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Chapter 3 – Texas Wetlands Texas Outdoor Recreation Plan The playa lakes region of the United States includes portions of Colorado, Kansas, New Mexico, Oklahoma, and northwestern Texas. Texas alone has over 19,000 playas (Guthery et al., 1981). Playas, surrounded by vast acreages of winter wheat, corn and other grain crops, are the migrating, wintering and breeding area for several million ducks, geese, and other migratory birds. The area historically has also wintered a large portion of the Shortgrass Prairie Canada goose population. Hundreds of thousands of mallards, pintails and other ducks terminate their southward migration in this checkerboard of water havens and grainfields.
Other wildlife species in the Panhandle, a region of limited habitat availability, rely heavily upon the habitat associated with the playa basins. Several threatened and endangered species use wetland habitat in the playa lakes region, including the bald eagle. Many neotropical (summer) migrant birds use playas as well, including the longbilled curlew, American avocet, killdeer, mountain plover, lark bunting, and American kestrel.
Because playa lakes are fed by rainwater, many may be dry for extended periods of time. The unpredictable and dynamic nature of the playa is natural and necessary to maintain primary productivity and biodiversity. The 86 plant species living in playas have adapted to this rapidly changing environment. The most common plants found in the playa lakes include spikerush, curly dock, bulrush, cattail, pink and willow smartweed, pondweed, wollyleaf bursage, and barnyard grass. Woody species in riparian habitats include Plains cottonwood, buttonbush, netleaf hackberry, native plum, western dogwood, and persimmon.
Central Texas Central Texas wetlands, including seeps, springs, and freshwater streams and their associated riparian systems, are found throughout the limestone formations of the Edwards Plateau.
Riparian systems and associated woodland areas are the most widespread wetland type found in Texas (Photo 8), as they are found in the Rolling Plains of the Panhandle to the South Texas brushlands to the forests of East Texas. The riparian zone of a river, stream or other water body is the land adjacent to that water that is, at least periodically, influenced by flooding. Aridity, topographic relief, and presence of depositional soils most strongly influence the extent of high water tables and associated riparian ecosystems. In the eastern and central United States, riparian zones are called bottomlands and floodplain forests, while in the west they are recognized as bosque or streambank vegetation (Johnson and McCormick, 1979). Riparian areas provide protective pathways of migration for birds, deer and small mammals, as well as habitat for many animal species. Vegetation found along Central Texas streams includes bald cypress, pecan, possumhaw, smartweed, sugarberry, boxelder, buttonbush, and black willow.
Central Texas contains numerous springs, which typically flow into freshwater streams.
Springs are fed by groundwater that travels through a natural opening in the rock or soil.
In comparison to streams fed by surface water, spring-fed streams have a more constant supply of water, which supports vegetation such as marsh purslane, water pennywort, and cattail (Brune, 1981). Spring systems are highly vulnerable to water pollution and over-utilization by nearby cities and agricultural projects. Many springs no longer flow because aquifer waters have been over-utilized. Edwards Plateau and the Trans-Pecos springs support threatened and endangered species whose numbers will continue to decline with reductions in stream flow.
The Trans-Pecos Region, located in far western Texas within the Rio Grande and Pecos River basins, is dominated by Chihuahuan Desert salt basins and flats, desert scrub, desert and semi-desert grasslands, and very locally by evergreen woodlands and montane forests. Wetlands occur within each of these ecosystems.
Although Trans-Pecos wetlands probably account for less than 2% of the total regional land surface, they are highly significant to the region’s wildlife diversity. Desert wetlands shelter endemic desert fishes, reptiles, and invertebrates and are especially important to the region’s diverse bird life.
Desert basin salt flats, which are remnants of ancient lakes, contain water seasonally or permanently, depending on annual rainfall. Vegetation may include algal mats or plants (mostly grasses) adapted to saline conditions (Brown, 1982).
Chapter 3 – Texas Wetlands Texas Outdoor Recreation Plan Perennial riparian corridors have narrow bands of woodland vegetation, many of which have been invaded by salt cedar (Tamarix), an exotic shrub. Stream water quality varies from saline to fresh and crystal-clear to heavily mineralized, or it may be laden with sediments, pollutants, or sewage (Brown, 1982).
The region still shelters many headspring areas varying from fresh to slightly saline. At one time, headsprings were associated with desert marshes, called cienegas (Photo 9), which are dominated by grasses, sedges, and rushes. Most cienegas today, however, have been lost by water mining, water diversion, or overgrazing.
Cienegas still occur throughout the Trans-Pecos in areas with abundant soil moisture, for example, in mid-elevation and montane areas in the Davis Mountains sub-region.
Cienegas that occur where soil is lacking or very shallow are called seeps or hanging gardens, which are dominated by columbine, poison ivy, ferns, and orchids (Hendrickson and Minckley, 1984).
Photo 9. Desert cienega at Balmorhea State Park, © TPWD.
Texas Wetlands: Status and Trends Data and information on the status and trends of Texas wetland resources are primarily limited to project-scale assessment and mapping projects that, although valuable, are limited in their ability to support a statewide evaluation of wetland resources or to provide landscape-scale considerations in project planning and design. Regional and statewide habitat mapping efforts are underway in Texas (e.g., Texas Ecological Systems Classification Project, http://www.tpwd.state.tx.us/landwater/land/maps/gis/tescp/index.phtml), which will enhance the ability of conservation practitioners to assess habitats at range-wide or landscape scales. Until those tools and datasets become available, the most current and detailed information available on the status and trends of wetlands resources are
Texas Outdoor Recreation Plan Chapter 3 – Texas Wetlandsreported at the national scale through periodic assessments conducted by the U.S. Fish and Wildlife Service.
