基于CT研究冻融对高寒草甸土壤孔隙结构的影响

冻融是影响高寒地区土壤结构的重要物理因素,以青海湖流域高寒草甸作为研究对象,通过野外采集原状土柱、室内冻融循环模拟、CT扫描和图像解译等方法,研究冻融循环对高寒草甸冻胀丘和丘间地的土壤大孔隙结构特征的影响。结果表明,随着冻融循环次数的增加,高寒草甸冻胀丘和丘间地土壤大孔隙度均呈现“减小—增加—减小”的趋势,冻融循环对土壤大孔隙度的降低主要在第1次冻融循环内形成的,且大孔隙的平均等效直径、平均体积、平均分枝长度、分枝密度和节点密度的变化规律与大孔隙度变化规律基本一致;冻融循环对高寒草甸冻胀丘土壤大孔隙的影响明显大于丘间地,其土壤大孔隙度随土层深度变化存在2个峰值,受冻融循环的影响,峰值大小和位置有所变动,且30—80 mm土层深度的土壤孔隙结构较草毡层其他位置更为敏感。     

小叶锦鸡儿灌丛化对退化沙质草地土壤孔隙特征的影响

以内蒙古太卜寺旗地区退化沙质草地为研究对象,对该地区的小叶锦鸡儿灌丛化草地中的灌丛斑块和草地斑块分别取原状土柱各三个进行CT扫描,利用Fiji软件分析土壤孔隙结构特征的差异。研究结果表明,小叶锦鸡儿灌丛化对土壤的孔隙结构有较大影响,灌丛斑块土壤的总孔隙数、大孔隙数、总孔隙度、大孔隙度和孔隙等效直径均大于草地斑块土壤,灌丛斑块土壤的平均大孔隙度是草地斑块土壤的3倍。草地斑块土壤的大孔隙主要分布在0~50 mm土层深度,而灌丛斑块土壤的大孔隙在0~400 mm深度都有分布,这与土壤中灌丛的丰富根系分布有关。     

风化花岗岩坡地土壤剖面大孔隙特性的空间分布

为了揭示侵蚀性风化花岗岩坡地不同部位土壤剖面大孔隙特性的空间分布,在浙江嵊州市水土保持监测站,同一坡面不同侵蚀强度的坡顶、坡中、坡底选取3个土壤剖面,进行了原状土柱(70cm)样品采集,用CT分层扫描与Arc GIS10.1图像解译技术,获得了系列数据,并计算了分析指标,研究了3个剖面大孔隙的分布规律和影响因素。结果表明:(1)3个土壤剖面均以大孔隙为主,1~3 mm孔径占比最大,5~7 mm占比最小。大孔隙个数的排序:坡中坡底坡顶。(2)大孔隙度与总孔隙度的差值随深度递减。大孔隙度大于均值的层位分布在0~30 cm之间。(3)成圆率影响大孔隙度与总孔隙度的关系。土壤黏粒和粉粒含量越多,成圆率越大。大孔隙度与土壤粗砂粒呈显著正相关,与黏粒和粉粒为显著负相关。(4)土壤侵蚀强度越大,大孔隙占比越大,孔隙结构性越差,漏水漏肥越严重。     

不同耕作措施下土壤孔隙的多重分形特征

首先利用数字图像处理技术提取了东北黑土区长期免耕(no tillage,NT)和翻耕(moldboardtillage,MT)制度下土壤切片中的孔隙信息,然后应用矩方法研究了两种耕作制度下土壤孔隙结构的多重分形特征。结果表明,免耕降低了表层(0~5 cm)大孔隙度(500μm),但是提高了10~15 cm和20~25 cm深度的孔隙度和大孔隙度。土壤孔隙结构在64~1 024像素尺度上具有多重分形特征。广义维(Dq)和多重分形谱(f(α))及相关参数能够反映切片中孔隙结构的特征。表层土壤孔隙多重分形谱明显右偏,随深度增加趋于对称。在同一深度下,免耕处理的Δα(α-10-α10)和ΔD(D-10-D10)均大于翻耕处理,免耕处理增加了孔隙结构的复杂程度,尤其是10~15 cm和20~25 cm深度下的孔隙结构。     

