Mammals include rice rats, raccoons, and feral pigs. Reptiles and amphibians include several species of frogs and toads, mud and red-eared slider turtles, Gulf Coast ribbonsnake, and alligators. Many of the same animals found in mainland marshes are also present in the barrier island wetlands, although the diversity of species is less than on the mainland. Typical species include saltmeadow cordgrass, southern cattail, bulrushes, coastal water-hyssop, coastal plain pennywort, spikerushes, flatsedges, sedges, burhead, marsh fimbry, white-topped sedge, frogfruit, coffee bean, seashore paspalum, bushy bluestem, and other grasses. Wetland plants are similar to those found in other freshwater marshes, but may include some brackish-water species due to elevated soil salinity in some areas. ![]() On North Padre island, within the Padre Island National Seashore, this process has caused an apparent increase in freshwater wetlands. This natural subsidence is greatly magnified in regions where people have pumped massive quantities of groundwater or oil and gas. As the sediment layers of the coastal plain subside under their own weight, there is a relative rise in sea level and the freshwater lens rises closer to the surface. On the barrier islands, fresh groundwater, which is less dense (lighter) than saltwater, forms a freshwater lens, which sits atop the underlying saltwater. Many of these swales in fact rarely have ponded water on the surface, but because groundwater is found just under the surface for extended periods of time, only wetland vegetation can survive. Water percolates through the sandy dunes very easily, and generally comes to the surface in the swales between the dunes. ![]() Water in the nontidal barrier island troughs is derived from a combination of runoff from the adjacent dunes and from groundwater. The subsoil from 6 to 72 inches is a single grained, light gray fine sand, with few fine faint yellowish brown iron coatings along root channels in upper 20 inches. (Mustang Soil Series, Mustang Island, Nueces County)įrom 0 to 6 inches the surface soil is a loose, single-grained, brownish gray fine sand, with many fine roots and few shell fragments. The dunes of the wet upper coast barriers are better vegetated and less subject to wind and water erosion than dunes on the semiarid lower coast barriers. The Gulfward advance of successive beach ridges over time has resulted in a series of ridges and troughs. The barrier islands formed as a result of wave action that reworked sands delivered to the Gulf by the coastal rivers and creeks. The Gulf-fringing barrier islands are about 4,000 years old. Tidally influenced wetlands on the bay margins of the islands are included with the Tidal Fringe wetlands. (EARL NOTTINGHAM FOR TEXAS PARKS AND WILDLIFE)īarrier island nontidal, freshwater wetlands are found in interdune swales (troughs between dune ridges) and on the larger, interior wind-eroded flats on the barrier islands that line the Texas coast. The Matagorda Lighthouse is visible in the left foreground. ![]() The interdune swales are particularly apparent in this aerial of Matagorda Island.
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