Soil erosion assessment tools from point to regional scales—the role of geomorphologists in land management research and implementation

Geomorphological research has played an important role in the development and implementation of soil erosion assessment tools. Because policy and management approaches include the use of soil erosion assessment tools, soil erosion research directly affects the public in terms of providing information on natural hazards and human impacts, and also as the basis for regulatory policy on land management. For example, soil loss calculations and geomorphological expertise are used to support soil conservation planning, both through agricultural legislation that defines maximum tolerable soil loss rates, and through federal and local legislation that requires soil erosion controls on many construction sites.To be useful for decision makers, soil erosion models must have simple data requirements, must consider spatial and temporal variability in hydrological and soil erosion processes, and must be applicable to a variety of regions with minimum calibration. The growing use of erosion models and Geographic Information Systems (GIS) in local to regional scale soil and water conservation raises concerns about how models are used. This has prompted interest in methods to assess how models function at management scales and with the types of data that are commonly available to users. A case study of a GIS-based soil erosion assessment tool using the process-based Water Erosion Prediction Project (WEPP) shows that using commonly available data rather than research grade data can have (predictably) a significant impact on model results. If model results are then used in management decisions, it is critical to assess whether the scale and direction of variation in results will affect management and policy decisions. Geomorphologists provide unique perspectives on soil erosion and can continue to affect policy through soil erosion research. This research should focus on fundamental processes, but equally important is continued development and evaluation of models that are matched to real world data availability, geomorphic settings, and information needs.     

Soil erodibility and processes of water erosion on hillslope

The importance of the inherent resistance of soil to erosional processes, or soil erodibility, is generally recognized in hillslope and fluvial geomorphology, but the full implications of the dynamic soil properties that affect erodibility are seldom considered. In Canada, a wide spectrum of soils and erosional processes has stimulated much research related to soil erodibility. This paper aims to place this work in an international framework of research on water erosion processes, and to identify critical emerging research questions. It focuses particularly on experimental research on rill and interrill erosion using simulated rainfall and recently developed techniques that provide data at appropriate temporal and spatial scales, essential for event-based soil erosion prediction. Results show that many components of erosional response, such as partitioning between rill and interrill or surface and subsurface processes, threshold hydraulic conditions for rill incision, rill network configuration and hillslope sediment delivery, are strongly affected by spatially variable and temporally dynamic soil properties. This agrees with other recent studies, but contrasts markedly with long-held concepts of soil credibility as an essentially constant property for any soil type. Properties that determine erodibility, such as soil aggregation and shear strength, are strongly affected by climatic factors such as rainfall distribution and frost action, and show systematic seasonal variation. They can also change significantly over much shorter time scales with subtle variations in soil water conditions, organic composition, microbiological activity, age-hardening and the structural effect of applied stresses. Property changes between and during rainstorms can dramatically affect the incidence and intensity of rill and interrill erosion and, therefore, both short and long-term hillslope erosional response. Similar property changes, linked to climatic conditions, may also significantly influence the stability and resilience of plant species and vegetation systems. Full understanding of such changes is essential if current event-based soil erosion models such as WEPP and EUROSEM are to attain their full potential predictive precision. The complexity of the interacting processes involved may, however, ultimately make stochastic modelling more effective than physically based modelling in predicting hillslope response to erodibility dynamics.     

关于虚拟地理环境研究的几点思考

该文主要回答了目前被频繁问及的有关虚拟地理环境的几个问题。重点阐述了虚拟地理环境的概念、发展现状及其基本理论、方法、关键技术与应用,以及与传统地理信息系统的区别。指出虚拟地理环境是在空间数据库和地理模型管理基础上构建的、同时表达地理静态和模拟动态现象的、面向多用户的分布式协同虚拟环境。因此,虚拟地理环境突破地理信息系统以数据共享为核心的框架,走向以数据库和模型库为双核心的知识共享平台,进而形成一个新知识的生成环境。     

Heliotropium europaeum only germinates following sufficient rainfall to allow reproduction

