Tuesday, March 27, 2012

Excellent Study on Oysters and Water Shows They Do Improve Water Quality by Filtering and Removing Nitrogen

Our friends at the Division of Marine Fisheries have frequently voiced doubts about oysters' ability to filter water. In several meetings they have asked us to prove that this is the case. In many ways this is like proving that smoking causes cancer. That link was obvious to everyone for years, but actually proving the link took time and a lot of money. And with MOP being a non-profit with limited resources, everyone sitting at that table knew it would be a herculean task for us to accomplish.

Interestingly, a very thorough study on this very topic just came out from the Virginia Institute of Marine Sciences. The report entitled Assessment of Oyster Reefs in Lynnehaven River as a Chesapeake Bay TMDL Best Management Practice pretty thoroughly lays out the case for oyster reefs and their filtration abilities and their ability to fix nitrogen. We have forwarded the report to the relevant parties for their consideration.

There are several intriguing aspects of this. The first is that the City of Virginia Beach and the U.S. Army Corps of Engineers is thinking of oysters as a way to reduce the effects of water pollution. The second is that the study was very involved and very technical. Like all scientific work, their techniques and assumptions are subject to debate, but this looks like it should stand up pretty well..  

There are several interesting bits in the executive summary which I paste in here.
  1. In previous investigations, it has been found that oysters modify biogeochemical cycles by filtering large quantities of organic matter from the water column. The majority of this organic matter is either used directly by the oysters for growth and maintenance or deposited by oysters on the sediment surface where it becomes a source of food for an abundant and diverse community of organisms.
  2. Our study clearly demonstrates that oyster reef restoration can improve water quality both by sequestering nitrogen in the tissues and shells of organisms and by converting organic nitrogen to nitrogen gas that is removed from the water column via diffusion back to the atmosphere, and by depositing TSS within the reef matrix.
  3. Our first-order estimate of 103 lbs. of N acre-1 yr-1 removed as a result of denitrification associated with oyster reefs needs to be improved using seasonal measurements and static sequestration values need to be converted to rates of nutrient sequestration based upon annual growth and survival rates of oysters and reef-associated macrofauna.
It is ironic that the Mass Oyster Project's effort to place oysters in the water quality challenged Fort Point Channel was denied in part because of--- Pollution. 

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