Soil Storage Capacity Research Articles

植物篱篱前淤积带与篱下土坎土壤水库和抗剪性能对比研究

PDF HTML阅读 XML下载 导出引用 引用提醒 植物篱篱前淤积带与篱下土坎土壤水库和抗剪性能对比研究 DOI: 10.5846/stxb201807061477 作者: 作者单位: 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（41501288）；中央高校基本科研业务费专项（XDJK2018B044）；重庆市基础科学与前沿技术研究一般项目（cstc2017jcyjAX0472）；西南大学资源环境学院"光炯"项目（201719） Comparative study on soil water reservoirs and shear strength between the sedimentation zone in front of and ridge behind hedgerows Author: Affiliation: Fund Project: 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:为探究紫色土坡地植物篱篱前淤积带与篱下土坎处土壤贮水能力和抗剪性能的差异及变化规律，选取四川遂宁水土保持试验站10°新银合欢植物篱小区（L10）、10°香根草植物篱小区（V10）和15°香根草植物篱小区（V15），分上、中、下坡采集篱前淤积带和篱下土坎（无下坡）0-30 cm耕层土壤，测定土壤基本物理性质和土壤抗剪强度，计算土壤水库总库容、滞洪库容、内摩擦角φ和粘聚力c。结果表明：（1）同一篱带，篱前淤积带土壤保水贮水能力优于篱下土坎，其中篱前淤积带土壤自然含水率较之篱下土坎显著高6.52%-12.13%。（2）同一篱带，篱下土坎土壤透气性以及土壤抗剪性能均优于篱前淤积带，其中篱下土坎土壤非毛管孔隙度较之篱前淤积带显著高5.61%-57.70%。（3）同一小区，篱前淤积带保水贮水能力均表现为下坡 > 中坡 > 上坡，而篱下土坎均为上坡>中坡。其中V15小区上述趋势最明显，其下坡篱前淤积带（上坡篱下土坎）的土壤总库容和滞洪库容分别为上坡篱前淤积带（均为中坡篱下土坎）的1.04倍和1.03倍（1.02倍）。（4）同一小区，篱前淤积带土壤内摩擦角、粘聚力c和抗剪强度均表现为上坡 > 中坡 > 下坡，篱下土坎均为上坡>中坡。其中V10小区上述趋势最明显，其上坡篱前淤积带（上坡篱下土坎）上述指标依次为下坡篱前淤积带（均为中坡篱下土坎）的1.06、1.09倍和1.05倍（1.04倍）。（5）一个雨季前后篱前淤积带和篱下土坎土壤透气性、保水贮水能力及抗剪性能均无显著变化。 Abstract:The aim of the present study was to explore the differences and variation of the water storage capacity of soil and shear performance between the sedimentation zone in front of and ridge behind hedgerows on Purple Soil Slopping Farmland. This study set 10° Leucaena leucocephala hedgerows (plot L10), 10° Vetiveria zizanioides hedgerows (plot V10), and 15° V. zizanioides hedgerows (plot V15), from the Soil and Water Conservation Experimental Station in Suining, Sichuan. There were sedimentation zones in front of the hedgerows on the up, middle, and down slopes and a ridge behind the hedgerows on the up and middle slopes at each plot. We collected samples of arable soil from these zones to a 30 cm depth. Some basic physical properties and shear strength of soil were measured, and soil total storage capacity, flood detention storage, internal friction angle φ, and cohesion c were calculated. The results showed that:(1) in the same plots, the water storage capacity of the sedimentation zone in front of the hedgerows was better than that of the ridges behind the corresponding hedgerows, and that the sedimentation zone had a higher natural water content by 6.52%-12.13%; (2) soil disturbance and shear resistance of the ridges behind the hedgerows were higher than that of the sedimentation zone in front of the corresponding hedgerows. The soil non-capillary porosity of ridges behind the hedgerows was significantly higher than that of the sedimentation zone in front of the hedgerows by 5.61%-57.70%; (3) in the same plot, the water storage capacity in the sedimentation zone in front of the hedgerows showed the following order:down slope > middle > up slope, and that of the ridge behind hedgerows was up > middle slope. This trend was obvious in plot V15; the soil total storage capacity and flood detention storage of the sedimentation zone in front of the hedgerows on the down slope were 1.04 times and 1.03 times higher than those of the up slope, respectively, and those of the ridge behind the hedgerows on the up slope were all 1.02 times higher than that of the middle slope; (4) in the same plot, the internal friction angle φ, cohesion c, and shear strength in the sedimentation zone in front of the hedgerows were in the order of up > middle > down slope, and that on the ridge behind the hedgerows were up > middle slope. This was evident in plot V10, where the internal friction angle φ, cohesion c, and shear strength of the sedimentation zone in front of the hedgerows on the up slope were 1.06, 1.09 and 1.05 times greater than those of the down slope, respectively. However, those of the ridge behind the hedgerows on the up slope were all 1.04 times higher than that of the middle slope; (5) the rainy season had no significant effect on soil disturbance, water storage capacity, and shear performance for both the sedimentation zone in front of and ridge behind the hedgerows. 参考文献 相似文献 引证文献

