Significant Differences In Particle Size Distributions Research Articles

红壤坡面土壤团聚体特性与侵蚀泥沙的相关性

PDF HTML阅读 XML下载 导出引用 引用提醒 红壤坡面土壤团聚体特性与侵蚀泥沙的相关性 DOI: 10.5846/stxb201611112299 作者: 作者单位: 浙江大学环境与资源学院,浙江大学环境与资源学院,浙江大学环境与资源学院 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（41471221） The relationship between soil aggregates and eroded sediments from sloping vegetated red soils of South China Author: Affiliation: College of Environmental and Resource Sciences,Zhejiang University,Zhejiang Provincial Key Laboratory of Agricultural Resources and Environment,College of Environmental and Resource Sciences,Zhejiang University,Zhejiang Provincial Key Laboratory of Agricultural Resources and Environment,College of Environmental and Resource Sciences,Zhejiang University,Zhejiang Provincial Key Laboratory of Agricultural Resources and Environment Fund Project: National Natural Science Foundation of China [grant number 41471221] 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:借助室内人工模拟降雨试验为研究手段，以强降雨过程中红壤丘陵区坡菜地侵蚀泥沙颗粒组成及土壤团聚体稳定性变化特征与规律为研究目的，分别在不同坡长（2，3，4m）、不同植被覆盖度（0，30%，60%，90%）条件下进行了有效模拟降雨试验共计12场次，每场次降雨试验的产流历时设计为30min，固定雨强为2.0mm/min。试验结果表明：1）侵蚀泥沙中颗粒粒径以 < 2μm粘粒和2-20μm细粉粒为主。在原土中，粘粒（0-2μm）和细粉粒（2-20μm）含量之和占总量的43.92%，在泥沙中粘粒和细粉粒之和占总量的约57.08%，均出现不同程度的增加；2）在不同处理中，坡面土壤 > 1mm干筛法团聚体含量明显大于湿筛团聚体（ > 1mm）的含量，可认为水稳性团聚体的含量更能作为衡量土壤结构的稳定性的指标。 > 0.25mm团聚体分散度（PAD0.25）和 > 2mm团聚体分散度（PAD2）含量均出现增大，而 > 0.25mm水稳性团聚体含量（WAS0.25）减少，植被覆盖度对土壤团聚体稳定性影响明显强于坡长；3）WAS0.25含量是影响侵蚀泥沙的颗粒粒径分布的主要因素，随着坡面土壤中WAS0.25的增加，侵蚀泥沙的平均重量直径逐渐降低。同时，泥沙颗粒平均直径与土壤团聚体平均重量直径（MWD团聚体）含量呈极显著负相关，可知坡面大团聚体越稳定，坡面土壤的粗化过程越不易形成。 Abstract:Soil erosion is a serious problem that has significant environmental impacts, including declines in soil quality, sedimentation of reservoirs, and nonpoint source water pollution. Thus, it is important to study soil erodibility and mechanisms for nutrient loss on sloping land. Plenty of studies have researched soil erosion factors, such as land use patterns, plant cover type and ratio, slope length and gradient, rainfall intensity and amount, and raindrop kinetic energy; these studies have been key to characterizing these processes. It is generally recognized that plant cover and slope length have a significant impact on soil erosion and nutrient loss. However, these parameters have often been studied in isolation, and few have researched the combined effects of sedimentation and nutrient loss. In this study, we analyzed the effects of slope length and plant cover ratio on the particle size distributions (PSDs) of soil and eroded sediments from sloping vegetated fields under heavy rainfall. We evaluated the change in soil aggregate stability characteristics to explain the relationship between PSDs of the eroded sediment and soil aggregate stability. Twelve simulated rainfall experiments were conducted in a glasshouse with a rainfall intensity of 2mm/min and runoff was produced within 30min. For this study, we implemented three slope lengths, 2, 3, and 4m, and four levels of vegetation cover ratios, 0, 30%, 60%, and 90%, in 2014 and 2015. The micropipette method was used for particle size analysis of soils and eroded sediments. Surface soil samples before and after rainfall were separated into five soil aggregate sizes, > 2mm, 1-2 mm, 0.5-1mm, 0.25-0.5mm, and < 0.25mm, by dry sieving and wet sieving. The experimental indexes to evaluate soil aggregate stability included water stable aggregates (WSA), mean weight diameter (MWD), and dispersion degree of soil aggregate (PAD). The results showed that clay particles ( < 2μm) and fine silt particles (2-20μm) were the main size fractions in eroded sediments. Surface runoff, which causes soil erosion, is a selective transport process; hence, there were more clay particles and fine silt particles in the eroded sediments (approximately 57.08%) than in the original soils (43.92%). The proportion of clay particles in the eroded sediment increased slightly as the vegetation cover ratio increased. There were no significant differences in PSDs of eroded sediments for different slope lengths with the same cover ratio (P > 0.05). The content of > 2mm and > 0.25mm PAD (PAD0.25, PAD2) increased, whereas the content of > 0.25mm WSA (WSA0.25) decreased after rainfall. Vegetation cover ratio had a more significant effect on > 0.25mm soil aggregate stability than did slope length. We found that the WSA index generally reflected the difference in soil structure stability. WSA0.25 was the main factor affecting PSDs of eroded sediments; the MWD content of the eroded sediments decreased gradually whereas WSA0.25 content increased. We also found a significant negative correlation between PSDs of eroded sediment and MWD of soil aggregate. Finally, we observed that more stable soil macro-aggregates resulted in less coarse soil surfaces. 参考文献 相似文献 引证文献