利用CT扫描技术对太湖地区主要水稻土中大孔隙的研究

采集了太湖地区3种主要水稻土（白土、黄泥土和乌栅土）的原状土柱为供试土样，利用CT扫描技术，在不破坏土体结构的前提下，准确地得出了不同深度土壤剖面上各种大孔隙的数量、面积以及分布状况。结果表明，3种水稻土均以表层的大孔隙度最大，在30～40cm处达到一个最低点，再往下又呈波浪形变化。土柱各截面上大孔隙面积的变异系数随着深度的变化与大孔隙度相似，大孔隙度大的层次其变异系数也较大。等效直径越大的孔隙（〉5mm）在土壤不同深度下数量的变化也越大。表层上大直径（〉5mm）的大孔隙较多，在土壤剖面30～40cm以下其数量急剧减少；而直径较小孔隙（〈1mm）的数量在土壤剖面不同深度下相差不大。     

耕作方式对东北黑土坡耕地土壤物理性状及根系垂直分布的影响

为了明确耕作方式对东北薄层黑土坡耕地土壤物理性状以及玉米根系垂直分布的影响,该研究以东北薄层黑土坡耕地土壤为研究对象,设置免耕和翻耕2种耕作方式,研究耕作方式对不同坡位土壤水稳性团聚体粒径分布与稳定性、土壤容重、土壤孔隙度、土壤贯入阻力以及玉米根系在垂直方向主要分布深度的影响,并进一步探究各指标间的相互关系。结果表明,与免耕相比,翻耕处理通过增加土壤1～2 mm粒级水稳性团聚体含量,降低0～20 cm土层土壤容重,改善0～20cm土层土壤孔隙度,降低10～20cm土层土壤贯入阻力,增加玉米根系在垂直方向主要分布深度;但同时翻耕处理条件下5mm粒级土壤团聚体含量平均减少59.1%,平均重量直径平均降低31.9%。翻耕处理下,坡位对土壤孔隙度、5 mm粒级水稳性团聚体含量以及平均重量直径的影响都呈现坡中位与坡下位优于坡上位。研究结果表明,对于东北薄层黑土坡耕地,在坡中位和坡下位采用翻耕有利于降低土壤紧实度,促进玉米根系下扎;在坡上位可采用免耕改善土壤结构及其稳定性。该研究可为促进黑土可持续发展提供理论依据与参考。     

青藏高原高寒草原草甸土壤团聚体及养分因子变化特征

为探讨青藏高原高寒草原草甸的土壤团聚体稳定性及有机碳等养分因子的变化分布，在青海省三江源区高寒地带选取样点分层采集土壤样品，进行室内测定并分析2种植被下土壤团聚体和养分因子的变化特征。结果表明：研究区土壤>0.25 mm水稳性团聚体含量（WSA）、平均质量直径（MWD）与几何平均直径（GMD）均为草甸>草原，而分形维数（D）与结构体破坏率（PAD）为草原>草甸，即青藏高原高寒草甸土壤团聚体稳定性大于高寒草原。高寒草甸土壤稳定性及养分含量随土层深度增加显著降低（P<0.05），草原土壤稳定性和养分含量随土层深度无显著变化趋势。高寒草原土壤稳定性与各养分含量随海拔升高而降低，高寒草甸土壤团聚体稳定性与养分随海拔升高先降低后增加。高寒草甸土壤团聚度与养分含量呈极显著相关（P<0.01），高寒草原土壤团聚度与养分无显著相关；>4，4~2，2~1 mm粒级团聚体是影响研究区土壤养分含量的主导粒径，其稳定性程度主要受大团聚体作用。研究结果对于青藏高原土壤质量评价、生态环境保护具有重要科学意义。     

青海湖流域土壤大孔隙特征与理化性质的相关性研究

土壤大孔隙是土壤水分、空气和化学物质运移优先流的主要途径。本文以青海湖流域土壤为研究对象,在青海湖沙柳河流域取原状土柱,利用CT扫描与Fiji软件相结合的方法,实现了土壤大孔隙结构的三维可视化,以及断层横截面土壤大孔隙度、大孔隙数量和大孔隙等效直径等的量化;并探讨了样地土壤大孔隙特征与理化性质的相关性。结果表明:青海湖流域土壤大孔隙主要分布在土壤表层0~100 mm,100 mm以下大孔隙较少;土壤全磷含量分别与土壤大孔隙数量、大孔隙等效直径有显著相关性;土壤全氮、有机质含量分别与土壤大孔隙平均等效直径有显著相关性;土壤体积质量与大孔隙度、大孔隙平均等效直径等有显著相关性;土壤中0.002≤Ф0.02 mm的颗粒含量与大孔隙的分布特征相关性较大。     

