The major wetland changes in the last 25 years in 

 the Chenier Plain have been cultural and include im- 

 poundment of wetlands, canal dredging and spoil de- 

 position, and draining for agricultural and urban use. 

 The rapid loss rate to inland open water habitat can- 

 not reasonably be attributed to natural erosion and 

 subsidence alone. These natural processes can explain 

 about one-third of the wetland loss. Tlie rest is pre- 

 sumed to be due to hydrologic changes incurred by 

 the dredging of numerous canals and especially the 

 major ship channels through the Chenier Plain wet- 

 lands and the removal of httoral sediments which are 

 placed in spoil banks during channel maintenance. 



3.5 RENEWABLE RESOURCE 

 PRODUCTIVITY 



3.5.1 INTRODUCTION 



Analysis of the quantity and quaUty of renew- 

 able resources of the Chenier Plain is the heart of this 

 ecological characterization. The living resources have 

 evolved along with the major long-term geologic and 

 climatic processes that formed the Chenier Plain. The 

 mixture of land and water areas, which we have called 

 habitats, continue to change slowly with time under 

 the influence of natural processes characteristic of 

 any coastal zone. 



These habitats, maintained to a large extent by 

 the flow of water over, around, and through them, 

 support a characteristic flora and fauna. Some plants 

 and animals are commerciaUy important; some are 

 prized by sportsmen; some have important functions 

 in habitats; and others are threatened with extinction. 

 One could consider these living organisms to be the 

 end products of the physical and chemical processes 

 of the Chenier Plain. The organisms interact with 

 each other in a complex trophic web. The environ- 

 ment limits species diversity and productivity. 



By modifying any of the physical and chemical 

 processes in this long chain of events, man can alter 

 the living resources. The human activities that affect 

 the environment, described in part 3.2, have been 

 shown to influence the system's hydrology (part 33) 

 and the system's habitats (part 3.4). Habitat modifica- 

 tion in turn is responsible for long-term changes (per- 

 haps the most significant changes) in the potential liv- 

 ing resource production in the Chenier Plain. Direct 

 exploitation of living resources is also capable of 

 changing the resourcepotential(part 3.5.2). Deteriora- 

 tion of the quantity and quality of water can change 

 habitats both in areal extent and in their ability to 

 maintain their characteristic flora and fauna. Water 

 quality on the Chenier Plain is evaluated in part 3.5.3. 



3.5.2 THE POTENTIAL FOR RENEWABLE RE- 

 SOURCE PRODUCTION IN THE CHENIER 

 PLAIN 



This section discusses the importance of habitat 

 potentials for renewable resource production in the 

 Chenier Plain. In part 3.4, the area of habitats was 



considered. In this section net photosynthesis and an 

 index of wetland-water coupling (ratio of marsh edge 

 to marsh area) are two indices of quality that will be 

 examined to evaluate the potential for resource pro- 

 duction. Water quality is a third facet of basin quality 

 and is treated separately in part 3.5.3. Renewable re- 

 source productivity has already been defined (part 

 3.1.3) as representing the "quality" of a basin. This 

 quality is partially expressed as the capacity of a basin 

 to support organisms that are valued by man for their 

 food, recreational and esthetic value, and/or functional 

 value to the system; but the concept of habitats also 

 includes refuge value for the many species whose eco- 

 logical function is poorly recognized or whose exis- 

 tence is still unknown. 



A primary requirement for a high quality ecosys- 

 tem is an abundant source of food energy. Emergent 

 wetland vegetation is the main energy source for fish 

 and wildlife resources in the Chenier Plain basins. (A 

 detailed description of the function of wetland habi- 

 tat is presented in part 4.2.) The organic carbon pro- 

 duced in emergent wetlands is deposited as peat, 

 grazed or decomposed in place, or washed into the 

 inland open water habitat. This last energy pathway, 

 the export of organic carbon, is critical to many im- 

 portant aquatic species that are supported by a 

 detritus-based food web (part 4.3). Thus, the inter- 

 play between wetlands and water bodies is important. 



The average annual net photosynthesis for the 

 Chenier Plain calculated from annual production esti- 

 mates is 1 7,628,5 19 t (19,432,1 16 tons) (table 3.59) 

 and is discussed in part 4. The magnitude of produc- 

 tion for each basin varies directly with the amount of 

 wetland area. All vegetation produced is not eaten by 

 consumers in the food web so the values listed in table 

 3.59 represent the potential organic energy available 

 in each Chenier Plain basin. Average values exceed 

 1,300 t/km^ (3,711 tons/mi^ or 1300g/m^ or 4.26 

 oz/ft^) and are extremely high when compared to 

 ecosystems worldwide. The resource potential of the 

 Chenier Plain is probably as high as that found any- 

 where else in the United States. 



Natural habitats are steadily being lost to those 

 modified by man, and wetland habitats in particular 

 are being lost at a rate of about 0.1%/yr(part 3.4.6). 

 In addition, productivity of existing habitats may be 

 decreasing because of culturally induced stress; that 

 is, habitat quality may be degraded. In both cases, the 

 long-term trend is a decrease in net photosynthesis 

 and living resources in the Chenier Plain. 



The second index of basin quality, marsh edge: 

 marsh area ratio, has been used less as a diagnostic 

 tool. However, the importance of wetland-aquatic 

 coupling in general, the evidence for high diversity 

 and productivity along marsh-water edges (part 4.2), 

 and the relative ease of determining this index sug- 

 gests that it may be a useful tool for comparing 

 productivity in coastal environments. 



Because tidal currents scour small channels in the 

 marsh, the marsh edge: marsh area ratio tends to be 

 highest in salt marsh habitat and decreases as marshes 



81 