Regions with Mediterranean climates are seasonally arid and provide a niche for ephemeral species which germinate following discrete and variable rainfall during summer. These species must be able to detect when conditions are suitable for completion of their life cycle. Common heliotrope (Heliotropium europaeum) is one such species. It is considered a weed in its naturalised habitat in southern Australia as it uses resources that could be used by ensuing crops, and is toxic to livestock.We examined common heliotrope's germination responses to temperature and water potential, the effect of simulated rainfall on seedling emergence and plant growth in lysimeters.Fresh seeds of common heliotrope have relatively high optimum temperatures and water potentials for germination (around 35 °C and 0 MPa). Germination percentage of seeds extracted from the soil seed bank varies seasonally. In the soil types and climate of the study area, 24.2 mm is the minimum amount of rainfall resulting in emergence. Evapotranspiration required to reach minimal reproductive output was 19.4 mm.Common heliotrope's germination requirements have been selected to ensure that it will only germinate after sufficient rainfall to allow reproductive output. This is the mechanism through which common heliotrope detects its temporal niche.     

From water to tillage erosion dominated landform evolution

While water and wind erosion are still considered to be the dominant soil erosion processes on agricultural land, there is growing recognition that tillage erosion plays an important role in the redistribution of soil on agricultural land. In this study, we examined soil redistribution rates and patterns for an agricultural field in the Belgian loess belt. ¹³⁷Cs derived soil erosion rates have been confronted with historical patterns of soil erosion based on soil profile truncation. This allowed an assessment of historical and contemporary landform evolution on agricultural land and its interpretation in relation to the dominant geomorphic process. The results clearly show that an important shift in the relative contribution of tillage and water erosion to total soil redistribution on agricultural land has occurred during recent decades. Historical soil redistribution is dominated by high losses on steep midslope positions and concavities as a result of water erosion, leading to landscape incision and steepening of the topography. In contrast, contemporary soil redistribution is dominated by high losses on convex upperslopes and infilling of slope and valley concavities as a result of tillage, resulting in topographic flattening. This shift must be attributed to the increased mechanization of agriculture during recent decades. This study shows that the typical topographical dependency of soil redistribution processes and their spatial interactions must be accounted for when assessing landform and soil profile evolution.     

关于中国农业文化遗产保护若干问题的解答（英文）

Although the urgency of their conservation has been recognized, Globally Important Agricultural Heritage Systems(GIAHS) designated by the Food and Agriculture Organization(FAO) since 2002 and China Nationally Important Agricultural Heritage Systems(ChinaNIAHS) certified by the Ministry of Agriculture(MOA) of China since 2012 are faced with questions as to why to conserve them, what is to be conserved, who should conserve them, and how? This paper attempts to clarify and respond to such questions focusing on the conservation of agricultural heritage systems in China based on a review of both theoretical and practical progress. Agricultural heritage systems exhibit a multitude of values for sustainable and equitable development and therefore should be conserved for both present and future generations. Unlike most conventional heritages, the conservation of agricultural heritage systems is a complex, systematic "engineering" in which both physical and biological components and associated socio-cultural processes should be conserved in a dynamic way. Farmers and heritage sites must benefit from the continuance of traditional agricultural production under the premise of ecological functions being sustained and traditional culture being inherited. For a more effective conservation, a multi- stakeholder process should be established involving governments at different levels, multi-disciplinary scientists, communities and farmers, and business enterprises as well as social organizations. As has been demonstrated, the conservation of agricultural heritage systems aims to promote the regional sustainable development, to improve the livelihood, food security and well-being of farm people, and to provide references for the development of modern agriculture in China.     

市场经济条件下黄土高原建设方针的调整

本文对黄土高原现有建设方针进行反思,认为它所导致的黄土高原封闭,产业结构单一等现实使其已不能适应市场经济的需要。     

Spatial Distribution of Surface Soil Organic Carbon Density and Related Factors along an Urbanization Gradient in Beijing

