Aransas National Wildlife Refuge 



The Aransas NWR was selected as one study site to determine the ecological 

 effects of gas and oil exploration and development in the coastal upland eco- 

 system of the Texas and Louisiana Gulf coast. Determination of potential 

 ecological impacts requires: (1) a thorough understanding of the normal abiotic 

 and biotic processes and interactions regulating the communities of concern 

 and (2) an accurate ecological model of these systems to serve as an analytical 

 tool for the assessment routine. The following provides a description of the 

 environmental setting of the refuge. 



Location . Aransas Refuge lies in the Texas Coastal Bend; it encompasses 

 parts of Aransas, Refugio, and Calhoun Counties and occupies nearly 22,000 ha 

 (55,000 acres) of the Blackjack (St. Charles) Peninsula and nearby mainland. 

 It is bounded by St. Charles Bay and Highway 35 on the west and by Aransas, 

 Mesquite, and San Antonio Bays on the east. St. Joseph and Matagorda Islands 

 protect these bays fron, the open waters of the Gulf of Mexico. 



Although located roughly in the center of a rural section of the Texas 

 Coastal Bend, Aransas NWR is within a 4-hr drive of 2.5 million people. San 

 Antonio, 24C km (150 mi) to the northeast. Corpus Christi, 104 km (65 mi) to 

 the southwest, and Houston, 280 km (1975 mi) to the northeast, contribute the 

 largest portion of this total. 



Geology . Aransas Refuge is situated on a Pleistocene barrier-strand plain 

 system known as the Ingleside complex. This system consists of a 4.8 to 12.8 

 km (3 to 8 mi) wide strip of deep whitish sand deposits (referred to as the 

 Live Oak Ridge) north of Corpus Christi Bay that represents the remnants of 

 ancient barrier islands and shorelines that formed though the erosion and 

 redeposition of deltaic sands (Jones, 1975; McGowen et al., 1976). Deposition 

 of these sands occurred from Baffin Bay north to San Antonio Bay and beyond. 

 Strand-plain sand commonly overlies mud and is bound landward by Pleistocene 

 deltaic sand, mud, and clay deposits. This boundary occurs north of the refuge. 



These sand bodies form local shallow aquifers, commonly with perched water 

 tables. Relict beach ridges are easily distinguished in aerial photography as 

 a series of live-oak-covered ridges oriented parallel to the existing shoreline. 

 These low ridges are locally truncated by mud-filled swales and depressions. 

 Freshwater marshes occupy the many remnant swales and relict drainage systems 

 that were cut into the strand-plain sand. Mud-veneered sheet sands (derived 

 from outwash and eolian sand from the stand plain) are located inland (northwest 

 corner of the refuge, near Burgentine Lake) of the main strand-plain sand body 

 (McGowen et al., 1976). 



Soils and topography . Refuge topography ranges from nearly level to gently 

 undulating. The land slopes slowly but steadily southward toward the coastline. 

 Slope gradients are generally less than 5 percent (frequently much less), but 

 some remnant dune areas of the interior may approach as much as 12 percent. 



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