Defense in Geophysics
Student: Letícia Rangel Dantas
Program: Geophysics
Title: "Critical Zone Observatory Seed Site in the city of São Paulo: a study of anthropogenic impacts on the Critical Zone."
Advisor: Profa. Dra. Andréa Teixeira Ustra
Judging Committee:
- Profa. Dra. Andréa Teixeira Ustra - Presidente e Orientadora - IAG-USP/ Geofísica
- Prof. Dr. André Campos Guaragna Kowalski - IGc-USP/ Geologia
- Prof. Dr. Leonides Guireli Netto - IPT
- Dr. Plínio Francisco Jaqueto - ON
- Profa. Dra. Suzan Sousa de Vasconcelos - UFBA/ Geofísica
Other Members:
- Prof. Dr. Vagner Roberto Elis - IAG-USP/ Geofísica
- Prof. Dr. Carlos Alberto Mendonça - IAG-USP/ Geofísica
- Prof. Dr. César Augusto Moreira - UNESP/ Geologia
- Prof. Dr. Wilbor Poletti Silva - UFVJM/ Engenharia Geológica
- Prof. Dr. Luciano Soares da Cunha - UnB/ Instituto de Geociências
Abstract:
The Critical Zone (CZ) is the dynamic system at the Earth’s surface that extends from the top of the vegetation to groundwater, regulating essential energy flows and ecosystem services through its porous interfaces. Important for predicting responses to climate and land-use changes, CZ research still focuses mainly on environments with low human impact, overlooking the growing pressure of global urbanization on its biogeochemical and structural functions. There is still a gap in conceptual models of the CZ regarding how urbanization affects hydrogeological and biogeochemical interactions at the local scale, especially in floodplains, where integrated studies and long-term monitoring initiatives remain lacking in Brazil. This study aimed to implement a Critical Zone Observatory (CZO-São Paulo) Seed Site in the floodplain of the Tietê River and to investigate its architecture and dynamics under the combined influence of natural factors and historical human interventions. The investigation was carried out at two highly impacted sites in the eastern part of São Paulo (EACH – USP East Campus and Núcleo Engenheiro Goulart - Tietê Ecological Park) using a multidisciplinary and long-term approach. A multi-method strategy was adopted, integrating geophysical imaging of the subsurface, seasonal physicochemical data from surface water and groundwater, and magnetic mineralogy indicators from soil samples. These data were combined with local geological and meteorological parameters to characterize, in an integrated way, the physical structure, redox variations, and water flows within the urban CZ system. The results revealed contrasts in the subsurface organization of the two sites, with greater continuity of the deposits in the park and greater heterogeneity associated with technogenic materials on the campus. Seasonal changes in electrical properties depended on local sediment characteristics, especially pore distribution and hydraulic conductivity. Environmental magnetic parameters revealed changes in grain size and iron-bearing mineral phases, indicating the presence of redox-associated interfaces and the influence of surface waters. Overall, these results showed distinct signatures of hydrogeological and biogeochemical processes, depending on the depositional setting and the land-use history of the sites. This thesis helps fill the gap in understanding how the Critical Zone functions in urban environments by establishing the CZO-São Paulo as an integrated research initiative in a highly impacted floodplain. The study shows how depositional architecture and the resulting heterogeneities control water flows and the hydrogeophysical and biogeochemical responses of the system. The integration of methods allowed the identification of the combined influence of seasonality and human interventions on CZ dynamics, providing a new database and a reference framework for long-term monitoring and for understanding the resilience of this environment to urbanization and climate change.
Keywords: Alluvial plain, Urban critical zone, Hydrogeophysics, Environmental magnetism