term, low-level nutrient enrichment. Twenty years after experimental nitrogen addition, carbon stocks in vegetation and organic soil had almost halved. In contrast, where phosphorus was added with nitrogen, carbon storage increased by more than 50%. These responses were explained by changes in the depths of the moss and organic soil layers. Nitrogen apparently stimulated decomposition, reducing carbon stocks, whilst phosphorus and nitrogen co-stimulated moss productivity, increasing organic matter accumulation. The altered structure of moss and soil layers changed soil thermal regimes, which may further influence decomposition of soil carbon. If climate warming increases phosphorus availability, any increases in nitrogen enrichment from soil warming or expanding human activity in the Arctic may result in increased carbon sequestration. Where phosphorus is limiting in tundra areas, however, nitrogen enrichment may result in carbon loss.

Fuel-reduction management alters plant composition, carbon and nitrogen pools, and soil thaw in Alaskan boreal forest.

Increasing wildfire activity in Alaska's boreal forests has led to greater fuel-reduction management. Management has been implemented to reduce wildfire spread, but theecological impacts of these practices are poorly known. We quantified the effects of hand-thinning and shearblading on above- and belowground stand characteristics, plant species composition, carbon (C) and nitrogen (N) pools, and soil thaw across 19 sites dominated by black spruce (Picea mariana) in interior Alaska treated 2-12years prior to sampling. The density of deciduous tree seedlings was significantly higher in shearbladed areas compared to unmanaged forest (6.4 vs. 0.1 stems/m2 ), and unmanaged stands exhibited the highest mean density of conifer seedlings and layers (1.4 stems/m2 ). Understory plant community composition was most similar between unmanaged and thinned stands. Shearblading resulted in a near complete loss of aboveground tree biomass C pools while thinning approximately halved the C pool size (1.2kg C/m2 compared to 3.1kg C/m2 in unmanaged forest). Significantly smaller soil organiclayer (SOL) C and N pools were observed in shearbladed stands (3.2kg C/m2 and 116.8g N/m2 ) relative to thinned (6.0kg C/m2 and 192.2g N/m2 ) and unmanaged (5.9kg C/m2 and 178.7g N/m2 ) stands. No difference in C and N pool sizes in the uppermost 10cm of mineral soil was observed among stand types. Total C stocks for measured pools was 2.6kg C/m2 smaller in thinned stands and 5.8kg C/m2 smaller in shearbladed stands when compared to unmanaged forest. Soil thaw depth averaged 13cm deeper in thinned areas and 46cm deeper in shearbladed areas relative to adjacent unmanaged stands, although variability was high across sites. Deeper soil thaw was linked to shallower SOL depth for unmanaged stands and both management types, however for any given SOL depth, thaw tended to be deeper inshearbladed areas compared to unmanaged forest. These findings indicate that fuel-reduction management alters plant community composition, C and N pools, and soil thaw depth, with consequences for ecosystem structure and function beyond those intended for fire management.

Linking major and trace element concentrations in a headwater stream to DOC release and hydrologic conditions in a bog and peaty riparian zone

In the organic-rich environments of peatlands and peaty riparian zones, dissolved organic matter (DOM) can act as a carrier for major and trace elements. However, the mobilization and export patterns of elements from these systems are largely unknown. This study elucidates the annual and short-term event-based dynamics of major and trace element concentrations in a headwater stream draining an ombrotrophic peatland and a peaty riparian zone. Elements are expected to exhibit specific export patterns depending on their biogeochemical reactivity and source area. We hypothesize that most elements are released during organic matter decomposition and are co-transported with DOM in the bog catchment, whereas in the riparian zone, other element pools, such as shallow groundwater, also play a major role.Most of the variance in the data, as revealed by Principal Component Analysis, integrated the DOM concentration pattern (element loadings > 0.8: Al, Ca, Fe, Mg, Mn, Zn, Li, Co, As, Sr, Cd, Pb, and DOC). Ca, Mg and Sr were also found to load on this principal component, suggesting that the main control on element mobilization is not DOM, but rather similar source areas and mobilization processes. The DOM-related export was driven by plant uptake, plant decomposition and the bog water level in terms of hydrologic connectivity. The differences between the bog and the riparian zone were mainly driven by different hydrologic conditions and additional elemental sources, such as mineral weathering. The export patterns of Rb, Cs, K, NO3− and SO42− were predominantly controlled by the season and plant uptake, and they were particularly exported by a surficial fast flow path. In addition to other elements, Ga, Y and Ba were enriched in the upper peat and organic soil layer, likely due to anthropogenic pollution. The specific export pattern of these latter elements indicates their predominant mobilization by the dissolution of dust particles and their subsequent mobilization by coupling to DOM.

