Our Livini^ RfS(nini's — Coaslal & Miiriue Ecosystems 



271 



The Baratciria and Tenebonnc hasins suffer 

 the highest land loss rates (all land but mostly 

 wetlands) m Louisiana (2.880 hii/yr [7,120 

 acres/yr] and 2.630 ha/yr [6.500 acres/yr], 

 respectively), accounting for 64% of all land 

 loss in the 1978-90 period. In contrast, this area 

 accounted for only 43% of all loss in the 1956- 

 78 period. The Mennentau and Sabine basins 

 (Fig. 2) have the next highest loss rates ( 1.080 

 h;i/yr [2,670 acres/yr] and 660 ha/yr [1.630 

 acres/yr]), with losses largely confined to the 

 northern and central portions, except for shore- 

 line erosion along the Mennentau Basin's 

 coastline. Loss rates within the Teche- 

 Vermilion. Mississippi, Breton Sound, and 

 Pontchartrain basins (Fig. 2) are all less than 

 930 ha/yr (2,300 acres/yr). which seems to indi- 

 cate more stable environments. The Atchafalaya 

 and Pearl River basins (Fig. 2) experienced 

 losses of less than 130 ha/yr (321 acres/yr). In 

 summary, land loss rates in coastal Louisiana, 

 although decreasing, remain high for the 1978- 

 90 period. 



The National Biological Service is providing 

 future land loss updates for coastal Louisiana by 

 using Landsat Thematic Mapper satellite 

 imagery on a 3-year basis. 



Mobile Bay 



Non-freshwater marshes surrounding 

 Mobile Bay declined by more than 4.047 ha 

 (10,000 acres) from 1955 to 1979, representing 

 a loss of 35% (Roach et al. 1987). Freshwater 

 marshes in all of coastal Alabama declined by 

 about 69% from 1955 to 1979. More than 2.500 

 ha (6.200 acres) were lost during that time 

 (Roach etal, 1987). 



When comparing these data to 1988 wetland 

 habitat maps prepared for upper Mobile Bay, it 

 appears that in this portion of the bay no addi- 

 tional net loss of non-freshwater marsh has 

 occurred since 1979. Some marsh has obvious- 

 ly continued to be lost in certain areas, primari- 

 ly because of dredge disposal associated with 

 navigation and industry. These losses, though, 

 seem to have been offset by the growth of emer- 

 gent marsh in existing spoil sites (Watzin et al. 

 1994). 



The Southern Science Center's 1988 areal 

 estimates show a substantial increase of 189 ha 

 (467 acres) in freshwater marsh from 1979 to 

 1988 in upper Mobile Bay. Further investigation 

 revealed that some of this gain was the result of 

 the growth of emergent vegetation in existing 

 disposal areas and in ditches along railroads and 

 highways. Because of disparities in photointer- 

 pretation between dates, it is also quite likely 

 that some of these differences are simply due to 

 mapping errors and differences in mapping 

 technique (Watzin et al. 1994). 



As a result of mapping errors associated 



Louisiana 



with interpreting forested and scrub-shrub wet- 

 lands in the 1956 photographs. Roach et al. 

 (1987) had little faith in the quantitative esti- 

 mate of change between 1956 and 1979 for 

 these wetland types. The Southern Science 

 Center's 1988 wetland area figures for forested 

 wetlands appear relatively accurate; they indi- 

 cate that about 486 ha ( 1.201 acres) of forested 

 wetlands (2.7%) were lost in upper Mobile Bay 

 between 1979 and 1988. These losses can be 

 attributed to conversion of forested habitats to 

 scrub-shrub areas (e.g.. clearcutting associated 

 with timber harvest), small impoundments, and 

 commercial and residential development 

 (Watzin et al. 1994). 



Tampa Bay 



Haddad (1989) reported emergent wetlands 

 decreased from 29.000 ha (71.700 acres) in the 

 1950's to 23.900 ha (59.100 acres) in 1982. 

 about an 18% loss. Mangroves decreased from 

 8.629 ha (21,320 acres) to 8.032 ha (19,847 



Fig. 1. Locations of wetland loss 

 study sites along the Gulf of 

 Mexico recion. 



\ Calcasieu 

 Sabine 



Terrebonne 



Barataria 



Mississippi River 



acres), a decline of about 7%. Salt marshes 

 declined from 2,063 ha (5,097 acres) to 1,423 

 ha (3,538 acres), or a loss of 30%. Freshwater 

 wetlands decreased 21% from 18,335 ha 

 (45,305 acres) to 14,440 ha (35,681 acres). 



Lewis et al. (1985) estimate that 44%. of the 

 salt marsh and mangrove has been lost in Tampa 

 Bay since the late 1800's. Although their num- 

 bers and those of Haddad ( 1989) are not readily 



Fig. 2. Coastal Louisiana basins as 

 defined in the Coastal Wetlands 

 Planning. Protection, and 

 Restoration Act Plan. 



