Critical zone (bio)geochemical reactivity and hydrologic transport recorded by the stable lithium isotope ratios of fluids draining upland watersheds

The interaction between water and silicate minerals regulates landscape functioning (e.g., soil formation, nutrient export, CO2 drawdown), shaping the Critical Zone or the region of the Earth surface between the top of trees and the base of aquifers. Such biogeochemical processes that sustain this near-surface environment are typically inferred from streamflow chemistry. However, the extent to which this stream signal can represent the pathways fluid transits and the fluid-rock reactions that occur during flow remains unresolved. I address this knowledge gap by (1) establishing an understanding of how fluid-rock reactivity initiates and spatially propagates in the Critical Zone followed by (2) an investigation of transient perturbations that reveal the coupling between hydrologic transport and reactivity during storms. This stepwise approach is applied to two small, pristine upland catchments using reactive transport modeling and lithium (Li) as a tracer given the sensitivity of its isotopes (7Li and 6Li) to fluid-rock reactivity. Using the highly-instrumented Elder Creek catchment in northern California, I first demonstrate that subsurface fluid contributing to streamflow can be distinguished by lithium isotope signatures that resemble unique compartments of a weathering profile (i.e., soil, weathered bedrock, and fresh bedrock). Then, I show that streamflow Li during storms records shifts in flow rates and the expansion of the footprint of subsurface fluid-rock reactivity as a result of a rise in the groundwater table. The conceptual framework established by this work is then translated to the relatively less characterized Sapine Creek catchment in Mont-Lozère, southern France. Here, I simulate the development of the weathering profile to reveal that the reactivity underlying unique streamflow Li signatures are due to high retention of weathering byproducts and significant input of exogenous dust. Finally, I leverage a novel set of streamflow Li observations from two storm events that are preceded by unique background hydrological conditions (i.e., dry vs. wet) to show how reactive fluids are routed in the Critical Zone during infiltration and discharge. These findings contribute to a greater understanding of landscape and ecosystem biogeochemical response during periods of transient hydrological disturbance, which is critical given that the occurrence of such extreme events is predicted to intensify in the future.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Geology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Golla, Jon Kenneth Kabigting

Contributors dc:contributor

• Druhan, Jennifer L
• Conroy, Jessica L
• Johnson, Thomas M
• Bouchez, Julien

• Critical Zone
• Hydrology
• Biogeochemistry
• Weathering
• Isotopes

Statement dc:rights

• Copyright 2023 Jon K. Golla

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/121342

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F121342