Re-defining tillage erosion: quantifying intensity–direction relationships for complex terrain

Abstract. Current tillage erosion models account for the influence of tillage direction in the magnitude of the soil (tillage) transport coefficient. It is argued here that this is counter-intuitive and causes significant problems in modelling tillage erosion in areas of complex terrain. This article examines whether a re-modelling of tillage erosion is possible that separates tillage direction (an interaction with the landform) from the soil transport coefficient (a measure of tillage intensity representing the combination of implement erosivity and soil erodibility). Experimental data for mouldboard ploughing upslope, downslope and cross-slope at Coombe Barton Farm, Devon are examined. Integration of data for all directions into a single relationship, which relates translocation in the direction of tillage to slope in the direction of tillage and translocation perpendicular to tillage to slope perpendicular to tillage, is not possible using previously published methods of analysis. However, when total translocation distance is regressed against the tangent of the slope at 45° to the tillage direction (bisecting the tillage direction and the direction of overturning) it is found that a single relationship can be used to describe tillage in all three directions. Therefore, this relationship is used to determine a single value of the soil transport coefficient ( k _fTa) for constant soil and implement conditions but different tillage directions. This redefinition of tillage is important both for true estimation of tillage erosion severity, the adirectional coefficient being 40% larger than the directional coefficient, and for modelling of tillage erosion in complex terrain. These improvements are vital when tillage erosion simulation is used to direct soil conservation strategies.     

Spatial pattern analysis of pre- and post-hurricane forest canopy structure in North Carolina,USA

Existing spatial patterns of a forest are in part a product of its disturbance history. Using laser altimetry and field measures of canopy top height to represent pre- and post-hurricane canopy topography, respectively, we measured changes in spatial patterns of stand structure of a United States southern mixed coniferous-deciduous for est. Autocorrelative and fractal properties were measured in this opportunistic study to quantify changes in canopy architecture along twelve, 190-250 m transects that were subjected to moderate to high levels of wind disturbance. Prior to the hurricane, canopy heights were autocorrelated at scales <40 m with an average fractal dimension of 1.71. After the disturbance, autocorrelation disappeared; the average fractal dimension rose to 1.94. This shift towards spatial randomness illustrates part of the cyclical nature of ecosystem development. It shows how a catastrophic collapse of biomass accumulation corresponds to a decrease in ecosystem organization across a landscape. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于GIS技术的小型水库规划方法

在小流域治理中，为了提高水库规划的精确度和速度，提出了基于GIS技术来实现小型水库规划的方法。主要是基于GIS技术的库客曲线的制作方法；小型水库规划的可视化。在GIS中，真实地形在计算机中的表达用数字高程模型(DEM)表示，水库规划的三维可视化环境的实现需利用0penGL技术。     

黑土小流域沟道分布遥感监测及主控因素研究

为了对典型黑土区小流域沟道分布进行遥感监测,并解析影响其发育的主控因素,选择黑龙江省海伦市光荣村为研究区,通过对遥感影像和地形图的目视解译判读和空间分析,量化汇水区面积、坡长等12个变量,结合对264条切沟与等高线分布关系的地貌学分析、统计分析和野外详查,解译地表径流和机耕道作用等6种情形,对典型黑土区小流域切沟发育主控因素进行探讨。结果表明,研究区林地面积大小不能直接控制切沟发育,林地内活跃沟长占活跃切沟总长的46.2%。小流域汇聚坡是切沟发育的典型地形,沟长占总长的68.1%,汇聚坡导致地表集中径流,沟长占总长的63.0%。汇水区面积和坡长是影响沟长的最主要因素,而小流域坡度是影响沟密度的显著因素。同时,切沟侵蚀多伴生于农田机耕道路一侧,机耕道旁沟长约占其总长的23.3%。研究表明,黑土区切沟侵蚀主要与机耕道促进地表径流的作用密切相关,侵蚀沟综合治理必须考虑小流域景观布局和山水林田湖草综合治理,应将农田机耕道路周边大型活跃切沟防控作为黑土区保护的重中之重。     

