Abstract

A stable isotope sampling network was implemented at the Susquehanna Shale Hills Critical Zone Observatory. The objective was to determine the δ²H and δ¹⁸O signature in the catchment pools to determine the flowpaths and timescales of the hydrologic system. The stable isotope network covers all phases of the hydrologic cycle, including precipitation sampled adaptively during precipitation events with an Eigenbrodt NSA-181/S wet-only collector (six-hour samples), soil water sampled weekly along four transects with 80 suction-cup lysimeters, groundwater sampled daily at two wells with ISCO automatic samplers and bi-weekly at 16 wells
and stream water sampled daily with an ISCO automatic sampler. The comprehensive sampling of the network was possible because of the DLT-100 liquid water stable isotope analyzer from Los Gatos Research, with a reproducibility of ± 0.2%0 for δ¹⁸O, ± 1.0%0 for δD and the capability to run 30 samples per day. The δ²H and δ¹⁸O data showed the dominance of cold season infiltration and recharge, with recharge specifically occurring over the period of late September – May. The δ²H and δ¹⁸O record also showed that groundwater regularly flushed the deep soil water, and that groundwater is the major component of streamflow. Preferential flowpaths in the soil during the cool or non-growing season was identified and is related to stream stormflow. A piecewise constant model for flow, tracer concentration and age was based on the work of Duffy and Cusumano (1998) and Duffy (2010), and was unique in that it solved for transient flow. The finding of the age model was that the mean age of the water in the catchment ranged between 4.5 – 9 months. The oldest ages occurred during the summer drought and the youngest ages occurred during times of maximum recharge over the winter. This research was performed as part of the NSF-funded Critical Zone Observatory and the importance of this effort multi-investigator effort was essential to the success of this research.

Citation

Holmes III, G.H., (2011): Usings δ2H AND δ18O To Determine The Flowpaths and Timescales of Water at the Susquehanna Shale Hills Critical Zone Observatory, . Master of Science, Civil Engineering, The Pennsylvania State University, p. 70..

This Paper/Book acknowledges NSF CZO grant support.