Salt Marsh Aboveground Production in New England Estuaries in Relation to Nitrogen Loading and Environmental Factors

Aboveground production responses of Spartina alterniflora and S. patens in estuaries in Massachusetts, USA were assessed in relation to temporal (date) and physical (elevation and distance from creek edge) factors as well as nitrogen loading using stem N-15, water column dissolved inorganic nitrogen (DIN), and upland nitrogen loading as nitrogen input proxies. All nitrogen input proxies had negative relationships with S. alterniflora stem density while stem height and biomass increased or were unaffected. Nitrogen content of S. alterniflora increased with stem N-15 but was not related to DIN or upland nitrogen loading proxies. For S. patens, stem density, biomass, and height all increased with stem N-15 while nitrogen content decreased. Stem density and biomass also varied with elevation. For S. alterniflora, this relationship was parabolic for stem density and declined linearly for biomass. Both stem density and biomass increased linearly for S. patens. Across the growing season, S. alterniflora stem density decreased, S. patens biomass increased, and nitrogen content declined for both Spartina species. S. alterniflora stem height also decreased with distance from the creek edge. Results show different responses for Spartina species to upland and water column nitrogen inputs and provide complementary information to results from controlled fertilization experiments.