Salt marshes atmospheric inputs

Inputs, outputs and exchanges of N with systems adjacent to salt marshes are generally much smaller in magnitude than internal fluxes (Table 22.7). The source and relative importance of various external inputs of N to salt marshes varies from system to system. While the input of N from rivers is potentially large, most of this N is probably not taken up by salt marshes but is processed in aquatic portions of estuaries or routed to the open ocean. On average, the largest input is from N fixation (2-15 g N m year ), followed by atmospheric deposition (0.5-2.2 g N year ). Groundwater inputs are a major source of N in some smaller salt marshes with developed uplands such as found in the northeastern United States. 

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