Scientists Use Sediment Cores to Look Into the Past at Rodeo Lagoon

Sediment cores can act like windows into the past, containing information like what animals lived there and what their surroundings were like. In fall 2020, scientists collected about 21 four-inch sediment cores from throughout Rodeo Lagoon.

NPS / Yi-Chuan Luk

December 2020 - Have you ever wondered what an environment looked like in the past? Or how much human-caused change has altered an area? So have scientists at Golden Gate National Recreation Area and the US Geological Survey (USGS)!

Sediment cores can act like windows into the past, containing information like what animals lived there and what their surroundings were like. They are cylindrical tubes of sediment, which can be mud, sand, dirt, gravel, or anything that makes up the surface of the Earth. Sediment washed from the surface of the earth accumulates in low points like lakes or lagoons and forms layers, which scientists can see in the sediment core. Changes in the layers of sediment often correspond with environmental changes, like nutrient levels, salinity, flooding, fire, or algae blooms. Sometimes you can even see what organisms lived there in the past.

Scientists have noticed several fish die-offs and water quality issues in Rodeo Lagoon in recent years. But they aren’t sure to what extent these are unusual for the lagoon. As a result, they hope to use sediment cores to reconstruct past conditions in Rodeo Lagoon, see how salty it was, and identify some of the past lagoon inhabitants.

For example, USGS is looking for diatoms in the lagoon cores. Diatoms are small single-celled algae with cell walls made of silica, which preserves well in the sediments. Since different species of diatoms prefer different salinity levels, scientists can describe how salty the lagoon was based on these diatoms.

So far, scientists have found that Rodeo Lagoon supported large numbers of clams. Unfortunately, the species that they found, Limecola balthica-petalum complex, were invasive. Moss Landing Marine Labs helped identify this specimen.

NPS / Darren Fong

In addition, cores can help describe the types of filtering animals that may have lived in the lagoon. Animals such as clams and mussels are filter feeders and help clarify water quality by eating things like phytoplankton that float in the water column. Knowing what the lagoon conditions were like when the mussels lived there would help with efforts to re-establish the native mussel population and improve the water quality.

In fall 2020, scientists collected about 21 four-inch sediment cores from throughout Rodeo Lagoon. Most did contain shell fragments. The good news is that the lagoon supported large numbers of clams. The bad news is that the species that scientists found, Limecola balthica-petalum complex, were invasive.

Stay tuned for progress about this cool project in the parks!

For more information

• Contact Darren Fong

By Science Communication Intern Laurel Teague, San Francisco Bay Area Inventory & Monitoring Network

---

See more from the Bay Area Nature & Science Blog