The short version
Towns that want to count oyster farming toward their nitrogen targets need a reliable way to estimate how much nitrogen a farm will remove before it is built. NOAA scientists and partners improved a widely used computer model for this, called FARM, by feeding it a year of detailed measurements from a working oyster farm in Greenwich, Connecticut. The improved model estimated that the 6.3-acre farm removes 400 to 691 kg of nitrogen a year, in line with measurements elsewhere in the Northeast, including on Cape Cod.
What the researchers did
The FARM model simulates how farmed shellfish grow and what they take out of and put back into the water. Earlier versions had not been checked against local nitrogen data. Skylar Bayer and colleagues at NOAA’s Milford Laboratory worked with Stella Mar Oysters and the Greenwich Shellfish Commission to collect those data.
- The farm: a 6.31-acre lease where oysters are planted directly on the bottom without gear, at 75 per square meter. They reach a 4-inch harvest size in two to three years.
- Field and lab work, 2019–2020: monthly water samples and oyster samples, feeding experiments that measured how much nitrogen oysters filter and absorb, and lab measurements of how much ammonia oysters give back to the water.
- Two harvest scenarios: picking oysters as soon as they reach harvest size (“harvest when ready”), or harvesting them all at one time, which leaves many in the water longer and lets them grow bigger.
What they found
- The model matched the real farm. It simulated 125.1 metric tons of oysters per growing cycle, close to the roughly 136 tons the farm reports.
- What one oyster does. Over a 2.5-year growing cycle, an average oyster clears 47.6 cubic meters of seawater and removes more than 0.88 g of nitrogen. Oysters absorbed about half the nitrogen they filtered.
- What the whole farm does. The farm removes about 400 kg of nitrogen a year if oysters are picked when ready, or 691 kg if they are harvested all at once. That works out to 159 and 274 kg per hectare per year.
- Bigger oysters hold more. An oyster picked at harvest size (77 g) carried 0.62 g of nitrogen; the larger oysters in the all-at-once scenario (117.5 g) carried 1.15 g.
- Consistent with Cape Cod. The results were very similar to a multi-year study of floating oyster farming in Lonnie Pond on Cape Cod, which estimated 133.2 to 203.8 kg of nitrogen removed per hectare per year.
What it means for Waquoit Bay today
Shellfish farming is one of the tools Cape towns are using alongside sewers and septic upgrades. Before a town relies on it, it needs credible numbers for how much nitrogen a given farm will remove in its own waters. This study shows that a model tuned with local data can provide them. The authors note it lets managers test possible lease sites without the need to implement an actual farm
(Bayer et al., 2024), which takes two to three years.
The numbers also show the scale involved. A farm of several acres removes hundreds of kilograms of nitrogen a year, while the state’s targets for Waquoit Bay are measured in thousands. Shellfish can help, but they work best as one part of a plan built mainly on cutting wastewater nitrogen. For local measurements of how much nitrogen Cape Cod oysters and quahogs hold, see our summary of the Cape Cod shellfish study.
Read the paper
Bayer, S. R., Cubillo, A. M., Rose, J. M., Ferreira, J. G., Dixon, M., Alvarado, A., Barr, J., Bernatchez, G., Meseck, S., Poach, M., Pousse, E., Wikfors, G. H., & Bricker, S. (2024). Refining the Farm Aquaculture Resource Management Model for Shellfish Nitrogen Removal at the Local Scale. Estuaries and Coasts, 47(5), 1184–1198. https://doi.org/10.1007/s12237-024-01354-7
License: © The Author(s) 2024. Open access under the Creative Commons Attribution 4.0 (CC BY 4.0) license. The full PDF below is reproduced unmodified from the publisher, Springer. The project was funded by the NOAA Office of Aquaculture. The card image is Figure 1 from the paper (CC BY 4.0).
Drafted with AI assistance from the linked source.
