Catchment Structure Regulates Hydrodynamic Drivers of Chemical Weathering in Shallow Forest Soils

Determining where, when, and how subsurface flow affects soil processes and the resulting arrangement of soil development along flow paths is challenging. While hydrologic regime and soil solution acidity are known to influence weathering rates and soil transformation processes, an integrated understanding of these factors together is still lacking. This dissertation explores the effects of subsurface flow on the mobility and distribution of dissolved organic carbon (DOC) and base cations to explain spatial patterns in chemical weathering in a forested headwater catchment. In the first chapter, relationships between hydrologic behavior, fluxes of weathered elements, and the extent of soil elemental loss across landscape positions are established. The second chapter investigates what specific groundwater behavior best explains spatial patterns in solution DOC concentrations during storm events. Lastly, in the third chapter, near surface saturation dynamics are examined to determine when and where DOC mobilization might be enhanced by subsurface flow. Results show that weathering extent was greatest in the upper reaches of the catchment, where O horizon saturation frequency and DOC concentrations are highest. Annual base cation fluxes, which were also greatest in these positions, could indicate where weathering is likely still enhanced. Additionally, while O horizon saturation occurred across the catchment, spatial differences in DOC concentrations suggest there are other sources of acidity to groundwater solutions other than just leaching from O horizons. Shallow organic soils, near bedrock outcrops at the top of the catchment is likely this additional C source, in which drainage water is transported downslope to nearby mineral soils when water tables are high and hydrologic connectivity between soils is increased. Spring and fall storm events were identified as times when groundwater most frequently reached O horizons during the snow-free year, providing insight into the timing of these processes throughout the year. This dissertation highlights how catchment structure mediates DOC flushing events, which in turn, influences the spatial architecture of soil development and chemical weathering processes across the landscape.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Forestry

Department dc:contributor.department

Forest Resources and Environmental Conservation

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2023

Author dc:creator

• Pennino, Amanda

Chairs dc:contributor.committeechair

• McGuire, Kevin J.
• Strahm, Brian

Committee members dc:contributor.committeemember

• Schreiber, Madeline E.
• Gill, Benjamin C.
• Bailey, Scott W.

• mineral weathering
• forest soils
• pedology
• hydrology
• catchment science
• carbon
• ecosystem science

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

vt_gsexam:37759

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/115410