What does saltwater intrusion refer to?

Saltwater intrusion refers to the movement of saltwater into freshwater aquifers, which typically occurs in coastal areas where groundwater is replenished by freshwater sources. As groundwater is extracted for agricultural or urban use, the reduction in pressure can allow denser saltwater from nearby oceans or seas to push inland and upward into these aquifers. This phenomenon threatens freshwater supplies, making it a critical issue for environmental health and water resource management.

Thus, option B accurately describes the process of saltwater intrusion by specifically addressing the transition of saltwater into freshwater zones, effectively capturing the potential impacts on drinking water sources and ecosystems dependent on freshwater availability. The other choices do not accurately capture the specific process of intrusion; they either refer to unrelated movements of water or incorrect interactions between freshwater and saltwater.