Susquehanna Shale Hills Critical Zone Observatory: Shale Hills in the Context of Shaver's Creek Watershed

Abstract

Core Ideas Studying the critical zone requires targeted research on water, energy, gas, solutes, and sediments. The SSHCZO targets a 165‐km2 watershed on sedimentary rocks in the northeastern United States. One SSHCZO subcatchment, Shale Hills, provides extraordinary data describing a shale CZ. The Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) was established to investigate the form, function, and dynamics of the critical zone developed on sedimentary rocks in the Appalachian Mountains in central Pennsylvania. When first established, the SSHCZO encompassed only the Shale Hills catchment, a 0.08‐km2 subcatchment within Shaver's Creek watershed. The SSHCZO has now grown to include 120 km2 of the Shaver's Creek watershed. With that growth, the science team designed a strategy to measure a parsimonious set of data to characterize the critical zone in such a large watershed. This parsimonious design includes three targeted subcatchments (including the original Shale Hills), observations along the main stem of Shaver's Creek, and broad topographic and geophysical observations. Here we describe the goals, the implementation of measurements, and the major findings of the SSHCZO by emphasizing measurements of the main stem of Shaver's Creek as well as the original Shale Hills subcatchment.

Soil CO2 and O2 Concentrations Illuminate the Relative Importance of Weathering and Respiration to Seasonal Soil Gas Fluctuations

“…1 and 2). This is probably not the driver of ARQ <1 in the soils of the SSHCZO because the soil pH is too low to support the presence of carbonates and there is no evidence of carbonates in the subsurface of the Garner Run and Shale Hills sites (Brantley et al, 2018; Li et al, 2018).…”

Non‐linear quickflow response as indicators of runoff generation mechanisms

“…Median depth to bedrock ranges from roughly 40 cm to 1 m depending on soil type and soils tend to be deeper on south‐facing hillslopes (Lin et al, 2006). Stands are dominated by mature oaks, which compose 64% of the basal wood area (Brantley et al, 2019). The remaining vegetation includes species of maple, hickory, and pine in addition to eastern hemlock (Smith, Eissenstat, & Kaye, 2017).…”

Nitrogen Budget and Topographic Controls on Nitrous Oxide in a Shale‐Based Watershed

“…In order to characterize the N saturation status of the Shale Hills CZO we assessed the following four indicator symptoms in fall (September-November) versus spring (March-May): (1) high relative rates of net nitrification, (2) elevated nitrate (NO 3 À -N) concentrations in stream water, (3) low seasonal variability in stream water NO 3 À -N concentrations, and (4) a close balance between inputs and outputs of inorganic N (i.e., low retention of inorganic N). Indicator symptoms were evaluated using soil and pore water data collected from this study, as well as utilizing available Shale Hills CZO data sets (Brantley & Duffy, 2010;Brantley, Bazilevskaya et al, 2013aBrantley, Jin, Andrews, Holmes, Bhatt et al, 2013aDuffy, 2012;Kaye & Smith, 2013). Watershed N accumulation or loss was determined by subtracting N outputs from N inputs, while internal N cycling processes were measured in order to identify possible N retention pathways in the watershed.…”

“…Potential net nitrification and mineralization rates for each season were estimated using samples collected and analyzed as described previously at one time point (October 2014 for Fall and March 2015 for Spring), but these seasonal averages are based on the mean of 24 total surface mineral soil samples (0-15 cm) taken throughout the catchment. Stream water, groundwater, and soil pore water NO 3 À -N concentrations were estimated from data sets collected from 2008 to 2010 (Brantley & Duffy, 2010;Brantley, Bazilevskaya et al, 2013aBrantley, Jin, Andrews, Holmes, Bhatt et al, 2013a. Details of sample collection and analysis can be found in Jin et al (2011) and Andrews et al (2011).…”