export by currents accumulates and 

 increases marsh elevation. Higher ele- 

 vation means more frequent exposure of 

 the soil surface to air, increasing the 

 loss rate (oxidation) of carbon and 

 limiting further increases in elevation. 

 Soil that is so low as to be permanently 

 waterlogged (never exposed to air) de- 

 velops an oxygen deficit that retards 

 macrophyte production. There is pre- 

 sumably an optimum inundation frequency 

 for each wetland community type that 

 provides energy subsidies in the form of 

 nutrients and other plant requirements 

 that stimulate production rates. The 

 highest plant biomass occurs along the 

 banks of natural streams and bayous. 

 More inland portions of the region are 

 inundated less frequently than are 

 coastal marshes, and they are covered by 

 standing water for longer periods. The 

 highest productivity levels are shown by 

 brackish marshes, in which flushing and 

 inundation frequencies are intermediate 

 (Day et al. 1982) . 



Macrophyte vegetation in wetlands 

 also contributes to inorganic deposition 

 by reducing water-current velocity and 

 increasing sedimentation rates. This 

 current-damping effect is also important 

 for absorbing the energy of storm surges 

 that would rapidly erode unvegetated 

 sediments. The root mat of wetland 

 plants can be more extensive and contain 

 2 to 3 times the biomass of the above- 

 ground portion (Stout and de la Cruz 

 1981) in the MDPR. 



Other roles of wetland vegetation 

 at the regional level include the en- 

 hancement of water loss through evapo- 

 transpiration and the decrease in 

 albedo, or reflectance, both of which 

 affect local climate (Hansen et al. 

 1981). In addition, the marshes in the 

 MDPR attract a majority of the migrating 

 waterfowl that use the Mississippi 

 f lyway . 



Certain so-called pest organisms 

 have significantly influenced the urban 

 and agricultural development of the 

 MDPR. For example, numerous species of 

 mosquitoes have always affected the 

 residents of New Orleans. The city 



experienced many outbreaks of malaria 

 and yellow fever until 1900 (Lewis 

 1976). Water hyacinths ( Eichhornia 

 crassipes ) were accidentally introduced 

 to New Orleans from South America during 

 the Cotton Exposition of 1883 (Lewis 

 1976). They have since spread throughout 

 the South, where they cover freshwater 

 ponds and canals in which nutrient 

 levels are high, especially during the 

 summer. 



Agricultural pests, including 

 sugarcane borers, nematodes, aphids, and 

 fire ants reduce crop production or 

 otherwise hinder agricultural opera- 

 tions. They also create an active 

 market for chemical pesticides. These 

 chemicals ultimately enter water, sedi- 

 ments, and organisms in the MDPR. Some 

 chemicals, such as DDT and toxaphene, 

 are persistent and dangerous to humans 

 and to other vertebrates inhabiting the 

 MDPR. For example, during the 1960's, 

 the entire natural breeding population 

 of the Louisiana State bird, the brown 

 pelican, was eliminated by interference 

 in its shell metabolism by some of these 

 chemicals (Blus et al. 1979). 



SOCIOECONOMIC SETTING 



The economy of the MDPR is based on 

 abundant renewable and nonrenewable 

 natural resources and its location at 

 the mouth of the country's major navi- 

 gation system. Several studies have 

 addressed the economic conditions and 

 history of coastal Louisiana (Jones and 

 Rice 1972; Renner 1976) and the MDPR 

 specifically (Larson et al. 1980). Rates 

 and patterns of natural resource con- 

 sumption and pollution and other envi- 

 ronmental impacts are a principal 

 concern of this report. The research 

 strategy employed throughout this study 

 has been to treat economic and ecologi- 

 cal processes as comparable phenomena 

 that can be incorporated in the same 

 models. Quantitative descriptions of 

 the standard economic sectors in the 

 MDPR (such as agriculture, forestry, 

 mining, and manufacturing) are included 

 as "economic habitats" along with the 

 ecological habitats in a following 

 section. 



26 



