Using stable isotopes to trace sewage-derived material through Boston Harbor and Massachusetts Bay

Using stable isotopes, we assessed the effects of long-term sewage inputs within Boston Harbor and extending into adjacent Massachusetts Bay. We used nitrogen and sulfur stable isotopes (δ15N and δ34S) to distinguish between sources of these elements to sediments, particulate organic matter, algae, and animals. The isotope data revealed the widespread presence of sewage-derived particulate and dissolved materials. Incorporation of sewage-derived effluent particulates into sediments of the harbor and into Massachusetts Bay was apparent in the δ15N values of surface sediments and in sediment profiles. Changes towards more typical marine values over time indicated a lessening of sewage inputs. The incorporation of sewage particulates into blue mussels as revealed by the combination of δ15N and δ34S values in their tissues was also evident and suggested the importance of sewage-derived nutrients to the local food web.