What’s Going on in our Aquifers?

By: Jessica Robertson

Most of us rely daily on ground water stored in aquifers, whether it provides our drinking water or our morning shower or whether it irrigates the crops that we consume. We don’t often think about the goings on that occur deep underground before we see any of that water, but the aquifers are an important habitat for complex microbial life. This interesting ecosystem may hold a promising answer for removing harmful carbon dioxide from our atmosphere.

Deep underwater in the aquifers, oxygen content is very low, if present at all. Microbes must rely on other substances, namely minerals like iron and sulfur, to produce energy. The byproducts of the microbes’ “breathing” these solid minerals are reactive ions that will readily interact with other chemical compounds present in the aquifer. These reactions can dramatically shape the environmental state of the nearby water, soil, or rock, and, importantly, the crops watered by groundwater.

When samples of some deep aquifer microbes were studied, it was determined that even though iron is a better source of energy, many organisms were using iron and sulfur, an unusual combination. With the pH of many aquifers being more alkaline than surface waters, reconsideration of microbial energy calculations showed that sulfur is more important to deep aquifer dwelling microbes than previously known. With interactions occurring between different species of microbes and their dependence on each others’ reactions, even without measureable levels of a given byproduct, the amount of energy cycling through the aquifer could be very high.

What this new understanding means is significant. Carbon sequestration has become difficult in light of new findings suggesting that soil is a less efficient carbon capturer than previously assumed. With the high levels of reactive ions residing in the deep aquifers thanks to the symbiotic relationships between mineral-fueled microbes, it may be possible to inject harmful carbon dioxide from the atmosphere into the aquifers; it will react with ions there, forming stable and solid compounds and sinking to the bottom of the aquifers, never to seep to the surface again.

Finding this new information regarding these deep-water microbes has been an illuminating piece of the puzzle that is carbon sequestration. Now knowing more details of the dependent relationship of iron- and sulfur- reducing microbes, it may be possible to clean up our atmosphere.