Doctoral Dissertation Research: Spatio-Temporal Soil Variability on Late Quaternary Fluvial Surfaces of the Southeastern Atlantic Coastal Plain

这个博士论文项目的目标是了解时间对土壤形成过程的影响。土壤空间变异性存在于所有景观，可能会发生可预测的，在已知的地貌和土壤形成因素，或不可预测的，没有任何明显的关系，土壤形成因素的条件下可测量的变化。 这种变异性对土壤时序研究具有重要意义，土壤时序研究评估了时间对土壤发育的影响。 了解土壤性质如何随时间变化是至关重要的退化土壤的恢复和使用土壤作为相对年龄的工具，在第四纪地质研究，土壤年代序列仍然是经验数据的主要来源，以评估率和理论的土壤发展。 然而，空间变异性土壤的等效年龄可以提出理论和实际问题的时序方法。 在时间序列框架内，在确定主要的土壤形成过程、测试土壤形成模型并估计土壤形成速率之前，需要充分代表均匀年龄表面上的土壤空间变异性。 然而，相对较少的研究涉及这一主题。 因此，该项目的目标是表征土壤发育的范围内，不同年龄的晚第四纪河流表面在东南大西洋沿岸平原，以评估土壤变异和发展的时空趋势，并评估这些变化的驱动因素。这项研究将检查土壤的形态和化学发展的滚动条组件的三个河流表面，跨越约两个数量级（1,000与10,000与100,000年）沿着奥康-阿尔塔马哈（格鲁吉亚）和皮迪（南卡罗来纳州）河流的年龄范围。 将在每个河谷的每个表面上对两个滚动条进行采样，总共有12个采样滚动条，采样将由一项试点研究指导，该研究将确定在单个滚动条上充分描述土壤变异性所需的剖面数量和间距。 将对土壤特性进行评价，这些特性已被证明是该区域宝贵的时序参数，包括土壤总厚度、淋溶层厚度;以及厚度、粘土含量、红度、可提取的铁，和全土（2 mm）和细砂的总化学（0.125-0.250 mm）表现最好的土层的部分，其中有活跃的土壤形成发生（B层）。 多元统计技术将用于识别土壤变异的驱动因素，评估主导土壤形成过程，并评估空间变异对使用时序作为土壤形成和地貌研究工具的影响。通过在时序框架内表征土壤变异性，这项研究将直接解决近几十年来土壤地理研究中出现的关键问题，例如：1）土壤是朝着空间均匀的稳定状态条件收敛，还是随着时间的推移发散成越来越复杂的空间镶嵌; 2）观测到的土壤变异性在多大程度上可归因于系统驱动因素，而变异性在多大程度上无法用可测量因素解释，并可能与混沌行为或随机随机变异有关。 研究结果不仅将推进土壤地理学思想，而且对更广泛的科学问题具有重要意义，这些科学问题涉及秩序和无序、空间变异的来源以及跨越学科界限的自然系统的演变，从自然地理学到土壤科学和地质学，再到生态学和自然资源管理。 此外，该项目还将为冲积洼地环境中退化土壤和生态系统的恢复提供宝贵的参考信息。 它还将评估在最后一次冰期-间冰期循环期间土壤特性的持久性，这一时期东南部经历了环境条件的剧烈波动，并将提高对土壤抵抗过去和预测的未来气候变化及其对土地利用的影响的认识。 该项目包括与美国地质勘探局合作绘制该地区沉积物地图的计划。 此外，还计划在学术和非学术领域传播这些成果，并将与一所地区中学开发一个教育推广模块。 作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个独立的研究生涯。

The goal of this doctoral dissertation project is to understand the effect of time on soil formation processes. Soil spatial variability exists in all landscapes and may occur predictably, in response to known geomorphic and soil-forming factors, or unpredictably, without any apparent relationship to measureable changes in soil forming factors conditions. Such variability has important implications for soil chronosequence studies, which evaluate the influence of time on soil development. Understanding how soil properties change over time is critical for the restoration of degraded soils and the use of soils as relative-age dating tools in Quaternary geologic studies, and soil chronosequences remain the primary source for empirical data to evaluate rates and theories of soil development. However, spatial variability among soils of equivalent age can pose both theoretical and practical problems for the chronosequence approach. Within a chronosequence framework, adequate representation of soil spatial variability on even-aged surfaces is needed before dominant soil forming processes can be ascertained, models of soil formation can be tested, and rates of soil formation can be estimated. Nevertheless, relatively few studies have addressed this topic. Thus, the goal of this project is to characterize the range of soil development within and among late Quaternary fluvial surfaces of different ages in the southeastern Atlantic Coastal Plain in order to assess spatiotemporal trends of soil variability and development and evaluate drivers of these changes. This research will examine the morphology and chemistry of soils developed on the scrollbar components of three fluvial surfaces that span an age range of approximately two orders of magnitude (1,000 vs. 10,000 vs. 100,000 years) along the Oconee-Altamaha (Georgia) and Pee Dee (South Carolina) Rivers. Two scrollbars will be sampled per surface in each river valley, for a total of twelve sampled scrollbars, and sampling will be guided by a pilot study that will determine the number and spacing of profiles needed to adequately characterize soil variability on a single scrollbar. Soil properties will be evaluated that have been shown to be valuable chronosequence parameters in the region, including overall soil thickness; leaching (E) horizon thickness; as well as the thickness, clay content, redness, extractable iron, and total chemistry of the whole soil (2 mm) and fine sand (0.125-0.250 mm) fractions of the most well expressed horizon in which there is active soil formation occurring (B horizon). Multivariate statistical techniques will be used to identify drivers of soil variability, assess dominant soil forming processes, and evaluate the implications of spatial variability for the use of chronosequences as tools in soil formation and geomorphic research.By characterizing soil variability within a chronosequence framework, this research will directly address key problems that have emerged in soil geographic research in recent decades, such as 1) whether soils converge toward a spatially uniform, steady state condition or diverge into an increasingly complex spatial mosaic over time, and 2) the extent to which observed soil variability can be attributed to systematic drivers versus the degree to which variability is unexplained by measurable factors and possibly linked to chaotic behavior or stochastically random variation. Results will not only advance soil geographic thought, but have important implications for broader scientific questions about order and disorder, sources of spatial variability, and the evolution of natural systems through time that span disciplinary boundaries, from physical geography, to soil science and geology, to ecology and natural resources management. In addition, this project will provide valuable reference information for the restoration of degraded soils and ecosystems in alluvial bottomland settings. It will also evaluate the persistence of soil properties during the last glacial-interglacial cycle, a period when the Southeast experienced drastic fluctuations in environmental conditions, and will improve understanding of soil resistance to past and projected future climate change and its implications for land use. The project includes plans to collaborate with USGS on a map of the sediments of the region. There are also plans for academic and non-academic dissemination of the results, and an educational outreach module with a regional middle school will be developed. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish an independent research career.