The Interplay of Bedrock Lithology, Regional Geomorphology, and Human Activities on Soil Physical and Chemical Properties: Case studies from the forests of central Pennsylvania and cacao farms in Colombia and Peru

Open Access
- Author:
- Guarin, Daniel
- Graduate Program:
- Soil Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 12, 2024
- Committee Members:
- Margot Kaye, Program Head/Chair
John Spargo, Major Field Member
Andrew Smye, Outside Unit & Field Member
Marc McDill, Major Field Member
Thomas Raab, Special Member
Patrick Drohan, Chair & Dissertation Advisor
Mary Ann Bruns, Major Field Member - Keywords:
- Periglacial
Geomorphology
soil development
loess
Solifluction
cadmium
cacao
biocycling
food safety - Abstract:
- Regional geomorphology and bedrock lithology, fundamental building blocks of soils, have a profound influence on modern soil properties and processes and should be a determining factor in agricultural and forestry management decision-making. Across the chapters, we (I will refer to every aspect of this dissertation as ‘we’, given that this has been a group effort involving every member of this committee, graduate and undergraduate students at the Soil Characterization Lab, and friends who helped on every step leading up to this document) have explored how the weathering of different bedrock types, with varying mineral and chemical compositions, can contribute to variations in soil fertility, texture, and the presence of potentially harmful elements like cadmium (Cd) in cacao (Theobroma cacao) crops of Colombia and Peru, as well as forests in the central Appalachians of Pennsylvania. The role of geomorphology, the study of landforms and the processes that shape them is a central element of this work, as it shapes soil formation dynamics. This work highlights how periglacial features, such as solifluction terraces in central Pennsylvania, can create distinct landscape positions that influence soil moisture regimes, nutrient availability, and ultimately, the prevalence and distribution of tree species. Likewise, interacting with the multiple geological and geomorphological factors that condition soil evolution processes, this research has delved into the role of eolian (windblown) sediments in shaping mountain slope soils, contributing to the formation of fragipans and promoting rapid soil development in the windward aspect of the central Appalachians. Similarly, in the cacao-growing regions of Peru and Colombia, we have investigated how alluvial soils and the sediments transported by the stream network that create them, can exhibit higher concentrations of Cd due to the deposition of sediments potentially bearing Cd-rich minerals. Additionally, we have explored the influence of soil-plant interaction processes, such as the biocycling of Cd through the leaves-litter-soil system, on the accumulation of Cd in topsoil and its uptake by cacao plants, leading to a potential heavy metal pollution risk, endangering the livability of farmers, the continuation of social programs with cacao as a strategic replacement for illegal crops, and the safety of food product made from these crops. Overlaying these natural processes are the anthropogenic influences of land management practices. In the forested regions of Pennsylvania, we have examined how selective logging and forest management have contributed to the ongoing oak decline, potentially exacerbated by soil moisture and nutrient variations across periglacial landforms. Likewise, in the cacao-growing regions, the focus has been on the impact of fertilizer application and cultivation practices on Cd accumulation in soils and plant tissues. By integrating these diverse aspects – bedrock lithology, geomorphology, soil evolution processes, and land management practices – this dissertation aims to provide a holistic understanding of the intricate relationships that control soil development, nutrient dynamics, and contaminant accumulation in both forest and agricultural ecosystems. This approach not only advances our scientific knowledge but also tries to inform adaptive management strategies tailored to specific site conditions, ensuring the long-term cultural and economic sustainability of forest and agricultural systems. In chapter 1, the research focuses on evaluating the contribution of windblown sediments to the formation of mountain slope soils in the central Appalachian region. Through the analysis of soil profiles from different aspects and underlying bedrock lithologies, the study suggests that windblown sediments mixed with colluvium slope deposits on windward slopes during the last glaciation alter the soil's physical and chemical properties. This input of eolian sediments is evident from increases in finer soil particles, enrichment of certain elements like magnesium, titanium, and rare earth elements in argillic soil horizons (what we call silt mantles) and in dense subsurface water restrictive horizons (fragipans). Our results also suggest that the windblown sediments originated from a source rich in clay minerals and potassium feldspars but low in carbonates. Overall, the influx of