How Hurricane Helene Changed Groundwater Chemistry

Research presented at the Geological Society of America’s Connects 2025 meeting explores the storm’s hidden impact beneath Florida’s coast.

Late at night on 26 September 2024, Hurricane Helene made landfall on Florida’s big bend. The physical damage was devastating and well-documented, but an additional, unseen potential impact lurked underfoot.

Within just a few weeks, hydrologists Dr. Dini Adyasari from Texas A&M University and from Florida Atlantic University were at the site of Helene’s first landfall in Apalachee Bay to sample the shallow coastal aquifers and examine how the storm surge, flooding, and extreme precipitation were impacting groundwater resources—research that Adyasari presented this week at GSA Connects 2025 in San Antonio, Texas, USA.

With sea level and extreme storms already increasing in an anthropogenically warming climate, aquifers near the coast are likely to experience changing hydrologic conditions. Especially with Florida’s low-lying and permeable bedrock geology, Adyasari says, this is a system that needs to be more thoroughly investigated.

In her session at Connects, Adyasari reported the results of four trips to Apalachee Bay over the eight months after Helene to investigate the immediate and lingering impacts of the extreme storm on the region’s shallow coastal aquifers.

In October and November 2024 and January and May 2025, Adyasari and her team took groundwater samples about two meters below the ground surface, which they then analyzed for a variety of chemical properties, including nutrients.

But, well before Adyasari conducted lab analyses, the first clue to changes caused by the storm came from her nose. During the first few trips, samples at some of the sites didn’t have much of a smell, but as time went on, the water got stinky. The samples she collected during the last trip in May “were so smelly, like sulfide,” says Adyasari, “which means that it’s already in anoxic conditions.”

Lab results confirmed that suspicion. Adyasari found that soon after the storm, the usually oxygen-free, or anoxic, shallow groundwater had been flushed with an influx of storm and sea water. Then, months later, the introduced oxygen had disappeared, likely used up by microbes, and the groundwater was back to its normal rotten-egg-smelling state. But that storm-induced pulse of oxygenation led to the production of nutrients like nitrate.

The increase in nutrients, and potential resultant phytoplankton blooms, could have potential disruptive impacts on connected surface waters like rivers and lakes that host important aquatic ecosystems. Additionally, any changes to shallow aquifers could spell trouble for deeper groundwater reservoirs that people use for drinking and irrigation.

Interestingly, salinity didn’t change much despite the large storm surge, likely because the conditions were already brackish in the shallow coastal aquifers they sampled.

More research is still needed to build an understanding of how these interconnected groundwater systems respond to extreme storms and rising sea levels. As a next step, Adyasari is already looking into the microbes present in her groundwater samples to understand how they could be changing the water chemistry.

“We want to see if the microbial analysis will support the geochemical findings that we have now,” says Adyasari. The processes she thinks are causing the geochemical nutrient changes are “supported by microbial activities, so I'm really waiting for those results.”

About The Geological Society of America
The Geological Society of America (GSA) is a global professional society with more than 17,000 members across over 100 countries. As a leading voice for the geosciences, GSA advances the understanding of Earth's dynamic processes and fosters collaboration among scientists, educators, and policymakers. GSA publishes Geology, the top-ranked geoscience journal, along with a diverse portfolio of scholarly journals, books, and conference proceedings—several of which rank among Amazon's top 100 best-selling geology titles.