The abiotic system is dominated by two important and intimately associated 

 subsystems, the hydrological cycle and the nutrient cycle. However, the nutrient 

 cycle, important as it is, is contingent upon the hydrological cycle to make 

 the nutrients available for use (Spurr, 1964). This is one reason it is es- 

 sential to consider the hydrological cycle in detail. The treatment points 

 out factors which regulate the flows within and between each subsystem. 



The hydrology of the Aransas Refuge is discussed in the refuge descriptions 

 in this chapter. The primary source of water input to the local hydrologic 

 system is rainfall and groundwater flows in shallow aquifers (Bernard 

 and LeBlanc, 1965). Other coastal upland areas may receive significant fresh- 

 water inputs from additional sources - sheetflow from further inland and riverine 

 flooding. 



Water is stored in the abiotic system as surface water or as groundwater. 

 The rurface-water storage includes nonpoint surface runoff; standing water bodies 

 such as Bergentine and Long Lakes and numerous ponds, sloughs, and wet depres- 

 sions; and flowing streams such as Bergentine, Twin and Salt Creeks. 



The surface and groundwater storages interface through soil water storages. 

 The two soil water storages (macropore and micropore water) are functions of 

 two physical attributes of the soil: soil structure and soil texture. These 

 two in;portant physical properties regulate water-holding capacity and gaseous 

 exchange capabilities. Soil structure, as it controls the effective pore size 

 of the soil, is the regulator of water and air permeability (Buckman and Brady, 

 1969). The macrostructure of the soil provides larger pore spaces (macropores) 

 between aggregates of soil material, which facilitate the rapid movement of 

 air and percolating water. In contrast, the microstructure of a soil (micro- 

 pores) pertains to the intergranular porosity. Pore sizes are much reduced, 

 and consequently air movement is greatly impeded and water movements are 

 restricted to capillary action. Soil water is stored temporarily as macropore 

 water and more permanently as micropore water. Soil texture regulates the 

 development of soil structure. Sandy soils permit the rapid movement of water 

 and air because of the dominance of macropores, and they are typically mositure 

 deficient (Spurr, 1964). Particle cohesion is high in fine-textured soils (clays 

 and silts) and restricts the development of macropore spaces; micropore spaces 

 are dominant and become easily filled with firmly bound soil water. Since the 

 effective pore spaces are water-filled, soil aeration becomes inadequate for 

 satisfactory root development and microbial activity. 



Surface-water infiltration into the soil macropore spaces is regulated by 

 land slope and vegetative cover. Increasing land slope tends to reduce perco- 

 lation rates, but presence of vegetative cover will increase this rate (Spurr, 

 1964). Surface-water runoff contributes to the export and loss of nutrients 

 and soil materials from the system. Adjacent systems receive these flows as 

 inputs. Water filtering through the soil horizons may enter the groundwater 

 storage or be retained as soil moisture. The rate and extent of downward perco- 

 lation is affected by soil structure, soil texture, clay content, and the 

 concentration of organic microdetritus, which contributes to high water-retention 

 properties. Throughout much of the low-lying coastal areas, the groundwater 



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