DISCUSSION 



Environmental Conditions in the Park 



The results of the ecological study indicate the following trends: (1) there was a slight salinity 

 increase over the past 30 years accompanied by an encroachment of more salt-tolerant plant 

 species, (2) this encroachment of salt-tolerant species occurred without resulting in marsh breakup, 

 (3) accretion rates were lower than regional subsidence, (4) sediment accretion rates were 

 significantly lower in areas inland behind spoil compared with areas with access to direct sediment 

 sources, (5) soil characteristics were the firmest and accretion rates were the highest along areas 

 with access to mineral sediment sources compared to floating and inland locations, (6) the 

 hydrology of the park has been drastically altered over time beginning in the 1700's, (7) some areas 

 of the park were impounded and covered by approximately 0.6 m of water year-round, (8) most 

 of the park is a quaking marsh, and (9) the park has been experiencing a sediment accretion deficit 

 and is evolving into a floating marsh as a response to this deficit. Large areas of scrub-scrub have 

 invaded the floating marsh. Each of these points will be addressed in the following sections. 



Effects of Saltwater Intrusion in Jean Lafitte National Park 



Over the past 30 years, mean salinity in Bayou Barataria at Lafitte increased by 1.2 ppt. This 

 salinity increase is reflected in vegetation changes. The western (lakeside) portion of the park, 

 which was characterized as fresh marsh in 1956 (U.S. Fish and Wildlife Service 1983), is now 

 intermediate marsh, as indicated by soil salinity and vegetation dominated by Spartina patens. 



Saltwater intrusion does not seem to be a serious problem in the park for the following reasons: 

 (1) significant wetland loss has not occurred, (2) vegetation composition is changing to reflect a 

 successional adjustment to salinity changes in the area, (3) marsh soils with the highest bulk density, 

 highest mineral content, and lowest water content occur in the areas where the increase in salinity 

 has been highest, and (4) the healthiest and firmest marshes occur in the areas where salinity 

 increase has been highest. Few open water areas have developed and the lakeside soil 

 characteristics (where salinity is highest) have the highest bulk density, lowest organic content 

 levels, highest mineral content levels, and highest accretion rates. In addition, the mean salinity 

 tolerance ranges of the dominant vegetation (Myrica certifera, Sagittaria lancifolia, and Spartina 

 patens) indicate that these species are occurring within tolerable salinity ranges, relative to the 

 conditions that exist in the park. For example, while salinity levels in the western portion of the 

 park usually fall below 3 ppt, laboratory studies show that Myrica certifera and Spartina patens do 

 not experience stunted growth below 8 and 10 ppt, respectively (Odum et al. 1984; Williamson et 

 al. 1984). 



Soil Characteristics 



Sediment input plays an essential role in maintaining both nutrient input and vertical accretion 

 which allow wetlands in the Louisiana coastal zone to offset the current rate of apparent water 

 level rise (AWLR). Results from this study indicate that vertical accretion in wetlands of the park 

 are significantly less than the AWLR of 1.0 cm/yr. Vertical accretion rates and soil characteristics 

 showed three important trends: (1) vertical accretion rates were highest near sediment sources 

 (lakes and Millaudon Canal), (2) vertical accretion rates were significantly lower behind spoil banks, 

 and (3) only sediment accretion sites near the lake had >60% mineral content. Thus, although 

 vertical accretion rates in the park were low compared with the AWLR, the healthiest marshes with 

 the highest accretion rates and best soil characteristics were close to new sediment sources. 



263 



