Abstract
Compliance with the United States Clean Water Act requires states and municipalities to reduce nitrogen (N) pollution and document the effectiveness of mitigation efforts. Oyster aquaculture is a cost-effective and sustainable approach to N removal; however, direct measurement of oyster N content is time- and resource-intensive. Meanwhile, existing predictive models are either broadly general or developed for specific regions outside of Massachusetts (MA). Consequently, the MA Department of Environmental Protection (DEP) requires site-specific measurements. In this study, oysters from 21 southeastern MA estuaries were analyzed as a case study to quantify region-specific relationships of N content, calculated as both mass and percent of whole oyster dry weight, in relation to oyster size, deployment method (surface versus bottom), and water quality metrics. A nonlinear model was used to estimate oyster N mass from shell height (SH), whereas a stepwise linear regression model was used to identify tissue weight, shell weight, water column total N, and oyster deployment method as significant predictors of percent N content. A potential benefit of regional models is to provide a better fit to local data than a general model that incorporated data from across a broader range (e.g., in the present case North Carolina to Maine), particularly for the upper range of oyster SH. These region-specific models enable municipalities to estimate N removal from harvests without laboratory analyses, supporting state level DEP-approved nutrient crediting.