This data includes the organic carbon (Corg) and nitrogen (N) content and their stable isotopes (delta 13C and delta 15N) in the surface sediment (top 5 cm) of three eelgrass meadows in boreal Newfoundland and Labrador, Canada. Sediment cores were collected from different locations (i.e., inside, edge, outside) relative to each meadow. Data also include meadow traits, such as blade length, width, and sediment characteristics. Samples were collected in August 2020.