were responsible for most of this 

 production; floating mats of Cladophora 

 were also important. 



5.2 DECOMPOSITION 



5.2.1. Aboveground 



A part of the marsh grass produced 

 each year is eaten directly by herbivores 

 feeding on the grasses and by animals 

 eating the algae from the marsh surface or 

 filtering it out of the water. Another 

 measurable amount of production is 

 released directly into the water when 

 living leaves are immersed by high tides. 

 This portion amounts to about 

 60 kg C/ha/yr in Georgia (Gallagher et al. 

 1976), which is a little less than 1% of 

 the total production for that region. 

 This material is very readily absorbed by 

 microbes and can promptly enter the food 

 web. The loss is probably similar in New 

 England (Valiela et al., unpubl. data). 



Almost three-quarters of the 

 aboveground plant biomass produced is not 

 consumed directly. It dies in place on 

 the marsh surface and decomposes to 

 variable extents before being eaten by 

 animals. It may decompose in place or in 

 a location to which it has been carried by 

 the tides. The greatest exception to this 

 is in areas where snow geese congregate 

 during the winter; they may eat over half 

 of the annual production, which at that 

 time may be stored mainly belowground as 

 rhizomes (Smith and Odum 1981). Since 

 geese have very inefficient digestive 

 systems that remove only soluble compounds 

 from their food, most of what they eat is 

 still decomposed on the surface of the 

 marsh by bacteria and fungi. The 

 cellulose in the grass passes through the 

 digestive systems of the geese almost 

 unchanged except that it is broken into 

 small bits and is probably more readily 

 attacked by the micro-organisms as a 

 result. 



Late in the growing season, plants 

 enter senescence and the grass 

 decomposition process begins. The leaves 

 become leaky to both organic compounds and 

 to nutrients and lose large amounts of 

 soluble compounds to the water. The dead 

 leaves fall onto the mud surface and are 



invaded by fungi and bacteria. In Great 

 Sippewissett Salt Marsh, the aboveground 

 decay process occurs in three stages once 

 the plants have died and become a part of 

 the litter. In the leaching phase, the 

 litter loses about one-third of its weight 

 within 2 weeks as a result of further loss 

 of soluble components. In the second or 

 decomposer phase, the structural parts of 

 the leaf are attacked 

 The loss of material 

 slower than in the 

 occurs more rapidly 



by micro-organisms, 

 from the litter is 

 leaching phase but 

 the more frequently 



the litter is submerged. At the end of a 

 year only about 10% of the original litter 

 remains (Figure 19). The refractory 

 phase, which begins about 1 year after the 

 plants die, occurs, as the name implies, 



Weight of litter remoining 



*■ 10 



Soluble proteins 



• F, Nitrogen enriched 

 o C, Control 



100 200 



300 



400 



500 Days 



1 1 1 1 1 1 T 1 1 1 1 1 1 1 1 ' ' T 



ND J FMAMJ J ASON DJ FMA 



Figure 19. Results of aboveground 

 decomposition experiments at Great 

 Sippewissett Salt Marsh. These litter 

 bags were incubated in creek bank marsh. 

 The leaching phase is shown by the rapid 

 weight loss between the first two points; 

 the decomposer phase is the period of 

 steady decline in weight up to the second 

 winter; the refractory phase follows with 

 very little weight loss. (Teal and 

 Valiela, unpubl. data, Great Sippewissett 

 Salt Marsh, MA). 



32 