Under the provisions of the Emergency Wetlands Resources Act, the U.S. Fish and Wildlife Service is required to assess and report on the status and trends of the Nation’s
wetland resources at 10-year intervals, with the most recent report published in 2011:
Status and Trends of Wetlands in the Conterminous United States 2004 to 2009. This series of reports is intended to help guide decisions by providing resource professionals and policy-makers information on wetland-related issues, such as, the need for potential changes to incentive and disincentive policies, measures to conserve wetlands, funding priorities for wetlands protection, restoration and enhancement, and landscape-scale planning to address emerging issues that have the potential to negatively affect wetland resources (e.g., climate change, sea-level rise, urbanization).
The 2011 report measured trends by the examination of remotely sensed imagery for 5,042 randomly selected sample plots located throughout the conterminous United States. This imagery, in combination with field verification provided a scientific basis for analysis of the extent of wetlands and changes that had occurred over the four and half year time span of the study. Excerpts from the national report on the status and trends of important wetland habitat types found in Texas are provided below. Although results are presented by wetland habitat type for the entire conterminous United States and are not able to be summarized for Texas alone, the issues that threaten wetlands are somewhat consistent nationwide, providing an indication of the status of Texas wetlands.
[Adapted from Dahl, T.E. 2011. Status and trends of wetlands in the conterminous United States 2004 to 2009. U.S. Department of the Interior; Fish and Wildlife Service, Washington, D.C. 108 pp.] Trends in Estuarine Emergent (Salt Marsh) Wetland The largest acreage change in the saltwater system was an estimated loss of more than 111,500 acres (45,140 ha) of estuarine emergent wetland. This rate of loss was three times greater than estuarine emergent losses from 1998 to 2004 and continued a longterm trend in the decline of estuarine emergent wetland areas.
An estimated 99% of the losses of estuarine emergent wetlands between 2004 and 2009 were attributed to effects from coastal storms, land subsidence, and sea level rise or other ocean processes with the vast majority of these losses located in the northern Gulf of Mexico along the coastline of Louisiana and Texas.
Factors responsible for the loss of estuarine emergent wetland in the northern Gulf included land subsidence (sinking of the land), compaction of sediments, and extraction of subsurface fluids (such as oil, gas, and water). In portions of coastal Louisiana and Texas, oil, gas, and groundwater extractions have been recognized as factors that contributed to subsidence and relative sea level rise (Galloway et al. 1999; Morton et al.
Chapter 3 – Texas Wetlands Texas Outdoor Recreation Plan 2003; Dokka 2006; Lavoie 2009). Throughout the northern Gulf coastal region, marine and estuarine wetlands have been adversely impacted by the cumulative effects of energy development, coastal storms, and development in the upper portions of the watershed.
The construction of levees and canals also weaken the sustainability of the landscape and have contributed to coastal wetlands loss (GAO 2007). These actions have reduced freshwater and sediment, which are crucial for maintaining estuarine wetland elevation as a mechanism to overcome rising sea levels. In these areas and elsewhere, wetlands have been vulnerable to salt water intrusion and marsh disintegration as development has interfered with natural hydrological processes that transport sediment and the freshwater necessary to sustain the structure, function, and extent of wetland ecosystems (Kling and Sanchirico 2009). The interconnection between fresh and saltwater systems has become more apparent as impacts to freshwater wetlands have compounded the effects of sea level rise and the ability of wetlands in coastal watersheds to adapt.
Since the mid-1980s, there has been recognition that the majority of losses to these tidal wetlands have resulted from coastal erosion and inundation by salt water. This situation has been exacerbated by a series of hurricanes in the Gulf of Mexico that damaged property and natural resources in proximity to coastal areas. Attempts to renourish tidal wetlands have been implemented following several hurricane events from 2005 to 2008. There also has been considerable work in the northern Gulf of Mexico to shield near-shore areas that were damaged as a result of hurricanes or relative rise in sea level.
Estuarine Shrub Wetlands
Overall, estuarine shrubs had a small net gain in area (0.1 %), as losses to upland were outdistanced by gains. Area gains in estuarine shrubs came from both palustrine wetlands (1,789 acres or 724 ha), presumably from salt water inundation of low lying freshwater wetland; and from agricultural lands and unspecified other uplands (2,314 acres or 937 ha collectively). There were an estimated 1,370 acres (555 ha) of estuarine shrub wetlands lost to upland between 2004 and 2009. Eighty-three percent of those losses were attributed to urbanization and related development. Human induced impacts to mangrove wetlands included proliferation of invasive species, cutting/removal, coastal development resulting in drainage, filling or changes to shoreline structure.
Long-term trends in area of estuarine shrub wetland has remained fairly constant since the 1980s, despite long-term stressors including invasion by exotic species such as Brazilian pepper (Schinus terebinthifolius) and a high vulnerability to change due to natural causes such as coastal storms, drought, frost, fire, sea level changes, and stress due to increased salinity. Climax stands of mangrove forest are uncommon in the conterminous United States as they survive within a very limited geographic range and
Marine and Estuarine Non-Vegetated Wetlands Over the time-span of this study, the area of intertidal non-vegetated wetland increased by an estimated 2.2% (26,800 acres or 10,850 ha). All of these changes occurred along the south Atlantic and Gulf coastlines and were attributed to storm events that transported sediments, over-washed barrier islands, or scoured shorelines and other near-shore features along the coast. Intertidal non-vegetated wetlands (shores and flats) have exhibited marked change and instability and, despite an increase in acreage, are most likely to sustain additional changes from ongoing and future coastal processes. Seaward events such as storms, tidal-surge causing erosion and deposition, in addition to saltwater intrusion and inundation have contributed to the modification of these coastal wetland types and extent (Steadman and Dahl 2008).