Evaluation and enhancement of permafrost modeling with the NASA Catchment Land Surface Model.

Besides soil hydrology and snow processes, the NASA Catchment Land Surface Model (CLSM) simulates soil temperature in six layers from the surface down to 13m depth. In this study, to examine CLSM's treatment of subsurface thermodynamics, a baseline simulation produced subsurface temperatures for 1980-2014 across Alaska at 9-km resolution. The results were evaluated using in situ observations from permafrost sites across Alaska. The baseline simulation was found to capture the broad features of inter- and intra-annual variations in soil temperature. Additional model experiments revealed that: (i) the representativeness of local meteorological forcing limits the model's ability to accurately reproduce soil temperature, and (ii) vegetation heterogeneity has a profound influence on subsurface thermodynamics via impacts on the snow physics and energy exchange at surface. Specifically, the profile-average RMSE for soil temperature was reduced from 2.96°C to 2.10°C at one site and from 2.38°C to 2.25°C at another by using local forcing and land cover, respectively. Moreover, accounting for the influence of soil organic carbon on the soil thermal properties in CLSM leads to further improvements in profile-average soil temperature RMSE, with reductions of 16% to 56% across the different study sites. The mean bias of climatological ALT is reduced by 36% to 89%, and the RMSE is reduced by 11% to 47%. Finally, results reveal that at some sites it may be essential to include a purely organic soil layer to obtain, in conjunction with vegetation and snow effects, a realistic "buffer zone" between the atmospheric forcing and soil thermal processes.

Vertical distribution of 137Cs in the contaminated soil of a spruce forest in Southern Germany 12 years after regeneration cutting

Abstract The Chernobyl fallout of 1986 contaminated soils in Southern Germany. Levels of 137Cs activity still remain high in forest soils. The contamination of forest food products still poses a serious problem for consumer health. Silvicultural interventions may offer an option to reduce the bioavailability of 137Cs. The objective of this study is to investigate a possible effect of canopy opening and clearcutting as well as the selection of conifers and broadleaves for stand regeneration on the vertical soil profile of 137Cs. The investigation uses a long-term silvicultural experiment on the artificial regeneration of a spruce stand 30 km southwest of the town Augsburg, Germany. 12 years after silvicultural intervention soil samples were taken horizon-wise and analysed to compare among the treatments. A suite of soil physical and chemical properties was determined per horizon including 137Cs radioactivity, total carbon, texture, and cation exchange capacity. The results show that (i) the 137Cs contamination at this site is high compared to other sites in Central Europe, (ii) regeneration cuttings did not markedly change the vertical 137Cs profile in general within one decade, (iii) clear cutting modified the boundary between the organic soil layer and the mineral soil with expectable effects on the future 137Cs bioavailability.

Mechanical Parameters of Rubber-Sand Mixtures for Numerical Analysis of a Road Embankment

