Table 31. The estimated economic value of 

 harvests from the Barataria basin, 

 Louisiana (Mumphrey et al . 1978). 



Capitalized value for indicated annual 

 return. 



Environmental Quality 



Another set of values society 

 receives from wetlands can be grouped 

 under the heading of environmental 

 quality. This includes a number of 

 ecological functions of coastal wetlands 

 that contribute to the improvement of 

 water and air quality taken in the 

 broadest sense. Much has been made of the 

 ability of wetlands to remove organic and 

 inorganic nutrients and toxic materials 

 from the water that flows across them. In 

 the delta, Meo et al.(1975) found that 

 fresh marshes effectively removed nearly 

 all the organic material and most of the 

 nutrients from a menhaden processing 

 plant's effluent when that effluent was 

 allowed to filter through the marsh. 

 There have been similar reports of 

 efficient waste-water treatment from a 

 number of other studies elsewhere (Bastian 

 and Reed 1979; Kadlec 1975; Kadlec and 

 Kadlec 1979). Nevertheless, these reports 

 can not be taken uncritically. Most 

 studies have been short term, and there is 

 a persisting question of what happens if 

 and when the system becomes saturated with 

 the pollutant. The answer depends on the 

 circumstances. In some systems the 

 pollutants begin to appear in the outflow. 

 Other marshes have been used for 20 - 50 

 years and still seem to function 

 effectively. 



Where environmental circumstances are 

 appropriate, nitrogen may be denitrified 

 and lost to the air. But other pollutants 

 such as heavy metals and phosphorus must 

 accumulate or be washed out. There have 

 been no long-tenn studies in the 

 Mississippi delta, but the capacity for 

 permanent storage of nutrients in these 

 marshes is unusually high because of the 

 rapid subsidence rate. Craig et al . 

 (1977) showed that the upper part of the 

 Barataria basin was heavily polluted, but 

 that water quality rapidly improved 

 downstream. This improvement would not 

 have occurred if the marshes and streams 

 were unable to "remove" the pollutants 

 from the water. In spite of this 

 cleansing capacity, the delta marshes are 

 not used explicitly, with one or two minor 

 exceptions, for water quality improvement. 



Marshes function in the maintenance 

 of water and air quality on a much broader 

 scale. Nitrogen and S are good examples. 

 The natural supply of ecologically useful 

 N comes from the fixation of atmospheric 

 nitrogen gas (N2) by a small group of 

 plants and microorganisms that can convert 

 it into organic form. Today the produc- 

 tion of ammonia from N2 for fertilizers is 

 about equal to all natural fixation 

 (Delwiche 1970). Wetlands may be 



important in returning part of this 

 "excess" N to the atmosphere through 

 denitrifi cation. The close proximity of 

 an aerobic and a reducing environment, 

 such as the marsh surface, is ideal for 

 deni trif ication as discussed in Chapter 3. 

 The denitrif ication rate seems to increase 

 with the nitrate supply (Reddy et al . 

 1980; Engler et al. 1976). Because 

 coastal wetlands are the downstream 

 receivers of fertilizer-enriched river 

 runoff and are ideal environments for 

 deni trif ication, it is likely that they are 

 important in the world's fixed N balance. 



Sulfur is another element whose cycle 

 has been modified by man. The atmospheric 

 sulfate load has been greatly increased by 

 fossil fuel burning. VJhen sulfates are 

 washed out of the atmosphere by rain they 

 acidify oligotrophic lakes and streams. 

 However, when washed into marshes, the 

 intensely reducing environment of the 

 sediment reduces them to sulfides which 

 form insoluble complexes with phosphate 

 and metal ions. In salt marshes this 



85 



