Crops

• More than 90 percent of the water pumped from the Ogalla aquifer in the High Plains is for crop irrigation. The aquifer stretches from South Dakota to Texas and irrigates one fifth of U.S. cropland that produces corn, cotton, soya, alfalfa and wheat. The development of irrigated crop production since the 1940s has led to a gradual decline of the water table within the aquifer. Rainfall does not recharge the aquifer in any significant way. According to the Texas Water Development Board, the agricultural use of groundwater will decline over the next half century because the energy costs associated with pumping water from a declining aquifer will be too high.
  
  

Livestock

• Livestock feeds on most of the crops irrigated by groundwater. They provide 40 percent of the feed to beef cattle in the United States. The aquifer depletes as groundwater accessed by boreholes irrigates increasing amounts of grazing land and provides for increasing livestock production.
  
  

Urban Growth

• The use of groundwater by growing cities and tourism worldwide is increasing. Massive groundwater depletion in Mexico City since the early 1900s has led to severe land subsidence. The porous rock formations that once held water have collapsed. Throughout Mexico, more than 51 percent of the groundwater pumped from aquifers is over-pumped. Buildings, roads and driveways increase the extent of nonporous surfaces and reduce the seepage of rain and run-off water that could recharge the aquifer.
  
  

Ecosystems

• Estuaries, deltas and riparian -- river and stream -- ecosystems depend on groundwater. They rely on this water resource to tide them over drought seasons. They control the salinity of the water and add nutrients to ecosystems. Aquifers themselves are host to a variety of bacterial ecosystems. Groundwater over extraction threatens the existence of these ecosystems. It increases the pollution from human or farmed animal waste, reduces the oxygen in the system, and increases carbon dioxide.