Vertical Accretion Over Marker Horizons 



Vertical accretion results illustrated that (1) sediment accretion rates in the park were relatively 

 low compared with apparent water level rise, (2) sites having free communication with natural 

 waterways experienced significantly greater accumulation rates than sites behind spoil, and (3) 

 streamside sites generally experienced greater sedimentation accumulation rates than inland sites 

 (Table 2). Vertical accretion rates during the 9-month study ranged from 1.0 to 5.9 mm. The rates 

 were extrapolated to 1.3 to 7.9 mm/yr. These accretion rates were lower than the average 

 subsidence rates (1.0 cm) measured elsewhere in the Barataria Basin. Sites with open access to 

 natural waterways (51, 9S, and 121) experienced significantly greater accretion rates than sites 

 distant from a sediment source or behind spoil banks (5S, 6S, 61). 



Bulk Density, Organic Content, and Water Content 



Bulk density, water content, organic content, and mineral content are highly interrelated soil 

 characteristics. Organic content (on a dry weight basis) determines the amount of water in a given 

 volume of saturated soils (Rainey 1979) because highly organic materials are porous and hold large 

 amounts of water when saturated (Boelter 1974). 



Analysis of the soil characteristics in Jean Lafitte National Park revealed the following 

 conclusions: (1) bulk density values were generally low, ranging from 0.04 to 0.10 g/cm 3 at 14 of 

 the 17 sites, (2) soil water content throughout the park was high and fell in the range of 78%- 

 94% for all sites, and (3) organic content was high and ranged from 43.7%-87.1%. These low bulk 

 densities, high water contents, and high organic content concentrations are consistent with values 

 for fresh and intermediate marsh (Baumann 1980; Hatton et al. 1983; Swarzenski 1987). These 

 soil characteristics are a result of peat soils composed almost entirely of living and dead plant 

 material (Leet et al. 1982; Odum et al. 1984). 



Cluster analysis of the bulk density, organic content, and water content data revealed three 

 distinct clusters: (1) a group with high bulk density, low organic content, and low percent water, 

 characteristic of sites with open access to mineral sediments, (2) a group with low bulk density, high 

 organic content, and high percent water, characteristic of floating marsh sites and inland sites 

 affected by spoil, and (3) a group with intermediate bulk density, organic content, and percent 

 water values, characteristic of interior, quaking marsh sites (Figure 6). There was 87% correlation 

 between water content and bulk density. 



Table 2. Mean sediment accretion rates and significance for groups of stations 

 with sediment sources (sites 51, 121, 9S), behind spoil (6S, 61, and 5S), or 

 inland (sites 61 and 91). Note that groups are listed in order of decreasing 

 accretion rates. 



Group Mean sediment accretion rate Significance 8 



Sediment source 5.42 mm/9 mo. A 



Inland 2.12 mm/9 mo. B 



Behind spoil 1.41 mm/9 mo. C 



a as determined by Tukey's Studentized Range with a =0.05; groups with 

 different letters are significantly different. 



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