compared with other freshwater marsh 

 ecosystems (Whigham 1978). Above and 

 below ground standing crop values range 

 from 353 g dry wt/m 2 for Sagittaria 

 communities, to 687 g dry wt/m 2 for 

 Typha latifolia communities, to 660 g 

 dry wt/m 2 for the Salix nigra community. 

 These relatively low values may reflect 

 the successional youthfulness of the 

 ecosystem. Low primary productivity 

 does not mean that emerging delta land 

 is not heavily used by waterfowl. 



VERMILION HYDROLOGIC UNIT (VII) 



The Vermilion hydrologic unit is 

 adjacent to and west of the Atchafalaya 

 unit. From a functional and historical 

 (geological) standpoint, the Vermilion 

 and Atchafalaya units are closely 

 related as they occupy the oldest por- 

 tion of the MDPR, the former Teche Delta 

 system that was active about 6,000 years 

 B.P. (Coastal Environments, Inc. 1977). 

 This advanced age is reflected in the 

 coastline, which is smoother and less 

 irregular than in younger coastal areas 

 (Figure 61). This is said to indicate 

 an advanced state of coastal erosion 

 (Coastal Environments, Inc. 1977). The 

 Vermilion Hydrologic unit is being 

 strongly influenced by the emerging 

 Atchafalaya Delta complex. 



The Vermilion unit occupies the 

 western extremity of the MDPR as well as 

 the eastern extremity of the Chenier 

 Plain. The western half of the 

 Vermilion hydrologic unit was described 

 in the characterization study of the 

 Chenier Plain region (Gosselink et al. 

 1979). The areas of the habitats com- 

 prising the Vermilion hydrologic unit, 

 and their changes between 1955 and 1978 

 are shown in Table 23. 



Much of the Vermilion hydrologic 

 unit (about 49%) is occupied by 

 Vermilion Bay (estuarine open water 

 habitat). This water body was described 

 in 1969 (Dugas 1970) in terms of its 

 ecological characteristics. Although 

 Vermilion Bay is a part of the Atcha- 

 falaya-Cote Blanche-Vermilion complex, 

 Dugas reported that it is somewhat 

 distinct from the other three bays in 



having larger sediment grain size, more 

 shell inclusions, and more organic mat- 

 ter in the sediment. This difference 

 was presumably due to the distance of 

 Vermilion Bay from the fine sediment 

 outwelling from the Atchafalaya River 

 and the presence of oyster reefs that 

 block sediment transport. 



Nevertheless, Vermilion Bay has 

 become less saline because of the 

 influence of the Atchafalaya. In 1966 

 the marshes surrounding the bay were 

 described (perhaps incorrectly) as salt 

 marshes (Norden 1966) . They were 

 brackish by 1969 (Dugas 1970). Average 

 water salinity in the bay was reported 

 as ranging from 2 to 5 ppt in 1969 

 (Dugas 1970). In 1979 they were partly 

 intermediate (Chabreck and Linscombe 

 1978). 



Vermilion Bay is quite shallow 

 (average depth about 1.5 m or 4.92 ft) 

 with the exception of a scour hole over 

 50 m (164.0 ft) in Southwest Pass to the 

 west of Marsh Island (Juneau 1975). 

 Water temperatures reflect the shallow 

 depth, ranging from 10 deg. to 33.5 deg. 

 C, or 50 deg. to 92.3 deg. F (Dugas 

 1970). The average sediment grain size 

 in the nearshore zone in the Vermilion 

 hydrologic unit is the smallest (finest) 

 of any coastal estuarine area because of 

 Atchafalaya influence (Juneau 1975). 



Oyster reefs are not distinguished 

 as a separate habitat in the technical 

 report for the Mississippi Deltaic Plain 

 Region, and were not delineated on the 

 Wicker et al. 1980b maps which form part 

 of the information base for this study. 

 Reefs that are periodically (or aperi- 

 odically) exposed by low water levels 

 are limited in their distribution in the 

 MDPR. In the Atchafalaya and the 

 Vermilion hydrologic units, however, 

 oyster reefs are quite extensive, and 

 presumably important in the nearshore 

 habitat. A huge reef system is located 

 directly in front of Atchafalaya Bay, 

 and another is to the west in front of 

 Marsh Island, as shown in Figure 62. 

 Many of these reefs are not living 

 because the oysters that comprise them 

 have been killed by the increasing sedi- 

 ment and freshwater flow emerging from 



144 



