Salt marshes provide important ecosystem services, such as buffering the nutrient runoff from land to sea, and as nurseries for economically important fish species. Upland development in southern New England salt marshes has led to drastic increases in nitrogen runoff and associated changes in marsh diversity as Spartina alterniflora displaces high marsh species. How upland development impacts nitrogen levels and community parameters on northern New England salt marshes is not known. We assessed if upland development was associated with increased nitrogen and changes in plant community composition in a northern New England salt marsh. We found nitrate levels were higher in areas adjacent to development relative to those associated with intact upland, but that marsh nitrogen levels were generally much lower than those reported from southern New England. Areas associated with development had high Triglochin maritimum abundance but low S. alterniflora abundance relative to areas with no upland development. Correlations between nitrate and plant abundance corroborated these patterns. Our work suggests that in northern New England salt marshes, T. maritimum, rather than S. alterniflora, may be an early indicator of nitrogen runoff from upland development.