Monitoring Earth's critical zone

Developments in Earth Surface Processes, 2015

Mineralogical Magazine, 2008

We live at the dynamic interface between the solid Earth and its outer fluid envelopes. This interface, extending from the outer vegetation canopy to the base of active groundwater, was recently named the Critical Zone because it supports life and is increasingly impacted by human actions. Understanding the complex interactions between processes that operate in and shape the Critical Zone requires interdisciplinary approaches that span wide spatial and temporal scales. Tectonic processes, weathering, fluid transport, and biological processes control the function and structure of the Critical Zone. Three Critical Zone Observatories recently established by the U.S. National Science Foundation are designed to integrate studies of process interactions up to the watershed scale. A goal of the program is to build the three independently conceived observatories into a network from which broader understanding — larger spatial scales but also deeper insight — can emerge.

2020

Rooting depth is an ecosystem trait that determines the extent of soil development and carbon (C) cycling. Recent hypotheses propose that human-induced changes to Earth’s biogeochemical cycles prop...

Anthropocene

Expansion and intensification of managed landscapes for agriculture have resulted in severe unintended global impacts, including degradation of arable land and eutrophication of receiving water bodies. Modern agricultural practices rely on significant direct and indirect human energy inputs through farm machinery and chemical use, respectively, which have created imbalances between increased rates of biogeochemical processes related to production and background rates of natural processes. We articulate how these imbalances have cascaded through the deep inter-dependencies between carbon, soil, water, nutrient and ecological processes, resulting in a critical transition of the critical zone and creating emergent inter-dependencies and co-evolutionary trajectories. Understanding of these novel organizations and function of the critical zone is vital for developing sustainable agricultural practices and environmental stewardship.

Earth Surface Dynamics Discussions, 2017

The critical zone (CZ), the dynamic living skin of the Earth, extends from the top of the vegetation canopy through the soil and down to fresh bedrock and the bottom of groundwater. All humans live in and depend on the critical zone. This zone has three co-evolving surfaces: the top of the vegetation canopy, the ground surface, and a deep subsurface below which Earth’s materials are unweathered. The US National Science Foundation supported network of nine critical zone observatories has made advances in three broad critical zone research areas. First, monitoring has revealed how natural and anthropogenic inputs at the vegetation canopy and ground surface cause subsurface responses in water, regolith structure, minerals, and biotic activity to considerable depths. This response in turn impacts above-ground biota and climate. Second, drilling and geophysical imaging now reveal how the deep subsurface of the CZ varies across landscapes, which in turn influences above-ground ecosystems....

Vadose Zone Journal

In intensively managed landscapes, interactions between surface (tillage) and subsurface (tile drainage) management with prevailing climate/weather alter landscape characteristics, transport pathways, and transformation rates of surface/ subsurface water, soil/sediment, and particulate/dissolved nutrients. To capture the high spatial and temporal variability of constituent transport and residence times in the critical zone (between the bedrock and canopy) of these altered landscapes, both storm event and continuous measurements are needed. The Intensively Managed Landscapes Critical Zone Observatory (IML-CZO) is comprised of three highly characterized, well instrumented, and representative watersheds (i.e., Clear Creek, Iowa; Upper Sangamon River, Illinois; and Minnesota River, Minnesota). It is organized to quantify the heterogeneity in structure and dynamic response of critical zone processes to human activities in the context of the glacial and management (anthropogenic) legacies. Observations of water, sediment, and nutrients are made at nested points of the landscape in the vertical and lateral directions during and between storm events (i.e., continuously). The measurements and corresponding observational strategy are organized as follows. First, reference measurements from surface soil and deep core extractions, geophysical surveys, lidar, and hyperspectral data, which are common across all Critical Zone Observatories, are available. The reference measurements include continuous quantification of energy, water, solutes, and sediment fluxes. The reference measurements are complemented with event-based measurements unique to IML-CZO. These measurements include water table fluctuations, enrichment ratios, and roughness as well as bank erosion, hysteresis, sediment sources, and lake/floodplain sedimentation. The coupling of reference and event-based measurements support testing of the central hypothesis (i.e., system shifts from transformer to transporter in IML-CZO due to the interplay between management and weather/climate). Data collected since 2014 are available through a data repository and through the Geodashboard interface, which can be used for process-based model simulations.

Elements, 2007

Frontiers in Water

The critical zone has been the subject of much discussion and debate as a term in the ecosystem, soil and earth system science communities, and there is a need to reconcile how this term is used within these disciplines. I suggest that much like watershed and soil ecosystems, the critical zone is an ecosystem and is defined by deeper spatial and temporal boundaries to study its structure and function. Critical zone science, however, expands the scope of ecosystem and soil science and more fully embraces the integration of earth sciences, ecology, and hydrology to understand key mechanisms driving critical zone functions in a place-based setting. This integration of multiple perspectives and expertise is imperative to make new discoveries at the interface of these disciplines. I offer solid examples highlighting how critical zone science as an integrative science contributes to ecosystem and soil sciences and exemplify this emerging field.

T he Big Bang, the point in space and time from which all matter and energy in the universe supposedly emanated, is thought to have occurred sometime around 13.7 billion yr ago . During the past 4.5 billion yr since the Earth coalesced and cooled, the planet has undergone alterations and transformations via (for example) plate tectonics, volcanism, and orogenies, which spawned severe changes in the composition and structure of the atmosphere, the oceans, and the land surface-including the biosphere and pedosphere. Other major natural forcing factors have included solar processes and orbital and galactic variations, which changed the amount of solar energy the Earth received (Intergovernmental Panel on Climate Change, 2007). Solar insolation and the structure and composition of the Earth's surface drive many ecosystem processes that have formed the soils we observe on the landscapes of today.

Environmental Science and Pollution Research, 2014