On the trail of water using environmental DNA

On the trail of water using environmental DNA

Hydrogeologist Oliver Schilling analyzing spring water at Mount Fuji. © T Schilling

Where does the water that the people in a region use come from? A study using the example of the region around the Japanese volcano Fuji shows evidence of the origin and route of the precious liquid by detecting the genetic material of certain microbes in the water. In addition to other tracer substances, DNA traces of microbes from deep rock layers proved that the rainwater sometimes seeps in surprisingly far on the mountain and then flows underground to the springs at the foot of the volcano. The study thus clarifies the potential of this detection method for hydrogeology, say the researchers.

Nature, agriculture and the supply of the population – as is well known, our world is fundamentally dependent on water. Therefore, research into the factors associated with the precious elixir of life is also of great importance. Hydrogeology deals with the water in the earth’s crust. Among other things, the focus is on the question of how sources feed themselves in a region. Insights can benefit sustainable water management. If you understand the system better, you can also understand how contamination can occur. Certain substances in the water can already be used to draw conclusions about the origins and paths of the water. But in order to further refine the detection options, new tracer methods are always welcome. The study by researchers led by Oliver Schilling from the University of Basel now shows the potential of biological components.

How does the water flow in Mount Fuji?

Her focus was on the hydrogeology of the famous volcanic mountain on the Japanese main island of Honshū: Mount Fuji, also known as Mount Fuji, is referred to there as a “water mountain” because numerous springs originate in its foot area. Although Mount Fuji’s geology has been studied extensively, there are still uncertainties about its hydrology. It was previously assumed that the water originating from precipitation flows only in near-surface aquifers to the lower-lying springs. “Until now, the groundwater system of Mount Fuji could not be examined so well using standard methods,” explains Schilling. Together with his colleagues, he therefore tried to use alternative approaches to trace the path of water. They carried out extensive studies of spring water and developed models.

In their study, they now show that three special tracer components in the water give a clearer picture of the hydrogeology of Mount Fuji. Accordingly, the relatively high levels of the noble gas helium and the trace element vanadium in the spring water provide important information. In connection with known geological features of the volcanic mountain, it is becoming apparent that these substances have entered the groundwater at great depths. However, the researchers were able to decisively confirm these indications by detecting biological molecules.

Traces of microbes from the depths

They were able to detect traces of DNA in the spring water, which, according to the characteristics, comes from so-called extremophile microbes. These are fragments of genetic material from special representatives of the Archaea, which are known to only occur at a depth of 500 to 1000 meters. Apparently, parts of the groundwater that feeds the springs flowed through corresponding areas of the mountain. “Microbial environmental DNA can provide an indication of groundwater flow paths when combined with other, independent tracers such as noble gases,” says Schilling. “All three natural tracers told us the same story: there is a systematic deep dynamics of the water at Mount Fuji. Such analyzes are the key to understanding the system,” says the hydrogeologist.

The results not only expand the hydrogeological understanding of Mount Fuji, but also show the fundamental potential of combining environmental DNA, noble gas and trace element analyzes for groundwater research, the scientists emphasize. “This is a huge toolbox that is new to our research area,” says Schilling. He also gives a concrete example with a view to Switzerland. There, the detection of environmental DNA could help to trace the origin of the water that is pumped from the underground to be treated as drinking water. “A large proportion of genome traces of special cold-loving microbes can indicate that meltwater from snow and glaciers accounts for a significant proportion of the groundwater,” says Schilling.

Source: University of Basel, specialist article: Nature Water, doi: 10.1038/s44221-022-00001

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