Department or Program



Estuaries that are in close proximity to densely populated areas and/or receive runoff from populated watersheds are particularly susceptible to nitrogen loading, which can lead to anthropogenic-caused eutrophication. In a past study by McClellend and Valiela (1998) stable nitrogen isotope ratios (δ15N) of dissolved inorganic nitrogen (DIN) and Zostera marina were proven to be enriched in 15N in densely populated estuaries relative to less poplulated estuaries in Cape Cod. Little is known about whether this technique for identifying the presence of anthropogenic nutrients can be used on the coast of Maine. In this paper, two areas in the Casco Bay were studied to see if a populated area (Mackworth Island, Portland) shows 15N enrichment relative to a less populated area (Maquoit Bay, Brunswick). The DIN and the Zostera marina from Mackworth Island were shown to have δ15N values ~2.5 ‰ enriched relative to Maquoit Bay, suggesting that nitrogen isotopes in Zostera marina can be used to detect the presence of anthropogenic nitrogen. This information has the potential to help indicate early signs of eutrophication and help prevent any further nutrient overloading in Casco Bay.

Level of Access

Open Access

Date of Graduation

Spring 5-2011

Degree Name

Bachelor of Arts

Number of Pages


Open Access

Available to all.