Mailing address update: As of 1/22/24, the Bureau will have a new mailing address. See our contact page for details.

Upper Coast Strandplain-Chenier System and Southern Coast Padre Island National Seashore

STATUS AND TRENDS OF INLAND WETLAND AND AQUATIC HABITATS

Download Report
Download Strandplain-Chenier Data
Download PINS Data

Presented in this report are results of two status-and-trend studies, (1) of the upper Texas coast along the strandplain-chenier system from Sabine Pass to East Galveston Bay, and (2) of the southern Texas coast along Padre Island National Seashore (PINS) that includes the central section of Padre Island.

The two study areas are very different. Geologically, the upper Texas coast is characterized by a modern strandplain-chenier system with well-preserved chenier beach ridges with interlying marsh filled swales (Fisher et al. 1973). Relict beach ridges and intervening swales have an orientation roughly parallel to today’s shoreline marked by the Gulf beach. The swales are the sites of extensive linear estuarine marshes. The strandplain-chenier system has gradually evolved through erosion, deposition, compaction, subsidence, and locally faulting. The strandplain extends along the Gulf shore toward the southeast to High Island. High Island is a salt dome near the Gulf shoreline with elevations exceeding 7.5 m (25 ft). The study area extends landward to the Gulf Intracoastal Waterway. The strandplain-chenier study area along the upper Texas Coast contains the most extensive contiguous marshland along the Texas Gulf Coast. Most of the marshland falls within the McFaddin National Wildlife Refuge, Texas Point NWR, J.D. Murphree Wildlife Management Area, and Sea Rim State Park. Extensive brackish- and salt-water marshes and ponds characterize this area. Although there are local fresh ponds and marshes that have been isolated by levees and dikes, most of the fresh-water marshes that are part of the McFaddin National Wildlife Refuge occur inland of the Gulf Intracoastal Waterway (Personal Communication, 2006, Dean Bossert, Refuge Manager).

Padre Island National Seashore, the South Texas study area, is a barrier island that separates the Gulf of Mexico from Laguna Madre. The barrier is characterized by broad beaches, fore-island dunes, vegetation stabilized dunes, active dune fields, expansive wind-tidal flats, hurricane wash-over channels, and salt-, brackish, and fresh-water ponds and marshes. The study area extends southward to Mansfield Channel, and landward to the Gulf Intracoastal Waterway.

Strandplain-Chenier System, Upper Texas Coast
Status, 2004

Major estuarine habitats in the study area include salt and brackish marshes, and open water. Uplands are next in areal distribution. Palustine marshes are limited in extent. The primary habitat mapped in the marine system is the Gulf beach, which consists of a topographically lower forebeach and a higher, less frequently flooded backbeach. In 2004, wetland and aquatic habitats were dominated by estuarine marshes, with a total area of 33,689 ha (83,179 acres), followed by estuarine open water and flats totaling 6,866 ha (16,952 acres), and palustrine marshes at 511 ha (1,262 acres). Palustrine flats and water bodies had a total area of 150 ha (370 acres), and wetland scrub/shrub wetlands 8 ha (20 acres). Along the Gulf shoreline, the area of mapped beaches totaled 229 ha (566 acres). Lacustrine habitats, consisting in part of impounded water and Star Lake, had a total area of 390 ha (962 acres).

Trends

From 1956 through 2004 within the upper coast study area, emergent wetlands (marshes) decreased from about 38,000 ha (93,819 acres) to 34,200 ha (84,454 acres), a loss of approximately 3,800 ha (9,382 acres) (Table 1; Fig. 1 & 2). Most of the loss (68%) occurred during the earlier period (1956-1979/83). The rate of marsh loss from1956 to 1981 (1981 is used as the average of 1979 and 1983) was about 115 ha/yr (284 acres/yr), and from 1981 to 2004, about 40 ha/yr (99 acres/yr). In contrast to the loss of marsh was a gain in total estuarine and marine open water. The gain in open water was approximately 3,800 ha (9,382 acres), which is equivalent to the loss in marsh. The rates of gain in water were about 138 ha/yr (341 acres/yr) during the earlier period, and 16 ha/yr (40 acres/yr) during the later period. The area of Gulf beaches decreased slightly through time, from 318 ha (786 acres) in 1956 to 229 ha (566 acres) in 2004. Uplands increased in area from 3,260 ha (8,050 acres) in1956 to 3,346 ha (8,260 acres) in 2004, a gain of about 86 ha (210 acres).

