Field and laboratory methods used to assess Late Quaternary Pedogenesis
Authors: Greg Pope, Liana Agrios, Miguel Torres, Salvatore Zerbo III
Soil profile descriptions provide an accepted means to assess pedogenesis, and the characteristics of pedogenesis reveal information of landscape evolution. However, soil profile field methods have limitations: inability to discern more detailed soil attributes such as particle size fractions (as opposed to texture), organic carbon content, and chemistry. Supplemental laboratory analysis provides particle size, organic carbon, and chemical composition. A combination of soil profile field methods and laboratory analysis was used to assess soil development in glacial sediments in Sussex County, Northwest New Jersey, part of a REU project based at Montclair State University in 2013. In the vicinity of the late-Wisconsin Ogdensburg-Culvers Gap recessional moraine (~18-19 ka), deposits of similar age allowed comparison of soil forming factors, as well as an assessment of field and laboratory methods used to characterize soil development.
Seven profiles were analyzed along a catena transect from moraine crest to moraine base, continuing to a terrace platform, terrace slope, and old floodplain. Horizon-specific data included horizon complexity, color (deriving melanization and rubification estimates), texture and consistency, and clast weathering. Compiled data were used to calculate horizon indexes and profile development index. Specific chemical composition employed ICP-OES for major elements, carbon content from loss on ignition, and particle size separation using a soil hydrometer. Individual parameters showed close relationships. Clay content was weakly but significantly correlated to leaching indexes across all profiles. Within profiles, element ratios corresponded as expected to horizons, more leaching with E-horizons, accumulations of Al and Fe in B horizons reflecting the degree of illuviation. The aggregate horizon index and the profile development index were poorly correlated with clay content and leaching indexes. Variation in profile environment and locally-derived parent material entered inconsistency in the calculations. Profile complexity appeared to associate with areas of greater moisture and organic input; definitive correlation will require additional data.