Research team to explore the role clams, salt marshes play in carbon cycling in estuaries

April 21, 2023

An interdisciplinary team of researchers across six institutions was awarded a $3.5 million grant from the National Science Foundation to investigate the role that clams, salt marshes and seagrasses—also known as macrobiota—play in carbon cycling in estuaries. The research will be carried out through a coordinated program of field measurements, laboratory experiments, historical data analysis, and numerical modeling, all focused on the Chesapeake Bay.

“Estuaries are highly productive and diverse ecosystems and hence deserve study in their own right,” said Raymond Najjar, professor of oceanography and lead investigator on the project at Penn State. “But estuaries also play an important role in the global carbon cycle, which regulates atmospheric carbon dioxide, the most important greenhouse gas.”

The global carbon cycle consists of the processes that transform and transport carbon on Earth. A key feature of the global carbon cycle is the transport of carbon from land to the open ocean. Before reaching the open ocean, the carbon carried by rivers must pass through estuaries, where significant transformations take place.

Transformations of carbon and alkalinity in the ocean are dominated by microscopic life, like phytoplankton and bacteria. These transformations are also influenced by macrobiota, such as clams, salt marshes and seagrasses, which are generally ignored in estuarine biogeochemical models and estimates of land-to-ocean fluxes of carbon and alkalinity, creating a gap in our knowledge and predictive capability, according to the researchers. Adequate measurements of how macrobiota respond to the large seasonal and interannual variability of the estuarine environment are also lacking.

“Such measurements are essential for developing formulations of fluxes as a function of environmental conditions, which is necessary for representing point measurements in the spatially and temporally continuous manner demanded by numerical models and by efforts to represent macrobiota accurately in global marine carbon and alkalinity budgets,” said Cassie Gurbisz ‘16, project collaborator and coastal system ecologist at St. Mary’s College of Maryland.

Many variables affect the form and amount of carbon in estuaries, including alkalinity, which is the capacity of a water body to neutralize acid. This research focuses on two contrasting tidal tributaries of the Chesapeake Bay: the Potomac River, where they found the alkalinity coming into the Bay was high; and the York River, where the alkalinity coming in was significantly lower.

“These two tributaries also have a wealth of monitoring data on water chemistry, benthic fauna, tidal marshes and submerged aquatic vegetation that span decades and which we have only begun to mine,” said Ryan Woodland, project collaborator and coastal ecologist at the University of Maryland Center for Environmental Science. “Finally, we have developed numerical models of this region that can be readily leveraged and improved upon.”

The project also includes creation of an affinity group, named "The Buffer Zone," which will connect high school and undergraduate students from a variety of programs working in the Chesapeake Bay region.

“The idea is to build a cohort of undergraduate researchers, largely from underrepresented groups, to participate in the research,” said Lora Harris, project collaborator and estuarine ecologist at the University of Maryland Center for Environmental Science. “Undergraduate students will serve as mentors to underrepresented high school students. Students also will present their research to managers and policy makers from the Chesapeake Bay Program during annual summits.”

The research team will also engage estuarine managers in the Bay area through presentations on macrobiota influence on biogeochemistry.­

Led by Penn State, participating institutions include the University of Maryland Center for Environmental Science, Virginia Institute of Marine Science, St. Mary's College of Maryland, USGS, and Woods Hole Oceanographic Institution.