There’s more than one way to skin a cat, or protect Cape Cod’s coastal waters from septic system pollution. Local environmental reporter Elise Hugus says growing shellfish presents an economically-beneficial way to meet state-mandated nitrogen limits (so-called Total Maximum Daily Loads) without the “lengthy, costly, and energy-intensive installation of a sewer system.”
A 2006 study of aquaculture in Waquoit Bay by WHOI’s Marine Policy Center found that 500 oysters and quahogs removed 0.1 kilograms of nitrogen per liter from the water, and an additional 0.1 kg from the sediment underneath the growing tray per year. … If grown on an exponential scale, aquaculture could potentially meet [Total Maximum Daily Load] targets, especially if the inlets to some coastal ponds are also widened.
In a spreadsheet analysis of four coastal ponds in Falmouth facing Vineyard Sound, Mr. Zweig recommends setting aside 8-9% of Bournes Pond, Great Pond, and Green Pond for aquaculture, and about 22% of the heavily polluted Little Pond, in order to meet the state-mandated [Total Maximum Daily Loads].
But Hugus admits the aquaculture option isn’t perfect:
One additional issue that aquaculture does not address is the need for a wastewater solution that removes not only nitrogen, but a range of “contaminants of concern” from products consumed and eliminated by humans, now concentrated in your drinking water.
Even if shellfish were capable of filtering and sequestering aspirin, Viagra, and shampoo chemical residues from the water, would that solve the problem? (And would you want to eat them?) Or does it just point to a larger question: why are we contaminating fresh drinking water with our waste?
In my humble opinion, we need a variety of options to deal with our wastewater worries. If it is not conceivable to place aquaculture operations in coastal ponds on the scale necessary to remove the entire nitrogen load, it would be wise to eliminate the main cause of the contamination: septic tanks.