Battered Roads Just Might Help Restore Bay Oysters
A lengthy, three-part research project at Morgan State University determined that two problems affecting the Chesapeake Bay region could be the solution for each other.
The first problem: To restore the Bay's oyster population, baby oysters called spat are grown in tanks and placed on oyster shells, which then are planted on a hard reef that keeps them from sinking into the Bay's silty bottom. The reefs themselves were once made of oyster shells, but those shells are now scarce due to the declining oyster population.
The second problem: Maryland is committed to maintaining its roads, continually removing old concrete, which is often discarded, necessitating a disposal site. The state is looking for ways to recycle the old concrete, which can be reused by crushing and milling it into a material called recycled concrete aggregate (RCA).
Could that RCA take the place of oyster shells to create reefs? And could it do so without leaching pollutants into Bay waters? Would it somehow make spat more vulnerable to predators? And if oysters did thrive, would commercial watermen be able to harvest them from an RCA reef? Would oil and gas spilled on concrete when it was a road be a problem, and how could that be evaluated?
The Maryland State Highway Administration funded a three-phase research project through Morgan State University's Patuxent Environmental & Aquatic Research Laboratory (PEARL) and its National Transportation Center to answer those questions. The first phase began in 2011 and the final phase was completed in late 2016.
"Native oyster populations are at less than 1 percent of historic levels due to protozoan diseases, overharvesting and pollution," Kelton Clark, director of PEARL, said. "This tremendous decline has dramatically changed the Bay's ecosystem and oyster industry. Individual oysters filter 4 to 34 liters of water per hour, removing sediments and pollutants. Historic oyster populations could filter the Bay's entire water every three or four days, but today that takes nearly a year."
The first phase of the research evaluated the potential leachability of chemicals in extensive tank tests at PEARL, using water drawn from the Bay. Oyster growth and spat survival was also evaluated in flow tanks, comparing traditional shell and a mixture of shell with RCA as a base material.
"The results showed that using RCA as a base for oyster reefs did not adversely affect either oyster growth or the surrounding environment," Dr. Clark said. "None of the materials leached at a rate that exceeded the Environmental Protection Agency's drinking water standards, and the RCA did not raise the pH above the threshold for introduction into Maryland waters."
The second phase involved actually constructing reefs with a base of RCA in two locations in the Bay with different salinities, one in the Patuxent River just north of Broomes Island and the other in Fishing Bay on the Eastern Shore, and measuring whether potential predators would be attracted to such reefs. The research showed that the recruitment and survival of oysters with RCA was the same as a traditional reef.
The involvement of local watermen was critical to the success of the research. Researchers created a tank divided in half with boards that simulated the washboards of an oyster boat, and recruited watermen from around the region to tong for oysters. One half of the tanks had traditional oyster shells while the other had RCA . Watermen discovered that since the RCA weighs more than oyster shells, it was more difficult to tong. The watermen suggested that it could be used with a veneer of oyster shells or in areas not used for harvesting oysters.
Since accidental spills of oil and gas occur on roads, the final phase evaluated the RCA for petroleum byproducts and provided evaluation methodologies.
Samples were collected from three different concrete dumping sites twice, and all analysis was performed at least three times.
"As alternative materials are introduced in marine environments, the State Highway Administration needs a testing protocol to assess their potential impacts," said Dr. Dong Hee Kang, one of the researchers. "In all of the samples, organic chemical concentrations were below the detection limit. We did detect hydrocarbons from two samples, but the detected concentrations were 100 times lower than the water quality standard of Maryland. It's safe to say that RCA is not a cause for concern for hydrocarbon components leaching when used as a base for oyster reefs."
One of the next steps will be developing a permitting process for such artificial reefs. Currently, Maryland does not have any established criteria for artificial reef materials. A permit to place material in the tidal waters of the Chesapeake Bay water requires sign‐off from MDE, DNR, Maryland Department of Health, Maryland Board of Public Works, ACOE, Coast Guard, in some cases the U.S. Fish and Wildlife Service (USFWS), and (rarely) the Department of the Interior.
"This research has established some valuable methodologies and results that will provide a basis of knowledge for future permitting," Dr. Andrew Farkas, director of the National Transportation Center at Morgan State University, said.
The final reports for all three phases of the research are available on our completed project page.