Scientists Discover Missing Piece of Biogeochemical Puzzle in Deep Aquifers

Deep beneath the Earth's surface n aquifers, a complex dance of microbes and minerals takes place. Now, scientists have taken a closer look at these interactions, which can drastically impact groundwater quality.

Deep underground, microbes don't have much access to oxygen. That's why they've evolved ways to breathe other elements, including solid minerals. When these microbes use these elements, they transform them into highly reactive dissolved ions that are they much more likely to interact with other minerals and dissolved minerals in an aquifer. This, in turn, drastically changes the makeup of the rock, soil and water in the aquifer.

About a fifth of the world's population relies on groundwater from aquifers for drinking water. Many others rely on this water for crops and agriculture. That's why it's so important to understand the interactions that take place-especially when it comes to avoiding polluting these water sources.

For decades, scientists have thought that when iron was present in these aquifers, microbes who could breathe it would out-compete those who couldn't. While the scientists found that iron is frequently among the most abundant minerals in many aquifers while solid sulfur is almost always absent, something didn't add up. A lot of microorganisms had the ability to breathe both iron and sulfur, which didn't seem to make sense; why bother breathing sulfur when iron was abundant?

The scientists decided to take a closer look. They found that older and deeper aquifers tend to be more alkaline than surface waters, which meant that it got harder and harder to get energy out of iron. It's possible that the sulfur is used up almost immediately. More specifically, a group of microorganisms breathe sulfate and exhale sulfide, which reacts with iron minerals to form sold sulfur and iron.

"This hypothesis runs counter to the prevailing theory, in which microorganisms compete, survival-of-the-fittest style, and one type of organism comes out dominant," said Ted Flynn, one of the researchers, in a news release. Instead, the iron-breathing and the sulfate-breathing microbes depend on each other to survive.

The findings reveal a little bit more about the complex interplay of microorganisms in aquifers. This, in turn, can show scientists a bit more about how certain chemicals might impact aquifers.

The findings are published in the journal Science.