To accommodate construction, Shaver's Creek Environmental Center will be closed Tuesday, May 28, through Thursday, May 30.

What Is a Critical Zone and What Is the Susquehanna Shale Hills Critical Zone Observatory

For her capstone project, graduating environmental resource management student Bryn Wambaugh investigated the work being done in the Shaver’s Creek watershed by the Shale Hills Critical Zone Observatory. We are sharing a series of Bryn’s articles, written with the public in mind, to educate readers while illustrating the great research done at the Shale Hills CZO and supported by Shaver’s Creek.

Read the previous entries in Bryn’s series:
What Is Nutrient Pollution and What Are Its Impacts?
Riparian Buffers and Denitrification

The critical zone is “an environment where rock, soil, water, air, and living organisms interact and shape the Earth’s surface” (The Critical Zone). It supports all terrestrial life on Earth, regulates water quality, and provides fertile land to grow food on. Critical zones have short-term responses and long-term responses to environmental changes. Short-term responses are to events like rainfall, human activities, and land-use changes. Long-term responses are to more significant climatic and tectonic geological changes over time (The Critical Zone). Since humans depend on the critical zone for its services, it is important that we understand how human activities affect the critical zone.

Critical Zone Observatories (CZOs) examine the zone from the top of tree canopy to the groundwater. Researching the critical zone (CZ) is a way for us to understand how important processes in the CZ work, how climate change and land use changes will affect the CZ, and what we can do to enhance CZ services (Brantley et al., 2018). The Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) continuously monitors three catchments within the CZO, Garner Run, Shale Hills, and Cole Farm. 75% of the Shaver’s Creek watershed is within the SSHCZO’s boundaries (Wayman, 2018). Since these catchments are continuously monitored, it gives us a chance to better understand the levels of and fluctuations of nitrate in the groundwater.

CZOs like the SSHCZO can help us better understand the critical zone and our impact on it, and answer important questions about its processes. The next articles in this series will address specific research from the CZO and what it means for the Shaver’s Creek Watershed.


  • Brantley, S. L., White, T., West, N., Williams, J. Z., Forsythe, B., Shapich, D., Kaye, J., Lin, H., Shi, Y., Kaye, M., Herndon, E., Davis, K. J., He, Y., Eissenstat, D., Weitzman J., DiBiase, R., Li, L., Reed, W., Brubaker, K., Gu, X. (2018). Susquehanna Shale Hills Critical Zone Observatory: Shale Hills in the context of Shaver’s Creek watershed. Vadose Zone Journal, 17(1), 180092. doi:10.2136/vzj2018.04.0092
  • The critical zone: National critical zone observatory. (2012). Retrieved May 05, 2021, from
  • Wayman, C. R., & Brantley, S. L. (2018). Understanding the effects of hydrologic connectivity, land use, and lithology on land use across scales: from a zeroth order catchment to a HUC 10 watershed in the Susquehanna River Basin [Unpublished master’s thesis, The Pennsylvania State University]