Study finds land use influences organisms living underground

Researchers at Eawag (Swiss Federal Institute of Aquatic Science and Technology) and University of Zurich have complied and analyzed a globally unique data set on the occurrence of various amphipods in groundwater.

They were able to show that land use within a radius of up to 1 kilometer from the groundwater extraction site has an impact on these sensitive creatures. This could indicate that the current groundwater protection zones are not large enough.

Four-fifths of Switzerland’s drinking water comes from hidden underground aquifers. Numerous groundwater extraction sites tap into these reserves. Drinking water supplies are under increasing pressure.

“In order to fulfill the quality criteria, some extraction sites have to be taken off the grid or water from impacted sites has to be mixed with less impaired water,” says aquatic ecologist Mara Knüsel, who is currently completing her doctorate in Professor Florian Altermatt’s research group at the aquatic research institute Eawag and the University of Zurich.

In recent years, Knüsel and her colleagues have been working intensively on researching small creatures that are at home in dark and cold water: groundwater amphipods. They resemble tiny shrimp, but unlike the differently pigmented freshwater amphipods on the surface, they are white and blind. They play an important role in the function of groundwater ecosystems.

Less nitrate at groundwater extraction sites surrounded by forests

In their latest article, which has just been published in the journal Ecological Applications, the researchers link the occurrence of amphipods to the type of land use on the Swiss Central Plateau.

The researchers often found amphipods at groundwater extraction sites in the middle of a forest, whereas they encountered amphipods much less frequently at groundwater extraction sites near farmland. The groundwater at the extraction sites close to crops also tended to be more contaminated with nitrate than at the sites surrounded by forest, which indicates poorer drinking water quality.

However, Knüsel’s colleague Roman Alther points out that it would be premature to conclude that the water quality is poor because amphipods are absent. “Hydrogeology also plays a role,” he explains. “Factors such as the structure of the local groundwater aquifer, including pore size and water chemistry, can also influence whether or not amphipods are present.”

The researchers therefore regard the presence or absence of the small organisms more as a supplementary indicator. “As an indication that the biology at a particular location may be impaired,” says Alther.

Influence of farmland still found within a distance of up to a kilometer

The researchers also show that the type of land use has an impact on the occurrence of amphipods in a larger radius. In the data set, farmland located 600 to 1,000 meters away from the groundwater extraction site also leaves a negative signal in the groundwater.

In Switzerland, the Water Protection Act stipulates that protection zones must be created around groundwater extraction sites in order to protect valuable drinking water from contamination and other harmful influences. On the Swiss Central Plateau, however, these protection zones cover an area that extends on average only 300 to 400 meters around the extraction site.

“We conclude that the currently established protection zones may not be large enough to prevent possible negative effects of land use on groundwater communities,” the researchers state in their article.

A unique habitat

Just like lions in the savannah, amphipods in groundwater are at the top of the food chain. As a result, they also influence all other living organisms at lower trophic levels. “The great diversity of life forms in groundwater is still largely unexplored,” says Knüsel.

The researchers have therefore only just laid the foundations with their data set on amphipods: their findings could be an argument in favor of a possible extension of the groundwater protection zones. Beyond this, they are keen to “raise awareness among the general public that groundwater is not only a precious drinking water reserve,” says Alther, “but also a unique habitat that needs to be preserved.”

New findings about amphipods

The Eawag researchers worked closely with water supply managers who are responsible for more than 900 different groundwater extraction sites throughout Switzerland and “without whose help this work would not have been possible,” as Knüsel emphasizes. The collaboration resulted in a systematic collection of amphipods, in which the researchers also discovered several previously unknown species with the help of genetic analyses.

The researchers also traced how the last ice age around 20,000 years ago affected the spread and the present occurrence of groundwater amphipods. “We find some species only in places that were not glaciated,” says Knüsel.