What is meant by "freshwater lens" in aquifers?

The term "freshwater lens" refers to a specific hydrogeological phenomenon that occurs in coastal aquifers, where less dense freshwater floats on top of denser saltwater. This occurs because freshwater is lighter than saltwater, allowing it to occupy the upper layer of the water table within an aquifer. As rainwater and surface water infiltrate through the soil and rock formations, they accumulate as a freshwater layer above the more saline groundwater below.

This concept is crucial for understanding groundwater resources in coastal areas, where saltwater intrusion can threaten freshwater supplies. The freshwater lens supports an ecosystem and provides water for drinking, irrigation, and other uses. The management of this resource is essential in regions facing pressures from both population growth and rising sea levels, which can lead to increased saltwater intrusion.

The other options do not accurately describe the freshwater lens. A layer of saltwater above groundwater does not constitute a lens, nor does a layer of sediment or ice within aquifers. The freshwater lens is specifically defined by the layering of freshwater over saltwater in coastal aquifers, making it a critical concept in hydrology and environmental management.