about 50 cm (20 inches) (Sasser 1977). 

 Marshes rely on the deposition of sedi- 

 ment and organic matter to maintain 

 their elevation above water level, and 

 hydrologic, sediment, or salinity regime 

 disturbances can dramatically affect 

 marsh condition. The anomalously rapid 

 apparent increase in sea level in the 

 MDPR is of great importance to the 

 future of the region. Figure 6 shows 

 the variability in rates of elevation 

 change along the gulf coast. Management 

 plans should obviously take this ongoing 

 process into consideration. 



After a delta lobe is abandoned by 

 the major distributary, resuspended 

 sediments are the primary source for 

 local deposition. This is also true for 

 the present case in which Mississippi 

 River sediments are being lost offshore. 

 The majority of deposition occurs during 

 winter storms associated with frontal 

 passages and during summer tropical 

 storms. A 5-year study (1975-1979) was 

 done of sedimentation in the saline 

 marshes surrounding Barataria Bay, an 

 area artificially cut off from spring 

 overbank flooding of the Mississippi 

 River. Forty percent of total sedimen- 

 tation took place during the winter, 40% 

 during two tropical storms, and 20% 

 during other times (Baumann 1980). There 

 was a statistically significant differ- 

 ence between the rate of sedimentation 

 in marshes adjacent to tidal creeks (1.5 

 cm/yr or 0.59 in/yr) and the rate in 

 marshes farther inland (0.9 cm/yr or 

 0.35 in/yr). The subsidence rate (1.2 

 cm/yr or 0.47 in/yr) was 0.3 cm/yr 

 greater than sedimentation in inland 

 marshes, but less than sedimentation in 

 streamside marshes. Thus, inland 

 marshes are deteriorating. The loss of 

 riverine sediment (because of flood 

 control levees) and the difference in 

 sedimentation rates between inland and 

 streamside marshes should be considered 

 in assessing wetland loss in abandoned 

 delta lobes. 



Geological processes in the MDPR 

 formed traps which have collected de- 

 posits of oil, gas, and sulfur. The 

 weight of sediments deposited over 

 ancient salt beds in the MDPR pushed up 

 huge pillars of salt called salt domes. 



Oil and gas are concentrated enough to 

 be recovered economically only where 

 they are trapped in geologic disconti- 

 nuities. Salt domes are an important 

 category of discontinuity in the MDPR. 

 The salt itself is also economically 

 important . 



Caverns leached or mined from salt 

 domes are now being used for the storage 

 of oil. The Clovelly salt dome, near 

 Golden Meadow, Louisiana, stores import- 

 ed crude oil from the Louisiana Offshore 

 Oil Port (LOOP) located 19 mi off the 

 coast in the Barataria hydrologic unit. 

 The Hackberry salt dome in Cameron 

 Parish currently holds an oil reserve 

 under the Federal Strategic Reserve 

 Program. Under consideration is the 

 storage of compressed air in salt domes 

 to generate electricity during peak 

 demand. In addition, a large study has 

 been mounted to examine the feasibility 

 of permanently storing in salt domes the 

 current stockpile of 8,000 metric tons 

 of high-level radioactive waste from 

 nuclear reactors (Martinez et al. 1979; 

 Marshall 1982). 



Hydrology 



Hydrologic processes integrate the 

 entire region by regulating biological 

 processes (especially wetland plant 

 production), eroding and depositing 

 sediments, modifying the climate, 

 transporting aquatic organisms and human 

 commerce, and disposing of wastes. 

 Hydrology encompasses all water rela- 

 tions, including water budgets (inputs 

 and losses) , above and belowground 

 storages, water quality parameters such 

 as salinity, and flow rates. 



Hydrologic processes include all 

 interactions mediated by water movement, 

 and almost everything that happens in 

 the MDPR is somehow related to such 

 processes. River water carries sedi- 

 ments to the region and deposits them 

 differentially. The river water flow, 

 rain water runoff, and ocean water in- 

 undation erode and deposit sediments. 

 Water movements and waterborne mate- 

 rials, acting under the local climatic 

 influence, control plant production, 

 which contributes markedly to the land- 

 building process. 



12 



