While a great deal of research has been directed at salt marsh productivity, few if any studies have undertaken large scale studies of diversity in salt marsh systems. using large mesocosms, this study examined the effects of groundwater nitrogen levels and plant species and trophic level diversity on plant production in salt marsh systems. Four treatments were used with three replications of each: low nitrogen low diversity, low nitrogen high diversity, high nitrogen low diversity, and high nitrogen high diversity. Low diversity mesocosms included Spartine alterniflora, Spartina patens, and Distichilis spicatum. High diversity mesocosms were characterized by the addition of Scirpus olyney. High diversity mesocosms included included Spartine alterniflora, Spartina patens, and Distichilis spicatum. High diversity mesocosms were characterized by the addition of Scirpus olneyi. High diversity cosms also included fiddler crabs (Uca minax), periwinkles (Littorina irrorata), grass shrimp (Paleomonites pugio), amphipods (Gammarus mucronatus), ribbed mussels (Geukensia demissa) and infaunal clams (Rangia cuneata). Cosm production was variable within each treatment and demonstrated a definite increase from May to August Scirpus tended to outcompete other species in the high diversity cosms. Production was much greater in high nitrogen cosms than in low nitrogen cosms and did not show a significant difference between diversity levels. This study suggests no significant influence of diversity level on salt marsh production leading to the hypothesis that a reconstructed marsh would not need to possess as high level of diversity in order to be as productive as a natural system.