青海湖流域高寒草甸壤中流水分来源研究

通过对青海湖流域高寒草甸壤中流水分来源进行研究,以期揭示青海湖流域高寒草甸系统壤中流的产流机制。收集了大气降水、土壤水和壤中流中δ~(18)O和δD及实测降水数据,对比分析了大气降水、土壤水和壤中流的氢氧同位素特征,并使用了二源线性混合模型对壤中流进行了产流来源计算。结果表明:青海湖高寒草甸分布区大气降水线(LMWL)的斜率和截距均高于全球大气降水线(GMWL),降水较多的月份δ~(18)O、d-excess值较低;壤中流的水分来源与地形及其土壤深度密切相关,具体表现为:(1)壤中流在坡下土壤上层(0—40cm)和下层(40—80cm)产流氢氧同位素值相对聚集,并具有较明显的蒸发富集特征,表明该部分壤中流多源于降雨前储存于土壤中的水分,雨前土壤水对于壤中流在坡下土壤上层(0—40cm)和下层(40—80cm)产流的平均贡献率为85.88%和83.48%;(2)坡中壤中流水分来源因土壤深度而异,雨前土壤水对壤中流在坡中土壤下层(40—80cm)产流的平均贡献率为57.59%,表明大气降水和雨前土壤水贡献相当;壤中流在坡中土壤上层(0—40cm)产流与当地大气降水的季节变动基本一致,雨前土壤水对该层壤中流产流的平均贡献率为39.90%,表明其主要受到大气降水的驱动,与坡中金露梅灌丛根系和土壤孔隙分布有关。同时,随着雨前含水量、降水量和降水特征的不同,雨前土壤水和大气降水对于壤中流的贡献特征也会发生变化。     

重庆四面山草地土壤大孔隙的数量和形态特征研究

以重庆四面山草地为研究对象,利用染色示踪法观察优先流的发生区域,采用水分穿透曲线和Poiseulle方程分析土壤大孔隙的数量、形态特征及其对优先流的影响。结果表明:研究地土壤剖面大孔隙呈现聚集态分布,孔径范围在0.3~2.2mm之间,其中半径大于1.3mm的大孔隙是优先流发生的主要通道。各孔径范围内染色区土壤大孔隙数量较未染色区高出1个数量级,大孔隙数量随土壤深度增加而减小,这样的分布特征有利于水压梯度的形成,有助于水分的快速垂直运移。染色区较非染色区有更大的稳定出流速率,约1.12~2.02倍,这得力于大孔隙数量和密度上的优势,这一优势极大地影响了优先路径分布和优先流发生。     

Soil Macropore Structure Characterized by X-Ray Computed Tomography Under Different Land Uses in the Qinghai Lake Watershed, Qinghai-Tibet Plateau

Quantification of soil macropores is important to enhance our understanding of preferential pathways for water, air, and chemical movement in soils. However, the soil architecture of different land uses is not well understood in elusive alpine regions. The objective of this study was to quantify the architecture of soil macropores in a Kobresia meadow, farmland, and sand in the Qinghai Lake watershed of northeastern Qinghai-Tibet Plateau, China using X-ray computed tomography. Nine soil cores at 0–50 cm depth were collected at three sites with three replicates. At each site, the three collected cores were scanned using a GE Hi Speed FX/i medical scanner(General Electric, USA). To analyze soil architecture, the number of macropores, macroporosity, and mean macropore equivalent diameter within the 50 cm soil profile were determined from the X-ray computed tomography. Analysis of variance indicated that land use significantly influenced macroporosity, mean macropore equivalent diameter, and number of macropores. The soils of the Kobresia meadow and farmland had greater macroporosity and developed deeper and longer macropores than that of sand. For the Kobresia meadow, macropores were distributed mainly in the 0–10 cm soil layer, while they were distributed in the 0–20 cm soil layer for the farmland. The large number of macropores observed in the soils of the Kobresia meadow and farmland could be attributed to greater root development. The results of this study provided improved quantitative evaluation of a suite of soil macropore features with significant implications for non-equilibrium flow prediction and chemical transport modeling in soils.     

