Bay Journal

Will oyster aquaculture clean up the Potomac? Not so fast

  • By Karl Blankenship on April 16, 2014

A recent study has some folks thinking that oyster aquaculture could be the solution for nitrogen pollution in the Bay.

A study recently produced by scientists from the National Oceanic and Atmospheric Administration and the U.S. Geological Survey suggests that significant water quality improvements could be made in the tidal Potomac River through widespread oyster aquaculture which, they argue, would remove large amounts of nitrogen.

But the study is a modeling exercise, and there is actually little real-world data to support the conclusion.

In fact, two panels of scientists have explored the nitrogen removal potential of oyster restoration and aquaculture in the last couple of years. Both concluded it was premature to bank on oysters producing large nitrogen reductions.

Oysters can filter large amounts of water, but they absorb relatively small amounts of the nutrient in their shells and flesh. The rest is excreted back into the water.

Oyster reef communities also have the potential to remove the nutrient through denitrification — the process through which nitrogen is converted to a harmless gas.

But only a few studies examined the denitrification potential of oyster reefs in the Bay. While some have suggested that oysters can remove large amounts of the nutrient through denitrification, their ability to do so appears to be vary greatly from place to place based on site-specific factors.

When it comes to oyster aquaculture, the panels found a lack of any good information about nitrogen removal potential.

It’s also important to note that by the time nitrogen reaches the tidal Potomac, where oysters grow, it has already been causing water quality problems in upstream areas, such as the Shenandoah River, where the nutrients originated.

Even if oysters helped to improve water quality in the tidal Potomac, they do nothing to alleviate that upstream pollution. The authors of the recent Potomac study agreed, noting that any nitrogen removal by oysters “should be considered a complement — not a substitute — for land-based measures.”

Restoring oysters and growing them in aquaculture is a perfectly fine thing to do. But they should be done for the right reasons, such as improving habitat, filtering water and supporting the Bay’s fledgling aquaculture business. Nitrogen removal should be considered a bonus of such efforts — not their purpose.

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About Karl Blankenship

Karl Blankenship is editor of the Bay Journal and Executive Director of Chesapeake Media Service. He has served as editor of the Bay Journal since its inception in 1991. .(JavaScript must be enabled to view this email address).

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