provide a spectrum of products and ser- 

 vices to the economy. Some products, 

 such as shellfish, fish, and furbearers, 

 have well-defined markets, and their 

 contribution to the economy is rela- 

 tively easy to quantify (Table 2). 

 Natural work services, such as waste 

 assimilation, recreation, microclimate 

 control, and flood protection, are not 

 traded in well-defined markets so their 

 contributions are harder to quantify. 

 This report describes the ways in which 

 natural and economic habitats are inter- 

 connected. Ultimately an informed man- 

 agement system should be based on the 

 knowledge of those interconnections. 



The connection of the MDPR via 

 waterways to most of the United States 

 and to the world provides an obvious 

 economic advantage. The existence of 

 natural waterways, built and maintained 

 in large part by natural hydrologic 

 processes, saves users the expense of 

 constructing and maintaining alternative 

 transportation. Water transport thus 

 has a significant cost advantage over 

 other transport modes. Figure 16 shows 

 the major navigable waterways in Lou- 

 isiana and the number of commercial 

 vessels using them in 1978. The Port of 

 New Orleans is the major port in the 

 MDPR and handles more cargo than any 

 other port in the Nation (USACE 1981). 

 Table 3 lists the quantities of major 

 commodities shipped on waterways in 

 Louisiana in 1976: natural resource and 

 agricultural commodities make up most of 

 the waterborne shipments, indicating the 

 importance of natural resources to the 

 economy of the MDPR. 



Waterways are also a significant 

 source of fresh water for varied eco- 

 nomic activities. The Mississippi River 

 in particular is used for drinking 

 water, for industrial processes and 

 cooling, and as an outlet for municipal 

 and industrial waste. Reconciling these 

 conflicting uses is a major management 

 concern. 



Waterways in the MDPR have been 

 modified by dredging and levee construc- 

 tion to facilitate transport and flood 



control. Levees now flank the Missis- 

 sippi all the way from Cairo, Illinois, 

 to the active delta, 113 km (70 miles) 

 below New Orleans. The main navigation 

 channel through Southwest Pass is con- 

 tinually dredged to prevent siltation 

 from blocking transport (USACE 1981). 



While flood control and navigation 

 structures and dredging facilitate the 

 short-term economic interests related to 

 river-borne commerce, they inhibit some 

 natural processes that support natural 

 habitats. This is especially true of 

 annual overbank flooding that should 

 provide sediments and nutrients to 

 maintain the growth of the delta. Given 

 the region's dependence on natural re- 

 sources, long-term regional economic 

 viability is thus jeopardized. 



Marshes in the region are in a 

 delicate balance between sedimentation 

 and erosion. The leveeing and dredging 

 of the Mississippi have allowed the 

 delta to build out to the edge of the 

 Continental Shelf so that water and 

 sediments are shunted out Southwest 

 Pass, South Pass, and Pass a Loutre into 

 deep water where it cannot build land. 

 Sediments that were once distributed to 

 the MDPR marshes are now lost over the 

 shelf. This situation has been identi- 

 fied as a major cause of Louisiana's 

 current land-loss (Craig et al. 1979). 

 Along with the loss of sediment, the 

 Mississippi is tending to take the 

 shorter Atchafalaya route to the sea 

 (Kazmann and Johnson 1980). The impli- 

 cations of this change, if it were 

 allowed to continue, would be profound. 

 The net loss of MDPR land could be 

 reversed as the Atchafalaya delta ex- 

 panded, even though erosion in the 

 densely populated eastern portion of the 

 MDPR would probably accelerate. There is 

 a growing need to examine the probable 

 effects of the river switch, and its 

 overall costs and benefits. Meanwhile, 

 the cost of maintaining the present 

 course of the river against a natural 

 gradient can only increase. These kinds 

 of problems indicate the difficulty of 

 the critical management decisions that 

 must be made in the near future. 



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