引用本文:胡亚鲜,Nikolaus J. Kuhn.利用土壤颗粒的沉降粒级研究泥沙的迁移与分布规律[J].土壤学报,2017,54(5):1115-1124. DOI:10.11766/trxb201703100056
HU Yaxian,Nikolaus J. KUHN.Using Settling Velocity to Investigate the Patterns of Sediment Transport and Deposition[J].Acta Pedologica Sinica,2017,54(5):1115-1124. DOI:10.11766/trxb201703100056
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利用土壤颗粒的沉降粒级研究泥沙的迁移与分布规律
胡亚鲜1, Nikolaus J. Kuhn2
1.西北农林科技大学水土保持研究所;2.瑞士巴塞尔大学环境科学系
摘要:
了解不同粒径泥沙迁移运动规律,有助于深入理解侵蚀条件下碳、氮、磷等元素的生物地球化学过程。土壤营养元素的迁移转化与泥沙颗粒的运动规律密切相关,而泥沙的运动规律由颗粒大小、性状、孔隙度和密度等因素共同决定。依据泥沙颗粒沉降速度分选的原理,针对中国两种典型侵蚀土壤(红壤和黄绵土),分别进行了土壤机械组成(矿质土粒分选)和沉降速度分选测定。结果表明,土壤颗粒的沉降粒级可有效区分红壤和黄绵土中不同粒径团聚体的沉降速度,能够更加准确地反映出同一粒径颗粒因性状、密度和孔隙度的差异而形成的不同沉降速度。相对于质地疏松的黄绵土,红壤的机械组成显示,有86.9%的有机碳与 ≤32 μm 的矿物颗粒相结合,很有可能随悬移过程汇入下游水体。但土壤颗粒沉降速度分布表明,约有90.5%的红壤有机碳与等效石英粒径 ≥63 μm的团聚体相结合,易在经历较短的迁移过程后,快速沉积于下坡面。这表明,现有的土壤侵蚀模型大多利用土壤机械组成(即矿质粒径大小)在反映泥沙运动或元素迁移规律方面存在片面性。土壤的团聚过程可有效缩减有机碳和无机碳的迁移距离,从而使其更易沉积于陆生环境。土壤颗粒的沉降速度分级对认识泥沙颗粒和养分元素在侵蚀—迁移—沉积过程中的生物地球化学过程提供了新的途径和视角。
关键词:  沉降管法  沉降速度  团聚体  迁移距离  有机碳  无机碳
基金项目:国家自然科学基金项目(41371279)和西北农林科技大学基本科研业务费专项基金项目(2452017191)资助
Using Settling Velocity to Investigate the Patterns of Sediment Transport and Deposition
HU Yaxian1, Nikolaus J. KUHN2
1.Institute of Soil and Water Conservation, Northwest A&F University;2.Physical Geography and Environmental Change, Department of Environmental Sciences, University of Basel
Abstract:
【Objective】 Knowledge about the transport patterns of sediment helps to understand the erosion-induced biogeochemical processes of C, N and P. The sediment transport distance is closely associated with its settling velocity distribution, which is dependent on the size, shape, density and porosity of sediment particles. In fact, aggregation processes turn fine particles into large aggregates, speeding up the settling velocity of individual particles and shortening their transport distances. However, most of the soil erosion models currently available are using soil texture or mineral particle distribution, therefore cannot fully reflect the transport behavior of sediment particles. 【Method】 Two typical types of soils in China, red soil (Hapli-Udic Ferrosols) and loess soil (Loessi-Orthic Primosols), were investigated in this study. The two soils had similar texture, but were distinctive in aggregate stability and soil organic carbon content. They were, therefore, considered as suitable objects in this study to explore the potential differences between settling velocity distribution and mineral size distribution. The two soils were fractionated by two methods: conventional wet-sieving into mineral size distribution; and settling tube fractionation into settling velocity distribution. The weight distribution, total organic carbon concentration and total inorganic carbon concentration of individual classes were measured and compared. 【Result】 Results show that, compared with the conventional soil mineral size distribution, fractionation using settling tube is more effective in distinguishing the settling velocity distributions of red soil and loess soil. This is because clay-sized particles are more likely to be cooperated into aggregates, which facilitate the settling velocity of individual mineral particles, and thus largely shorten their potential transport distance. In particular in the better aggregated red soil, about 86.9% of the soil organic carbon was associated with fine particles ≤32 μm, which is very likely to stay as suspension and thus transported downstream once erosion occurs. However, as a matter of fact, about 90.5% of the soil organic carbon was combined with coarse aggregates of equivalent quartz size ≥63 μm, which would probably be deposited at the footslope immediately after short transport distance. Similar patterns of soil inorganic carbon distributions were observed in the loess soil. All the findings demonstrate that aggregation effects can effectively shorten the transport distance of soil organic and inorganic carbon and skew their distributions towards the terrestrial system than if otherwise predicted by mineral size distributions. 【Conclusion】 Settling velocity specific redistribution of sediment particles casts new light on our current understanding of C, N and P biogeochemical processes during soil erosion and sediment transport and deposition. Therefore, settling velocity specific distribution of sediment particle should be considered as a soil erodibility parameter to be applied to soil erosion models.
Key words:  Settling tube  Settling velocity  Aggregates  Transport distance  Organic carbon  Inorganic carbon