Nutrient effects on Spartina patens decomposition dynamics in a New England salt marsh

Organic matter decomposition is a crucial process in salt marshes, determining their status as carbon sinks or sources and affecting their ability to maintain elevation with sea level. Nutrient enrichment, a growing problem in estuaries worldwide, may increase rates of decomposition in salt marshes directly by stimulating microbial decomposers, or indirectly by stimulating detritivore populations through bottom-up processes. This study examines the effect of 8 years of nitrate addition (15x ambient concentrations) on Spartina patens decomposition in the Plum Island Estuary, Massachusetts. Decomposition rates were measured using litter bags, which were filled with either leaf or root detritus and incubated in situ. CO₂ flux from litter and sediment was also measured to assess possible nutrient stimulation of microbial respiration. Faster aboveground decomposition rates were observed with chronic nutrient enrichment. Additionally, greater CO₂ respiration was observed from enriched sediments. These results suggest that chronic nutrient enrichment can accelerate decomposition processed and carbon respiration in the S. patens -dominated high marsh, and may decrease the capacity of a marsh to sequester carbon.