some way almost every biological pro- 

 cess. Microbial forms separate into two 

 broad groups, aerobic and anaerobic. 

 Aerobic microconsumers act as energy 

 flow mediators. They serve to convert 

 the relatively unpalatable cellulose 

 from marsh grass stems and leaves into 

 nutritious protein that supports many 

 macroconsumers in the coastal system. 

 It was previously thought that estuarine 

 microbes primarily functioned as miner- 

 alizers that returned inorganic nutri- 

 ents to the water column and sediments. 

 Now it is clear that the aerobic estu- 

 arine bacteria and fungi actually 

 compete for nutrients with the auto- 

 trophic organisms, and that the dis- 

 solved nitrogen and phosphorus they use 

 is converted to particulate organic 

 matter (Mann 1972). Aerobic bacteria 

 and fungi oxidize a significant portion 

 of the total organic carbon produced in 

 the system, but this carbon loss is the 

 price of enriching the remaining 

 detritus so that it can enter the food 

 web . 



Anaerobic microbes are found in 

 salt marsh sediments that are oxygen de- 

 pleted (from about 1 cm beneath the 

 surface to below the root zone) . These 

 organisms are instrumental in regulating 

 sediment geochemistry, nutrient cycling, 

 and a significant (but unquantif ied) 

 portion of total estuarine energy flow. 

 Most studies of these anaerobic forms 

 have been gathered in other salt 

 marshes, such as those in Massachusetts 

 and Georgia (Teal and Kanwisher 1961; 

 Howarth and Teal 1979, 1980). 



Some of the important general roles 

 of the complex anaerobic community are: 

 1) photosynthesis; 2) nitrogen fixation; 

 3) denitrif ication; 4) sulfate reduction 

 (giving salt marshes their characteris- 

 tic sulfury smell); 5) fermentation; 

 6) ammonif ication; and 7) methane gen- 

 eration. 



The entire group of microbes has 

 been compared to the digestive system of 

 a cow, which uses microconsumers to turn 

 low grade carbon (cellulose) into high 

 grade carbon (milk and meat) Mann 

 (1972). Unfortunately there is no good 

 estimate of microconsumer respiration 



for MDPR salt marshes. It is assumed in 

 this report that this value lies between 

 3,511 and 9,374 g dry wt/m 2 /yr (Costanza 

 et al. 1983). Based on this range for 

 decomposition, the marsh may be ex- 

 porting 4,650 g dry wt/m 2 /yr of organic 

 matter, or importing 1,200. 



Organic matter is lost to the 

 biotic portion of the marsh through 

 sedimentation, or by export to streams, 

 bayous, and/or the gulf. The loss of 

 organic matter to deep sediments is 

 small — about 731 g dry wt/m 2 /yr. Since 

 export of detritus has not been observed 

 directly and there are uncertainties in 

 the values for total net production and 

 total decomposition, the amount of or- 

 ganic matter actually leaving the salt 

 marsh cannot be estimated precisely. 

 Additional research on belowground pro- 

 duction, community respiration, and 

 detrital export is needed. 



Tidal flushing is the mechanism for 

 export of dead plant material. Tidal 

 ranges vary from 17 to 31 cm (7 to 12 

 in) (Table 7), although occasional hur- 

 ricanes and storms cause greater surges. 

 Tidal inundation of the marsh occurs 

 throughout the year, but water levels 

 are lower during the winter months be- 

 cause of northerly winds (Table 7). 

 Water movement also provides an exchange 

 of nitrogen, phosphorus, carbon, organ- 

 isms and sediment between the estuary 

 and the marsh. Water also leaves the 

 marsh through evapotranspiration. 



In addition to its contribution to 

 the estuarine food web and many commer- 

 cially and recreationally important 

 fishery species, the salt marsh provides 

 other commodities and services. The 

 marsh supports fur bearing mammals such 

 as raccoons and muskrats, and waterfowl 

 that are hunted or trapped for food and 

 sport. The salt marsh provides an im- 

 portant buffer of storm wave energy and 

 assimilates human waste products 

 (Mumphrey et al. 1978). 



SPOIL BANKS (18) 



Spoil is the term used to describe 

 the mixture of water and sediment that 



76 



