Final answer:
Overpumping of groundwater from coastal aquifers can cause saline intrusion, which is the movement of ocean saltwater into freshwater aquifer zones. This can lead to water resource depletion and environmental issues like water stress and subsidence.
Step-by-step explanation:
Extensive pumping of fresh groundwater from a coastal aquifer can induce saline intrusion. Saline intrusion occurs when the overpumping of freshwater lowers the water table and creates a 'cone of depression', which may reverse the direction of groundwater flow and allow saltwater from the ocean to enter and contaminate the freshwater aquifer.
Water stress, depletion of water resources, and subsidence are some of the broader environmental issues related to excessive groundwater extraction. Adding water to a recharge area would, in practical terms, increase the amount of groundwater (recharge the aquifer), potentially mitigating some of these adversities.