Guardians of the beach: How hidden microbes protect coastal waters amid climate change

Pore water samples were collected from a high-energy beach subsurface estuary in Stinson Beach, California, USA, over a 2-week spring tidal transition period during both the wet and dry seasons. Changes in microbial community composition analyzed by V4 16S rRNA gene sequencing were contextualized by extensive hydrological and physicochemical measurements. The vertical depth structure of the assemblage remained consistent throughout the tides and seasons, but was perturbed by overcoming waves several times in winter. Credit: Environmental Microbiology (2024). DOI: 10.1111/1462-2920.70009
A hidden world full of life lies beneath the sand of the beach. A new study led by Stanford University reveals how microbial communities in coastal groundwater respond to infiltrating seawater.
The study, published in the journal Environment Microbiology, reveals the diversity of microorganisms that live in these important ecosystems, and what happens when they are flooded by rising sea levels.
“Beaches act as filters between land and ocean, allowing groundwater and associated chemicals to be treated before they reach the ocean,” said Dr. Jessica Brinton, co-lead author of the study. student in Earth System Science at the Stanford Doerr School of Sustainability. “Understanding how these ecosystems work is key to protecting their ecosystem services in the face of rising sea levels.”
The research team conducted intensive research at Stinson Beach, north of San Francisco. Stinson Beach is the epitome of a “high energy” beach, but there are only a few previous papers on the microbiome worldwide.
guardian of microorganisms
Microbial communities living in the groundwater of sandy beaches play an important role in maintaining coastal water quality. These microorganisms help break down chemicals, including excess nutrients such as nitrogen. These chemicals can be obtained from natural sources such as decomposing plants and human resources such as agricultural runoff and wastewater.
To better understand the dynamics of this microbial filtration system, the research team headed to Stinson Beach. They collected samples from the beach’s underground estuary around the clock over two weeks during both the wet and dry seasons to capture tidal changes. The researchers then used advanced genetic sequencing techniques to analyze the microorganism’s DNA. This approach is the first of its kind at such a fine time scale and has provided unprecedented insight into the composition and stability of microbial communities.
The researchers found that the microbial communities remained relatively stable as tidal conditions and seasons changed. However, wave overtopping events, in which high-energy waves push seawater into aquifers, caused significant changes in the microbial composition. Such disruptions are expected to become more frequent as sea levels rise and storm surges make it harder for microorganisms to clean water.
“These microorganisms live in complex communities, many of which have specialized roles such as processing nutrients or producing and consuming greenhouse gases,” said co-senior author, Stanford Doerr Sustainable said Christopher Francis, professor of Earth system science and oceans in the School of Human Sciences.
“While the resilience of microbial communities under typical conditions is encouraging, disturbances like wave overtopping highlight the vulnerability of microbial communities to climate change,” said co-first author Katie Langenfeld. Postdoctoral researcher at the University of Michigan.
Impact on coastal resilience
The results of this study establish an important baseline for understanding how underground estuaries function and respond to environmental change. As sea levels rise, beach sand is pushed inland or eroded, changing the hydrology, chemistry, and microbial composition of groundwater.
This study adds an important piece to the coastal resilience puzzle. This study questions impending changes in coastal groundwater by highlighting the interaction between microbial dynamics and physical processes such as wave action. Researchers say policymakers and coastal planners need to consider the role of these hidden ecosystems when developing strategies to manage sea level rise.
“We depend on these microbial communities for important biogeochemical cycling at the land-sea interface,” said co-senior author Richard from the Stanford Doerr School of Sustainability and the Stanford School of Engineering. said Alexandria Boehm, Rhoda Goldman Professor of Environmental Studies. “If that capacity is reduced due to climate impacts, we could see cascading effects on coastal water quality and marine life.”
Further information: Jessica A. Bullington et al, Microbial Community of a Sandy Beach Subterranean Estuary is Spatally Heterogeneous and Impacted by Winter Waves, Environment Microbiology (2024). DOI: 10.1111/1462-2920.70009
Provided by Stanford University
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