Developing a Paradigm to Measure and Model the Form and Function of the Critical Zone

Abstract:

The Critical Zone (CZ) includes all chemical, physical, and biological processes in our environment. As humans change the CZ, it becomes more important for us to understand how the CZ will respond. The problem with understanding the CZ is that so many different processes are tightly coupled and exhibit threshold behaviors. We therefore have difficulty creating models that accurately describe CZ evolution.

CZ science targets the development of models to understand these processes. To parameterize the models requires CZ characterization and observatories to measure fluxes of water, energy, solutes, and sediments (WESS). WESS fluxes can then, in turn, be compared to the time-integrated histories of those fluxes that are recorded in soil profiles, sediment deposits, and rocks. By using scenarios of human behavior along with models to cross timescales from minutes to millenia, we will learn to forecast the impacts of anthropogenic activity.

In the Susquehanna Shale Hills Critical Zone Observatory, a large team of researchers are developing a suite of models to simulate CZ processes over a range of timescales. At the same time, this team is moving from a paradigm of "measure everything everywhere" to "measure only what we need" as we scale up from the 0.1 km² watershed at Shale Hills to the 165 km² Shavers creek watershed. At Shale Hills, we made densely spaced measurements. In the Shavers creek watershed, we are targetting catenas in sub-catchments of the watershed as well as measurements of the main-branch streams. Sub-catchments were chosen to explore the different lithologies and land use characteristics. Instrumentation is already deployed in one first-order sub-catchment located on Tuscarora sandstone. The next sub-catchment to be instrumented, like Shale Hills, will be located on shale bedrock. Unlike Shale Hills, however, the sub-catchment will host agricultural activity. We are targetting our intensive chemical, physical, and biological measurements on catenas on north- and south-facing hillslopes in recognition of the fact that we cannot measure all locations. By combining our suite of models with these targetted measurements, we will understand regolith distribution so as to allow a greater capacity to simulate WESS fluxes and changes in soils, sediments, and landscapes over a range of timescales.