Final answer:
The Ogallala aquifer's sustainability is primarily threatened by over-pumping for agricultural irrigation, which depletes the water faster than it can be replenished, leading to problems like saltwater intrusion and land subsidence.
Step-by-step explanation:
The primary cause affecting the sustainability of the Ogallala aquifer, which is the largest natural aquifer in the USA, is the intensive groundwater pumping surpassing its replenishment capacity. The aquifer spans various states and supports a significant portion of the agriculture industry through irrigation. Overuse and groundwater mining have led to a significant drop in the water table, making it necessary to drill deeper and more expensive wells, which often yield more saline water.
Problems such as saltwater intrusion, land subsidence, and pollution exacerbate the issue. The rapid depletion arose in part due to the politics of Western Libertarianism, which encourages individual usage over collective resource management, leading to overexploitation of this shared finite resource. Climate change, increased demand due to population growth, and unsustainable agricultural practices further strain the aquifer. The dilemma of balancing water use with economic growth and food production continues to challenge policymakers.