University of Virginia researchers made an interesting discovery in the world’s largest restored seagrass meadow off Virginia’s Eastern Shore. Their findings reveal that seagrass may help solve climate change issues for centuries, even after the seagrass dies. By using methods for sediment analysis, they have conclusively verified that the carbon captured by seagrass is securely preserved in the sediment. Seagrass meadows are important for more than just capturing carbon. They also benefit fisheries and improve water quality.
The University of Virginia explorers, wearing wetsuits, entered the largest restored seagrass meadow in the world. The meadow is located off the Eastern Shore of Virginia, near Chesapeake Bay. They installed a tall tripod on the Delmarva Peninsula. Then, they put an 8-foot-long tube and a small vibrating machine on top of it. The machine pushed the aluminum cylinders deep into the historical layers below.
Peter Berg, research professor at the University of Virginia said, “We took a couple of long cores, and we were really surprised when we saw what looked like seagrass tissue down at the bottom. Some of the cores took us back to about the year 1000, which is near the time when the Vikings came to the North American continent.” Professor Berg is an expert in oceanic carbon cycling.
The initial test results are positive. Berg and his team from the UVA Department of Environmental Sciences have discovered that seagrass beds can store carbon for a long time, even if the seagrass dies. This finding gives hope for using natural solutions to combat climate change.
It is known that Zostera marina seagrass, also known as eelgrass, can effectively capture carbon dioxide, a greenhouse gas that contributes to global warming.
Tidal marshes and mangrove forests also serve as natural storages of this kind. These rich ecosystems have the remarkable ability to extract carbon dioxide from the atmosphere as long as their plant life thrives. This exchange, often referred to as blue carbon, is aptly named because of the crucial role water plays in it.
It is indeed true that the individual shoots of seagrass only survive for a year or two. However, the spreading of eelgrass is truly remarkable. This plant has the ability to reproduce both sexually, through the dispersal of seeds carried by currents, and asexually, through its creeping rootstalks.
The outcome of this incredible process can be vast sea meadows, covering multiple square miles, that can endure for centuries. Eelgrass is incredible because it can thrive in the ever-changing sea. It grows near the shorelines and uses sunlight and carbon dioxide to create new plant material. Some of this material ends up buried in the sediment, effectively transforming sea floors into carbon banks.
What Happens to Stored CO2 When Seagrass Meadows Die?
Seagrass may help solve climate change issues but is the carbon trapped in the sediments that anchor seagrass able to remain locked up? Or does a portion or all the captured carbon dioxide escape back into the atmosphere, negating the climate advantages?
According to Professor Berg, “This question of permanence has been debated a lot. But there has been no strong science behind itâ€”until now.”
“Moving forward with blue carbon has truly become a pressing concern. The UVA researchers are currently studying restored areas which were unfortunately affected by Virginia’s Great Storm of 1933 and slime mold, an oceanic disease, resulting in the death of the seagrass meadow,â€ Prof. Berg further added.
Furthermore, as a result of climate warming, marine heat waves are becoming more prevalent. It is alarming to note that approximately 20% of the world’s seagrass meadows have been lost since the early 1900s.
They discovered a unique chance to study the sediment. They could analyze the deposits, much like examining the rings of a fallen tree, but in a vertical manner. This would allow them to compare the time periods before and after the meadowland loss caused by the 1933 storm.
The seagrass meadow was restored in 1999 and covers 10,000 acres. UVA, along with The Nature Conservancy and the Virginia Institute of Marine Sciences, takes care of the preserve. The scientists played the role of historical detectives, employing scientific dating techniques and analyzing sediment composition to unveil the truth.
Dr. Lauren Miller, an assistant professor, opened a large refrigerator to show her collection of sediment cores. These cores were split in half and covered with thin plastic. One half was used for testing, while the other half was preserved for future use.
Miller showed how the cores are prepared for analysis. She removed pieces of solid salt and used a small spatula-like tool to examine the contents, which resemble wet cement or clay. If you rub the contents between your thumb and index finger, they feel cool, mostly dry, and powdery.
Professor Peter Berg said, “You take small samples of the wet sediment, and you dry it at a low temperature, so all the water disappears, and you weigh it. Then you put it in a high-temperature oven, so all the organic material burns off, and you weigh it again. That difference is organic matter. You can then convert that to carbon.”
Age of Seagrass
The team had a general idea about which years in history corresponded to specific core depths. However, they needed to determine the exact matches.
1. Lead-210 Dating
The method enabled them to precisely track time by analyzing the decay of lead isotopes. By utilizing lead-210 dating, they were able to accurately determine the age of sediment dating as far back as around 1860.
2. Carbon-14 Dating
They then employed carbon-14 dating to ascertain the age of ancient sediment discovered in deeper layers.
Along with the discovery that seagrass may help solve climate change issues, Miller also found some small shells while sifting through the sediment. Unfortunately, some of the shells were broken and damaged by natural events like storms, so they couldn’t be used for carbon dating.
Dr. Miller said, “We can pick out shells from the sediment cores and know when they lived. The shells are like us as people. We’re taking in radiocarbon from the atmosphere, into our bodies and into our bones. But when we die, that stops happening. And this radiocarbon decays into different products once organisms die, and we can figure out when they lived in the past.”
The lab analysis confirmed that eelgrass remnants were captured several decades ago. This was followed by a period of almost 70 years of dormancy, during which the carbon was trapped.
“Given that the organic matter content is higher in the century-old sediment layers than in the top layers with modern seagrass, I think it is safe to say that close to 100% of carbon captured a long time ago has been preserved in the sediment,” Berg said.
The researchers were studying a period of 1,000 years. Blue carbon trapping is effective and strong even when the natural environment changes. This is important for finding resilient solutions to the climate dilemma.
McGlathery further added, “Seagrass meadows provide so many benefits beyond blue carbon, like promoting fisheries and improving water quality. We are now working on putting a market value on those benefits as well. That will give us the whole picture of why seagrass conservation and restoration are important.”