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

本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中，可能根据已知的地貌和土壤形成因素而可预测地发生，也可能与土壤形成因素条件的可测量变化无明显关系而不可预测地发生。这种变异对土壤时间序列研究具有重要意义，该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对于退化土壤的恢复和第四纪地质研究中使用土壤作为相对年龄测年工具至关重要，土壤时间序列仍然是评估土壤发育速率和理论的经验数据的主要来源。然而，等年龄土壤的空间变异性会给时间序列方法带来理论和实践上的问题。在时间序列框架内，在确定主要的土壤形成过程，测试土壤形成模型和估计土壤形成速率之前，需要在均匀年龄表面上充分表示土壤空间变异性。然而，相对较少的研究已经解决了这个问题。因此，本项目的目标是表征大西洋沿岸平原东南部晚第四纪不同年龄河流面内部和之间土壤发育的范围，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。这项研究将检查沿着奥科尼-阿尔塔马哈（乔治亚州）和皮迪河（南卡罗来纳州）河流的三个河流表面的滚动部件上发育的土壤的形态和化学成分，这些河流的年龄范围大约为两个数量级（1000年、1万年、10万年）。每个河谷的每个地表将采样两个滚动条，总共采样12个滚动条，采样将以一项试点研究为指导，该研究将确定在单个滚动条上充分表征土壤可变性所需的剖面数量和间距。将评估已被证明是该地区有价值的时序参数的土壤特性，包括总体土壤厚度；淋溶层(E)厚度；以及全土（2 mm）和细砂（0.125-0.250 mm）的厚度、粘土含量、红度、可提取铁和总化学性质，其中有活跃的土壤形成（B层）。多元统计技术将用于识别土壤变异性的驱动因素，评估主要的土壤形成过程，并评估空间变异性对使用时间序列作为土壤形成和地貌研究工具的影响。通过在时间序列框架内表征土壤变异性，本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)土壤是随着时间的推移向空间均匀、稳定的状态收敛，还是向日益复杂的空间马赛克分化；2)观测到的土壤变异性可归因于系统驱动因素的程度与可测量因素无法解释的变异性的程度，以及可能与混沌行为或随机随机变化有关的程度。研究结果不仅将推动土壤地理学思想的发展，而且对跨越自然地理学、土壤科学和地质学、生态学和自然资源管理等学科边界的自然系统的有序和无序、空间变异的来源以及自然系统随时间的演变等更广泛的科学问题具有重要意义。此外，该项目将为冲积滩地退化土壤和生态系统的恢复提供有价值的参考信息。它还将评估最后一次冰期-间冰期循环期间土壤特性的持久性，这一时期东南地区经历了环境条件的剧烈波动，并将增进对土壤对过去和预测的未来气候变化的抵抗力及其对土地利用的影响的了解。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。还计划在学术和非学术方面传播结果，并将与一所区域中学一起制定教育推广模块。作为博士论文研究进步奖，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.