Urban surface soil has a unique set of structures and processes that affect surface soil organic carbon density (SOC_density) and its spatial variations. Using Beijing as a case study, and assisted by field investigations and experiments, we analyzed the spatial distribution of SOC_density in different land use types and functional regions, and assessed associated factors such as urbanization level, the physiochemical properties of soil and plant configurations. The present study aims to provide useful information about the mechanisms driving soil organic carbon and climate change in developing and developed areas in urbanized regions like Beijing. Results indicate that P is the main factor positively influencing SOC_density in most regions. Because of the specific interference directly related to human beings in urban areas, with decreases in the urbanization level, more physiochemical factors of soil can influence SOC_density. SOC_density under grasses is not significantly different from that under other plant compositions. Urbanization processes decrease the heterogeneity of the spatial pattern of SOC_density in most land use types, but increased its contents when the area reached a developed level in Beijing. More factors related to human interference and spatial variation of surface soil carbon storage, especially under impervious land in urban areas, should be considered in future studies.     

Hydrological responses and soil erosion potential of abandoned cropland in the Loess Plateau, China

Recent changes in hydrological processes and soil erosion in the Loess Plateau, China, are immediate responses to cropland abandonment for revegetation, which lead to a long-term decrease in runoff generation and soil erosion. However, detailed hydrological responses and soil erosion changes have not been clearly evaluated. In this study, two issues were focused on the plot scale. The first issue relates to changes in vegetation cover and soil properties during the early stages of revegetation. Given the occurrence of soil compaction, it was hypothesized that runoff increased during this period and the soil erosion did not significantly decline, even though vegetation increased. The second issue is the effect of scale on runoff and soil erosion. Three plot groups of three vegetation types and two restoration stages were established for comparative experiments. The results from these experiments confirmed that the soil compaction occurred during revegetation in this region. Greater runoff was produced in plot group that experienced both a longer restoration time and with higher vegetation cover (such as Groups 2 and 3 in this study) than that with a shorter restoration time and lower vegetation cover (Group 1). In addition, the total soil loss rates of all plot groups were rather low and did not significantly differ from each other. This indicates that a reduction in runoff generation and soil erosion, as a result of revegetation, was limited in the early stages of restoration following the cropland abandonment. With increasing plot area, the runoff coefficient decreased for the plot group with a longer revegetation time (Groups 2 and 3), but gently increased for the one with a shorter restoration time (Group 1). In Groups 2 and 3, soil loss rate decreased when plot area enlarged. In Group 1, it decreased before a plot area threshold of 18 m² was exceeded. However, the increase occurred when plot area crossed the threshold value. In conclusion, the high vegetation cover alone did not lead to reduction in the runoff coefficient during the early stages of revegetation. When evaluating hydrological and soil erosion responses to revegetation, the soil compaction processes should be considered. Additionally, the effect of scale on runoff and soil erosion was found to be dependent on restoration extent, and thus on restoration time.     

南亚热带人工林林下芒萁层的凋落物拦截

在中国南亚热带人工林生态系统中,大面积的林下层被密集的蕨类植物芒萁所占据。作为森林土壤最重要的养分来源,很多冠层树种的凋落物在到达地表之前,会被芒萁拦截。通过调查南亚热带4种人工林林下芒萁层对冠层树种叶片的拦截量与拦截比例,发现林下芒萁层对凋落物的拦截量排序为湿地松＞厚荚相思＞尾叶桉＞红椎,而林下芒萁层对尾叶桉叶片的拦截比例最高,达99.8%,其次分别为厚荚相思（73.5%）、湿地松（56.3%）和红椎（27.0%）;所有人工林林下芒萁的下半层（0~50 cm）拦截了更大比例的凋落叶,最大为尾叶桉（64.7%）,最小为红椎（23.1%）。林下芒萁层的凋落物拦截效应可能会改变森林生态系统的地上过程和地下过程,进而影响整个森林的碳循环等生态系统功能。通过凋落物拦截实验,开展林下层植物对人工林生态系统碳循环的影响的相关机理研究,有助更好地理解在生态系统水平上林下植被对整个森林生态系统功能的影响。     

