Delmarva: Why seagrass beds are vital to health of coastal waters
Scientists have found still another reason why it is important to restore seagrass beds, including in Delmarva's coastal and bay waters.
Recently published research conducted in restored eel grass beds off the Virginia coast found the grasses increase filtration of nitrogen around 12-fold.
That is good news for water quality, and among other benefits keeps harmful algae from accessing the nutrient. Algae blooms are a problem in all 50 states and can have severe impacts on human health, aquatic ecosystems and the economy, according to the U. S. Environmental Protection Agency.
The project off the coast of Virginia's Eastern Shore is the world’s largest successful seagrass restoration project.
The project, which after two decades has resulted in some 9,000 acres of restored seagrass beds, increasingly is opening up new areas of study for scientists.
Once muddy bottom, South Bay’s seafloor now teems with underwater meadows of eelgrass. Thanks to the efforts of volunteers and a massive restoration project by The Nature Conservancy in partnership with the Virginia Institute of Marine Science and University of Virginia’s Eastern Shore laboratory, nearly 7,200 acres of the underwater grass now supports marine life from crabs and fish to bay scallops and seahorses. (Photo: Image courtesy of Bo Lusk/The Nature Conservancy)
It has long been understood that seagrass beds serve as the infrastructure for communities of crabs, fish, seahorses, shellfish and the larger sport fish that feed on them. They also formerly served as the foundation for the once-lucrative bay scallop fishery, which local scientists are working to restore.
The beds also protect nearby coastlines by taking some of the energy out of the waves that roll across them, according to scientists.
Additionally, the beneficial effects of restored seagrass beds on nitrogen pollution is something scientists now are starting to be able to quantify.
Major nutrient pollution sources include agricultural runoff and septic systems.
"Seagrass meadows in general have this important function, where they can act as nutrient filters. They act as a sponge, soaking up these nutrients — and that's a good thing, because it improves water quality and helps prevent the negative acts of nutrients such as harmful algal blooms and, ultimately, hypoxia — fish kills, things like that," said Lillian R. Aoki, a scientist who has been conducting research at the Virginia Coast Reserve Long-Term Ecological Research facility in Northampton County.
The Virginia coastal seagrass meadows in particular "are so exciting as a place to do research because it's this remarkable restoration — it's the biggest restoration in the world," she said.
Additionally, the successfully restored meadows in Virginia have good, long-term data available about them — data on which scientists like Aoki can draw.
"It's a really exciting place to ask these questions — and it's really the only place where they can be answered. So it's really the only place in the world where we can say, okay, we have a restoration that has been over two decades — how has that affected this nutrient filtering capacity? This is the only place you can answer that question," she said.
Findings by Aoki and her colleagues were published this year by the Association for the Sciences of Limnology and Oceanography.
Among the major takeaways of the study is that, where seagrass beds have been restored, scientists see more than 12 times the nitrogen filtration as elsewhere.
The rate is comparable to what has been measured in areas with natural seagrass beds — meaning the restored beds are working as they should.
"It is doing what it ought to be doing," Aoki said.
"This sort of research shows that this is very much so part of this ecosystem," said Cora Johnston, site director at the University of Virginia’s Anheuser-Busch Coastal Research Center in Oyster.
It can take years to see some of the positive effects the restoration project has had on the environment.
Lined seahorses are one of many species that make their homes in the eelgrass beds in Virginia’s coastal bays. (Photo: Image courtesy of Brittany Gonzales/The Nature Conservancy)
"To measure these changes, we really had to have this long-term data set. The rates are really picking up after around 10 years. The seeding was done, and then it wasn't for another decade before we really see the effects happening to these ecosystem functions," Aoki said, adding, "So, from the science perspective, it's really important to do long-term research."
"About a decade after the grass has been planted, everything just bumps up higher," Aoki said, adding, "You need a lot of patience to do this kind of restoration work.
That's why the kind of work being done at the LTER is important, according to Johnston. The facility is engaged in long-term research that results in findings not possible with shorter-term studies.
The study shows that in healthy coastal systems, restored seagrass meadows act as a filter for nutrients in the watershed, according to Johnston.
Bags filled with fertile eelgrass shoots float while volunteers collect more grass in South Bay last month. For a week in late May, they collected millions of seeds, which The Nature Conservancy workers will spread of in Virginia’s coastal bays this fall, just before the grass naturally germinates. (Photo: CLARA VAUGHN PHOTO)
The seagrasses take up nitrogen from the coastal bays before it reaches the open ocean, storing nitrogen through burial, assimilation and other processes.
Burial, the physical process by which seagrass roots help to stabilize sediments where nitrogen is stored, has not been studied much until now, Aoki said.
"Most papers really focus on denitrification, the microbial process, but we are seeing in our system that burial is actually the more important process," she said.
Seagrass restoration effect on nitrogen processes (Photo: Submitted image)
Nitrogen filtration benefits the meadows because the grasses not only use some of the nitrogen, but the filtration process, including burial of nitrogen into sediments, also clears the water, promoting conditions that in turn best suit additional seagrass growth.
The decline of eelgrass in Chesapeake Bay, especially since the mid-1970s, created an interest in restoring the habitat. The grasses declined in part as result of disease and the hurricane of 1933.
Researchers in 1978 began investigating ways to re-introduce eelgrass to areas where it had disappeared.
Virginia Institute of Marine Science professor Robert “JJ” Orth began sowing eelgrass seeds in South Bay, Spider Crab Bay, and Hog Island Bay, on the seaside of Virginia's Eastern Shore, in 1999.
That effort, boosted by volunteers, has resulted in over 9,000 acres of sea grasses thriving today.
Volunteers dip and dunk in the shallow waters of South Bay, where for the past decade they have helped collect seeds for the world’s largest seagrass restoration project. Their efforts have helped cultivated nearly 7,200 acres of underwater meadows from the southern tip of South Bay north to Hog Island. (Photo: CLARA VAUGHN PHOTO)
The restoration appears to result ultimately in a sort of ecological chain reaction, in which cleaner water promotes growth of the grasses, which in turn improve water quality even more.
Still, Johnston warned that too high of an input of nitrogen into the watershed can break down the beneficial filtration process of seagrass beds.
That is not a problem yet in the coastal bays, but the condition could arise if there is a loss of vegetative buffers along waterways, which intercept nutrients before they reach the coast, or if land use changes in the area increase nitrogen inputs, she said.
"Sea grass restoration isn't restoration just for the sake of sea grass," said Johnston, adding, "This study is one of many that shows that sea grass restoration has effects on the system that are more broadly beneficial."