Añana Saltern microorganisms help to clarify the groundwater flow pattern

The MicroIker group of the University of the Basque Country (UPV/EHU) has explored the diversity and distribution of unicellular organisms in the springs of the Añana Salt Valley. The study is published in the journal Microbial Ecology.

On the basis of the bacteria and archaea communities and their distribution in the waters, the UPV/EHU researchers saw that it is also possible to distinguish between the brackish and salty waters that emerge from the springs in the valley. The waters of two springs located about two meters from each other have different origins and microbial compositions. The researchers say that further research is needed to better understand the groundwater flows in the saltern.

The Añana Salt Valley is one of the best preserved continental salterns in Europe. Salt has been produced in this saltern in Álava for more than 7,000 years. The geological and hydrogeological complexity of the area means that in some parts of the valley very deep water flows combine with shallower ones, giving rise to water flows with different degrees of salinity from springs very close to each other.

“Depending on the path of the groundwater, the salinity of the water can be higher or lower,” explained Ilargi Martinez-Ballesteros, a UPV/EHU researcher. So some springs produce salty water (containing about 200 g of salt per liter) and others produce brackish water (containing about 20 g of salt per liter).

The UPV/EHU’s MikroIker research group explored the diversity of unicellular organisms in this habitat. “Using molecular techniques (mainly DNA sequencing), we studied which archaea and which bacteria are present in the waters of various springs in the valley,” explained Martínez-Ballesteros, a member of the group.

Archaea and bacteria can be distinguished according to their cell walls. “In the study, we saw that archaea predominate in very salty waters; this is normal because archaea usually live in extreme environments, whereas in brackish waters, there is a larger mix of bacteria.”

In line with hydrogeological studies

“Besides finding out which microorganisms are present in the water and how many there are,” said Martínez-Ballesteros, “this work also aimed to see whether there is a microbiological difference between types of water with such different salinity levels. We also observed great differences from a microbiological point of view between salty and brackish waters. We found that waters that are similar to each other are also microbiologically similar.” This coincides with the results of hydrogeological studies.

The MikroIker researchers collaborated with the UPV/EHU’s Water-Environmental Processes (HGI) research group “to understand the context of the Salt Valley.” In fact, halite or rock salt is present underneath the valley; “hydrogeologists still don’t know exactly what path the water follows, but it seems to emerge from great depths. Depending on the path through which the water flows, more or less of it passes through the rock salt, and that explains why the springs discharge water with varying salinity,” said the researcher.

“The extremely salty waters emerge from a very great depth, and the paths of the brackish water are less deep. That is how we saw that the waters of different origin have different bacterial and archaeal diversity,” she explained.

A clear example of this are the springs called El Pico and El Pico Dulce. “They are only two meters away from each other and, as the name [in Spanish] suggests, the former is salty and the latter is brackish. The water they contain is completely different, both in terms of the composition of the dissolved ions and in terms of the microorganisms. This means that they have no contact with each other, otherwise they would be more similar,” explained the MikroIker researcher.

The researcher was keen to point out that “microorganisms are an essential part of natural environments. It is very important to know about the microorganisms present in all ecosystems. They are present and we need them so that the whole ecosystem can function, because they guarantee the recycling of many of the compounds that exist on the planet.”

She said further research was needed: “We have discovered several microorganisms that have not been classified anywhere, and we have to go on defining and characterizing new species. We’ve got our work cut out.”

The MikroIker team has identified two new species in the Añana Salt Valley and in the laboratory they are currently growing the bacteria and archaea found in the saltern.