Environmental DNA analysis of microbial communities can help us understand how the water cycle works in a particular area. Basel hydrologist Oliver Schelling recently used this method to examine the water cycle on Mount Fuji. Its results have implications for other regions around the world.
Where does the water that provides drinking water to people in a particular area come from? What feeds these sources and how long does it take for groundwater to make its way back to the surface? This hydrological cycle is a complex interaction of various factors. A better understanding of the system allows us to understand, for example, why pollution is worse in some areas than others, and can help us implement sustainable water management policies and practices.
Environmental DNA (eDNA) provides some important data to improve our understanding. Combined with the evaluation of other natural detectors—the noble gases, for example—these microbial data provide important glimpses into the flow, circulation, and functioning of complex groundwater systems. “It’s a huge new toolkit in our field of research,” says Oliver Schelling, professor of hydrogeology at the University of Basel and at Eawag, the Swiss Federal Institute for Aquatic Science and Technology. Quantitative hydrogeology determines where and how quickly new groundwater accumulates.
Beginning in 2018, Schilling has taken various measurements on Mount Fuji in Japan in order to determine where the spring water comes from—that is, where the groundwater flows from before it returns to the surface and forms the hundreds of scattered pristine natural springs. around Mount Fuji. His results were published in the first edition of the journal Nature waterthat just came out.
Determination of water sources from eDNA
The choice of this particular mountain was no accident: “The geological setting of Mount Fuji is unique on Earth because it is the only place where three tectonic plates meet like this. This makes the groundwater system very complex and therefore unsuitable for research using standard methods,” explains Oliver Schilling.
Thanks to a Japanese colleague, he came up with the idea of examining microbial RNA in the region. “He told me about water sources in Mount Fuji that show noteworthy signatures, namely that eDNA in the water shows the presence of organisms that can only grow at a depth of 500 to 1,000 meters,” he recalls. This is an indication that some of the water sources come from deep groundwater. “This was the first indication that microbial eDNA may provide some clues to the trajectory of groundwater flow when combined with other independent tracers such as the noble gases,” Schilling continues.
piqued his curiosity. During his tenure as a postdoctoral researcher at Université Laval in Quebec, he traveled to Japan during his vacations and made various measurements with his Japanese colleague. He also delved into the existing scientific literature, which is mainly in Japanese. Along with the eDNA, the hydrogeologist also analyzed two groundwater tracers with a higher incidence due to Mount Fuji’s unique geological setting: the noble gas helium and the element vanadium. Schilling concludes, “All three natural tracers tell the same story: There is an orderly, deep circulation of water within Mount Fuji. Such analyzes are key to understanding the system.”
Possible results for Switzerland as well
This new application of tracers can be used to examine groundwater systems around the world. In Switzerland, for example, it can be applied to determine the source of water pumped from the ground for drinking water. “A large proportion of eDNA from cold-loving microbes in groundwater, for example, indicates that meltwater from snow and glaciers makes up a large proportion of groundwater sources,” explains Schilling.
Looking into the future, this means: “If we know the importance of these natural water reserves, we can look for alternatives early in order to protect areas affected by seasonal water shortages as much as possible,” the hydrogeologist continues. As a result of climate change, glaciers in Switzerland are melting and snow is decreasing, which means that these important sources of river and groundwater water are slowly disappearing. This will negatively affect water availability especially in the hot and dry summer months.
One possibility for preventing severe summer water shortages is to collect more rainwater in reservoirs during the winter half of the year, for example by artificially strengthening groundwater reservoirs or adapting how above-ground reservoirs are managed. “Microbiological eDNA analysis provides us with a new tool to improve the calibration of hydrological models used in groundwater management,” explains Schilling. This, in turn, is an important part of setting realistic expectations of water quality and availability and allows for sustainable, long-term planning for the management of groundwater – our most valuable and abundant source of drinking water.