Mapping Geospatial Processes Affecting the Environmental Fate of Agricultural Pesticides in Africa.

The application of agricultural pesticides in Africa can have negative effects on human health and the environment. The aim of this study was to identify African environments that are vulnerable to the accumulation of pesticides by mapping geospatial processes affecting pesticide fate. The study modelled processes associated with the environmental fate of agricultural pesticides using publicly available geospatial datasets. Key geospatial processes affecting the environmental fate of agricultural pesticides were selected after a review of pesticide fate models and maps for leaching, surface runoff, sedimentation, soil storage and filtering capacity, and volatilization were created. The potential and limitations of these maps are discussed. We then compiled a database of studies that measured pesticide residues in Africa. The database contains 10,076 observations, but only a limited number of observations remained when a standard dataset for one compound was extracted for validation. Despite the need for more in-situ data on pesticide residues and application, this study provides a first spatial overview of key processes affecting pesticide fate that can be used to identify areas potentially vulnerable to pesticide accumulation.

Perceived Climate Variability and Farm Level Adaptation in the Central River Region of The Gambia

In Sub-Saharan Africa, the recurring erratic and uneven rainfall distribution has resulted in low crop yields, income losses, and low food stock. In response to these climate change challenges, farmers have recourse to several coping strategies to survive. This present paper explores farmers’ perception of climate variability and the coping strategies in use in the Central River Region of The Gambia. The main purpose of this paper is to analyze perceived climate variability and farm level adaptation options in the region. Data were collected from 283 farmhouses through transect walks, quantitative surveys including the use focus group discussions. Data were analyzed using descriptive and inferential statistics. Results revealed that farmers generally perceive an increase in the frequency of extreme weather events and a decrease in the duration of the growing season. With regards to vulnerability and severity, nearly 95% of the respondents considered the dryness as the main threat to their farming activities and perceived its consequences as the most severe. The results equally showed that the perception of changes is linked to the adoption of some adaptation measures among which the preferred were the use of chemical fertilizers (66%), though it is stated to be the most expensive. The Spearman correlation test showed that the use of water conservation techniques is highly correlated with the quality of soil surface structure (p ≤ 0.01) and soil storage capacity (p ≤ 0.01). Findings of this study are of paramount importance in planning and implementing adaptation policies in The Gambia and beyond. To improve farmers’ resilience, drought tolerant crops should be promoted along with climate change and variability awareness campaigns.

