聚丙烯酰胺对凹凸型坡土壤侵蚀影响的室内试验

通过室内人工模拟降雨试验,研究了聚丙烯酰胺(polyacrylamide,PAM)施用量(0、0.5、1.0和2.0 g/m2)对凸型坡(上、下坡坡度分别为5°、10°、15°和20°、25°)和凹型坡(上、下坡坡度分别为20°、25°和5°、10°、15°)土壤侵蚀规律的影响。结果显示,无PAM应用时,凹型坡或小坡度凸型坡(上坡坡度为5°)径流含沙量随降雨历时逐渐减小,而大坡度凸型坡(上坡坡度≥10°)径流含沙量在降雨过程中会急剧增大。凸型坡平均土壤流失量是凹型坡的8.4倍。PAM应用显著增大了凹型坡和小坡度凸型坡径流含沙量和土壤流失量(P0.05),但减小了大坡度凸型坡土壤流失量。PAM应用后,土壤流失量与坡度大小无明显关系,此时凸型坡平均土壤流失量为凹型坡的1.2倍。在生产实践中PAM可用于控制较陡(≥10°)凸型坡的土壤流失。     

基于RUSLE的线状开发建设项目区土壤侵蚀动态监测——以浙江省宁波市北环快速路工程为例

[目的]全面调查浙江省宁波市北环快速路施工前后及施工过程中土壤侵蚀时空变化状况,为今后线状生产建设项目水土保持遥感监测提供参考。[方法]分别利用2010年宁波市土地利用/覆盖类型图、道路图及调查数据,结合项目区地形图和实测高程点生成的数字高程模型(DEM)、实测土壤属性数据、水文站降雨数据等资料分别获取RUSLE模型中各因子值的空间分布,然后通过RUSLE模型计算项目区3个不同阶段的土壤侵蚀量,最后进行分类统计。[结果]项目施工前期和自然恢复期的土壤侵蚀均以微度侵蚀为主,所占项目面积比例分别为98.53%和99.73%;而施工期的土壤侵蚀等级以轻度和微度侵蚀为主,两者分别占项目区面积的52.5%和35.4%;项目施工期的平均土壤侵蚀模数为1 380.9t/(km2·a),远高于施工前及施工期后的251.3,155.4t/(km2·a)。[结论]项目施工期土壤侵蚀区域主要分布在临时堆土区,进一步分析发现坡度因素对土壤侵蚀空间分布具有重要影响。     

流域系统径流侵蚀链内泥沙输移的空间尺度效应

尺度问题在地貌过程及水文模拟研究中具有重要意义,以黄土高原丘陵沟壑区岔巴沟小流域为例,基于毛沟-支沟-干沟尺度序列典型水文站的实测径流泥沙数据,分析流域系统基于事件的径流侵蚀链内泥沙输移的空间尺度效应。结果表明:1)基于侵蚀链毛沟-支沟-干沟不同空间尺度的平均输沙模数、平均含沙量、最大含沙量分别依次为3 912、3 285、3 522 t/km2,497、524、679 kg/m3,639、634、800 kg/m3,且在流域系统中均保持空间上的不变性;2)与单一力学指标相比,引入洪峰流量项的水流功率、单位面积径流能量及水流能量等复合能量指标能更好地描述侵蚀链不同尺度内及尺度间水沙关系;3)侵蚀链的输沙量主要取决于径流量,而洪峰流量能更好地解释侵蚀链内不同尺度径流输沙的差异,在侵蚀输沙的预测变量中引入表征径流变率的指标会提高中小型产沙事件泥沙预报的可靠性;单位洪峰流量(增加1 m3/s)引起的输沙增量是单位径流量(增加1 m3)增沙作用的875倍以上,欲消除侵蚀链内上下游径流输沙的空间尺度效应,则需将对应的洪峰流量比调控至5‰以下,或将对应的径流能量比调控至600以下;4)侵蚀链内上游含沙水流对下游的泥沙输移影响有限,随流域面积增大,含沙水流的空间尺度效应降低,输沙模数300 t/km2的大型侵蚀产沙事件尤为明显。分析结果突出了流域系统径流侵蚀的过程特性和洪水调控可能引起的巨大减沙潜力。因此,针对高含沙水流,侵蚀链内泥沙调控及其水土保持措施的效益评估和功能评价亦应基于过程。研究结果可为全面揭示径流调控系统的水土保持意义、推动水土保持措施效益的精细化评估提供理论依据和科学支撑。     

