Aquifer: an underground layer of soil, gravel, or porous rock that contains water.

Arachnid: a small invertebrate with four pairs of legs. Spiders, scorpions, and harvestmen – all found in the Barton Creek area – are arachnids.

Conduit: a natural opening that allows water to flow through an aquifer.

Contributing zone: land area upstream from the recharge zone where the watersheds of creeks and rivers catch rainfall.

Ecosystem: a collection of interacting plants and animals, together with their natural environment.

Edwards Aquifer: an aquifer that underlies portions of nine counties in central and south-central Texas. The central section of the aquifer supplies water to Barton Springs.

Edwards Plateau: the southern extension of the Great Plains, which covers much of south Texas, from the Rio Grande River to the Colorado River.

Evaporation: changing of a liquid to a gas; for example, when water becomes water vapor.

Fertilizer: any material in the soil or water that acts as a nutrient for plant growth.

Groundwater: water that seeps down from the Earth’s surface and is stored in aquifers, porous rock, or soil pores.

Karst aquifer: a geological landform typified by structures created by water, such as caves, sinkholes, and highly porous rock. The Edwards Aquifer is a karst aquifer.

Nitrate: a nitrogen compound that is a major plant nutrient.

Nonpoint Source Pollution: pollution caused by sediment, nutrients, organic and toxic substances; originates from land use activities; and is carried to lakes and streams and groundwater by surface runoff.

Pesticide: any chemical agent used to kill specific insects or animals.

Phosphorus: one of the primary nutrients required by plants, often the limiting factor for the growth of aquatic plants.

Point source pollution: pollution that originates from a single, well-defined point, such as a leaking underground storage tank, a factory, or a damaged sewer line.

Pollutants: toxic substances that enter the air or water.

Recharge zone: the area of land where surface water enters the ground and moves into an aquifer. The aquifer is exposed at the surface at some points in the zone.

Reservoir: any natural or man-made holding area used to store, regulate or control water.

Runoff: the portion of rainfall, melted snow, or irrigation water that flows across land surfaces and eventually enters a stream.

Sediment: water-transported and water-deposited particles of rock, soil, or biological material.

Silt: fine-grained sediment.

Toxic substances: poisonous materials that cause sickness, disease, and/or death in plants and animals.

Water pollution: the contamination of water by the addition of substances that degrade water quality.

Watershed: the land area that contributes surface water runoff to a given point in a drainage system.