Labile soil organic carbon loss in response to land conversion in the Brazilian woodland savanna (cerradão)

Conversion of native vegetation to agriculture may change the carbon cycle by reducing carbon soil storage capacity and increasing CO2 emissions. We aimed to comparatively assess the impact of land use change on labile pools and dynamics of soil organic carbon (SOC) in two land uses (Urochloa pastures and Eucalyptus forestry) relative to the native reference ecosystem (Brazilian woodland savanna, the cerradao), as a function of soil depth and season. For three replicated study sites, each of them including a control area of the native vegetation (Cerrado) and two land uses (Pasture, Eucalyptus), we sampled soil from 0 to 2 m depth in both dry and wet seasons. We quantified dissolved organic carbon (DOC) and microbial biomass carbon (MBC), estimated the microbial quotient (MBC/SOC) and DOC/SOC ratio, and evaluated C dynamics by assessing soil basal respiration and the metabolic quotient (qCO2). Compared with Cerrado, DOC, MBC and MBC/SOC decreased in both Pasture and Eucalyptus. Differences between land uses vanished below 30 cm soil depth. Seasonality affected most analyzed variables, with lower values for DOC, DOC/SOC and qCO2, and slightly higher values for MBC and MBC/SOC in the wet season. In the dry season qCO2 increased in the Eucalyptus topsoil as compared to Cerrado, suggesting higher stress in the microbial community and/or lower decomposition efficiency in Eucalyptus. Overall, our results show that cerradao conversion to pastures and Eucalyptus plantations negatively affects labile pools and dynamics of SOC, with the effects surpassing a strong spatial and seasonal variability in the soil response to land conversion.

Factors controlling the variation in organic carbon stocks in agricultural soils of Germany

This study gives an overview of soil organic carbon (SOC) stocks in Germany's agricultural soils, and quantifies and explains the influence of explanatory variables such as land use and management, soil type and climate. Over 2500 agricultural sites were sampled and their SOC stocks determined, together with other soil properties. Machine‐learning algorithms were used to identify the most important variables. Land use, land‐use history, clay content and electrical conductivity were the main predictors in the topsoil, whereas bedrock material, relief and electrical conductivity governed the variation in subsoil carbon stocks. We found that 32% of all soil profiles were anthropogenically transformed. The influence of climate variables was surprisingly small, whereas site variables, in particular in the subsoil, explained a large proportion of the variation in soil carbon. The understanding of SOC dynamics at the regional scale requires a thorough description of the spatial variation in soil properties. The effect of agronomic management on SOC stocks was important near the soil surface, but was mainly attributable to land use (grassland or arable and not to other management factors.Highlights Factors affecting spatial variation of soil organic carbon stocks are largely unknown. More than 200 possible predictors for this variation were assessed for over 2500 sites. Land use (history), texture, electrical conductivity, bedrock and relief were main controlling factors of carbon stock variation. Aggregation and carbon storage capacity of soil determine much of the spatial variation in carbon stocks.

Probability mapping of soil thickness by random survival forest at a national scale

Soil thickness (ST) is a crucial factor in earth surface modelling and soil storage capacity calculations (e.g., available water capacity and carbon stocks). However, the observed depths recorded in soil information systems for some profiles are often less than the actual ST (i.e., right censored data). The use of such data will negatively affect model and map accuracy, yet few studies have been done to resolve this issue or propose methods to correct for right censored data. Therefore, this work demonstrates how right censored data can be accounted for in the ST modelling of mainland France. We propose the use of Random Survival Forest (RSF) for ST probability mapping within a Digital Soil Mapping framework. Among 2109 sites of the French Soil Monitoring Network, 1089 observed STs were defined as being right censored. Using RSF, the probability of exceeding a given depth was modelled using freely available spatial data representing the main soil-forming factors. Subsequently, the models were extrapolated to the full spatial extent of mainland France. As examples, we produced maps showing the probability of exceeding the thickness of each GlobalSoilMap standard depth: 5, 15, 30, 60, 100, and 200 cm. In addition, a bootstrapping approach was used to assess the 90% confidence intervals. Our results showed that RSF was able to correct for right censored data entries occurring within a given dataset. RSF was more reliable for thin (0.3 m) and thick soils (1 to 2 m), as they performed better (overall accuracy from 0.793 to 0.989) than soils with a thickness between 0.3 and 1 m. This study provides a new approach for modelling right censored soil information. Moreover, RSF can produce probability maps at any depth less than the maximum depth of the calibration data, which is of great value for designing additional sampling campaigns and decision making in geotechnical engineering.