实验地貌的动态观测装置

实验地貌的动态观测对于研究沟坡的侵蚀过程和发生机制具有重要意义.在介绍实验地貌动态观测装置——MX - 2010 -G型地貌仪的基础上,采用传统钢尺+水准仪观测方法以及地貌仪测量方法,测量同一坡体的体积,以率定地貌仪的观测精度.结果表明:对于5组不同坡度、体积约为2.4万cm3的沟坡模型,地貌仪测量的体积相对误差可以控制在±10％以内,其中绝对值最大相对误差为9.0％,绝对值最小误差为-0.4％;对于120 cm×140 cm范围内的坡面,10个检查点空间坐标在x、y、z 3个方向上的均方误差平均值分别为0.99、0.84和0.42 cm;在6个断面测点系列高程值线性回归分析中,回归系数6与相关系数R2值均接近于1.结果表明,该地貌仪能够对沟坡微地貌的变化过程进行精确的观测.     

基于地形校正的植被净初级生产力遥感模拟及分析

植被净初级生产力（NPP）模拟研究对碳平衡监测及深入理解碳循环具有重要意义。高空间分辨率、短重访周期的遥感数据和地形校正成为精准模拟山区植被NPP研究的必然选择。在利用DEM数据对太阳总辐射和气温进行地形校正的基础上,估算了研究区植被吸收光合有效辐射因子、温度胁迫因子、水分胁迫因子和典型植被类型的最大光能利用率,构建了改进的CASABTC估算模型,利用HJ-1CCD数据模拟了2009年大别山区植被的NPP,并探讨了其时空变化特征。结果表明：1）由该文模拟值与MOD17A3的精度验证结果分析,基于地形校正的CASABTC模型和HJ-1数据适合精确模拟山区植被的NPP;研究区NPP在冬季比在春、秋、夏季受地形起伏的影响大。2）该文模拟的年NPP平均值为413.7 g/(m2·a)比MOD17A3平均值偏小4.9%,在空间分布上前者更加详细,地表特征更明显。3）研究区2009年NPP模拟值范围为0～1143.6 g/(m2·a),研究区总面积66.1％的NPP值在200～600 g/(m2·a)之间;年总NPP为9.891×106t,约占全国年总NPP的3.2‰,整体上呈现高、低值区交错分布的不规则特点。4）月NPP值随季节而变化,所有植被类型的NPP季节变化曲线都呈典型的单峰分布,且不同植被类型NPP的季节变化幅度有差别。月NPP值的季节变化与气温、太阳总辐射及NDVI的季节变化基本吻合,而降水量年内分配不均与NPP无相关性特点。5）各植被类型的月NPP和总NPP随海拔高度上升而逐渐变大,对于后者当海拔高度上升至1100 m时达到最大值,继续上升,其保持在600 g/m2左右不变。该研究可为后续基于HJ-1数据的山区植被NPP模拟提供参考。     

Roughness of biopores and cracks in Bt‐horizons assessed by confocal laser scanning microscopy