黔西高原侵蚀性降雨特征分析

侵蚀性降雨的特征与土壤侵蚀的研究密切相关。利用径流小区观测法以及黔西高原地区典型小流域的降雨、径流与泥沙资料,对黔西高原地区侵蚀性降雨的特征进行了分析,结果表明:(1)降雨总动能(E)和最大60分钟雨强(I60)的乘积是研究区降雨侵蚀力(R)的计算指标;(2)中雨以上降雨事件的产沙量约占总产沙量的99.5%,6次暴雨事件的产沙量占总产沙量的79.4%。对大雨以上等级降雨事件的土壤侵蚀模数与降雨特征拟合分析得到:M=1.319EI60以及M=0.328PI60;(3)降雨侵蚀力大于500 MJ·mm/(h·hm2)等级的降雨事件的产沙量占总产沙量的73.6%,对降雨侵蚀力大于100 MJ·mm/(h·hm2)等级的降雨事件的土壤侵蚀模数与降雨特征拟合分析得到:M=1.269EI60以及M=0.324PI60;(4)降雨集中时间在1~6h的降雨发生概率大,且泥沙侵蚀量大。6月、7月份降雨事件的产沙量占总产沙量的78%左右,汛期(尤其是6月、7月份)的水土保持工作尤为重要。6月、7月份降雨事件的土壤侵蚀模数与降雨特征拟合分析得到:M=1.378EI60以及M=0.346PI60。     

Repeatability of fin length measurements using digital image analysis and studies of fin erosion as indicator of social interactions in Atlantic cod (Gadus morhua)

The aims of this study were to examine fin erosion caused by social interactions between Atlantic cod (Gadus morhua) juveniles, and to evaluate the repeatability of recorded fin length using digital image analysis (DIA). Fin length of 2100 juvenile Atlantic cod was analysed using DIA, during a 6 weeks experiment. The lengths of the three dorsal fins and the caudal fin were measured by three different assessors (M, K, B) three times during the experiment. Repeatability was based on a sub set of data from 42 randomly chosen fish. Assessor M measured the length of the fins of the 42 fish three times (M1, M2, M3). M1 and M2 were done on the same day, while M3 was conducted 2 weeks later. Assessor K measured two times with a 2‐year interval, and assessor B measured the fin length only once. The correlations between replicated measurements within assessor were highest for assessor M measured on the same day indicating an effect of memory. Repeatability of fin length ranged from 0.57 to 0.73 for the four fins. Social interaction with respect to fin erosion was studied using data on the four fins from all 2100 fish. ‘Relative fin length’ (fin length/total body length × 100) was calculated to assess fin erosion. Results indicated that all four fins were eroded due to social interactions, but the caudal fin was most severely eroded. In conclusion, DIA can be used to measured fin length but the method could be improved by using chromatic pictures.     

黄土坡面径流输沙能力试验研究

为了建立合理的土壤侵蚀评价和预报模型,基于坡面流理论,通过室内径流冲刷模拟试验,以黄土坡面为研究对象.研究了坡面径流输沙能力.研究结果表明,当坡面侵蚀达到相对平衡时,在同一坡度条件下,坡面径流输沙率随流量的增加呈阶梯性增加,即表现为"缓一陡一缓一陡"的变化过程;坡面径流输沙率与坡度和流量之间存在指数函数关系,且流量对输沙率影响大于坡度;坡面径流输沙率与坡面径流切应力、单位水流功率及Re之间均存在着良好的线性关系.     

Threshold wind velocity as an index of soil susceptibility to wind erosion under variable climatic conditions

Wind erosion starts when the threshold wind velocity (µ_t) is exceeded. We evaluated the sensitivity of µ_t to determine the wind erosion susceptibility of soils under variable climatic conditions. Three years field data were used to calculate µ_t by means of the equation µ_t = ū ‐ σ Φ⁻¹ (γ), where ū is the mean wind speed (m s⁻¹), σ the ū standard deviation (m s⁻¹), γ the saltation activity and Φ the standard normal distribution function of γ. Saltation activity was measured with a piezoelectric sensor (Sensit). Results showed that ū of the whole studied period (3·41 m s⁻¹) was lower than µ_t (7·53 m s⁻¹), therefore, wind erosion was produced mainly by wind gusts. The µ_t values ordered in the sequence: Winter (6·10 m s⁻¹) < Spring (8·22 m s⁻¹) = Summer (8·28 m s⁻¹) < Autumn (26·48 m s⁻¹). Higher µ_t values were related to higher air humidity and lower wind speeds and temperatures. The µ_t values did not agree with the erosion amounts of each season, which ordered as follows: Summer (12·88 t ha⁻¹) > Spring (3·11 t ha⁻¹) = Winter (0·17 t ha⁻¹) = Autumn (no erosion). Low µ_t and erosion amounts of Winter were produced by a scarce number of gusts during eroding storms. We concluded that µ_t is useful as an index of soil susceptibility to wind erosion of different climatic periods. The use of a unique µ_t value in wind erosion prediction models can lead to erroneous wind erosion calculations. Copyright © 2008 John Wiley & Sons, Ltd.     

