UVM Theses and Dissertations
Format:
Print
Author:
Bourgault, Rebecca
Dept./Program:
Plant and Soil Science
Year:
2014
Degree:
Ph. D.
Abstract:
Hydropedology is the synergistic integration of soil science and hydrology. Emerging evidence shows that the interactions between soils and hydrologic flowpaths contribute to spatial variations in biogeochemical conditions in headwater catchments. Watershed 3 (WS3), a podzolized hydrologic reference catchment at Hubbard Brook Experimental Forest, New Hampshire, was studied in order to better understand soil development processes and their relationships to water table dynamics. Classical podzolization studies assume vertical percolation and pedon scale horizon development. However, hillslope scale lateral podzolization also occurs where lateral water flux predominates.
In WS3, 99 soil profiles were observed, sampled, and assigned to a hydropedologic unit (HPU). The HPU system is a functional soil classification scheme developed using topographic position and morphology, which indicates distinct water table regimes. Soil samples were extracted and analyzed for Al and Fe associated with spodic materials, as well as the rare earth elements. Total organic carbon, optical density of oxalate extract, and pH were also measured. In order to compare vertically vs. laterally developed spodic horizons, amorphous organometallic complexes were observed in thin section, for which Al, Fe, Mn, and C were quantified using a microscopic technique (SEM-EDS). A manganese (Mn) hot spot was identified in a seep area in WS3. This seep area was sampled using a grid scheme, and the above chemical variables were measured on the soils. Variables were interpolated to show spatial relationships to one another. Mineralogy and reactivity of Mn oxides were studied using synchrotron techniques, chromium oxidation and reduction tests.
Results indicate redistribution of mobile elements via vertical and lateral podzolization. Spodosols developed in the majority of the catchment, where vertical unsaturated percolation dominates. However, lateral ground water flow is an important soil-forming factor that has produced Spodosol variants with different pedogenesis, morphology and chemistry. The Ce-anomaly (Ce/Ce*) in soils proved to be an indicator of lateral flow in hillslopes. In the Mn-rich seep area, ground water appeared to be the source of excess Mn, which was mainly found as vernadite ([sigma]-MnO₂), a nanocrystalline, highly reactive Mn(IV) oxide mineral. Three locations in the seep area were identified with different hydrologic regimes that resulted in different Mn abundance and reactivity.
The results of this study suggest that spatial variation in soil composition and lateral soil formation should be considered when predicting catchment parameters. Also, each HPU has unique chemical and morphological characteristics and water table regimes. Seeps are different from the rest of the catchment and can act as hot spots for reactive elements. This information will be useful in predicting spatial patterns in biogeochemical functions such as carbon sequestration, denitrification and nutrient availability, or in predicting variations in headwater stream chemistry.
In WS3, 99 soil profiles were observed, sampled, and assigned to a hydropedologic unit (HPU). The HPU system is a functional soil classification scheme developed using topographic position and morphology, which indicates distinct water table regimes. Soil samples were extracted and analyzed for Al and Fe associated with spodic materials, as well as the rare earth elements. Total organic carbon, optical density of oxalate extract, and pH were also measured. In order to compare vertically vs. laterally developed spodic horizons, amorphous organometallic complexes were observed in thin section, for which Al, Fe, Mn, and C were quantified using a microscopic technique (SEM-EDS). A manganese (Mn) hot spot was identified in a seep area in WS3. This seep area was sampled using a grid scheme, and the above chemical variables were measured on the soils. Variables were interpolated to show spatial relationships to one another. Mineralogy and reactivity of Mn oxides were studied using synchrotron techniques, chromium oxidation and reduction tests.
Results indicate redistribution of mobile elements via vertical and lateral podzolization. Spodosols developed in the majority of the catchment, where vertical unsaturated percolation dominates. However, lateral ground water flow is an important soil-forming factor that has produced Spodosol variants with different pedogenesis, morphology and chemistry. The Ce-anomaly (Ce/Ce*) in soils proved to be an indicator of lateral flow in hillslopes. In the Mn-rich seep area, ground water appeared to be the source of excess Mn, which was mainly found as vernadite ([sigma]-MnO₂), a nanocrystalline, highly reactive Mn(IV) oxide mineral. Three locations in the seep area were identified with different hydrologic regimes that resulted in different Mn abundance and reactivity.
The results of this study suggest that spatial variation in soil composition and lateral soil formation should be considered when predicting catchment parameters. Also, each HPU has unique chemical and morphological characteristics and water table regimes. Seeps are different from the rest of the catchment and can act as hot spots for reactive elements. This information will be useful in predicting spatial patterns in biogeochemical functions such as carbon sequestration, denitrification and nutrient availability, or in predicting variations in headwater stream chemistry.