The Unseen Underground

It’s fitting that the Invisible Man in Ralph Ellison’s classic novel lives underground, hidden beneath a manhole in New York City. His social invisibility is articulated through subterranean metaphor: no one sees what’s going on underground, and no one cares. We take the ground beneath our feet for granted—until it begins to shake, or crack, or sink.

California’s Central Valley is sinking, in some places almost a foot per year. Over the past century, Californians have pumped so much of the groundwater underneath the valley that the ground is now caving in beneath them, swallowing the bottom floors of houses and damaging roads, bridges, canals and dams. How could things have gotten so out of hand? To start with, we know relatively little about groundwater. Nearly every study of groundwater laments how understudied it is. Only in 2020 was Africa’s groundwater recharge—the natural replenishment of groundwater, mostly through rain and snow sinking into the ground—mapped for the first time.

My first encounter with groundwater was philosophical. I remember someone arguing in the spirit of interconnectedness that “groundwater has no nations.” Indeed, some U.S. courts have even refused to exercise jurisdiction over groundwater, arguing that it can’t be determined whether groundwater is “water of the United States.” Under the current legal conduit theory, polluters of groundwater can only be held liable when it permeates “navigable waters,” when polluted groundwater contaminates rivers, oceans or canals. Yet groundwater is an open system with porous boundaries. And it’s increasingly being relied on for drinking water, crop irrigation, geothermal energy provision and industrial uses.

Today 25% of fresh water used in the United States is groundwater, but groundwater makes up roughly 90% of the available fresh water. As U.S. groundwater is replenished largely by rainwater, it will become both increasingly valuable and scarce in the coming decades of deepening drought. Worldwide, dependence on groundwater is even greater. At least 75% of people in Africa and 75% of EU residents rely on groundwater for drinking water. India is the most groundwater-dependent country in the world, relying on groundwater for 85% of its drinking water and 60% of agricultural irrigation. At the current rate of use, 60% of Indian aquifers will be critically depleted by 2032. Groundwater contamination from human activities, ranging from agriculture to mining, is a global problem particularly concentrated in rapidly developing countries. While water quality in the U.S. is among the best in the world, millions of Americans still drink water contaminated by industrial and agricultural chemicals. Around the world, we are facing groundwater crises of both quality and quantity.

The problem of groundwater depletion and degradation is likely farther-reaching than we know. Here, another invisible actor comes into focus: microorganisms. Broadly speaking, the diverse metabolic processes of microbes provide for life as we know it. The critical difference between dirt and soil is that soil is alive, while dirt is not. Soil contains organic matter and living organisms—bacteria, fungi, earthworms, etc.—whose processes are vital to sustaining plant life. Dirt is just the lifeless medium: tiny particles of sand, silt and clay. There are more microorganisms in a teaspoon of soil than there are people on the planet. And yet because of centuries of unsustainable agricultural practices depleting the soil of microbial life, we are about 60 years from running out of topsoil—the medium in which we grow 95% of our food.

Regenerative agriculture has emerged as a way out of the catch-22 that we need to keep farming, but if we keep farming like this, we won’t be able to farm much longer. Regenerative agriculture is soil-first, organized around preserving and expanding the biodiversity of soil microbes as a necessary precursor to growing healthy plants. This is a revelatory reorientation towards what’s happening below ground. And this reorientation has been happening for forests too: the discovery that mycorrhizal fungi connect entire forests underground has sparked an explosion of literature surrounding trees’ “social lives,” their interconnected root networks resembling an organic internet. There is reason to hope that these newly excavated truths about how ecosystems function can help us to prevent their extinction.

What’s becoming clear is that the fate of groundwater and soil microbes are linked. Soil microbes free up nutrients that are vital for plant life, and groundwater availability impacts soil-plant nutrient cycling in groundwater-dependent ecosystems. Such ecosystems include very wet environments, like wetlands, rivers, lakes and springs, but they also include very dry regions, where phreatophytic or deep-rooted desert plants commonly extend their roots all the way down to the water table. When more groundwater is pumped than is naturally replenished, this lowers the water table, which means that wells run dry, wet ecosystems get drier (and die), and even the long roots of desert plants can no longer reach their water source. And that’s just the impact this has on above-ground flora and fauna.

Like soil, groundwater is full of microorganisms. Their role is even less understood than soil microbiota, though recent research has pointed out a number of vital biogeochemical processes. For instance, microorganisms in soil and groundwater purify water of pollutants, purposefully recharging groundwater reservoirs with contaminated surface water like a natural filter, making the water drinkable again. Likewise, bioremediation is the use of microbes to clean up contaminated sites, an effective biotechnology harnessing what’s already happening beneath our feet. And we have barely scratched the surface of all the potential uses of microbes in reversing environmental destruction.

Lately, conversations about climate change have honed in on carbon sequestration as a vital piece of the solution. Levels of carbon dioxide in the atmosphere are dangerously high—a safe concentration of CO2 is 350 ppm, but in June 2021 we reached 419.73 ppm, the highest in 800,000 years. Even as carbon removal technologies remain woefully underdeveloped in the face of our pressing need, plants remove carbon dioxide from the atmosphere naturally and store it in the soil. This understudied process of carbon fixation by groundwater microbes may also prove significant for climate change mitigation efforts. There is, in brief, a powerful tool for mitigating climate change hidden in the ground beneath us. But it requires that we think systemically.

Ecosystems need to be healthy and functioning for a forest or an ocean to act as a carbon sink. That requires attention being paid to the unseen actors—microscopic, underground, underwater—which make everything else possible. The loss of microbial life in water and soil would have unimaginable consequences for life on earth. But the inverse is also true: the solutions to our macroscopic problems may be quite literally rooted in microscopic processes.


Image courtesy of Flickr. Originally published by S&S on June 23, 2021.

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