NITROGEN POOLS AND FLUXES IN A GEORGIA SALT MARSH

Abstract

Preliminary data on standing stocks of nitrogen and on rates of nitrogen fixation and denitrification in Spartina alterniflora salt marshes on the Georgia coast have yielded a general concept of the nitrogen cycle in this system. The Georgia salt marsh is characterized by fine-textured clay soils, a tidal amplitude of two meters, and high rates of primary production throughout the year. Most combined nitrogen in the system is in the soils in forms not readily available to primary producers. The amounts of exchangeable ammonium, nitrate, and nitrite are small and change seasonally. The presence of nitrate and nitrite in the soil implies that nitrification occurs in the aerobic microzones around Spartina roots. The annual input to the marsh via nitrogen fixation and other quantified sources of nitrogen is as large as the seasonal accumulation of nitrogen by Spartina growth; the input is balanced by the loss of nitrogen via denitrification. The nitrogen input to the marsh is, however, smaller than the estimated nitrogen flux through the marsh plants. Thus, mineral regeneration must satisfy a large part of the nitrogen requirements of Spartina and benthic algae in the Georgia salt marsh.