Shallow poorly drained depressions are scattered throughout the uplands and 

 may exist as either fresh marshes or seasonally flooded wetlands. Elevation 

 of the highest surface features, which are concentrated in the northeast corner 

 of the refuge, approach 6.1 m (20 ft). Most of the refuge, however, lies at 

 or below the 4.5-m (15-ft) elevation contour. Upland communities begin 

 occurring above the 1.5-m (5-ft) contour (Allen, 1952). 



The refuge soils belong to the Galveston-Mustang-Dianola association 

 (USDA, 1976). Due to the geologic history of the Blackjack Peninsula, the 

 soils are primarily deep eolian and depositional sands of low fertility and 

 rapid permeability. Soil horizons are typically indistinct. The water table 

 lies near the lC2-cm (40-inch) depth and is normally shallow enough to maintain 

 available moisture within reach of grass and tree roots. Upland swales and 

 other depression areas with poor drainage may pond water permanently or sea- 

 sonally, depending upon the depth of the water table. These soils have a high 

 organic content. 



Portions of Aransas Refuge north and northwest of Burgentine Lake and 

 between St. Charles Bay and Texas State Highway 35 have soils with higher clay 

 and silt contents (Victoria, Orelia, and Clareville series) than the strand- 

 plain sands. Consequently, these soils are more fertile and exhibit low to 

 moderate permeability and drainage characteristics. These northermost soils 

 are derived from lagoons which formed behind the ancient barrier islands. 



Climatology . The climate is humid subtropical with warm summers. The 

 prevailing southeasterly winds from the Gulf of Mexico provide a moderating 

 oceanic climate. Daily temperatures are warmer in winter and cooler in summer 

 than for inland locations. Mean annual relative humidity is estimated at 65 

 percent at noon. Cold air masses, greatly moderate in severity by the time 

 they reach the Texas coast, provide seasonal variation and can produce rapid 

 temperature reductions for a few days during the period from November to 

 February. 



Mean annual precipitation is 93.5 cm (36.8 inches), with the greatest 

 monthly average occurring in September. March is the driest month, averaging 

 4.1 cm (1.6 inches). Heaviest precipitation occurs from mid-July to late 

 October as a result of the numerous slow-moving thunderstorms or occassional 

 tropical disturbances characteristic of the season. However, the total annual 

 precipitation is quite variable and may fluctuate more than 50.8 cm (20 inches) 

 between years. Therefore, alternating periods of flooding and drought conditions 

 are characteristic of the climatic history of the area. The mean annual evapor- 

 ation potential for the area ranges between 317 and 150 cm (124 and 59 inches) 

 and thus exceeds the mean annual rainfall of 102 cm (Springer, 1975). 



The long-term mean monthly temperatures (1942-71) varied from ll.ioc 

 (52°F) in January to 30°C (860F) in July and August. The extreme temperatures 

 recorded during this period were -12.20C (109F) and 39.40C (103OF) (Springer, 

 1975). 



58 



