Drakes Bay Oyster Company: Nitrogen Removal by Oysters Insignificant

[Update 4/17: "Not So Fast" - More questions about the NOAA/USGS paper on nitrogen removal arise.  Read here]

NOAA Overstates Benefits of Nitrogen Removal

DBOC Overstates Effect of Ceasing Operations 

Delusional beliefs
In an email dated April 16, copied below, University of Texas at Austin's Professor Emeritus Lynton S. Land questions the recent article published by NOAA and whether removal of nitrogen by oysters from the Potomac River estuary is significant. The article is currently being promoted by Drakes Bay Oyster Company supporters to support the continued commercial operation in Drakes Estero, part of the Philip Burton Wilderness Area. Professor Land describes the belief that oysters will significantly improve the water quality of the Potomac River estuary as a delusion. Bob Rheault with the East Coast Shellfish Growers Association calls his belief valid.

Sop-up up strategies do not work - control the upland source
Professor Land goes on to note the only effective way to control nitrogen input into the Potomac River is by controlling upland inputs. He states "sop-up  strategies are never effective." He suggests a more effective means is controlling crop fertilization through the use of slow release nitrogen fertilizer and banning the on ground application of poultry litter and manure.

Drakes Estero does not benefit from the continued operation
Of significance for DBOC supporters is to remember that Drakes Estero is not the Potomac River. Agriculture on the surrounding uplands is minimal. Ranching activities are well controlled and have little impact. In a 2007 paper by Corey Goodman, he summarized the impacts on Drakes Estero this way:

The Anima (1991) study shows no impact of the ranches on the sediments, herbicides, pesticides, or nutrients in Drake’s Estero. The Wechsler masters thesis shows no major impact of the oyster farm on the fish communities. The Elliott-Fisk et al. (2005) study shows no impact of the oyster farm on the sediments or the eelgrass in Drake’s Estero.

Aquaculture disruption is not restoration of a wilderness area
The question left for supporters on both sides of the issue is whether ceasing commercial operations will have a long term impact on the Philip Burton Wilderness Area. Removal of pressure treated racks, plastic tubes and grow out bags will have a one time impact of short duration on Drakes Estero. Ceasing the disruption to the ecosystem which harvesting activities create will be long term.

 

 

Professor Land's Email

The NOAA & USGS study proposing that more oysters can significantly improve Potomac River estuary water quality is unrealistic. A 1946 paper states “...in the late 1800’s it [the oyster harvest] averaged approximately 1,600,000 bushels." Given 300 market-sized oysters per bushel, for few years, 480 million oysters were harvested annually. Then the harvest crashed and in recent years it has rarely exceeded 5,000 bushels. We can never restore the ecosystem to its condition in the late 1800’s. Given urbanization and chemically fertilized fields and lawns we can never return to late 1800’s nutrient levels.

One million market-sized oysters contain at most 150 kilograms of nitrogen (N), with sub-equal amounts in the shell and dry tissue. Even if we could harvest 480 million oysters again, only 72,000 kg of N would be removed (150 kg N/ million oysters * 480 million oysters). Today, the Potomac River receives about 30 million kilograms of N each year. So the maximum oyster harvest ever recorded could only remove 0.2% of today’s N load (72,000 / 30,000,000). Meaningless! If we take into account N removal from the ecosystem by denitrification and sediment burial, about the same amount of N is removed from the ecosystem as by harvesting the oysters. But if oyster shells are returned to the water to serve as a substrate for more oyster strike, as they certainly should, the N in the shell is not removed from the ecosystem. The required annual harvest remains preposterous. 

The authors of the study state “There is increasing recognition, however, that returns on investment in both point- and nonpoint-source controls are diminishing, that additional management will not lead to significantly greater reduction in nutrient loads….” They are certainly correct for point source discharge from wastewater treatment plants, which has been reduced about as far as can reasonably be expected. But despite all the money that has been spent, Chesapeake Bay water quality has not improved. The reason for this sad fact is that, according to EPA’s final TMDL, agriculture is responsible for more than half of Chesapeake Bay’s N load. Nothing substantive has changed in the way crops are fertilized. Pollution always needs to be reduced at the source and “sop-up” strategies (oysters in this case) are never effective. The authors are incorrect about nonpoint source pollution because they ignore “additional management” by 1) banning the disposal of poultry litter, sewage sludge and manure by land application. This practice causes half of all agricultural pollution, more than is derived from point source discharge from wastewater treatment plants. It could be stopped with the stroke of a pen and the waste used for biofuel, and 2) phasing in controlled (timed-, slow-) release fertilizers to double the efficiency of N uptake by crops from about 65% to at least 80% (it is 30% for sludge).

Grow more oysters for the right reasons – they create habitat for other organisms and make great meals. Delusions about their role in improving water quality merely detract from the only action that will improve Bay water quality, significantly improving crop fertilization efficiency.  Dr. Lynton S. Land, Ophelia VA     www.VaBayBlues.org      April 16, 2014

Bob Rheault with the East Coast Shellfish Growers Association notes:

"His [Professor Land] concerns about the magnitude of that impact [nitrogen removal] are valid"