Long-term analysis reveals that groundwater is threatened by drought and heavy rains

Extreme weather events allow rainwater to bypass natural purification processes in the soil, putting groundwater quality and stability at risk. This was demonstrated in long-term groundwater analysis using a new analytical method, as described in a recent study in the journal Nature Communications. With billions of people relying on sufficient, clean groundwater for drinking, it is critical to understand the impact of climate extremes on future water security.

Rock formations containing groundwater, called aquifers, are typically recharged by precipitation that infiltrates the soil. During this passage, substances introduced to the earth’s surface are either removed from the water by adsorption to soil minerals or metabolized by soil microorganisms. This natural filtration process results in highly purified groundwater resources.

However, rainfall sometimes quickly flows into deep soil layers, thereby avoiding purification and transporting large amounts of dissolved materials from the surface and upper soil layers into groundwater aquifers.

This is especially true after extreme rainfall or periods of drought. Prolonged droughts cause large cracks in the soil and reduce rainwater absorption into the surface soil. In these situations, water flows more directly into groundwater or into rivers, lakes, or the ocean.

In that case, the groundwater is not adequately replenished and is also contaminated by undesirable and potentially harmful substances from the surface and upper soil layers. These may include organic matter, herbicides and pesticides, microbial products such as antibiotics, and other contaminants.

Using a new experimental approach, Simon A. Schroeter and Gerd Gleixner of the Max Planck Institute for Biogeochemistry conducted long-term groundwater analysis in Germany with a large research team. They used the detection of dissolved organic matter as a proxy for water contaminants and confirmed fundamental changes in groundwater stability.

“Our findings suggest that extreme weather events caused by climate change are already altering groundwater quality and the dynamics of its recharge,” said Schroeder, a postdoctoral researcher.

The research team studied groundwater and the corresponding hydroclimatic conditions at three geologically distinct research sites in Germany between 2014 and 2021. They analyzed water quality by tracking thousands of individual molecular entities as they pass from soil to groundwater. In contrast to standard methods, which target the bulk concentration of dissolved organic carbon, the newly developed untargeted approach allows detection of any changes in the amount and chemical composition of organic molecules. It has become.

Through analyzes spanning up to eight years, scientists found a consistent long-term trend of increasing amounts of surface-derived organic material accumulating in groundwater and lowering groundwater levels. Furthermore, we were able to clearly correlate this increase in groundwater contamination with extreme weather events, particularly the 2018 drought.

Their results suggest that the new method is significantly more sensitive for detecting changes in groundwater quality than commonly used carbon measurements. Therefore, this could serve as an early indicator of future groundwater quality deterioration. Although this method relies on organic molecules as indicators of water contamination, the actual contaminants may include contaminants washed away from surfaces.

As climate change continues to intensify, scientists are calling for increased attention to groundwater management and mitigation strategies for the effects of extreme hydroclimates. A decline in the soil’s natural water purification processes will amplify the stress our society already faces due to declining groundwater levels. Recent studies have warned that climate-induced declines in groundwater quality could exceed anthropogenic pollution.

“Our method helps identify groundwater quality risks in aquifers that are considered clean and safe for future use,” said Gleichsner, head of the research group. “The findings highlight the urgent need for sustainable water management practices,” he added. To protect this important resource. ”

The study is part of the German joint research center Aquadiva, led by Kirsten Küssel, Susan Trumbore and Kai Tocsche, which investigates the interactions between surface and subsurface ecosystems and their responses to environmental change. It is an interdisciplinary effort focused on understanding. By integrating expertise in biogeochemistry, hydrogeology, and microbiology, AquaDiva aims to unravel the complex processes governing groundwater ecosystems and their resilience to climate change.