农业活动与岩溶山区土地利用的可持续性探讨

以 4项专题研究及抽样调查为主要资料来源 ,对西南岩溶山区的土地利用进行研究。结果表明 ,由于该区土地土层薄且通透性强和母岩漏水 ,长期耕种后土壤肥力明显下降、粮食产量对化肥的依赖性增强。长期施化肥的土地耕种约 6 0年后 ,土壤有机质含量相当于天然状态下的 30 %。垦殖率在 2 0 %～ 30 %、覆被率在 35 %～ 45 %时粮食产量高而稳定。土层厚度 <5 0～ 80cm、地形坡度 >16°时的梯地对水肥保持及旱情缓解的作用甚小 ,不是解决干旱的途径。该区耕地的持续利用须建立在适当的垦殖率、森林覆盖率及合理施肥基础上。实现该目标的关键是建立生态农业体系 ,缩小耕地面积、减少人口是发展生态农业的前提。     

甘宁蒙陕退耕还林(草)中的适地适树问题

通过对退耕还林工程中适地适树问题的探讨,我们认为在退耕还林(草)工程实施过程中一定要坚持适地适树,适地适树是造林中的一项基本原则。在退耕还林和造林过程中应该遵循生物气候带原则,演替前期植物种与演替后期植物种搭配,浅根系植物与深根系植物合理配置。植物种的选择应该坚持立地条件与生物学特性和生态学特性相适应;与地带性特点相适应;与降水条件和土壤水分条件相适应,做到"林水平衡";与植物群落的演替特征相适应。     

Long-term impact of agricultural practices on biological soil crusts and their hydrological processes in a semiarid landscape

The natural landscapes of semiarid areas worldwide comprise a series of scattered patches of shrubs within a matrix of biologically crusted soils (BSC). As BSCs are considered ecosystem engineers the relationships between the BSC and the shrub patches determine system functioning. The objective of our study was to investigate long-term effects of agricultural practices on biological soil crusts and their influence on hydrological aspects of a semiarid ecosystem. During 1991, we experimentally simulated five of the area's agricultural practices; 1) Scraping – the topsoil was removed to a depth of 2 cm, 2) Spraying – phototrophic organisms were chemically killed with herbicide, 3) Mowing – perennial vegetation was cut and spread to simulate grazing practices, 4) Car track – a heavy roller was used to simulate car-tracks, 5) Control – undisturbed natural plots. Sixteen years later, in 2007, these agricultural practices were found to have a long-term effect on the crusted soil surface and the related soil-surface properties. Mowing and car-track treatments led to decreased overland runoff and increased hydraulic conductivity, whereas scraping and spraying treatments led to increased overland runoff production and decreased hydraulic conductivity. We conclude that the practices had a long-term residual impact on BSC succession and related soil surface properties, which affected the hydrological processes and system functioning.     

Simulating loss of primary silicate minerals from soil due to long-term weathering using Allogen: Comparison with soil chronosequence,lake sediment and river solute flux data

This paper presents ALLOGEN, a process model of soil mineral chemical weathering. Though designed principally to aid interpretation of lake sediment geochemical records by providing mass balance constraints for competing interpretations, the model is also applicable to more general questions about long-term weathering and soil development. The model is constructed around a generalised version of the mineral-weathering submodel of PROFILE, modified to minimise the need for site-specific data and to optimise performance for long-term change. Comparison with observed weathering rate data (river flux studies, chronosequences and lake sediment chemical stratigraphy) suggests that soil mineral depletion can be usefully simulated over timescales applicable to Quaternary and Holocene studies. To illustrate this, the plausibility of a weathering interpretation is demonstrated for sediment records at Lake Hope Simpson and Moraine Lake and the lake chronosequence at Glacier Bay. While long-term soil mineral depletion appears predictable, reliable simulation of past runoff quality is hampered by lack of a suitable long-term model for soil carbon.     