Interdisciplinary and multidisciplinary approaches to the study of long‐term soil degradation: A case study from Schleswig‐Holstein,Germany

Soil degradation is a serious problem and an important environmental issue in many ecosystems. Without integrative, interdisciplinary and historical approaches, understanding the effects of long‐term soil degradation is difficult. According to this idea it is hypothesized that in order to study long‐term natural and human‐induced soil degradation, it is necessary to use interdisciplinary and multidisciplinary approaches with respect to temporal and spatial landscape changes. The results of the investigation of colluvial sediments and soils in research area in Schleswig‐Holstein (Germany) with a high resolution in space and time—using the four‐dimensional landscape analysis—indicated the temporal and spatial variation of soils and sediments from the Mesolithic until Modern times. Intensive soil degradation occurred as a result of the land clearance and agricultural land use in the investigation areas since the Neolithic time. The general results of this investigation show that the use of an interdisciplinary and multidisciplinary approach with pedological and geomorphological perspectives for different times and places can help to reconstruct the long‐term natural and human‐induced soil degradation. Copyright © 2009 John Wiley & Sons, Ltd.     

Assessment of soil erosion hazard and prioritization for treatment at the watershed level: Case study in the Chemoga watershed,Blue Nile basin,Ethiopia

Soil erosion by water is the most pressing environmental problem in Ethiopia, particularly in the Highlands where the topography is highly rugged, population pressure is high, steeplands are cultivated and rainfall is erosive. Soil conservation is critically required in these areas. The objective of this study was to assess soil erosion hazard in a typical highland watershed (the Chemoga watershed) and demonstrate that a simple erosion assessment model, the universal soil loss equation (USLE), integrated with satellite remote sensing and geographical information systems can provide useful tools for conservation decision‐making. Monthly precipitation, soil map, a 30‐m digital elevation model derived from topographic map, land‐cover map produced from supervised classification of a Land Sat image, and land use types and slope steepness were used to determine the USLE factor values. The results show that a larger part of the watershed (>58 per cent of total) suffers from a severe or very severe erosion risk (>80 t ha⁻¹ y⁻¹), mainly in the midstream and upstream parts where steeplands are cultivated or overgrazed. In about 25 per cent of the watershed, soil erosion was estimated to exceed 125 t ha⁻¹ y⁻¹. Based on the predicted soil erosion rates, the watershed was divided into six priority categories for conservation intervention and 18 micro‐watersheds were identified that may be used as planning units. Finally, the method used has yielded a fairly reliable estimation of soil loss rates and delineation of erosion‐prone areas. Hence, a similar method can be used in other watersheds to prepare conservation master plans and enable efficient use of limited resources. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification of sediment source and sink areas in a Himalayan watershed using GIS and remote sensing

Erosion is a natural geomorphic process occurring continually over the Earth's surface and it largely depends on topography, vegetation, soil and climatic variables, and therefore, exhibits pronounced spatial variability due to catchment heterogeneity and climatic variation. This problem can be circumvented by discretizing the catchment into approximately homogeneous sub‐areas using GIS. In this study, the remote sensing and GIS techniques (through Imagine®8.6 and ArcGIS®9.1 software) were used for derivation of spatial information, catchment discretization, data processing etc. for the Himalayan Chaukhutia watershed (India). Various thematic layers for different factors of USLE were generated and overlaid to compute spatially distributed gross soil erosion maps for the watershed using 18‐year rainfall data. The concept of transport limited accumulation was formulated and used in ArcGIS® for generating the transport capacity maps. Using these maps, the gross soil erosion was routed to the catchment outlet using hydrological drainage paths, for derivation of transport capacity limited sediment outflow maps. These maps depict the amount of sediment rate from a particular grid in spatial domain and the pixel value of the outlet grid indicates the sediment yield at the outlet of the watershed. Up on testing, the proposed method simulated the annual sediment yield with less than ±40% error. Copyright © 2009 John Wiley & Sons, Ltd.