Precision agriculture in oil palm plantations: diagnostic tools for sustainable N and K nutrient supply

Predicting the fertilizer requirements of an oil palm plantation has long been a difficult task. Two main methods have emerged. Leaf analyses (LA) were used for fertilization management as early as the 1950s. Leaf contents are compared to optimum references, making it possible to adjust the fertilizer rates applied in each block. Another approach, based on the nutrient balance (NB), is to evaluate and replace nutrients that are exported from the field, or immobilized by the plant. Plantations must adopt environmentally friendly practices; in particular, fertilizer inputs must be estimated with sufficient precision to achieve the highest possible yields, without applying excessive amounts of nutrients in relation to plant demand and the storage capacity of soils. We questioned the relevance of each method for achieving these objectives. We did so using some long-term fertilization trials to compare the optimum N and K rates recommended by each method in the adult phase. It appeared that LA led to moderate rates compared to NB. It also appeared that calculating a precise nutrient balance on a field scale was hampered by a lack of precise information (i) about the biomasses produced and their composition and (ii) about the highly variable outputs of the environmental losses. On the other hand, LA provided a simple indicator of the ability for each block to achieve its potential yield. We believe that this perfectible method is more protective of the environment, without the risk of a significant decrease in yields or a decrease in soil mineral reserves.

Physico-chemical Properties Tests of Palm Oil Based Foaming Agent Using Water Solvent Media from Peatland

The water supply requirement to extinguish the fire on the occurrence of land fires is enormous. The water used is usually water available in the field, without certain parameter requirements. For frequent peatland fires, the available peat water in the field becomes an option for use in dissolving the tested foaming agent. Indonesia has a peat land area that has a very large water storage capacity of peat soils. Peat water is the surface water of peat soil with characteristic of brownish red color, contains high organic matter, high iron content, acid taste, pH 3-5 and low level of hardness. This study aimed to determine the effect of peat water use as a solvent on the physico-chemical properties of foaming agent concentrate made from palm oil. Tests were performed using two types of foaming agent concentrate products (CFA-1 and CFA-2) with foaming agent concentrates used were 1, 2 and 3%, and well water was used as a comparison (control). The analysis results showed that the use of peat water as a solvent for palm foaming agent concentrate can be done because it still produces high foam stability, high foaming ability, low interfacial tension, and high decrease of contact angle, as well as the use of well water. The analysis results of CFA-1 using peat water were not quite different from those of CFA-2.

Inter-annual variation in species composition and richness after coppicing in a restored coppice-with-standards forest

AimsCoppice-with-standards (CWS) management was one of the most important disturbances in Central European forests in the past. As our knowledge about the effects of coppicing on species richness and composition needs to be enhanced, we carried out vegetation studies in the currently largest CWS project in Germany. In this article we focus on two issues: 1. Coppicing induced changes and trends in species richness and composition from year to year and 2. Development of species richness and composition in 19 years of CWS restoration. LocationSalzgitter Höhenzug mountains between Liebenburg and Goslar, Lower Saxony, Germany. Climate: subatlantic to subcontinental; soil: Limestone rendzina with low water storage capacity. MethodsIn 2013 we resurveyed the plant species composition of 12 permanent plots analysed every year from 1994 till 2002. The dates of coppicing were recorded for all of these plots, which enabled us to analyse the dynamics of species richness and composition after coppicing on a year to year basis. Differences in species richness and composition were analysed using ANOVA, H-test, DCA and GLMM. ResultsIn 19 years of CWS restoration mean plot species richness increased significantly, mainly attributed to the increase in woody species, such as Quercus robur and Sorbus torminalis. The Ellenberg indicator value for nutrients decreased significantly, whereas the indicator value for light increased significantly. The typical dynamic after coppicing consists of a continuous increase in shrub layer coverage and an increase in herb layer coverage with a maximum in years 3 and 4 after coppicing. Total species richness as well as richness of open habitat and forest species and true forest species also showed an increase with its maximum in years 3 and 4 after coppicing. ConclusionsOur results showed that the alternation of light and shaded phases had a positive impact on species richness, particularly on tree regeneration. Considering the trend of decreasing species richness level in Central European forests, CWS forests play a major role in the conservation of vascular plant species diversity. In contrast to other studies, the increase in species richness after coppicing did not result from an increase in weedy, nitrogen-demanding species. The so called “nitrogen time bomb” scenario (which other authors assumed to be happening after opening the canopy) did not occur in the studied area. The low water storage capacity of the limestone rendzina soil may be one reason, as there was not sufficient water and nitrogen for the more demanding species.

