As farmers sue and local officials complain (so far) over what's being asked of them to help finally restore the Chesapeake Bay, we keep hearing the refrain that the "real" answer to cleaning up the bay is getting more oysters back in it to filter out the nutrients causing water-quality problems.
Instead of squeezing more pollution reductions out of farmers, developers and municipalities, it is asked, why not do more to promote oyster aquaculture? Could oyster farming be the answer to a cleaner bay? Now comes a federally funded study that puts the idea in perspective.
It's well-established that oysters are good filter feeders. Scientists have estimated that in their heyday more than a century ago, the bay's bivalves were so abundent they could process all the water in the Chesapeake in a matter of days. The bay has lost 99 percent of its native oyster population, however, to overharvesting, habitat loss and disease.
Biologists at Virginia Commonwealth University took up the question. They measured the nutrient removal capacity of the native Eastern oyster at two aquaculture facilities raising the bivalves in floating rafts. In their study, published in the current issue of Journal of Environmental Quality, researchers calculate that eight large-scale oyster farms, each harvesting one million oysters three inches in diameter, could remove one ton of nitrogen from the bay. The project was funded by the Environmental Protection Agency, and administered by the National Fish and Wildlife Foundation.
"In terms of nutrients removed per unit area," the study abstract concludes, "oyster harvest is an effective means of nutrient removal compared with other nonpoint source reduction strategies."
Perhaps, but there's a certain matter of scale. The EPA estimates that to improve the bay's water quality, Maryland and all the other bay watershed states need to reduce the amounts of nitrogen getting into the bay from their sewage plants, farms, lawns and streets by some 63 million pounds annually. That's 31,500 tons, if my math is correct. Eight large-scale oyster farms per ton means we need more than 240,000 of them to do the trick.
Speaking for myself, I love to eat oysters, and would love to see more oyster farming. But in my wildest dream I can't see that many oyster farms developing in the bay - or us eating our way to a cleaner bay. Besides, there's the little matter of what happens to all those oysters we'd have to consume - don't at least some of their nutrients return to the bay via our plumbing?
Other scientists who have looked at this issue before concluded that oyster farming might help water quality in some coves and rivers if done on a large enough scale. But humans on their own can't hope to match the scale of baywide oyster production that nature once provided, gratis.
(Oysters growing in floats at the Choptank Oyster Co. in Cambridge. 2007 Baltimore Sun photo by Glenn Fawcett)