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

University Of Georgia Research Foundation Inc, Athens GA

Investigators

Abstract

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.