Frozen ground degradation may reduce future runoff in the headwaters of an inland river on the northeastern Tibetan Plateau

On the Tibetan Plateau, climate change, particularly increases in air temperature, significantly affects cryospheric and hydrological processes. Based on 5 typical future climate scenarios from the Coupled Model Intercomparison Project (CMIP5) under emission scenario RCP4.5 and a distributed ecohydrological model (GBEHM), this study analyzes the potential characteristics of future climate change (from 2011 to 2060) and the associated effects on the cryospheric and hydrological processes in the upper Heihe River Basin, a typical cold mountain region located on the northeastern Tibetan Plateau. The precipitation, air temperature, and frozen ground elasticities of runoff/evapotranspiration are then estimated based on the simulation results. The typical future climate scenarios suggest that air temperature will increase at an average rate of 0.34 °C/10a in the future and that precipitation will increase slightly by 6 mm/10a under the RCP 4.5 emission scenario. Based on the GBEHM-simulated results, due to the increase in air temperature, glaciers would be reduced to less than 100 million m3 by 2060, the permafrost area would shrink by 23%, the maximum frozen depth of seasonally frozen ground would decrease by 5.4 cm/10a and the active layer depth of the frozen ground would increase by 6.1 cm/10a. Additionally, runoff would decrease by approximately 5 mm/10a, and evapotranspiration would increase by approximately 9 mm/10a. The estimated elasticities indicate that annual runoff would decrease at an average rate of 24 mm/°C and evapotranspiration would increase at an average rate of 21 mm/°C with rising air temperature in the future. The impacts of increased air temperature on hydrological processes are mainly due to changes in frozen ground. The thickening of the active layer of the frozen ground increases the soil storage capacity, leading to decreased runoff and increased evapotranspiration. When the active layer depth increases by 1 cm, annual runoff decreases by approximately 1.3 mm, and annual evapotranspiration increases by approximately 0.9 mm. In addition, the shift from permafrost to seasonal frozen ground increases groundwater infiltration, which decreases surface runoff. Compared to that over the past 50 years, the effect of increased air temperature on the frozen ground in the upper Heihe River Basin will be greater in the future, which would result in a faster reduction in runoff in the future considering the effects of global warming.

Incorporating Influences of Shallow Groundwater Conditions in Curve Number-Based Runoff Estimation Methods

Runoff generation process in any watershed is mainly affected by precipitation, land use and land cover, existing soil moisture conditions and losses. Shallow groundwater table conditions that occur in many regions are known to affect the soil moisture retention capacity, infiltration and ultimately the runoff. A methodology that links soil moisture capacity to the shallow groundwater table or High-Water Table (HWT) using a nonlinear functional relationship within a curve number (CN)-based runoff estimation method, is proposed and investigated using single and continuous event simulation models in this study. The relationship is used to obtain an adjusted CN that incorporates the effect of change in soil moisture conditions due to HWT. The CN defined for average conditions is replaced by this adjusted CN and is used for runoff estimation. A single event model that uses Soil Conservation Service (SCS) CN approach is used for evaluation of variations in runoff depths and peak discharges based on different HWT conditions. A real-life case study from central Florida region in the USA was adopted for application and evaluation of the proposed methodology. Results from the case study application of the models indicate that HWT conditions significantly influence the magnitudes of peak discharge by as much as 43% and runoff depth by 48% as the water table height reaches the land surface. The magnitudes of increases in peak discharges are specific to case study region and are dependent on the functional form of the relationship linking HWT and soil storage capacity. Also, for specific values of HWT, an equivalency between HWT-based CN and wet antecedent moisture condition (AMC)-based CN can be established.

