The earth is a complex system and its study is the focus of research at the Department of Energy’s Pacific Northwest National Laboratory.
The subsurface is an especially important component of this system. It is home to large aquifers that provide drinking water and to valuable mineral deposits that fuel economies. It presents opportunities, such as a place we might store carbon to slow global warming, but also can provide unexpected pathways for the movement of chemicals into our environment.
Despite its importance, the subsurface is often overlooked because it is difficult to see what lies below. PNNL researchers have been taking on this challenge for more than 50 years. They seek to understand the fundamental physical, chemical, and biological processes that occur in the subsurface, the interplay among these processes and their impact. In the pursuit of this knowledge, PNNL has become an international leader in subsurface science.
The subsurface processes of interest occur over a wide range of time and space. Fluid flow through the tiniest microscopic pores can have an impact on an entire ecosystem. Reactions that take place in a fraction of a second can affect a region for centuries. PNNL researchers and their collaborators are working to understand these interactions, which could lead to improved environmental remediation, enhanced agricultural land management and a better understanding of climate change.
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For example, we know that soils contain a vast amount of carbon, but current computer models do not accurately predict how carbon processes in the soil affect the climate and vice versa. Colleagues from Idaho National Laboratory and EMSL (a DOE user facility called the Environmental Molecular Sciences Laboratory located at PNNL) teamed on a study to address this knowledge gap. They were the first to use a technique called ultra-high resolution mass spectrometry to compare the molecular composition of soil organic matter from different ecosystems. Studies like this provide a more complete understanding of the carbon cycle and the complex interactions between climate and soil processes, which could lead to improved regional and global climate models.
In another effort, PNNL scientists and collaborators from the University of Central Florida developed a novel model to simulate the flow of water above and below ground, as well as the interaction between these flows. Their model integrates hydrological processes from the microscopic level all the way to the ecosystem level and considers multiple hydrological domains that are often considered separately in other models. Bringing it all together in a single model leads to a better understanding of how nutrients are transported above and below ground — through land, water and places they meet — as well as the processes that affect greenhouse gas production.
Recently, two PNNL researchers received DOE Early Career Awards to learn more about soils. Ecologist Kirsten Hofmockel is studying the microbial activity in soils where crops for biofuels such as switchgrass are grown. She is also looking at how the choice of crops and soil properties influence micro-organisms and the fate of carbon in soil. James Moran, a biogeochemist, is using an imaging technique he developed to look at microbial communities near plant roots, a dynamic environment where plants, soil and microbes interact. His work will show how plants draw nutrients from the soil and how microbial communities behave in soil.
Much of PNNL’s subsurface science expertise builds upon decades of work to understand the contaminants beneath the Hanford site and how they move and change over time. PNNL researchers also have invented new sensors and monitoring technologies that allow us to better “see” what is going on below ground and whether remediation strategies are effective.
To enable an approach similar to medical imaging, PNNL environmental engineers have developed software for real-time, three-dimensional imaging of the subsurface. Their work centered on electrical resistivity tomography (ERT), a technique that measures how difficult it is to pass an electrical current through a material and lets researchers precisely locate contaminants and noninvasively observe subsurface processes as they occur.
The detailed images reveal information that could reduce the cost and risk of remediation. PNNL’s software pairs with supercomputing technology to process large quantities of data quickly and efficiently — overcoming limitations of commercial ERT software — and making it possible to perform one of largest ERT studies ever at Hanford’s B-tank farm. In that study, the software processed a dataset with 5,000 electrodes, 220,000 measurements and a computer model of about 3 million elements. The software also is used by DOE to verify the performance of systems designed to store carbon in land formations such as basalt.
So, the next time you take a stroll in a park, read about climate change or hear about the ongoing Hanford cleanup effort, remember that PNNL scientists and engineers are applying their creativity and ingenuity to discover the intricate processes that take place beneath the surface — and using this knowledge to ensure a more sustainable future for the complex system we call home.
Steve Ashby, director of Pacific Northwest National Laboratory, writes this column monthly.