 

1956

1979/83

2004

 

ha

acres

ha

acres

ha

acres

 

Emergent wetlands

                 37,999

       93,819

       35,117

      86,704

    34,206

      84,454

 

Open water and flats

                  

4,468

       11,031

         7,774

      19,193

     7,406

      18,284

 

Marine water

                 

 8,771

       21,656

         8,918

      22,019

     9,645

      23,812

 

Gulf beach

                   

  318

           786

           307

          759

        229

          566

 

Uplands

                  

3,260

         8,050

         2,731

       6,742

     3,346

        8,260

 

 

 

 

 

 

 

Table 1. Total area of major habitats in1956, 1979/83, and 2004 in strand-plain chenier study area.

 

Figure 1. Matagorda Bay Trends

Figure 1. Map showing distribution of major wetland and aquatic habitats in 2004, 1979/83, and 1956 in the upper coast study area.

 

 

Figure 1. Matagorda Bay Trends

Figure 2. Areal distribution of major habitats in the study area in 1956, 1979/83, and 2004, strandplain-chenier system.

 
Padre Island National Seashore
Status, 2003/04

In 2003/04, wetland, aquatic, and upland habitats covered 95,173 ha (235,077 acres) within the Padre Island study area. This area includes the Laguna Madre and Land Cut area between the Seashore boundary and the Gulf Intracoastal Waterway (GIWW). Approximately 20,681 ha (51,082 acres) within the study area was classified as uplands. Of the four wetland systems mapped, the estuarine system is the largest. The largest area of habitats are the wind-tidal and algal-flat classes, together covering 35,356 ha (87,329 acres). Emergent vegetated wetlands (E2EM, E2SS, PEM) cover 3,930 ha (9,707 acres), about 63% of which is palustrine marsh. Another important habitat class is seagrass (E1AB3), which in the study area has an area of almost 14,572 ha (35,993 acres).

Trends

Analysis of trends in wetlands and aquatic habitats from the 1950’s through 2003/04 shows that wind-tidal/algal flats increased slightly from the 1950’s to 1979, and increased significantly from 1979 to 2003/04 (Table 2; Fig. 3 & 4). Wind-tidal flats are, by far, the most extensive habitat. The lesser distribution in the 1950’s is primarily due to flooding of the Laguna Madre as a result of the construction of Mansfield Channel. Adjusting for the mid-1950’s flooding produces a trend towards loss (-5 %) of tidal flat through 2003/04. Most flat loss was in the southern part of the island where sand dunes migrated onto flats. Seagrasses appear to have spread significantly from the 1950’s to 2003/04. However, some of the change may have been an apparent and not real increase, as a result of under-mapping in the mid-1950’s. Palustrine habitat area declined somewhat by 1979 but gained substantially (25 %) over the length of the study time period. A combination of factors, including relative sea-level rise and park management practices provided favorable conditions for palustrine habitat expansion. Estuarine marsh area also fluctuated over time, but lost (-) 26 % of the original mid-1950’s resource. PINS has historically experienced both shoreline accretion and erosion. As a result of shoreline erosion, gulf beach has experienced a systematic decline in area over time.

Habitat

1950's

1979

2003/04

 

(ha)

(acres)

(ha)

(acres)

(ha)

(acres)

Tidal/algal flat

30,593

75,564

30,927

76,391

35,356

87,329

Seagrass

2,167

5,352

16,422

40,562

14,572

35,993

Palustrine habitats

2,062

5,093

1,885

4,655

2,575

6,361

Estuarine marsh

1,976

4,881

1,364

3,369

1,461

3,609

Gulf beach

1,085

2,680

849

2,097

558

1,378

Table 2. Total area of selected habitats, 1950’s to 2003/04, in the Padre Island National Seashore study area. Palustrine flat (US) and water (UB) are combined with palustrine marsh in the table.


 

Figure 1. Matagorda Bay Trends

Figure 3. Maps showing distribution of major wetland and aquatic habitats in 2003/04, 1979, and the 1950’s in the PINS study area.

 

 

Figure 1. Matagorda Bay Trends

Figure 4. Areal extent of selected habitats from the 1950’s to 2003/04 in the Padre Island National Seashore study area.

 


© 2021 Bureau of Economic Geology | Web Privacy Policy | Web Accessibility Policy