eolian sediments promoted rapid soil development via clay accumulation and illuviation processes, leading to a faster than expected evolution from Alfisols to Ultisols, enhancing soil fertility and forest productivity on windward slopes. In chapter 2, we delve into how legacy human made landforms for charcoal manufacturing in the 19th century, lobate solifluction terraces (a periglacial landform created as permafrost melted around the time of the last MIS2 glacial maximum), and underlying changes in bedrock lithology influence soil properties, and tree species composition on a southeast-facing slope in the Leading Ridge, central Pennsylvania. The study area exhibits how the presence of a lobate solifluction terrace creates distinct landscape positions, with different soil physical and chemical properties. Soil profiles revealed the presence of a shallow fragipan in the flatter bench-like solifluction lobe, promoting waterlogged soils with a shallower water table than the backslope. This solifluction lobe had higher total surface nutrient and acidity levels compared to other positions, but plant available nutrients were similar across positions. Soil moisture differed significantly, with the solifluction lobe being wetter in dry periods due to surface runoff trapping and a shallow fragipan but quickly saturated during rains, promoting surface runoff that is actively dissecting the lobate terrace. Tree growth rates were more influenced by local soil conditions than regional climate. Red oak (Quercus rubra) and black oak (Quercus velutina) species preferred the drier backslope positions, while white oaks (Quercus alba) showed no strong preference despite higher radial growth on backslopes. Chestnut oaks (Quercus montana) exhibited better growth on the wetter backslope below the terrace yet were concentrated in drier positions across all size classes. Regeneration was dominated by white pines (Pinus strobus) on the drier sites and red maples (Acer rubrum) elsewhere, confirming an ongoing oak decline likely stemming from past selective logging disturbances. Moving from forests to cacao agroforestry systems in South America, chapter 3 analyzed the levels of the heavy metal cadmium (Cd) in soils and plant tissues across five cacao farms in the Piura region of north Peru. The goal was to understand where the Cd accumulation comes from and what factors control its concentration. The results showed Cd levels were highest in the leaves, followed by the cacao beans, surface soils at 5 cm depth, and then subsurface soils at 20 cm depth. The higher Cd concentration in plant tissue and surface soils appears to be from biocycling and bioaccumulation of plant available Cd present in fertilizers and a decaying litter layer consistent of fallen leaves and harvest residues, covering the topsoil. This highly available Cd is being taken up and recycled by the cacao plants over time. Our results suggest that even when fertilizers meet regulations, repeated application combined with these biocycling, and bioaccumulation processes can lead to high Cd buildup in beans and leaves. On the other hand, farms on alluvial soils and flatter areas tended to have higher Cd levels in soils and plants. Farms at lower elevations with larger contributing areas were also more prone to higher Cd, likely from river borne sediments from Cd prone lithologies upstream and/or fertilizer contaminated water from upstream farm surface runoff depositing Cd in flooding episodes or irrigation. Variations in underlying rock types and soil minerals may also contribute Cd-bearing sediments in some areas. Overall, the high plant Cd appears mainly driven by bioaccumulation from fertilizers, with some influence from the local geology. Similarly, chapter 4 provides the first comprehensive study of cadmium (Cd) dynamics in cacao farming systems in the Sierra Nevada de Santa Marta region of Colombia. Soils, rocks, litter, and cacao plant leaves were analyzed from 30 farms to understand interactions between Cd pools. Overall, total Cd concentrations were low in both surface and subsurface soils, averaging 0.12 mg kg-1 and 0.05 mg kg-1 respectively. However, Cd levels were significantly higher in cacao leaves (0.42 mg kg-1) and litter (0.4 mg kg-1) compared to soils. The results suggest surface processes observed in Peru are also taking place in Colombia. These likely involve plant uptake and recycling of Cd through leaves, litter decay, and topsoil which drive Cd concentrations in cacao plants over time. Older cacao cultivars and trees exhibited higher Cd in leaves, litter, and topsoil, suggesting plant and topsoil Cd levels are primarily attributed to surface processes. In contrast, subsurface Cd appears mainly derived from weathering of the underlying bedrock, with some hypothesized contribution from Cd migrating down from topsoil. Overall, this research provides insights into how Cd accumulates differently in surface versus subsurface soil levels in cacao systems, with implications for the long-term buildup of soil Cd and plant uptake risk. Finally, chapter 5 presents a brief set of conclusions and closing remarks.