The belowground processes may also 

 vary in different areas of a marsh, 

 depending on water table and 

 groundwater flow, tidal inundation, or 

 sediment input. In analyzing a 1-m 

 (3.3-ft) long core from the S^. paten s 

 zone, McCaffrey (1977) found a 

 remarkably uniform organic content 

 with depth and a varying inorganic 

 component. Similarly, Redfield (1965) 

 reported on a 5-m (16.4-ft) core from 

 the S^. alterniflora zone in which the 

 organic content of the peat was rela- 

 tively constant with depth while the 

 ash content varied by a factor of 10. 

 Neither of these authors concentrated 

 on the fine structure of the top 10 cm 

 (4 inches) or so, where the production 

 of Spartina roots and rhizomes is 

 greatest and most variable (Figure 18; 

 Valiela et al. 1976). 



If the underground production 

 rates measured by Valiela et al. 

 (1976) on Cape Cod are representative 

 of other New England marshes, less 

 than a third of the belowground 

 production is buried. In the S^. 

 alterniflora zone of the Great 

 Sippewissett Marsh, it appears that 

 only about S% of the total Spartina 

 production (~7% of belowground pro- 

 duction) is accumulated in peat; the 

 larger part is consumed aerobically on 

 the marsh surface or through sulfate 

 reduction in the anoxic sediment. 



Decomposition 



It is not surprising that most of 

 the organic matter put below ground by 

 the Spartina does not remain to form 

 peat. If it did, Valiela et al. 

 (1976) calculated that it alone would 

 raise the level of Great Sippewissett 

 low marsh by about 1 cm each year. 

 Moreover, the distribution of organic 

 matter with depth in the sediment 

 (Figure 18) suggests that much of the 

 organic matter produced near the marsh 

 surface is not buried. At first, 

 the removal of such a large annual 



increment in belowground organic 

 matter seemed difficult to explain. 

 As Valiela et al. put it in 1976: 



"We did not expect the marked 



decay in dead matter , since 



we supposed that decomposition in 

 anoxic sediments would be slow. 

 However, dead parts still 

 attached to the living plant 

 would be supplied with oxygen 

 from the plant's air spaces..., 

 so that aerobic oxidation could 

 occur. " 



Later work at Great Sippewissett, 

 however, showed that sulfate reduction 

 by the microbial community in the 

 peat appeared to oxidize some 

 1,800 g C/m Vyr in the S. alterniflora 

 zone, an amount roughly comparable to 

 the belowground production (Howarth 

 and Teal 1980). It is also possible 

 that belowground production measure- 

 ments can be confounded by the 

 overwintering storage of organic 

 matter in basal portions of grasses. 

 In work with S. alterniflora , Lytle 

 and Hull (198(1) found that a large 

 fraction of late-season photosynthate 

 was translocated to rhizomes and that 

 this material was then used in spring 

 to support much of the growth of the 

 plants through the fourth or fifth 

 leaf stage. Even in midsummer, "new 

 rhizomes were regenerated largely 

 using energy stored in over-wintered 

 rhizomes." Unfortunately, similar 

 studies are not yet available for the 

 S^. patens high marsh, nor do we yet 

 have direct measurements of the 

 decomposition rate in the S^. patens 

 zone. 



The aboveground primary produc- 

 tion can be decomposed on the marsh 

 surface or it can be carried off 

 the marsh. If it is carried off the 

 marsh, it may accumulate on the bottom 

 of marsh creeks and embayments or 

 it may remain suspended in the water 



44 



