Oysters in those two states are experiencing a modest recovery because of the restoration and farming known as aquaculture.
In Virginia, 236,200 bushels of oysters were harvested two years ago, up from 79,600 bushels in 2005. Maryland took in 121,000 bushels in 2011, nearly 95,000 more than 2005.
Kellogg and her fellow researchers wanted to show that oyster reefs could greatly improve water quality and are worth the millions of dollars being invested in their restoration.
They also hoped to build on previous studies that had depended on simulations to estimate nitrogen removal at oyster reefs. Their study, started in 2009, used actual measurements of nitrogen levels.
"There was a huge amount of interest in nitrogen removal," said Jeff Cornwell, a researcher at the University of Maryland Center for Environmental Science who contributed to the study.
The researchers measured the amount of nitrogen gas production in water channels on a reef near the Emerson C. Harrington Bridge on the Choptank at Cambridge, Md. They did the same at a site where restoration had not occurred.
The study was funded by NRG Energy.
"The rates we've seen in the Choptank for removal is the highest we've seen anywhere," Cornwell said. "The . . . results are so promising. As we develop data sets we can calculate what oysters did when they were a larger population."
Bivalves scarf up phytoplankton that consume nitrogen. Phytoplankton produce algae blooms that die, turn into a sticky black goo and suck oxygen - needed by pretty much every inhabitant of bay tributaries - from the water. Dead zones deplete the bay of life and rob predators such as eagles and osprey of food.
When oysters and other creatures eat phytoplankton, they poop it into dark areas of the reef where microorganisms feed. Those organisms convert the nitrogen to nitrogen gas that wafts into the atmosphere, Kellogg said.