Climate change will directly impact groundwater; a German study shows how regular monitoring can check quality & quantity

Will the city of Bengaluru again approach a “Day Zero” situation this summer? Will other urban centres also join this city? That question is uppermost in the minds of all urban area residents who depend on groundwater. Come summer and are we going to see long queues in front of water tankers in the cities? Over and above, the latest report from Central Groundwater Board clearly talks about the contamination of groundwater in India. The clock is ticking — and it is high time we think about the sustainability of groundwater in a climate-risked world which will have fewer rainy days.

A recent study published in the journal Nature in January 2025 highlighted the increasing concern about the future of groundwater. The study was led by Simon A Schroeter from the Department of Biogeochemical Processes, Max Planck Institute for Biogeochemistry in Jena, Germany. It focuses on how climate change is impacting groundwater quantity and quality. Schroeter’s study is about how innovative technologies can help monitor and understand these changes.

The study, conducted from 2014 to 2021, focused on three distinct aquifer systems in central and northeastern Germany: The Hainich Critical Zone Exploratory (CZE), the Saale-Elster-Sandsteinplatte Observatory (SESO), and the Forschungsstation Linde. These systems provided an opportunity to examine how different aquifers respond to extreme weather events. To carry out the study, researchers used 254 groundwater wells and 268 soil seepage samples. This approach allowed them to analyse changes in groundwater quality and assess the influence of weather-related factors on the connection between soil and groundwater, particularly in fractured aquifer systems compared to porous sands.

A new technology, Direct-Infusion Ultra High-Resolution Mass Spectrometry (DI-HR-MS), was used to monitor and better understand changes in groundwater quality. DI-HR-MS analyses samples directly without the need for separation, providing highly accurate and detailed information about the molecules present in the groundwater sample. This technology enabled a detailed study of dissolved organic matter (DOM) and provided insights into groundwater quality and the health of the microbial communities living there.

For the study, groundwater was extracted monthly from wells using submersible pumps and sampled for dissolved organic carbon (DOC). Every third month, 10 litres of groundwater was collected for DOM analysis using DI-HR-MS. The samples were transported to the lab, filtered to <0.7 μm, acidified to pH 2, and stored at 4°C in the dark. Soil seepage was collected fortnightly from tension-controlled lysimeters in mixed beech forest and grassland at the Hainich CZE. The lysimeters used porous silicon carbide suction plates in undisturbed soil profiles.

The researchers also analysed the data from the groundwater wells between 2014 and 2021. Of the 13 groundwater wells in the studied aquifer regions, 12 showed consistent declines in hydraulic heads, ranging from −0.7 to −106 cm per year. This decline reflects broader trends across Germany, which are linked to climate change and increased groundwater extraction. Changes were also observed in soil seepage-derived substances using this method. The groundwater wells that showed significant declines in hydraulic head also exhibited increased amounts of soil seepage-derived substances, as indicated by seasonal time series decomposition (STL) analysis of similarities between groundwater and soil seepage DOM spectra. From 2014 to 2021, groundwater DOM at the Hainich CZE became more than 10 per cent similar to soil seepage DOM. For the three-and five-year time series at SESO and Linde, changes of 5 per cent and 1 per cent, respectively, were observed, as explained by the researchers.

The study highlighted that DOM, due to its complex and diverse composition, can serve as an early indicator of groundwater quality deterioration. DI-HR-MS analysis revealed a notable increase in soil seepage-derived contributions to groundwater DOM, while the concentration of DOC did not show significant changes over the study period. This shift in DOM composition is likely attributed to microbial metabolites and surface-derived substances that are not easily biodegradable. In 2018 and 2019, the study area faced severe droughts, which led to faster changes in groundwater DOM. Seven of eight wells showed more significant changes after July 2018, with steep drops in groundwater levels. These droughts, worsened by climate change, disturbed groundwater recharge and worsened groundwater quality. The study also highlighted that after a drought, when the ground gets wet again, raw DOM can move into underground water more quickly, skipping the natural filtering process. This can disturb the way aquifers are usually cleaned and may harm their ecosystems for a long time.

According to Nandakumaran P, former chairman, Central Groundwater Board, “DI-HR-MS could help Indian water managers detect early warning signs of groundwater quality deterioration by tracking changes in DOM molecular composition, before traditional bulk measurements show problems, which is crucial given India’s heavy reliance on groundwater for agriculture and drinking water. The technology’s ability to analyse DOM composition without chromatographic separation allows for comprehensive monitoring of groundwater quality changes, especially during extreme weather events like droughts and intense rainfall that are becoming more frequent in India. However, it’s important to note that while implementing this technology could be transformative for India’s groundwater management, considerations would need to be made regarding the cost and technical expertise required for widespread deployment in rural areas.”

As climate change continues, it is important to regularly monitor groundwater systems to better understand and address its impacts. With more extreme weather events occurring, the global groundwater crisis could worsen, threatening the livelihoods of millions who rely on groundwater for drinking, farming, and other essential needs.