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The State of the Bay Galveston Bay Area Project

Estuarine Wetlands

Estuarine wetlands exist in the Galveston Bay system across a salinity gradient and are classified into salt marshes and brackish marshes. Estuarine wetlands are often referred to as fringing marshes because they are found near the shoreline of the bay at the land-water interface.

Salt Marsh

Salt marsh communities are found in high salinity areas along protected estuarine shorelines. Prevalent species in the salt marsh community include smooth cordgrass (Spartina alterniflora), saltwort (Batis maritima), saltgrass (Distichlis spicata) and glasswort (Salicornia spp.) (White and Paine 1992). Smooth cordgrass, which is found in the intertidal zone, dominates the low salt marsh community (e.g., the portion of the marsh that is most frequently inundated by bay waters). While living, cordgrass is seldom eaten, and then by only a few herbivores. Once dead it provides nourishment to the large bay food web as detritus. Edges of the salt marsh serve as refuge and nursery habitat for juveniles of many species, especially brown and white shrimp. These habitats are also important feeding grounds for wading birds, such as herons and egrets. At higher elevations, marsh hay (or saltmeadow cordgrass; Spartina patens) and Gulf cordgrass (Spartina spartinae) occur, although they are more common in brackish marshes (White and Paine 1992).

Brackish Marsh

This community inhabits the transitional zone between salt marsh and fresh marsh and is affected by highly variable water levels and salinities. As would be expected, a number of species utilize this habitat, ranging from fresh water to salt-marsh species. In general, the brackish marsh is dominated by marsh hay and saltgrass. Other species include black needlerush (Juncus roemerianus), common reed (Phragmites australis) and big cordgrass (Spartina cynosuroides), seashore paspalum (Paspalum vaginatum), longtom in fresher areas (Paspalum lividum), and isolated clumps of saltmarsh bulrush (Bolboschoenus robustus) and Olney bulrush (Schoenoplectus americanus) (White and Paine 1992).

Estuarine Wetlands Distribution Trends

Historic Trends

An early land cover classification done for the Galveston Bay Estuary Program (White et al. 1993) estimated that 35,120 acres of emergent wetlands (estuarine and freshwater; does not include forested or scrub/shrub) disappeared from the Galveston Bay system over a 37 year period between 1953 and 1989. Of that total acreage, estuarine emergent marshes decreased in area by 9,480 acres or eight percent, which averages to a loss of approximately 256 acres of estuarine marsh per year from 1952-1989.  White et al. (2004 ) also found that estuarine marshes decreased by 3,833 acres between the 1950s and 2002 on Galveston and Follet’s Island and on Bolivar Peninsula.

Recent Trends

An analysis of the NOAA Coastal Change Analysis Program (C-CAP) data for the same area studied by White et al. (1993) shows a net gain in estuarine emergent wetlands of 2,268 acres or two percent between 1996 and 2005, which averages to a gain of 228 acres per year. 

When the same data were analyzed for the five counties surrounding Galveston Bay (Brazoria, Chambers, Galveston, Harris, and Liberty) 1,047 acres of losses due to development were offset by gains in wetland acreage yielding a net increase in estuarine emergent wetlands acreage of 199 acres between 1996 and 2005.  The table below depicts the change in wetland acreage in the Lower Galveston Bay watershed between 1996 and 2005.

 

Table 1.  Acreage of estuarine and freshwater wetland in the five counties of the Lower Galveston Bay watershed from 1996 to 2005. Data Source: (NOAA 2006; Lester and Gonzalez 2008).
 
Acreage
 
Wetland Classification 1996 2005 Total Change 1996 to 2005 Annual Change 1996 to 2005 Percent Change 1996 to 2005
Estuarine Emergent 163,029 163,228 +199 +20 0%
Freshwater Emergent 169,746 168,068 -1,678 -168 -1%
Freshwater Forested 564,715 546,451 -18,264 -1,826 -3%
Freshwater Scrub/Shrub
75,061 69,016 -6,045 -605 -3%

Total

972,551 946,764 -25,787 -2,579 -3%

 

As noted above, methodological differences in land cover classification studies make comparisons across studies difficult. However, both the analysis by White et al. (1993) and the Galveston Bay Status and Trends analysis of the NOAA C-CAP data show that:

  1. The loss of estuarine wetlands has slowed considerably since 1989, and
  2. The net losses in estuarine emergent wetlands in the Lower Galveston Bay watershed are much less than losses of freshwater wetlands.

Most of the loss of salt and brackish marsh has been caused by relative sea level rise and subsequent conversion to open bay and barren flats. However, the loss of these estuarine wetlands appears to have been dramatically slowed during the last ten years.The most likely explanations of the arrested decline of estuarine wetlands are the regulatory protection of estuarine wetlands under the Clean Water Act and numerous habitat restoration efforts by regional partners.

 

Literature Cited

Lester, L. J. and L. A. Gonzalez. 2008. Galveston Bay Status and Trends Final Report. Houston, TX, Texas Commission on Environmental Quality, Galveston Bay Estuary Program: 83 pp.

White, W. A. and J. G. Paine. 1992. Wetland plant communities, Galveston Bay System. Webster, Texas, Galveston Bay National Estuary Program Publication GBNEP-16.

White, W. A., T. A. Tremblay, R. L. Waldinger and T. R. Calnan. 2004 Status and trends of wetland and aquatic habitats on barrier islands, upper Texas coast, Galveston and Christmas Bays. Final report. , Texas General Land Office and NOAA under GLO Contract No. 03-057.

White, W. A., T. A. Tremblay, E. G. Wermund and L. R. Handley. 1993. Trends and status of wetland and aquatic habitats in the Galveston Bay system, Texas. Webster, Texas, Galveston Bay National Estuary Program Publication GBNEP-31.

 

 

 

 

Related Pages:

Freshwater Wetlands
Habitat

 

 

 

Wetlands Land Cover Map
Galveston Bay Wetlands Land Cover Map, Houston Advanced Research Center
Map of wetland habitats in the Lower Galveston Bay watershed. Data source Coastal Change Analysis Program land use/land cover data (NOAA 2006).

 

 

 

Sunset over an estuarine marsh.  Image courtesy of Dave Huss.
Sunset over an estuarine marsh. Image courtesy of Dave Huss.

 

 

 

 

 

 

SMOOTH CORDGRASS (SPARTINA ALTERNIFLORA) SALT MARSH LOCATED NEAR BAYOU VISTA. ©ISTOCKPHOTO.COM
Smooth cordgrass (Spartina alterniflora) salt marsh located near Bayou Vista. Copyright istockphoto.com

 

 

 

 

 

 

NOAA Gulf Coast Land Cover Data
Thumbnail image of NOAA gulf coast land cover data
NOAA Coastal Services Center

 

 

 

 

 

 

GALVESTON ISLAND STATE PARK WETLAND RESTORATION TERRACES. IMAGE COURTESY GOOGLE EARTH.
Galveston Island State Park wetland restoration terraces. Image courtesy Google Earth.

 
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