270 



Coastal & Marine Ecosyslems— Our Livinii Rc\inirces 



Table. Total area (hectares) of 

 selected vegetated wetlands by 

 state for the Gulf of Mexico (from 

 NOAA 1991),* 



shrub-scrub (mangroves), and freshwater 

 forested/shrub-scrub wetlands. Even though 

 wetland area has diminished greatly along the 

 gulf coast during the last 30 years, about 1 .3 

 million ha (3.3 million acies) still remain in 

 these three categories. 



Louisiana has the greatest area of coastal 

 wetlands with 55% of the total, followed by 

 Florida (18%), Texas (14%). and Mississippi 

 (2%). Louisiana contains 69% of the marshes, 

 while Florida has 97% of the estuarine scrub- 

 shrub, most of which is mangrove. Of the three 

 wetland types, 80% is marsh. 19% estuaiine 

 scrub-shrub, and 1% forested wetland. 



State 



Marsh 



Estuarine 

 scrub-shrub 



Fresh forested and 

 scrub-shrub 



Total 



% of total" 



1,100 



4,100 



400 



1,100 



248,400 



255,100 



3,000 

 1,900 



800 

 7,400 

 13,100 



188,000 



729,500 



24,200 



12,300 



363,900 



1,317,900 



14 



55 



2 



1 



28 



• Calculated based on Fish and Wildlife Services National Wetlands Inventory maps Area originally reported as 



acres x 100, hectare = 2 471 acres 

 •• Fractions ol percent rounded to the next highest whole percent (16 = 2.0%) 



Because of the age of the photogiaphs used 

 by NOAA and because national trends suggest 

 that the area of most wetland types is still 

 declining (Fiayer et al. 1983), the wetland sta- 

 tistics presented by NOAA may be overesti- 

 mates. No cunent studies summarize coastal 

 wetland area or loss rates for the entire Gulf of 

 Mexico tegion; therefore, four case studies con- 

 ducted by the National Biological Service's 

 Southern Science Center, the U.S. Fish and 

 Wildlife Service's National Wetland Inventory, 

 and their partners are presented to depict status 

 and trends from the I950's to 1970"s and the 

 1970"s to the late 1980"s. The areas chosen 

 (Fig. I) represent a cross-section of current 

 trends. 



Coastal Wetland Loss: Gulf of 

 Mexico Case Studies 



Galveston Bay 



White et al. (1993) reported both gains and 

 losses in Galveston Bay wetlands from the 

 1950"s to 1989, but the net trend was one of 

 wetland loss, going from 69.800 ha (171.000 

 acres) in the ''l950's to 56.100 ha (138,600 

 acres) in 1989. The rate of loss decreased over 

 time from about 405 ha (1,000 acres) per year 

 between 1953 and 1979 to about 283 ha (700 

 acres) per year between 1979 and 1989. The 

 rate of loss from 1979 to 1989 would probably 

 be lower if inaccuracies in wetland interpreta- 

 tion of the 1979 photographs could be taken 

 into account. In general, freshwater scrub-shrub 

 habitats decreased in area from the 1950"s to 



1979 and 1989. while forested wetlands 

 increased. Marshes (fresh and non-fresh) 

 decreased from about 67.000 ha (165.500 acres) 

 in the 1950's to about 52.800 ha (130,400 acres) 

 in 1989, producing a total net marsh loss of 

 about 21% of that resource. 



The five key factors contributing most to 

 wetlands decline in the Galveston Bay since the 

 1950"s are (1) industrial development: (2) 

 urbanization; (3) navigation channels; (4) tlood 

 control and multipui-pose water projects to meet 

 Houston's future water demand, especially 

 upstream impoundments on the Trinity and San 

 Jacinto rivers; and (5) pollution due to agricul- 

 tural runoff despite the diminished acreage lost 

 to agricultural expansion. It should be noted 

 that human-induced subsidence due to industri- 

 al development (oil and gas activities) and 

 urbanization (groundwater withdrawals) are 

 considered in this analysis (D. Whitehead, U.S. 

 Fish and Wildlife Service, personal communi- 

 cation). 



Coastal Louisiana 



Coastal wetland loss for Louisiana repre- 

 sents 67% of the nation's total loss. For the time 

 period 1978-90, the loss was 177,625 ha 

 (290.432 acres), representing an annual loss rate 

 of 9.802 ha/yr (24.203 acresVyr) for this 12-year 

 period; that is equal to 97.9 km- or 37.8 m7yr. 

 For the time period 1956-78, net wetland loss 

 was even greater, 267,800 ha (661,700 acres). 

 representing a loss rate of 12,170 ha/yr (30,000 

 acres/yr); that is equal to 121.7 km- or 47 

 mi-/yr. 



Although much of this loss is only indirect- 

 ly linked to human activities, most of the net 

 current, catastrophic wetland loss is primarily 

 the result of altered hydrology stemming from 

 navigation, flood control, and mineral extrac- 

 tion and transport projects (Sasser et al. 1986; 

 Louisiana Wetland Protection Panel 1987; 

 Turner and Cahoon 1988). These operations do 

 not always destroy wetlands directly, but they 

 do amplify tidal forces in historically low-ener- 

 gy systems, which upsets the balance of subsi- 

 dence and accretion, reduces nutrient and sedi- 

 ment influx, decreases freshwater retention, and 

 increases the levels of salt, sulfate, and other 

 substances potentially toxic to indigenous plant 

 species (Good 1993). 



Current wetland losses are concentrated in 

 the southern Deltaic Plain (78%; Fig. 1 ). In this 

 region, losses are especially severe in the fring- 

 ing marshes of the Terrebonne and Barataria 

 basins (Figs. 2 and 3). Previous losses in the 

 Deltaic Plain occuned primarily in large areas 

 of interior lands. In the Chenier Plain (Fig. I ). 

 loss rates were more constant (22%); many of 

 the larger areas of loss there seem related to 

 impounded areas with managed water levels. 



