PARENT SESSION
Oral Session #57: Aquatic Ecology: Wetlands, Estuaries, Marine. Presiding: T. Klinger.
Wednesday, August 8, 2001. 1:00 PM to 5:15 PM. Hall of Ideas J.

Organic matter turnover in coastal wetlands: links between macrophyte production, decomposition, nutrient limitation and nutrient cycling.

Daoust, Robert¹, Morris, James¹, ¹

ABSTRACT- The response of organic matter turnover to nutrient inputs is important to better understand the impacts of coastal eutrophication. Past research has shown that saltmarsh macrophytes respond dramatically when fertilized with nitrogen (N) or N and phosphorus (P) in combination, but not to P alone. This has generated a widely accepted paradigm that saltmarshes are N-limited and, therefore, susceptible to eutrophication in areas experiencing increased N loading. Recently, however, research has suggested that saltmarsh microbial communities may be P, rather than N, limited. This leads directly to the question of whether decomposition rates respond to fertilization in accordance with the macrophyte community (N-limited) or the microbial community (P-limited). If decomposition rates of aboveground material respond to P enrichment the effects of increased N-loading may be overestimated since rates of N-cycling would remain unaltered with any newly produced aboveground biomass serving to store N. In contrast, the effects of P enrichment may be underestimated since it would increase rates of nutrient cycling in coastal wetlands. We are testing this question using a combination of factorial N+P fertilization experiments and litter bag decomposition experiments in wetlands of the Plum Island estuary, Massachusetts. After 2 years of fertilization the macrophyte community has responded significantly to both the N and N+P treatments, but not to P-alone. The results of the litter bag study, while preliminary, suggest increased rates of decomposition in N+P treatments.

KEY WORDS: saltmarsh, Spartina alterniflora, Spartina patens, Typha sp.