Beneath sandy beaches, small organisms play a crucial role in filtering out harmful substances from groundwater, which is essential for the health of the ocean. A new study from Stanford University demonstrates how sneaker waves can shed light on the possible impacts of rising sea levels on the water movements, chemical composition, and microbial communities in beach areas.
Beneath sandy beaches, microbes filter chemicals from groundwater and protect ocean health. A study from Stanford reveals that sneaker waves provide insight into the potential impacts of rising sea levels on beach hydrology, chemistry, and microbiology.
A lively ecosystem thrives just below the surface of beach sands. Recent research from Stanford uncovers how microbial communities in coastal groundwater react when seawater seeps into these areas. The results, published on December 22 in Environmental Microbiology, highlight the diverse microbial life found in these vital habitats and the potential impacts of increased seawater exposure due to rising sea levels.
“Beaches act as a natural barrier between land and ocean, filtering groundwater and its chemicals before they enter the sea,” said Jessica Bullington, a Ph.D. student studying Earth system science at the Stanford Doerr School of Sustainability and one of the study’s co-authors. “Understanding how these ecosystems function is crucial for maintaining their protective roles as sea levels rise.”
The research team conducted their study at Stinson Beach, located north of San Francisco. This beach is characterized as “high-energy,” with limited previous research on its microbial communities performed globally.
Microbial Guardians
The microbial organisms found in groundwater beneath beach sands are vital for keeping coastal waters clean. They assist in breaking down chemicals, including excess nutrients like nitrogen, which can come from natural sources like decaying plants or from human activities such as farming runoff and wastewater discharge.
To explore how this microbial filtering system operates, the research team carried out an in-depth investigation at Stinson Beach. For two weeks during both dry and wet seasons, they took continuous water samples from the underground estuary to monitor changes caused by varying tides. They then employed advanced gene sequencing techniques to analyze the microbial DNA, marking the first study to examine microbial communities at such detailed intervals and providing valuable insights into their stability and structure.
The team’s findings revealed that microbial populations remained mostly stable, despite changes due to tides and the seasons. However, significant alterations in microbial composition were detected during wave overtopping events—when strong waves push seawater into the groundwater. Such disturbances are expected to increase with rising sea levels and more frequent storms, posing challenges to the microbes’ filtering abilities.
“These microbes exist in complex communities, many of which perform specific functions such as nutrient processing and greenhouse gas regulation,” stated Christopher Francis, co-senior author and professor of Earth system science and oceanography at the Stanford Doerr School of Sustainability. “While it’s reassuring to see their resilience during normal conditions, disturbances like wave overtopping highlight their vulnerability to climate change,” added co-first author Katie Langenfeld, who conducted this research while a postdoctoral scholar at Stanford and is currently a postdoctoral fellow at the University of Michigan.
Significance for Coastal Resilience
This study establishes a critical baseline for comprehending the functioning of underground estuaries and their responses to environmental changes. As sea levels rise, sandy beaches may shift inland or erode, altering the hydrology, chemical dynamics, and microbial populations of groundwater.
This research is a pivotal step in enhancing our understanding of coastal resilience. By stressing the connection between microbial dynamics and physical elements such as wave activity, the study prompts essential considerations regarding expected changes in coastal groundwater. Researchers urge policymakers and coastal planners to factor in these hidden ecosystems when devising strategies to manage sea level rise.
“We rely on these microbial communities for crucial biogeochemical processes at the interface of land and sea,” emphasized Alexandria Boehm, co-senior author and the Richard and Rhoda Goldman Professor of Environmental Studies at the Stanford Doerr School of Sustainability and the Stanford School of Engineering. “If their functions are compromised due to climate impacts, we might see a cascade of negative effects on coastal water quality and marine ecosystems.”
