Without light there is no need for eyes. Sensory adaptations such as antennae, chemoreceptors , and touch receptors are usually highly developed in underground dwelling species. These species also often have a very low metabolism, allowing them to live on very little food. This adaptation is aided by the constant temperatures of aquifer waters, compared to surface water temperatures which can vary quickly and widely. Groundwater species live in a very stable and predictable environment.
As with aquatic ecosystems above ground there can be overlaps with other ecosystems. This means species in the aquifer may not be completely isolated from life on the surface. The land surface above karst aquifers is an integral part of the habitat of animals inhabiting the underground areas.
Holes in the limestone and marble of these aquifers often extend to the surface. Here, a large opening in the stream bed of Cypress Creek is actually a water-filled cave extending deep into the aquifer.
There are also caves open to the surface that lead to the aquifer. Food in a cave can also come from organisms such as bats, mice, and crickets that take shelter in caves.
For example, bat and mouse feces dropped on a cave floor provides nutrients fungi need to grow. Fungi are eaten by several species of insects that may wander in and out of the cave. These insects reproduce rapidly, move about the cave, and become prey for predatory invertebrates that live their entire lives in the cave.
These invertebrates fall into the water and are swept deep into the aquifer where they can be eaten by species such as the Texas blind salamander. The aquifer ecosystem extends beyond the aquifer itself where groundwater emerges into the spring. Here the groundwater mixes with surface water in the spring, stream, rivers, and lakes.
We occasionally get a rare glimpse of life in the underground ecosystem when an invertebrate, fish or, salamander from the Edwards aquifer gets swept out at a spring. You may see one of these odd creatures, or one of the predators that like to eat them, when you tour the San Marcos Springs in a glass bottom boat. While many aquifers do not contain aquatic life, most major springs in Texas do. Some even contain species found nowhere else. The Edwards aquifer ecosystem and its springs contain over 60 species of plants and animals that live nowhere else in the world.
Species of salamanders, fish, amphipods, beetles, spiders, and others have evolved in isolated habitats within the aquifer and springs. Many of these live in the dry caves above the water table and others live in the many springs fed by the aquifer. Barton Springs, located in Austin, is the only place where the Barton Springs and Austin blind salamanders live. Fountain darters live only in the San Marcos and Comal rivers headwaters. Texas Wild Rice lives only in the San Marcos Springs and river immediately downstream of the springs.
Because springs are exposed to sunlight, aquatic plants and algae play a role in providing nutrients. A relatively constant temperature, at least near spring openings, allows species to adapt to a highly specialized lifestyle. Water temperatures in particular may limit a species adapted to a spring ecosystem from wandering beyond the vicinity of the spring. As a result, spring ecosystems tend to be small, allowing only relatively small populations of any one species to survive.
As with species adapted for a life completely underground, species in spring ecosystems may be greatly affected by even small changes to their habitat. For species in a spring, lowered spring flow due to drought or groundwater withdrawals may reduce habitat and create significant stress. Invasive species may quickly overwhelm and outcompete native spring species. Humans have made the most changes to springs. At such places, the native spring ecosystems no longer exist. Groundwater in an aquifer is like money in your bank.
Each time you put money in your bank, the amount of money you have grows. When you withdraw money from your bank to buy something, your bank account goes down and stays down until you put more money in.
Aquifers grow when nature puts water in through rainfall, snow, and other precipitation. More underground water is used for irrigation in Texas than for all other uses combined. Of all water pumped for irrigation purposes in Texas, 68 percent is produced in the Southern High Plains. In addition to municipal and irrigation uses, many industries have developed underground water supplies for cooling and industrial processes.
Characteristics of underground water that make it particularly desirable for industry are its uniform temperature and uniform quality at a given source. Although all underground water contains mineral matter derived principally from soil and rocks through which it moves, its quality and temperature will generally remain constant at a given locality unless it is contaminated by human activities. Several factors have contributed to the development and widespread use of underground water as a supply source in Texas.
Nearly all of the geologic formations in the state yield some water, generally in sufficient quantities for domestic and livestock purposes. Where it is available in sufficient quantities, underground water is generally cheapest to develop, since it does not need the extensive pipelines and treatment facilities required for surface supplies.
Unlike surface water, which flows in definite and limited channels, underground water can often be developed at the point of use, requiring little or no transportation. Large areas of Texas deficient in rainfall and having few perennial streams available for water supply contain vast quantities of underground water in storage. The Gulf Coast aquifer forms an irregularly shaped belt that parallels the Texas coastline and extends through 54 counties from the Rio Grande northeastward to the Louisiana border.
This system has been divided into three major water-producing components referred to as the Chicot, Evangeline, and Jasper aquifers. In , municipal uses accounted for 62 percent and irrigation accounted for 25 percent of the total pumpage from the aquifer.
Water quality is generally good northeast of the San Antonio River basin, but deteriorates to the southwest. Years of heavy pumpage have caused significant water-level declines in portions of the aquifer. Some of these declines have resulted in significant land-surface subsidence, particularly in the Houston-Galveston area.
A poorly defined groundwater divide in Hays County hydrologically separates the aquifer into the San Antonio and Austin regions. Water in the aquifer occurs in fractures, honeycomb zones or intergranular pores , and solution channels in the Edwards and associated limestone formations of Cretaceous age. In , about 72 percent of pumpage from the aquifer was for municipal use.
Irrigation was the principal use in Medina and Uvalde counties. Until recently, San Antonio was one of the largest cities in the world that relied solely on a single groundwater source for its municipal supply. The EAA has an active program to educate the public on water conservation and also operates several active groundwater recharge sites.
The San Antonio River Authority also has a number of flood-control structures that effectively recharge the aquifer. Conservation districts are promoting more-efficient irrigation techniques, and market-based, voluntary transfers of unused agricultural water rights to municipal uses are more common. Extending from the Rio Grande in South Texas northeastward into Arkansas and Louisiana, the Carrizo-Wilcox aquifer provides water to all or parts of 66 counties.
It exists within tiny pore spaces in rocks and sediments, and in larger spaces, such as fractures, within rocks. Groundwater and surface flow interact.
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