Waste production is one of the greatest problems of the modern world. It is inevitably related to the increase of industrialization. One of the most difficult, and growing in amounts, waste is scrap tyres. The most common method of utilization of end-of-life tyres by their incineration raises much concern in terms of air pollution. More sustainable seems to reuse the tyre derived products – rubber in particular – in civil engineering, where the interesting properties of this material may be effectively utilized. This paper presents results of direct shear strength tests on sand-rubber mixtures, which were next applied to a numerical FEM (finite element method) model of a road embankment built on soft ground. The laboratory tests, conducted for two types of scrap tyre rubber granulates (0.5 – 2 mm and 1 – 5 mm in size) mixed with medium fluvial sand in various proportions (5, 10, 30 and 50% by weight), proved that the unit weight of the mixtures is distinctly smaller that the unit weight of sand alone and at 50% rubber content it drops by half. The internal angle of friction stays almost unchanged for the mixtures with up to 10% of rubber (33 - 37°), but decreases by about 10° when the rubber content increases to 50%. In most of the cases analysed, the cohesion intercept is higher in case of sand-rubber mixtures when compared to sand alone. The numerical model simulated a 4.5 m high embankment with a 3 m thick layer made of sand-rubber mixtures, containing 0%, 10% or 30% of the waste product, founded on a weak subsoil (with a 3 m layer of organic soil). The results showed that stability factor of the structure built with the layer containing 30% of the coarser rubber granulate has increased from 1.60 – for sand only, to 2.15. The embankment was also able to carry load increased from 32 kPa to 45.5 kPa and its base showed much smaller settlement. The results prove that the use of tyre derived aggregates in embankment construction is not only an effective way of utilization of this problematic waste, but can also improve behaviour of such a structure.

Some Remarks on Practical Aspects of Laboratory Testing of Deep Soil Mixing Composites Achieved in Organic Soils

This paper presents the results of laboratory testing of organic soil-cement samples are presented in the paper. The research program continues previously reported the authors’ experiences with cement-fly ash-soil sample testing. Over 100 of compression and a dozen of tension tests have been carried out altogether. Several samples were waiting for failure test for over one year after they were formed. Several factors, like: the large amount of the tested samples, a long observation time, carrying out the tests in complex cycles of loading and the possibility of registering the loads and deformation in the axial and lateral direction – have made it possible to take into consideration numerous interdependencies, three of which have been presented in this work: the increments of compression strength, the stiffness of soil-cement in relation to strength and the tensile strength. Compressive strength, elastic modulus and tensile resistance of cubic samples were examined. Samples were mixed and stored in the laboratory conditions. Further numerical analysis in the Finite Element Method numerical code Z_Soil, were performed on the basis of laboratory test results. Computations prove that cement-based stabilization of organic soil brings serious risks (in terms of material capacity and stiffness) and Deep Soil Mixing technology should not be recommended for achieving it. The numerical analysis presented in the study below includes only one type of organic and sandy soil and several possible geometric combinations. Despite that, it clearly points to the fact that designing the DSM columns in the organic soil may be linked with a considerable risk and the settlement may reach too high values. During in situ mixing, the organic material surrounded by sand layers surely mixes with one another in certain areas. However, it has not been examined and it is difficult to assume such mixing already at the designing stage. In case of designing the DSM columns which goes through a thin layer of organic soil it is recommended to carry out each time the core drilling which checks the degree of material mixing and their strength.

Invasive earthworms erode soil biodiversity: A meta-analysis.

Biological invasions pose a serious threat to biodiversity and ecosystem functioning across ecosystems. Invasions by ecosystem engineers, in particular, have been shown to have dramatic effects in recipient ecosystems. For instance, invasion by earthworms, a below-ground invertebrate ecosystem engineer, in previously earthworm-free ecosystems alters the physico-chemical characteristics of the soil. Studies have shown that such alterations in the soil can have far-reaching impacts on soil organisms, which form a major portion of terrestrial biodiversity. Here, we present the first quantitative synthesis of earthworm invasion effects on soil micro-organisms and soil invertebrates based on 430 observations from 30 independent studies. Our meta-analysis shows a significant decline of the diversity and density of soil invertebrates in response to earthworm invasion with anecic and endogeic earthworms causing the strongest effects. Earthworm invasion effects on soil micro-organisms were context-dependent, such as depending on functional group richness of invasive earthworms and soil depth. Microbial biomass and diversity increased in mineral soil layers, with a weak negative effect in organic soil layers, indicating that the mixing of soil layers by earthworms (bioturbation) may homogenize microbial communities across soil layers. Our meta-analysis provides a compelling evidence for negative effects of a common invasive below-ground ecosystem engineer on below-ground biodiversity of recipient ecosystems, which could potentially alter the ecosystem functions and services linked to soil biota.