Study on the Influence of Water Storage Capacity of Aeolian Sandy Soil by Arsenic Sandstone: a Case Study in Mu Us Sandy Land in China

To analyze how the arsenic sandstone influence the water storage capacity of Aeolian sandy soil, experimental plots with different ratios of arsenic sandstone and Aeolian sandy soil were set in Mu Us sandy land in China, with spring maize planted one season per year, and the soil water of the depth 0-120 cm was monitored constantly during 2013-2015. The results conducted that, moderate arsenic sandstone could improve the water storage capacity of sandy soil from 100 mm of 2013 to over 200 mm of 2015, promoting the soil water to none deficiency state, strengthen the water storage capacity of soil, which was beneficial for the crops growth. Water storage capacity of soil layer below 40 cm was promoted most obviously, and the layers of 0-40 cm and 80-120 cm turned into more stable layers for water storage, which was helpful for the crop growth. Mixing the arsenic sandstone and Aeolian sandy soil with ratio 1:1, 1:2 and 1:5, with the addition of arsenic sandstone, the water storage capacity of the soil was enhanced, the soil water deficit degree decreased, the water storage variable coefficient increased.

Formation of litter crusts and its multifunctional ecological effects in a desert ecosystem

AbstractDesertification is one of the major issues in global environmental change, and it is of great concern to scientists and policy‐makers in the world. Litter crusts can be of great importance for the restoration and management of desert ecosystems. The formation of litter crusts and its ecological effects on desert surface microhabitats were studied in a wind–water erosion crisscross desert region. It was found that litter crusts, especially the four‐year litter crusts, exhibited a better soil storage capacity and temperature regulating ability when compared to the bare land, biocrusts, and two‐year litter crusts; the four‐year litter crusts significantly increased soil total porosity, soil water storage, and soil organic carbon content, but reduced soil bulk density. Furthermore, species richness, coverage, and plant height of seedlings in litter crusts were significantly greater than those in bare land and biocrusts. Although the bare land had the greatest total number of seedlings, the survival rate of seedlings was lowest there. Our findings revealed that litter crusts had significantly positive effects on soil moisture, soil temperature, soil physicochemical properties, and seedling establishment. The multifunctional ecological effects of litter crusts are more positive than lichen‐ and moss‐dominated biocrusts in desert ecosystems.

Improvement of Rainwater Infiltration Property and Its Effect on the Corresponding Storage Capacity of Soil in Urban Green Space

Urban green space whose soil permeability is the main factor affecting hydrological cycle plays a very important role in promoting rainwater infiltration, replenishing groundwater and reducing peak flow. In order to enhance the storage and infiltration ability of soil, different types and contents of conditioner are added to study the laws of the changes in permeability of various soils. The results showed that straw and sawdust can effectively increase the permeability coefficient of soil. According to the comparison under the same conditions, the improvement effects of straw is slightly better than sawdust, but no order of magnitude difference. The sandy soil reformed by 3.6% Straw or 4.2% Sawdust and the loam reformed by 29.5% Straw or 30.2% Sawdust can meet infiltration requires of rainwater whose rainstorm recurrence period is 10 years. The clay is not suitable for urban green space soils with higher rainwater storage and infiltration requirements. The reformed green space can effectively reduce the runoff peak flow and delay the generated time of the runoff. The higher the content of the modifier, the more obvious the advantage of promoting the hydrological cycle and reducing the runoff.

