Tidal marshes persist during periods of rising sea level through a variety of mechanisms that add elevation to the soil surface. Because many of these mechanisms are biotic, the ability of these important coastal ecosystems to match increasing rates of sea level rise depend on the response of marsh biota to anthropogenic perturbations. The first year of experimentation in a marsh dominated by Scirpus olneyi and Spartina patens revealed strong plant productivity responses to elevated CO₂ and nitrogen addition, particularly when the treatments were applied in combination. Initial measurements indicate that soil elevation follows trends in plant growth, with the most productive treatments yielding the largest gains in rooting-zone soil accretion (up to 4 mm per year greater than the control treatment). In this first growing season, patterns of elevation change likely arose from stimulation of subsurface plant biovolume. Long-term response of elevation in this highly organic marsh will depend on the balance of plant productivity and organic matter decomposition. Elevated CO₂ and nitrogen will most certainly continue to stimulate plant productivity, but the response of decomposition is uncertain.