Given that its now easier to find oysters from Duxbury and mussels from Prince Edward Island than it is to get locally-sourced seafood, this locovore’s dilemma begs the question: which came first? The shellfish or the septic system? The problem or the solution?

Sometimes, when overhearing discussions among wastewater experts, the idea is floated that Cape Cod should try to get back to 1619– that is, before Pilgrims landed on these shores.

Though it took until roughly 1990 for humans to load the estuaries with enough nitrogen to kill small fish, the basis for the idea is that we should limit our inputs to the environment to basically zero, just as the native Wampanoag did.

Here's what eel grass should look like

In the past three decades, we have developed our communities to the point where the nitrogen leaching from household septic systems and fertilized lawns has caused our beloved estuaries to seriously decline.

Across the entire Cape, algal blooms clog and stink up the water, leading to unpleasant swimming and boating experiences– and signaling a major ecological disaster.

A lack of eel grass is often the first sign that nitrogen loading has tipped the scales towards an unhealthy estuary. As nitrogen seeps in with the groundwater, it causes algae to grow– and infamously, bloom, when summer temperatures heat up.

Not only is it yucky to look at, algae blocks the sunlight needed by eel grass, causing a rapid decline for this aquatic plant species– as well as the shellfish that grow on its blade and stems.

Dying eel grass: a familiar sight in Falmouth harbors

As the algae dies off, it sucks up the oxygen in the water. If the die-off is extensive, it can cause dissolved oxygen levels to get so low that fish die– or swim to less suffocating areas.

The less lucky marine creatures– snails, worms, and shellfish– are not mobile, and tend to die at much greater rates than fish.

So how do we get back to the way it was in 1619? The state, through the Massachusetts Estuary Project, has set daily maximum nitrogen loading (TMDL) targets that we’ll need to achieve to restore the estuaries, but does not offer any guidance on how to get there.

We need only take a lesson from nature to understand how the nitrogen cycle has balanced itself out over millennia.

A bi-valve solution

While towns on Cape Cod brace themselves for a lengthy, costly, and energy-intensive installation of a sewer system, some residents have taken a back-to-the-Earth approach.

Drawing on his 30 years as an aquaculture consultant with the World Bank, Woods Hole resident Ron Zweig thinks that the solution to the Cape’s water woes could be staring at us from our dinner plates.

Mr. Zweig’s experience with aquaculture in Southeast Asia and at the New Alchemy Institute in Hatchville corroborate the findings of numerous studies establishing the ability of shellfish to filter and remove nutrients (mainly nitrogen and phosphorus) from water and suspended sediments.

A Falmouth Shellfish Cooperative cage, used for growing oysters in deep water.

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.

According to Mr. Zweig, one oyster, on average, is capable of removing 0.65 milligrams of nitrogen per year during two years of growth.

If grown on an exponential scale, aquaculture could potentially meet TMDL 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 TMDL’s.

Getting Aqua into the Culture

While these studies may be little more than numbers on paper, Mr. Zweig is working with members of the Falmouth Shellfish Cooperative, four companies that hold aquaculture permits in Buzzards Bay, to turn his hypotheses into action.

The Cooperative is currently working on a proposal to start up aquaculture plots in one or several of Falmouth’s coastal ponds. Not only would a more inland location make it easier for the farmers to get to their oyster cages, the development would also serve as an experiment on the potential for shellfish to remove nitrogen.

If successful, the Cooperative estimates that expanded aquaculture operations could create or maintain 165 permanent jobs in Falmouth, while restoring 3,700 acres of shellfish habitat.

An aquaculture site in Buzzards Bay operated by the Falmouth Shellfish Cooperative.

This summer, the Cooperative plans to market their first batch of the Sippewissett Oyster, sold straight from their retail location on Coonamessett Farm. With a fledgling mechanism already in place to put Falmouth’s seafood on the map, the oyster farmers say there is much more room to expand.

In Mashpee, Shellfish Warden Richard York hopes to build on the success of an aquaculture program he started in Mashpee River. The Mashpee Enterprise reports that Mr. York is writing a $75,000 grant to purchase, propagate, and plant 10 million quahog seeds in Waquoit Bay. Quahogs, he says, are ideal for aquaculture because of their resistance to predators.

Even if only half of the quahogs survive to maturity, the initiative will generate up to $750,000 in revenue, enough money for 15 shellfishermen to make a decent living, estimates Mr. York.

It may just turn out that doing the right thing for the environment is also good for the economy– and for our appetites.

The downside of aquaculture

However, the simple solution is not always the easiest. As Cape Codders know well, changes intended to solve environmental problems (think wind turbines) often come with a serious backlash from stakeholders.

The Marine Policy Center quantified the costs and benefits to aquaculture not only from the nitrogen removal angle, but also from the point of view of recreational users of Waquoit Bay.

Due to the potential “aesthetic costs” caused by exposed aquaculture gear at low tide, as well as decreased area for boating, the Marine Policy Center estimated that 1.5% of the head of Waquoit Bay could be used for aquaculture without negative consequences.

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.

A typical composting toilet: the only difference is the pipe.

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.

Even on a small scale, aquaculture can likely eliminate nitrogen released from non-point sources, namely fertilizer and road run-off. And by installing household composting toilets, we would eliminate at least half of the nitrogen load, while also pre-empting contamination by other, potentially very harmful, chemicals.