Effect of mastication on lipid bioaccessibility of almonds in a randomized human study and its implications for digestion kinetics, metabolizable energy, and postprandial lipemia

Background: The particle size and structure of masticated almonds have a significant impact on nutrient release (bioaccessibility) and digestion kinetics.Objectives: The goals of this study were to quantify the effects of mastication on the bioaccessibility of intracellular lipid of almond tissue and examine microstructural characteristics of masticated almonds.Design: In a randomized, subject-blind, crossover trial, 17 healthy subjects chewed natural almonds (NAs) or roasted almonds (RAs) in 4 separate mastication sessions. Particle size distributions (PSDs) of the expectorated boluses were measured by using mechanical sieving and laser diffraction (primary outcome). The microstructure of masticated almonds, including the structural integrity of the cell walls (i.e., dietary fiber), was examined with microscopy. Lipid bioaccessibility was predicted by using a theoretical model, based on almond particle size and cell dimensions, and then compared with empirically derived release data.Results: Intersubject variations (n = 15; 2 subjects withdrew) in PSDs of both NA and RA samples were small (e.g., laser diffraction; CV: 12% and 9%, respectively). Significant differences in PSDs were found between these 2 almond forms (P < 0.05). A small proportion of lipid was released from ruptured cells on fractured surfaces of masticated particles, as predicted by using the mathematical model (8.5% and 11.3% for NAs and RAs, respectively). This low percentage of lipid bioaccessibility is attributable to the high proportion (35–40%) of large particles (>500 μm) in masticated almonds. Microstructural examination of the almonds indicated that most intracellular lipid remained undisturbed in intact cells after mastication. No adverse events were recorded.Conclusions: Following mastication, most of the almond cells remained intact with lipid encapsulated by cell walls. Thus, most of the lipid in masticated almonds is not immediately bioaccessible and remains unavailable for early stages of digestion. The lipid encapsulation mechanism provides a convincing explanation for why almonds have a low metabolizable energy content and an attenuated impact on postprandial lipemia. This trial was registered at isrctn.org as ISRCTN58438021.

Observations on fresh forage intake, ingesta particle size and nutrient digestibility in four species of macropod

The particle-size distributions of the ingesta of the sacciform forestomach in free-ranging animals of a grazing macropod species [Macropus eugenii (tammar wallaby)], a grazer/browser [Macropus parma (parma wallaby)], a browser/grazer [Petrogale penicillata (brush-tailed rock-wallaby)] and a browser [Wallabia bicolor (swamp wallaby)] from Kawau Island, New Zealand, were compared with those of captive animals maintained on a standing ryegrass (Lolium perenne) sward. Nutrient digestibility was also measured in tammar and parma wallabies fed ryegrass or browse, i.e. fresh mahoe (Melicytus ramiflora) and this was related to particle-size distributions of the ingesta.There were significant differences in the particle size distributions of digesta from tammar and parma wallabies in the wild but not in captivity. In free-ranging animals the ingesta from both browsing species, the brush-tailed rock-wallaby and the parma wallaby, contained consistently greater proportions of coarse particles and smaller proportions of fine particles than did those of the tammar wallaby. These differences may be correlated with reported differences in their tooth morphologies. However, the presence of significant differences in particle-size distributions of the digesta between brush-tailed rock-wallabies and parma wallabies when constrained to grass, despite reported similarities in their tooth morphology, suggests that factors other than tooth morphology contribute to differences in the oral processing of food by browsing and grazing macropods. There were greater proportions of grass fragments in the coarse than in the finer fractions of ingesta from free-ranging brush-tailed rock-wallabies, indicating that this species is less effective at chewing grass.There were no overall differences between tammar and parma wallabies in the digestibilities of organic matter, neutral-detergent fibre (NDF) or acid-detergent fibre (ADF) but the NDF and ADF digestibilites of both species increased significantly with increase in the proportion of fine ingesta particles and with increase in mass of fermentative digesta.These findings indicate the importance of oral processing to digestive efficiency in macropods and the relationship between oral processing and tooth morphology.

The Role of the Western Harvester Ant (Pogonomyrmex occidentalis) in Soil Formation

AbstractThe effects of harvester ants (Pogonomyrmex occidentalis) on the physical and chemical properties of soils were determined for 20 ant mounds in the semiarid subalpine region of south‐central Colorado. Comparisons of soil materials in mounds of active colonies with surrounding unaffected soils showed significant differences in particlesize distribution and concentrations of CaCO3, exchangeable K, Na, Mg, and total N. The activity of ants in the study area appears to affect less ground surface area than in more humid regions (1 to 10% of respective land areas by regional comparison). The ants also tend to rearrange particles preferentially in the sand fraction instead of in the finer fractions as recorded for more humid regions. However, their role in nutrient enrichment of mound soils is similar to that of different ant species in other regions. The soil alterations induced by P. occidentialis are favorable for plant growth, and the ant mounds may aid revegetation in disturbed areas.