p <0.01) (Figure 2). Although there may have been differences in nutrient concentrations between 

 donor and recipient marsh soil, interstitial water concentrations indicated only minor differences 

 in NH 4 between the control sods and those transplanted to the recipient marsh (Table 1). Little, 

 if any, difference was noted in pH and Eh. Therefore, the primary difference between the donor 

 and recipient marsh plots was salinity and salinity-related parameters (saltwater intrusion would not 

 only bring in higher salt concentrations, but also more sulfate which, when reduced, would result 

 in higher sulfide levels in the soil). 



Increased water level significantly reduced the density and biomass (F=31.47 and 23.17, 

 respectively, p < 0.01), but not height, of this species (Figure 2). Interstitial water sulfide 

 concentrations were significantly higher in the lower elevation plots in both the donor and recipient 

 marshes (F = 19.92, p <0.01) (Table 1). There was also a significant negative relationship between 

 soil sulfide and biomass at the donor (r = -0.68) and recipient (r = -0.72) marshes. Soil NH 4 

 concentrations were significantly higher in the more waterlogged plots (F = 73.91, p <0.01), 

 particularly in the recipient marsh (Table 1). There were also significant relationships between soil 

 NH A and sulfide (r = 0.87, donor; 0.79, recipient), soil NH 4 and biomass (r = -0.69, donor; -0.79, 

 recipient), and soil NH 4 and density (r = -0.57, donor; -0.87, recipient). 



Live aboveground biomass was most reduced in the low elevation (-10 cm) treatment in the 

 recipient marsh, indicating a greater negative effect of the combination of increased salinity and 

 waterlogging on the growth of S. patens than either factor acting alone (Figure 2). However, the 

 interaction between the two factors was not significant and their combined effect on biomass was 

 additive. When the elevation of the transplanted plots was increased to 10 cm above the recipient 

 marsh surface, height, biomass, and density were not significantly increased above that of plots 

 placed equivalent to the ambient elevation (Figure 2). 



Factors Preventing Plant Reestablishment in a Brackish Marsh 



All of the sods that were transplanted to the dieback site at marsh elevation exhibited highly 

 reducing conditions compared to the controls (Table 2). Redox potentials were significantly lower 

 in the dieback sods placed at marsh elevation (Table 2). Sulfide concentrations in the dieback sods 

 (marsh elevation) were 1.5 times higher than in the control sods (Table 2). Aboveground biomass 

 and stem density of S. patens were significantly reduced in these plots compared to controls (Figure 

 3). However, the biomass produced in the S. alterniflora-dominaled sods transplanted into the 

 same dieback site was double that of its controls; stem density was also significantly increased. 



The reducing conditions of the dieback site were somewhat ameliorated in the elevated sods 

 (Table 2). Increasing the elevation of the S. patens sods in the dieback site resulted in greater 

 biomass production, but no further increase occurred in the elevated S. altemiflora sods (Figure 

 3). NH 4 concentrations in the interstitial water of the S. patens dieback plots were significantly 

 higher and salinity significantly lower than that in the control plots (Table 2). However, the NH 4 

 concentrations and salinity in the S. altemiflora soil did not differ significantly among sites. 



DISCUSSION 



Since the vertical accretion of marshes is dependent upon the accumulation of organic matter 

 produced by marsh macrophytes, any reduction in primary productivity will slow the aggradation 

 propess. A sudden change in the environment that leads to a rapid reduction in biomass or even 

 complete elimination of the emergent vegetation in a marsh would reduce the potential for the 

 marsh accretion rate to keep pace with subsidence and sea level rise. A reduction in belowground 

 roots and rhizomes, which bind the sediment and provide stability, would accelerate subsidence and 



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