Human activities have an impact on the fluid flow on Earth

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The impact of human activities—such as greenhouse gas emissions and deforestation—on Earth’s surface have been well-studied.
Now, hydrology researchers from the University of Arizona have investigated how humans impact Earth’s deep subsurface, a zone that lies hundreds of meters to several kilometers beneath the planet’s surface.
With oil and natural gas production, there is always some amount of water, typically saline, that comes from the deep subsurface, McIntosh said.
This becomes a cycle of producing fluid and reinjecting it to the deep subsurface.
“We show that the fluid injection rates or recharge rates from those oil and gas activities is greater than what naturally occurs,” McIntosh said.
Human activities have the potential to alter not just the deep subsurface fluids but also the microbes that live down there, McIntosh said.
There remain a lot of unknowns about Earth’s deep subsurface and how it is impacted by human activities, and it’s important to continue working on those questions, McIntosh said.
“We need to use the deep subsurface as part of the solution for the climate crisis,” McIntosh said.


Numerous studies have examined the effects of human activity on the surface of the Earth, including deforestation and greenhouse gas emissions. Scientists studying hydrology at the University of Arizona have now looked into how human activity affects the deep subsurface of Earth, which is located hundreds to thousands of kilometers below the planet’s surface.

The study’s lead author, Jennifer McIntosh, a professor in the UArizona Department of Hydrology and Atmospheric Sciences, explained, “We looked at how the rates of fluid production with oil and gas compare to natural background circulation of water and showed how humans have made a big impact on the circulation of fluids in the subsurface.”.

“We felt it was important to provide some context to these proposed activities, especially when it comes to our environmental impacts,” stated Grant Ferguson, the lead study author and adjunct professor in the UArizona Department of Hydrology and Atmospheric Sciences and the University of Saskatchewan’s School of Environment and Sustainability. “The deep subsurface is out of sight and out of mind for most people.”.

The study predicts that as strategies for mitigating climate change are put forth, these human-induced fluid fluxes will rise in the future. Geothermal energy production, which involves pumping water through hot rocks to generate electricity, is one such strategy. Another is lithium extraction from underground mineral-rich brine to power electric vehicles. Geologic carbon sequestration is the process of capturing and storing atmospheric carbon dioxide in porous rocks below the surface. Along with researchers from Harvard University, Northwestern University, the Korea Institute of Geosciences and Mineral Resources, Linnaeus University in Sweden, and the University of Saskatchewan in Canada, the study was conducted.

Co-author of the study and professor in the UArizona Department of Geosciences Peter Reiners stated, “Responsible management of the subsurface is central to any hope for a green transition, sustainable future and keeping warming below a few degrees.”.

According to McIntosh, there is always some water involved in the extraction of oil and natural gas, usually saltwater from the deep subsurface. Many times dating back millions of years, the subterranean water becomes salinized through a combination of evaporation from old seawater and mineral and rock reactions. To maintain reservoir pressure and make up for the oil removed, more water from near-surface sources is added to the salt water for more effective oil recovery. The subsurface is then reinjected with the blended saline water. This starts a cycle of creating fluid and injecting it again into the subsurface at a deep depth.

This same process is used in the production of geothermal energy, lithium extraction, and geologic carbon sequestration, all of which reintroduce residual saline water from below the surface.

“We demonstrate that the fluid injection rates or recharge rates resulting from those oil and gas operations surpass the natural occurrences,” McIntosh stated.

By utilizing available data from multiple sources, such as fluid movement measurements associated with oil and gas extraction and water injections for geothermal energy, the group discovered that the rates of fluid movement caused by human activity today are greater than those of fluid movement in the past.

The researchers additionally forecasted how human endeavors such as carbon capture and sequestration and lithium extraction might be documented in the geological record—the chronicles of Earth preserved in the rocks that comprise its crust—as these activities gain momentum.

According to McIntosh, human activity has the ability to change not only the deep subsurface fluids but also the microbes that reside there. Microbial environments can be changed by fluid movement due to alterations in water chemistry or the introduction of new microbial communities from the Earth’s surface into the subsurface.

An abrupt bloom of microbial activity, for instance, might occur in a deep rock formation that had previously shown no signs of microbial activity. Hydraulic fracturing is a technique used to fracture subterranean rocks with pressurized liquids in order to extract oil and gas.

According to McIntosh, there are still many unanswered questions regarding the Earth’s deep subsurface and how human activity affects it. It is crucial to keep researching these issues.

As part of the solution to the climate crisis, McIntosh stated, “we need to use the deep subsurface.”. Nevertheless, our understanding of the Martian surface surpasses that of water, rocks, and life found far below the surface. “.

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