Knowledge of subsurface flow paths and timescales is fundamental to the understanding of soil formation and hydrologic processes. Yet the fate of water through the Critical Zone, from when it enters as precipitation to its exist at a stream, is poorly understood. In order to better understand flow pathways and patterns in the subsurface, a stable isotope monitoring network was installed at the Shale Hills Critical Zone Observatory located in central Pennsylvania, USA. Event-based precipitation samples were collected using Eigenbrodt NSA-181S. Soil water samples were collected at approximately bi-weekly intervals using suction-cup lysimeters installed at multiple depths along four transects within the catchment. Groundwater and stream water samples were collected daily using automatic samplers. Our findings provide evidence for seasonal recharge to shallow groundwater during to the non-growing period (October-March) in the catchment. The isotope values of deep soil water closely resemble the average isotope values of groundwater. This is largely due to a rising water table from October -March and mixing with unsaturated pore water. Stream isotope values during October - March are similar to soil water and groundwater signatures, while the summer stream isotope values are dominated by groundwater but also show the impact of summer precipitation and runoff. This investigation suggests the need for additional sampling of tree xylem water to resolve whether the trees draw their water from the shallow or deep soil. (http://www.czo.psu.edu/)
Thomas, E., G. Holmes, H. Lin, and C. Duffy (2012): Spatial and Temporal Patterns of Stable Isotopes in Soil and Ground Water at the Shale Hills Critical Zone Observatory. 2nd International Conference on Hydropedology, Leipzig, Germany, July 22-27, 2012..
This Paper/Book acknowledges NSF CZO grant support.