Hydropedology Studies at the Shale Hills CZO: Hydropedology research being conducted at the Shale Hills CZO is multi-faced, cross-scale, and interdisciplinary. Two fundamental questions we seek to answer are:

(1) How do soil architecture and the distribution of soils over the landscape exert a first-order control on hydrologic processes (and associated biogeochemical and ecological dynamics) across spatio-temporal scales?
(2) How does landscape water (and the associated transport of energy, sediment, chemicals, and biomaterials by flowing water) influence soil genesis, evolution, variability, and functions?

We focus on interactive hydrologic and pedologic processes at the pore, pedon, hillslope, and catchment scales.

The following several studies have been ongoing:

Soil Moisture Spatial-Temporal Patterns across Scales: A spatially dense network of soil hydrology monitoring has been implemented in the Shale Hills since 2004 (Fig. 1). This includes (1) a total of 106 sites (covering all soil types, topographic positions, and landform units in the catchment) where approximately weekly measurements of soil volumetric water content, matric potential, and water table are conducted manually from soil surface down to bedrock, and (2) a total of 20 stations where real-time soil moisture, matric potential, temperature, and water table are monitored automatically at 10-minutes interval. An example of soil moisture spatial pattern and its temporal stability is illustrated in Fig. 2. We continue to investigate the complex and dynamic controls of soil moisture spatial-temporal patterns (such as soil type, depth to bedrock, landform unit, topography, vegetation, and climate).

Subsurface Preferential Flow Network – Its Monitoring, Imaging, and Modeling: We use a suite of non-invasive imaging techniques (X-ray tomography, ground penetrating radar or GPR, and electromagnetic induction or EMI) in combination with real-time soil hydrologic monitoring to detect and model subsurface flow networks and their dynamics (Fig. 3). In particular, we use time-lapsed approaches to reveal complex subsurface architecture and its controls on water and chemical fluxes through various soils in different seasons (Fig. 4). A large geophysical database has been developed for the Shale Hills over the years.

Defining and Delineating Hydropedological Functional Units: These are soil-landscapes units in the catchment that have similar soil properties and hydrologic functions. We plan to construct 3D stratified catchment to facilitate modeling and monitoring using these hydropedological functional units.

Coupling Hydropedology with Biogeochemistry with a Focus on Carbon: We are evaluating the coupling of hydropedological properties (e.g., soil type, depth, moisture content, water table, and redox dynamics) and biogeochemistry through the quantification of carbon dynamics. We have mapped out the spatial distribution of soil organic carbon throughout the catchment (Fig. 5). Soil pore waters from nested lysimeters in four hillslope transects (swales and planar hillslopes on both north and south sides of the catchment) in different landscape positions (ridge-top, mid-slope, and valley floor) are being continuously collected, along with bulk soil samples and stream and ground water samples, for analyzing dissolved organic carbon (DOC) and major cations and anions. Daily export of DOC from the stream and its flushing mechanism are also being investigated, as well as the role of redox and metals in stabilizing DOC to enhance carbon storage in the catchment soils (Fig. 6).

Contacts: Henry Lin (PI) henrylin@psu.edu
Collaborators: Jim Doolittle, Chris Duffy, Sue Brantley, Dave Eissenstat, Lixin Jin