In structured soils, water and reactive solutes can preferentially move through larger inter‐aggregate pores, cracks, and biopores. The surface roughness of such macropores is crucial for describing microbial habitats and the exchange of water and solutes between macropores and the soil matrix together with other properties. The objective of this study was to compare the roughness of intact structural surfaces from the Bt‐horizons of five Luvisols developed on loess and glacial till and to test the applicability of confocal laser scanning microscopy. Samples of 5 to 10 cm edge length with intact structural surfaces including cracks with and without clay‐organic coatings, earthworm burrow walls, and root channels were prepared manually. The surface roughness of these structures was determined with a confocal laser scanning microscope of the type Keyence VK‐X100K. The root‐mean‐squared roughness (R_q) the curvature (R_cu) and the ratio between surface area and base area (R_A) were calculated from selected surface regions of interest of 0.342 mm² with an elevation resolution of 0.02 µm. The roughness was smaller for coated as compared to uncoated cracks and earthworm burrows of the Bt‐horizons. This reduction of roughness by the illuviation of clayey material was similar for the structural surfaces of the coarser textured till‐Bt and the finer‐textured loess‐Bt. This similarity suggested a dominant effect of pedogenesis and a minor effect of the parent material on the roughness levels of structural surfaces in the Bt‐horizons. An expected “smoothing” effect of burrow wall surfaces by earthworm activity was not reflected in the roughness values compared to those of uncoated cracks at the chosen spatial scale. However, for root channel walls from one loess‐Bt, the roughness was reduced as compared to that of other structures. These results suggest that the surface roughness of the structural surface types should separately be considered when describing preferential flow and macropore‐matrix exchange or analysing root growth, microbial habitats, and colloidal transport in structured soils. The confocal laser scanning microscopy technique was found useful for characterizing the roughness of intact structural surfaces.     

秦巴山区土地利用时空格局及地形梯度效应

自然景观的垂直地带性为区域土地利用的垂直景观格局奠定了基础,同时也决定了垂直景观带上土地利用的强度及其变化情况。该文采用地形位指数、分布指数、土地利用程度综合指数和土地利用信息图谱法等,分析了1989-2010年秦巴山区土地利用格局的地形梯度效应和图谱信息,揭示地形控制下土地利用时空格局和土地转移的变化规律。结果表明:1)秦巴山区土地利用以林地和耕地为主,呈西林东耕分布;1989-2010年间林地减少显著,建设用地增加明显,其中耕地是建设用地主要转入来源,林、草地是耕地主要转入来源。2)秦巴山区各生态亚区用地类型差异明显,各生态亚区土地利用转移方向也存在差异性。3)秦巴山区土地利用强度指数呈东高西低,中高周低的态势;土地利用强度变化率稳定少动,增加趋势不明显;土地利用动态度呈中高周低的态势,整体变化不大。4)水域、建设用地和耕地主要集中在地形起伏度小和坡度小的低地形位,且耕地主要转移为其他两种用地类型,建设用地有向中低地形位分布的趋势。林地和草地集中在地形起伏大、坡度陡的中高地形位,且存在着相互转移演替现象,中低地形位往往是耕地、林地、草地间的相互转换,未来势必加强坡耕地和低山丘陵区林草地的管治工作。     

点云数据抽稀与加密对微地形数据分析的影响

针对不同观测尺度下,大起伏(20cm耕作处理)、微起伏(耙平裸坡处理)两种地形的点云数据进行抽稀、加密处理,选取地表曲率、坡向、地表糙度3种直观的指标对抽稀、加密处理对微地形数据分析的影响进行了评价。结果显示:抽稀与加密处理对于起伏较大的地形曲率影响更为明显,对于起伏较小的地形则影响不显著。5,10mm数据抽稀与加密处理后坡向变化不显著。1mm尺度抽稀地表糙度的影响十分规律,5mm加密与抽稀对于大起伏地形的影响十分复杂,10mm加密对于大起伏地形糙度变化较为复杂,裸坡变化则相对规律。     

六盘山香水河小流域地形与植被类型对降雨径流系数的影响

基于GIS和SPSS支持下的数据分析,结合宁夏六盘山区香水河小流域2004—2005年6—10月的降雨、径流观测资料,对流域的坡向、海拔和植被对降雨径流的影响进行研究,结果表明：就不同植被类型来看,径流系数以人工林的最大,灌丛的次之,亚高山草甸的最小;就海拔而言,径流系数大小依次为低海拔（2060-2350 m）〉中海拔（2350-2640 m）〉高海拔（2640-2930 m）,随着海拔从低到高的变化,天然林的径流系数表现为从高到低再升高的变化趋势,而人工林和灌丛则表现为先增加后减小的变化趋势,亚高山草甸从中海拔至高海拔区呈增大趋势;从不同坡向来看,径流系数大小依次为南坡〉西坡〉北坡〉东坡。