贵南牧场在潜在沙漠化地区的共和盆地木格滩合理垦殖的经验

在潜在沙漠化地区"乱垦"是有害无益的。但科学的合理垦殖不应该禁止, 而应积极提倡和支持, 贵南牧场成功的经验, 应引为借鉴。该场自1968年改军马生产为农牧业结合经营方式, 在木格滩进行实验性垦殖, 20多年来在生态环境和经济收入上取得了显著的双重效益。其具体措施是: 1. 有选择的开垦土地。在开垦之前先进行勘测, 选择地面平整、土层深度在2.5m以上的粉砂质或轻壤质土地块进行垦殖, 耕种深度不超过30cm。2. 保持地形原貌。对开垦土地不进行平整, 让其自然起伏, 保持原来地貌, 使表层2m以上的土层保持均匀一致、稳定。3. 实行"耕二休一"和草田轮作制。改良土壤的理性化状, 不断补充和提高土壤肥力。4. 合理耕作。春翻地采取边翻、边压、边播种, 翻后压两遍, 播后再镇压, 尽量缩短工作程序时间(以不超过24小时为准); 而夏翻地封冻前镇压, 来年免耕播种。5. 采取残茬越冬。尽量减少耕地面的裸露, 让地面被作物茬子和撒在地里的秸秆覆盖, 减轻风蚀。这为我国在容易发生沙漠化草原地区进行合理的农业开发利用提供了有益的启示和经验。     

新疆昌吉州耕地开垦轨迹对土壤肥力变化的影响

定量刻画区域尺度耕地开垦轨迹(初始地类、初始土壤类型和耕作年限)对土壤肥力变化的影响,对指导区域农业施肥管理措施、提高农田土壤肥力具有重要意义.本文以新疆昌吉州为研究区,通过叠加5期土地利用数据来识别耕地开垦轨迹,基于1980年和2018年两期大量样点数据,分析耕地开垦前的土地利用方式和土壤类型以及开垦后耕作年限的差异...     

气候变化对太行山土壤水分及植被的影响

在太行山低山区将自然植被移入蒸渗仪,观察当降水分别为常年平均降水量的80%、90%、100%、110%和120%等5种处理条件下,植被生产力和土壤的不同反映。研究发现:受验植被对降水反映敏感,降水每增加10%,植被生产力增加15%左右,预示未来全球变化导致的降水变化会对太行山低山区植被产生影响。同时在利用野外实验结果对WAVES模型进行验证的基础上,模拟了不同温度和降水变化情景下,土壤水分的可能变化趋势。结果表明:增温和减少降水对土壤水分负作用明显,尽管降水增加可改善土壤的水分供应状况,但降水增加10%对土壤水分的正面影响,大体被3 oC的增温抵消。由于模型模拟中采用的是与目前没有改变降水条件的实验相同的植被(LAI),而植被生长在太行山这一半湿润、半干旱地区又受土壤水分控制,因而估计未来气候变化情景下的植被变化与土壤水分的变化趋势相似。     

What can be learned from rotational motions excited by earthquakes?

One answer to the question posed in the title is that we will have more accurate data for arrival times of SH waves, because the rotational component around the vertical axis is sensitive to SH waves although not to P-SV waves. Importantly, there is another answer related to seismic sources, which will be discussed in this paper.
Generally, not only dislocations commonly used in earthquake models but also other kind of defects could contribute to producing seismic waves. In particular, rotational strains at earthquake sources directly generate rotational components in seismic waves. Employing the geometrical theory of defects, we obtain a general expression for the rotational motion of seismic waves as a function of the parameters of source defects.
Using this expression, together with one for translational motion, we can estimate the rotational strain tensor and the spatial variation of slip velocity in the source area of earthquakes. These quantities will be large at the edges of a fault plane due to spatially rapid changes of slip on the fault and/or a formation of tensile fractures.     

土壤侵蚀模型研究中的几个问题

土壤侵蚀模型是定量研究土壤侵蚀的有效工具,探讨土壤侵蚀模型研究中的有关问题对于土壤侵蚀模型的发展及相关研究具有重要意义。从模型的过程模拟、模型时空尺度变异、模型验证和不确定性几方面对模型研究现状及局限进行了归纳和分析,认为:不同过程的模拟及其模拟方法的不同导致了各具特色的土壤侵蚀模型的出现;大多水蚀模型是对不同时空尺度上的水流及相应侵蚀过程进行模拟预测,在不同的时空尺度上,不同的侵蚀过程占主导地位;现实过程和现象的复杂性、观测方法和手段的限制以及模型的自身的局限性是导致土壤侵蚀模型预测的不确定性的主要原因;与GIS结合的强预测力、低数据要求的模型是土壤侵蚀模型发展的趋势。