What We Know About Groundwater Makes a Short List

Jun 2, 2014

Not all the water is visible...
Credit J. J.

Groundwater is a big, black box connecting life on land to ocean ecosystems. We have a decent handle on what goes in, but scientists are just beginning to figure out what happens inside. 

It's a classic case of out-of-sight, out-of-mind. Groundwater is buried, well, under the ground and the only way is to get to it is drill a well. That may explain why we know so little about groundwater and the ecosystems it supports. Here are five surprising things scientists studying groundwater have discovered in the past two decades:

  1. Groundwater accounts for a whopping 97% of all usable freshwater globally, and as much as a tenth of freshwater flowing into the ocean. That makes it at least as important as rivers - a fact that even scientists didn't appreciate until as recently as the 1990s.
  2. Not all groundwater is the same. Regional geology is a major differentiating factor, but proximity to the ocean is another. Along the coast, there's a region where fresh and saltwater mingle to create a unique biological and chemical regime. Willard Moore of the University of South Carolina dubbed it the subterranean estuary.
  3. Despite the complete lack of sunlight and extremely low natural levels of the nutrients bacteria need to grow, there's life down there. Not the seagrasses and fish you find in surface estuaries, but life, nonetheless. Modern genetic techniques are helping scientists figure out their identities, but pinning down which ones are most abundant and active is important ... and difficult.
  4. Nutrients, especially nitrogen, from human wastewater are causing major shifts in groundwater ecosystems that could have ramifications for coastal waters, and humans. For example, bacteria in nitrogen-rich groundwater on Cape Cod are releasing twice the normal level of methyl mercury, the most toxic form of mercury. There's concern it could find its way into seafood, and then to humans.
  5. While we're beginning to understand the impacts of excess nitrogen on groundwater ecosystems, we still know next to nothing about what pharmaceuticals, or household chemicals, or industrial pollutants - all things that can, and have, been found in groundwater - do to such bacteria, or what bacteria may do to them.