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
What Is a Critical Zone and What Is the Susquehanna Shale Hills Critical Zone Observatory
Shale Hills
Shale Hills is a small (0.08km2) catchment of Shale Hills Critical Zone Observatory (SHCZO) that is entirely underlain by the Silurian-age Clinton group which is made up of iron-rich, organic-poor shale of the Rose Hill Formation (Brantley et al., 2018). Its consistent lithology makes Shale Hills particularly interesting for research on the critical zone. There are several groundwater wells drilled to different depths at Shale Hills. Surface water at Shale Hills is sampled at the catchment outlet at a weir (Wayman, 2018). Many measurements are recorded at Shale Hills, like relative humidity, precipitation, temperature, and gas fluxes.
Sampling from the groundwater wells and taking surface water samples at Shale Hills are important parts of the SHCZO’s research on nutrient pollution. Thirty-two groundwater wells are in Shale Hills, ranging from 1 to 35m deep (Brantley et al., 2018). In some wells, HOBO* sensors are deployed, and measurements are taken at 15-minute intervals. The measurements at Shale Hills come from a mix of vented and non-vented systems. Vented systems are vented to the atmosphere and account for barometric pressure. Non-vented systems do not account for barometric pressure and measurements must be adjusted to take this into account. The outlet and weir at Shale Hills is used to take surface water samples. Weirs are best for small streams. The weir is used to measure the discharge of the stream.
In addition to water samples, understanding Earth-atmosphere interactions is important to understanding the critical zone. A tower at the top of the watershed measures land-atmosphere exchanges of water, energy, momentum, and CO2 fluxes. Measurements are continuously taken, and carbon fluxes have a resolution of 30 minutes. Sensible heat flux**, evapotranspiration, momentum flux, and CO2 flux are measured via eddy covariance*** (Brantley et al., 2018). These measurements represent Earth-atmosphere exchange over an area of roughly 1km². This area varies with wind direction and atmospheric stability.
Two other ongoing projects that the SHCZO monitors are soil moisture and vegetation. There are four GroundHOG sites at Shale Hills. GroundHOG sensors are a cost-effective way to monitor the critical zone in a small catchment. These sites are at ridgetop, midslope, and valley floor along the south hillslope, with a fourth site at the north midslope (Brantley et al., 2018). When examining vegetation, surveying above-ground biomass is an easy way for us to keep track of growth. Every four years, all trees in the watershed with a diameter of more than 20cm are surveyed. During this survey, vitality and injuries are noted, diameter is measured, and the crown class compared with the surrounding trees is assigned. In addition, 100 trees in the watershed have dendrometers, tight bands used to measure annual diameter growth, that complement the data collected every 4 years (Brantley et al., 2018).
*HOBO Onset makes a wide range of water quality sensors for use in the field.
** Sensible heat flux is caused by conduction and convection.
***Turbulent eddies flow horizontally past eddy covariance towers. These turbulent eddies have a horizontal and vertical component. An eddy covariance system allows us to look at the system as a whole.
Garner Run
Garner Run is a forested catchment that is made up of trees that regrew after the widespread tree harvesting at the beginning of the 20th century. Because of this, the oldest trees in Garner Run are 90 years old (Li et al., 2018). Unlike Shale Hills that has a hummock-hollow topography from tree-throw, Garner Run’s topography is defined by periglacial movements (Li et al., 2018). The research at Garner Run is mostly focused on the topography of the area and the forested environment.
Soil CO2 has been monitored at Garner Run since 2015. CO2 increases with depth and is seasonally dependent. These seasonal differences are also influenced by topography (Li et al., 2018). Soil pits were dug in Garner Run to compare the root density at Garner Run to Shale Hills. Roots at Garner Run were observed to be deeper and denser than those at Shale Hills (Li et al., 2018).
While the data collection at Garner Run is like that of Shale Hills, the unique topography of Garner Run provides researchers with an interesting challenge. The research at Garner Run is primarily focused at examining the topography and its environment as a forest.
References
- 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
- Li, L., DiBiase, R. A., Del Vecchio, J., Marcon, V., Hoagland, B., Xiao, D., Wayman, C., Tang, Q., He, Y., Silverhart, P., Szink, I., Forsythe, B., Williams, J. Z., Shapich, D., Mount, G. J., Kaye, J., Guo, L., Lin, H., Eissenstat, D., Dere, A., Brubaker, K., Kaye, M., Davis, K. J., Russo, T., Brantley, S. L. (2018). The effect of LITHOLOGY and agriculture at the susquehanna SHALE HILLS Critical Zone Observatory. Vadose Zone Journal, 17(1), 180063. doi:10.2136/vzj2018.03.0063
- 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]