Infiltration into frozen soil: From core‐scale dynamics to hillslope‐scale connectivity

AbstractInfiltration into frozen soil is a key hydrological process in cold regions. Although the mechanisms behind point‐scale infiltration into frozen soil are relatively well understood, questions remain about upscaling point‐scale results to estimate hillslope‐scale run‐off generation. Here, we tackle this question by combining laboratory, field, and modelling experiments. Six large (0.30‐m diameter by 0.35‐m deep) soil cores were extracted from an experimental hillslope on the Canadian Prairies. In the laboratory, we measured run‐off and infiltration rates of the cores for two antecedent moisture conditions under snowmelt rates and diurnal freeze–thaw conditions observed on the same hillslope. We combined the infiltration data with spatially variable data from the hillslope, to parameterise a surface run‐off redistribution model. We used the model to determine how spatial patterns of soil water content, snowpack water equivalent (SWE), and snowmelt rates affect the spatial variability of infiltration and hydrological connectivity over frozen soil. Our experiments showed that antecedent moisture conditions of the frozen soil affected infiltration rates by limiting the initial soil storage capacity and infiltration front penetration depth. However, shallow depths of infiltration and refreezing created saturated conditions at the surface for dry and wet antecedent conditions, resulting in similar final infiltration rates (0.3 mm hr−1). On the hillslope‐scale, the spatial variability of snowmelt rates controlled the development of hydrological connectivity during the 2014 spring melt, whereas SWE and antecedent soil moisture were unimportant. Geostatistical analysis showed that this was because SWE variability and antecedent moisture variability occurred at distances shorter than that of topographic variability, whereas melt variability occurred at distances longer than that of topographic variability. The importance of spatial controls will shift for differing locations and winter conditions. Overall, our results suggest that run‐off connectivity is determined by (a) a pre‐fill phase, during which a thin surface soil layer wets up, refreezes, and saturates, before infiltration excess run‐off is generated and (b) a subsequent fill‐and‐spill phase on the surface that drives hillslope‐scale run‐off.

Effects of Permafrost Degradation on the Hydrological Regime in the Source Regions of the Yangtze and Yellow Rivers, China

Climate warming has intensified permafrost degradation, which could have a variety of implications on the hydrological regime in permafrost regions. In this study, we analyzed the effects of permafrost degradation on the hydrological regime via four hydrological variables for 10 unregulated catchments in the source regions of the Yangtze and Yellow rivers. The results demonstrate that catchments with high permafrost coverage are expected to have an increased winter discharge ratio (proportion of winter discharge contribution to total annual flow), a decreased recession coefficient and a decreased ratio of Qmax/Qmin due to permafrost degradation. However, the great storage effects of lakes and wetlands, which could contribute to more groundwater instead of direct surface discharge, may affect the hydrological effects of permafrost degradation and result in the abnormal performance at catchment scale. The correlation analysis between summer precipitation (July–September) and the following winter discharge (December–February) indicates that permafrost degradation may affect the redistribution of summer precipitation towards the following winter discharge via increasing the soil storage capacity and delaying the release of water into streams in permafrost regions. However, unlike the Arctic and sub-Arctic regions, no significant changes for the hydrological regime (four hydrological variables) are detected over the individual periods of records for each catchment. Decreased precipitation in summer seems to reduce the water infiltration to supply the groundwater, which weakens the effects of permafrost degradation on the hydrological regime. This study implies that the storage effects of lakes and wetlands and the changes of summer precipitation patterns should be considered in future permafrost hydrological simulations, which have suggested that a large increase in groundwater discharge to streams will likely occur in response to permafrost degradation due to the warming climate in the ideal scenario.

