Collaborative Research: The Significance of the Loess Mantle in Midwestern Soil Catena Evolution

美国中西部的景观至少部分被黄土覆盖，晚更新世期间沉积的风吹尘埃，然后通过山坡侵蚀广泛重新分布。 许多观察表明，薄黄土覆盖层的存在可以增加土壤形成过程的速率，并影响重要的生态特性，如养分或水分保持。 这项研究计划将探讨黄土覆盖层在土壤链演变中的相对重要性，土壤链是山坡土壤变化的可预测模式。 在可能的解释范围的一个极端，黄土厚度的局部模式可能已经确定在晚更新世，灰尘沉积和迅速重新分布下坡。 从那时起，黄土覆盖层就扮演了一个至关重要但基本上是静态的土壤形成控制角色。 另一方面，生物过程，如土壤物质的混合和分类的穴居动物，可能会增加或甚至取代所发挥的作用，黄土地幔在确定土壤性质的空间格局。 这种解释意味着一个更动态的历史链的发展，生物力学过程逐步移动土壤下坡，并产生一个细粒表面地幔，有利于土壤的快速发展。 在这个项目中，研究人员将进行粒度和矿物学分析，以估计明尼苏达州和威斯康星州研究区土壤链中黄土的实际含量。 在存在黄土的情况下，下坡再分布的时间将根据坡脚天然“陷阱”中的沉积物来解释。 将使用几种方法，包括光激发光测年法，来确定土壤混合的程度。 最后，黄土和生物力学过程对生态重要的土壤特性的相对影响将在两个研究领域的catenas调查，该项目的结果将有广泛的影响，长期和短期的变化，在土壤景观的中西部和世界上许多其他地区的黄土地幔可能会影响catenas的演变。 如果当地黄土厚度在很大程度上是对土壤形成过程的静态控制，那么加速侵蚀将黄土移走，可能会不可逆转地改变土壤发育的速度或方向，这反过来又会改变植物的生产力和许多人类土地利用的适宜性。 气候变化加速的史前侵蚀或近期土地使用变化引发的快速侵蚀都是如此，在估计土壤侵蚀的可容忍速度时显然需要考虑到这一点。 另一方面，如果生物力学过程在促进土壤形成方面发挥了重要作用，那么从长远来看，即使在严重侵蚀之后，土壤景观最终也可以恢复。 这项研究的这些影响将提交给科学界，并通过在研究领域的公众宣传，那里对可持续土地利用的兴趣日益浓厚。 研究生和本科生都将参与该项目，学习土壤成因和地貌学研究的许多最重要的技术。

Landscapes across the Midwestern United States are at least partially mantled by loess, wind-blown dust deposited during the Late Pleistocene and then extensively redistributed by hillslope erosion. Many observations suggest that the presence of a thin loess mantle can increase the rates of soil-forming processes and influence ecologically important properties such as nutrient or water retention. This research project will investigate the relative importance of a loess mantle in the evolution of soil catenas, which are predictable patterns of soil variation down hillslopes. At one extreme in the range of possible interpretations, the local pattern of loess thickness may have been determined in the Late Pleistocene, as dust was deposited and rapidly redistributed downslope. Since that time, the loess mantle has acted as a critically important but largely static control on soil formation. On the other hand, biological processes, such as mixing and sorting of soil materials by burrowing animals, may augment or even replace the role played by a loess mantle in determining the present spatial pattern of soil properties. This interpretation implies a much more dynamic history of catena development, as biomechanical processes progressively move soil downslope and generate a fine-grained surface mantle that is conducive to rapid soil development. In this project, the investigators will conduct analyses of particle size and mineralogy to estimate the actual amount of loess present in soil catenas of study areas in Minnesota and Wisconsin. Where loess is present, the timing of downslope redistribution will be interpreted from the sediments in natural "traps" at the foot of slopes. Several methods, including optically stimulated luminescence dating, will be used to characterize the extent of soil mixing. Finally, the relative influence of loess and biomechanical processes on ecologically important soil properties will be investigated in catenas of both study areas.The results of this project will have broad implications for long- and short-term change in the soil landscapes of the Midwest and many other regions of the world where a loess mantle may influence catena evolution. If local loess thickness is a largely static control over soil-forming processes, then accelerated erosion that removes loess may irreversibly change the rates or directions of soil development, which in turn can alter plant productivity and suitability for many human land uses. This would be true of prehistoric erosion accelerated by climatic change or rapid erosion triggered by recent land use change and would clearly need to be taken into account in estimating tolerable rates of soil erosion. On the other hand, if biomechanical processes play a major role in enhancing soil formation, then the soil landscape can ultimately be renewed over the long run, even after severe erosion. These implications of this research will be presented to the scientific community and through public outreach in the study areas, where there is a keen and growing interest in sustainable land use. Both graduate and undergraduate students will participate in the project, learning many of the most important techniques of research on soil genesis and geomorphology.