Points of interest:
Statement of Research
Other related interests:
Chemical, physical, and biological processes associated with the circulation of aqueous
fluids in shallow hydrogeologic settings. Investigations incorporate field
and laboratory work, and theoretical modelling of observations. Of particular
interest are questions concerning the measurement and prediction of the
rates of natural processes, including chemical weathering with and without
micro-organisms. Recent work has focused on the effect of microbial life
on mineral reactivity, and measuring and modelling how rock turns into regolith.
- Fe release and isotope fractionation during microbial alteration and weathering of shales, granites, and basalts
- Coupling between weathering and erosion
- Chemical, physical, and biological weathering in the Luquillo Critical Zone Observatory
- Chemical, biological, and physical weathering in the Susquehanna Shale Hills Critical Zone Observatory
- Neutron scattering analyses of weathering rocks
- Reactive transport modelling of weathering
The Susquehanna Shale Hills Critical Zone Observatory, SSHO: The SSHO is one of six Critical Zone Observatories funded by National Science Foundation to study chemical, physical, and biological interactions in the Critical Zone. The site is part of the Critical Zone Exploration Network (czen.org). More than 12 Penn State faculty are working together, from many disciplines, at the SSHO. In collaboration with geomorphologists, soil scientists, and ecologists, Brantley’s group is investigating the rates and mechanisms of regolith formation on shale in the Shale Hills watershed. A monitoring network has been designed to follow many of the important physical, biological and hydrogeochemical processes along several transects within the catchment. Some of the ongoing projects include:
- Weathering fronts, mineral transformation reactions, and long-term physical/chemical weathering fluxes are being assessed by sampling and characterizing the weathered soils and drilled core sediments geochemically and mineralogically, and by sampling and analyzing stream, ground, and soil pore waters.
- Small-angle neutron scattering experiments on shale chips from SSHO are being carried out to characterize variations in nano-porosity and micro-structure as shale weathering initiates and progresses. We have shown that the movement of the bedrock-regolith interface at SSHO is controlled by chemical reactions and changes in porosity and surface area at depth.
- Uranium-series disequilibrium isotopes (238U, 234U, and 230Th) of shale rocks and soils are being analyzed to derive the soil production function and estimate the residence time of regolith particles using mass balance models.
- Soils record the principal fluxes impacting the Critical Zone, including anthropogenic perturbations such as the deposition of air pollutants. Surface soils in the catchment are enriched in manganese, a common byproduct of steel production and coal combustion. By comparing Mn levels in the soil relative to the underlying shale bedrock, we are quantifying the total Mn enrichment factor and are deriving Mn input rates.
- We are interested in understanding how iron (Fe) is transformed and cycled within the SSHO. A related question involves whether microorganisms are involved in this cycling. We are measuring microbial cell density within the soils and relating this to Fe reactions as indicated by soil mineralogy and chemistry.
- Four satellite sites in NY, VA, TN, and AL have been identified to assess weathering of the Rose Hill shale as a function of climate variables. In addition, these sites are being compared to shale weathering in Puerto Rico and in Plynlimon, Wales. Finally, one site in the same climate as SSHO is being studied to investigate weathering of a black shale, the Marcellus shale.