Precipitation 



Fixation 



little exchange of nitrite (N0 2 ) 

 nitrate (N0 3 ) (Figure 22). 



or 



Figure 21. Nitrogen fluxes between a salt 

 marsh and surroundings. 



nitrogen is not very active biologically 

 and does not contribute much to the 

 nitrogen cycle of either marsh or estuary. 



Dissolved inorganic nitrogen (DIN), 

 on the other hand, exhibits significant 

 changes in concentrations with time and 

 tide--changes which have implications for 

 both marsh and estuary. The major part of 

 the inorganic nitrogen is in the form of 

 ammonium ion (NH 4 ). For most of the year 

 ammonium concentrations were similar in 

 the incoming and outgoing tides in Great 

 Sippewissett Salt Marsh and there was 



Ground water contributed about 12.5 g 

 N/m 2 /yr to Great Sippewissett Salt Marsh. 

 Some marshes have significantly less 

 ground water flow than Great Sippewissett 

 Salt Marsh, although in most marshes this 

 has not been measured. Flax Pond Marsh on 

 Long Island has a lower salinity than Long 

 Island Sound, which probably indicates 

 ground water intrusion. There is likely 

 to be a substantial contribution of 

 nitrogen from the ground water. Other 

 salt marshes along the southeastern coast 

 may receive nitrogen from the river flow 

 entering the estuaries. This amount has 

 been estimated to be about 3 g N/m 2 /yr to 

 southeastern salt marshes (Windom et al. 

 1975). At Great Sippewissett Salt Marsh, 

 there was about half as much nitrogen in 

 rainwater as in the ground water. Only 

 about 1% of the nitrogen input came from 

 direct rainfall and 16% came from ground 

 water flow (Valiela et al. 1978b). This 

 resulted from the much larger area of the 

 watershed in comparison to that of the 

 marsh itself. 



As sea level rises, the surface of a 

 healthy salt marsh maintains its relative 

 tidal level by accumulating sediments from 

 the water and peat from the grasses. 

 Organic nitrogen is buried in these 

 sediments until it is deep enough to be 

 beyond the reach of roots. This loss was 

 a small quantity in the nitrogen budget 

 for the marsh, amounting to about 1% of 

 the nitrogen contained in the upper 15 cm 



Table 6. Annual nitrogen exchanges for Great Sippewissett Salt Marsh. All 

 values are in kg/yr (Valiela and Teal 1979, and unpubl. data). 



Form 



Input 



Output 



Net change Net change/input 



64% 



-13% 



4% 



-22% 



-6% 



dissolved organic nitrogen. 



37 