Impact of multi-day rainfall events on surface roughness and physical crusting of very fine soils

Soil surface roughness (SSR), a description of the micro-relief of soils, affects the surface storage capacity of soils, influences the threshold flow for wind and water erosion and determines interactions and feedback processes between the terrestrial and atmospheric systems at a range of scales. Rainfall is an important determinant of SSR as it can cause the dislocation, reorientation and packing of soil particles and may result in the formation of physical soil crusts which can, in turn, affect the roughness and hydrological properties of soils. This paper describes an experiment to investigate the impact of a multi-day rainfall event on the SSR and physical crusting of very fine soils with low organic matter content, typical of a semi-arid environment. Changes in SSR are quantified using geostatistically-derived indicators calculated from semivariogram analysis of high resolution laser scans of the soil surface captured at a horizontal resolution of 78μm (0.078mm) and a vertical resolution of 12μm (0.012mm). Application of 2mm, 5mm and 2mm of rainfall each separated by a 24h drying period resulted in soils developing a structural two-layered ‘sieving’ crust characterised by a sandy micro-layer at the surface overlying a thin seal of finer particles. Analysis of the geostatistics and soil characteristics (e.g. texture, surface resistance, infiltration rate) suggests that at this scale of enquiry, and for low rainfall amounts, both the vertical and horizontal components of SSR are determined by raindrop impact rather than aggregate breakdown. This is likely due to the very fine nature of the soils and the low rainfall amounts applied.

Numerical simulation of the effect of different mulches on the heat storage capacity of a Mediterranean greenhouse soil

In the Mediterranean greenhouse areas, a large majority of growers rely on passive techniques to improve the microclimate of the greenhouse during the winter period, rather than using more expensive systems such as active heating. Some of these techniques such as different types of mulch (sand, plastic films, etc.) are used to improve the heat storage capacity of the greenhouse soil. A proper modeling of the role of the greenhouse soil a heat store would allow the verification of which techniques have a larger positive effect on the heat store capacity of the soil (i.e. type, color and thickness of the mulch, soil moisture content, etc.) and how to optimize their management by the grower. In recent years, CFD has been successfully used to model the greenhouse microclimate under very different scenarios, but little has been done to include in the simulations the role of passive techniques in the winter period microclimate, such as the role of the soil as a heat store. In the present work, a CFD model of a Mediterranean greenhouse and its soil has been developed, and the effect on the heat storage capacity of the soil as well as in the ambient of 2 different types of mulch (black plastic film, semi-transparent plastic film) was evaluated, by comparing the temperature measured at 4 different depths and ambient temperature (at two heights), during daytime period with the values provided by the model. The evolution of the temperatures at different soil depths followed the same pattern in both the experiments and the simulations. Good quantitative agreement was found between values predicted by the model and the measurements with differences being always lower than 2°C.

Climate‐Smart Agriculture

Climate‐Smart Agriculture

The effect of the bulk density and the decomposition index of organic matter on the water storage capacity of the surface layers of forest soils

Forests play an extremely important role in the formation of water circulation in a catchment. Despite numerous studies concerning the relations between forest and water, many problems still remain unexplained. Among them is the influence of the species composition in a stand on the water storage capacity of forest soils, especially of their surface horizons, whose physico-chemical properties are directly affected by the stand. The knowledge of those interactions is significant not only in the aspect of modelling of hydrological phenomena occurring in forest ecosystems but may also be helpful in indicating the directions of stand rebuilding aimed at extending the water-protective functions of forest.The aim of the present research is to analyse the influence of the bulk density and the index of decomposition of organic matter on the water storage capacity of the surface layers of forest soils formed under beech (Fagus sylvatica L.) and fir (Abies alba Mill.) stands in southern Poland. The water storage capacity of individual forest soil horizons shows a distinct relationship with their bulk density. In beech and fir stands there is a critical value of bulk density, amounting to 0.48 and 0.51g·cm−3, which corresponds to culmination of the water storage capacity. A strong correlation has been shown between water storage capacity and the index of decomposition of beech and fir organic matter. It has also been found that the index of decomposition of organic matter and the degree of saturation, an indicator of water-filled voids in the soil, can constitute useful measures for describing and comparing the water storage capacity of the surface layers of forest soils formed under stands with a different species composition.