不同坡位杉木林土壤碳储量研究

通过实地调查取样和室内实验测定,比较了上坡和下坡杉木的土壤碳库及其垂直分布差异,研究了坡位对杉木人工林固碳功能的影响。结果表明,杉木上坡和下坡的枯枝落叶层有机碳贮量分别为0.9和1.1t/hm2,坡下的枯枝落叶层有机碳贮量较坡上高出32%。坡上和坡下的土壤有机碳贮量分别为149.9和174.2t/hm2,且表层(0-40cm)碳贮量分别占整个碳贮量(0-100cm)的55%和56%。上坡和下坡的土壤有机碳含量和贮量随土层深度的加深而递减,各土层的有机碳含量和贮量均表现为下坡高于上坡。     

基于CT扫描的斜坡非饱和带土体大孔隙定量化研究和三维重建

[目的]系统开展植被发育斜坡非饱和带土体中大孔隙定量化和三维重建技术研究,为水分沿大孔隙迅速运移研究提供可靠理论依据,对于降雨型滑坡研究具有基础性意义。[方法]采用CT技术对云南省昭通市盘河乡头寨滑坡滑源区左侧斜坡区两个尺寸为25cm×25cm×50cm的大尺度土柱进行扫描,得到一系列平面和纵向CT切片图像。图像处理并计算得到了土柱中大孔隙随深度的变化情况以及3种物质(砾石、土体基质和大孔隙)的CT值范围;借助VolView 3.4体可视化交互系统实现了三维大孔隙通道系统的重组,研究其在空间内的连通性、分支性和复杂性。[结果]包括根系通道、动物通道、干缩裂缝及团聚体间的结构性孔隙广泛发育于非饱和带土体中,且大孔隙分布异质性明显,波动变异较大,随着深度的增加大孔隙呈逐渐减小的趋势。三维重组清晰可见土柱内含有较多独立分布的大孔隙通道,它们具有较好的连通性。[结论]CT扫描技术作为非破坏性获得技术在斜坡非饱和土体大孔隙定量化和三维重建研究中应用是可行的。     

Exclosure on CT-measured soil macropore characteristics in the Inner Mongolia grassland of northern China

Purpose

Grassland exclosure is a widely-used option to prevent from grazing in degraded grasslands for restoration. However, the influence of exclosure on soil macropore of grassland remain scarce. The objective of this study was to quantify the pore architecture of grassland soils under exclosure.

Materials and methods

Two treatments, 9E (grassland enclosed for 9 years) and 5E (grassland enclosed for 5 years), were designed, with grazing as a control in the experiment. Nine soil columns (0–50 cm deep) were taken at the three sites with three replicates. At each site, three soil columns were from the grassland, and cores were scanned with a Philips Brilliance ICT Medical Scanner. Numbers of macropores, macroporosity, network density, length density, and node density within the 50-cm soil profile were interpreted from X-ray computed tomography to analyze soil pore architecture.

Results and discussion

The results indicated that exclosure significantly influenced CT-measured soil macroporosity in the Inner Mongolia grassland of northern China. Soils under enclosed grassland had greater macroporosity, length density, total volume, and node density than that of under freely grazed grassland. Macroporosity increased as the enclosure age increased. For soils under enclosed grassland, macropores were concentrated at 0–300-mm soil layers, and macropores were mainly present at 0–100-mm soil depth under freely grazed grassland. The large number of macropores found in soil under enclosed grassland can be attributed to greater root development.

Conclusions

Exclosure increases soil macroporosity and improve soil structure.

     

石质边坡枯枝落叶层的水土保持功能研究

为了解石质边坡枯枝落叶层的水土保持功能,对广东省顺德区大睡牛岗石质边坡枯枝落叶的蓄积量,枯枝落叶持水性能,枯枝落叶减少土壤侵蚀量,枯枝落叶层下土壤理化性质等内容进行了研究。结果表明:大睡牛岗枯枝落叶蓄积量为219.18 g/m²。枯枝落叶层最大持水率为64%～75%。枯枝落叶层厚度及径流深度影响径流流出时间,随着枯枝落叶厚度的增加,径流流出时间延长,随径流深度增大,径流时间缩短。覆盖枯枝落叶层能极显著地提高土壤抗冲性,与未覆盖枯枝落叶的模拟边坡相比,坡度30°,枯枝落叶2 cm,径流深度1 cm条件下,下坡、中坡、上坡枯枝落叶可减少87.80%以上的土壤侵蚀量。大睡牛岗豆科植被较多的坡位（下坡与上坡）其枯枝落叶层下土壤理化性质优于豆科植被较少的坡位（平台与中坡）。     

3-D soil macropore networks derived from X-ray tomography in an alpine meadow disturbed by plateau pikas in the Qinghai Lake watershed,north-eastern Qinghai-Tibetan Plateau

Purpose

The plateau pika (Ochotona curzoniae) is one of the main native soil faunas on the Qinghai-Tibet Plateau and plays a key role in the terrestrial ecosystem there. However, few studies have analysed the macroporosity of soils disturbed by plateau pikas in alpine meadows. The objective of this study was to examine the soil macropores in different parts of an alpine meadow in the Qinghai Lake watershed, namely, an original grassland, a new mound, an old mound, and a bald patch.

Materials and methods

In this investigation, soil cores were obtained from four different parts of an alpine meadow, namely, from under an original grassland, a new mound, an old mound, and a bald patch. A total of twelve soil cores (0–50 cm deep) were excavated, which included three replicates of each treatment. The soil architecture of each soil core was explored using X-ray computed tomography.

Results and discussion

The macroporosity decreased and then increased from the original grassland to the new mound, old mound, and bald patch. The soil macropores were most abundant up to a depth of 400 mm in the original grassland and up to a depth of 250 mm in the old mound and bald patch soils.

Conclusions

The macropores in the original grassland were attributed to well-developed root systems. The smaller and less continuous macropores in the new mound, old mound, and bald patch soils were mainly disturbed by plateau pikas. It was expected that water would move preferentially through the macropores in the original grassland, while surface flow would more readily occur in the new mound, old mound, and bald patch soils, thereby leading to soil erosion.

     

华北土石山区森林土壤中石砾分布特征对土壤大孔隙及导水性质的影响

为了探究土壤中石砾对大孔隙形成的作用及对饱和导水率的影响,研究京郊密云水库水源涵养林内土壤石砾分布特征、大孔隙分布特征以及与饱和导水率之间的关系。结果表明:(1)林区0—30cm土壤层内石砾体积含量范围为7.10%~22.05%,质量含量范围为10.76%~38.20%,且石砾多集中分布于5~10mm粒径范围内;石砾含量随坡向呈现阳坡阴坡半阴半阳坡的规律;(2)石砾含量与当量孔径1.5mm的孔隙密度呈现极显著相关关系(p0.01),粒径5mm的石砾体积含量与大孔隙密度具有显著相关性(p0.05),说明砾石主要影响较大孔隙,特别是粒径5mm的石砾对大孔隙的形成影响较大;(3)当量孔径1.5mm的孔隙数量仅占总孔隙数量的1.41%,但对导水速率的贡献率为54.44%;饱和导水率与其呈线性关系。     

X射线CT确定土壤大孔隙结构

Undisturbed soil core with many macropores and disturbed soil core with only one macropore (diameter is 10 mm) were probed by x-ray computed tomography (CT). The size, number, shape and continuity of macropores in the transverse and vertical sections of soil were characterized using CT scanning images. The probability densities of macropores in the transverse section of soil core exhibited a logarithmic F distribution. Results indicated that CT scanning was a promising nondestructive method for characterizing macropores in soils.     

Localization of denitrification activity in macropores of a riparian wetland

Soil structure heterogeneity in the form of macropores and preferential flow channels can complicate efforts to quantify the physical and biological characteristics of wetland systems. We collected soil cores from two riparian wetlands to determine whether soil associated with macropores had elevated denitrification potentials compared to bulk soil from the same core. Cores were inspected for obvious macropores, which were distinguished as visible holes in the core, sometimes with decaying root matter, or as highly unconsolidated layers that appeared to have a substantially lower bulk density than the surrounding soil. Denitrification potentials were significantly higher in pores (P<0.05) for six of the 16 cores that were obtained from the Cheraw State Park site. In cores obtained from a second site, denitrification potentials were significantly higher in pores for six of 20 cores and the trend of higher denitrification in pores was present in the majority of cores that had measurable activity. In cores with significant differences, denitrification was often 1-2 orders of magnitude greater in soil surrounding the macropore than in the bulk soil. Denitrification potentials of the bulk soils were similar in magnitude to the potentials measured in composited cores from previous studies. It is possible that the difference between macropore and bulk denitrification rates developed due to preferential flow of nitrate-rich water through the macropores. Previous work showed that water entering these riparian systems in groundwater and storm runoff had elevated levels of NO₃⁻.